ex2000
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GEH-6375A
GE Industrial Systems
EX2000 PWM Digital Regulator User's Guide
GE Industrial Systems Document: GEH-6375A Orig Or igin inal al Issu Issuee Date Date:: 1997 1997-0 -066-01 01 Rev. A: 2000-07-20
EX2000 PWM Digital Regulator User's Guide
© 2000 General Electric Company, USA. All rights reserved. Printed in the United States of America.
These instructions do not purport to cover all details or variations in equipment, nor to provide every possible contingency to be met during installation, operation, and maintenance. If further information is desired or if particular problems arise that are not covered sufficiently for the purchaser’s purpose, the matter should be referred to GE Industrial Systems, Salem, Virginia, USA. This document contains proprietary information of General Electric Company, USA and is furnished to its customer solely to assist that customer in the installation, testing, operation, and/or maintenance of the equipment described. This document shall not be reproduced in whole or in part nor shall its contents be disclosed to any third party without the written approval of GE Industrial Systems.
Document Identification: GEH-6375, updated release
Windows NT is a registered trademark of the Miscrosoft Corporation. Windows is a registered trademark of the Microsfot Corporation. DIRECTO-MATIC is a registered trademark of the General Electric Company, USA.
Safety Symbol Legend
Indicates a procedure, condition, or statement that, if not strictly observed, could result in personal injury or death.
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Note Indicates an essential or important procedure, condition, or statement
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GEH-6375A User's Guide
Safety Symbol Legend
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This equipment contains a potential hazard of electric shock or burn. Only personnel who are adequately trained and thoroughly familiar with the equipment and the instructions should install, operate, or maintain this equipment. Isolation of test equipment from the equipment under test presents potential electrical hazards. If the test equipment cannot be grounded to the equipment under test, the test equipment’s case must be shielded to prevent contact by personnel. To minimize hazard of electrical shock or burn, approved grounding practices and procedures must be strictly followed.
To prevent personal injury or equipment damage caused by equipment malfunction, only adequately trained personnel should modify any programmable machine.
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Safety Symbol Legend
EX2000, PWM Digital Regulator GEH-6375A
Contents Chapter 1 Overview
1-1
Introduction...................................................................................................................... 1-1 System Overview.............................................................................................................. 1-2 Product Overview............................................................................................................. 1-3 Hardware Design ....................................................................................................... 1-3 Power converter module............................................................................................. 1-5 Software Design ........................................................................................................ 1-6 Human-Machine Interface (HMI)............................................................................... 1-8
Chapter 2 Hardware System Description
2-1
Introduction...................................................................................................................... 2-1 Packaging......................................................................................................................... 2-2 Environmental ........................................................................................................... 2-2 Enclosure................................................................................................................... 2-2 Ratings ............................................................................................................................. 2-3 Input Ratings ............................................................................................................. 2-3 Output Current Rating................................................................................................ 2-4 Voltage Control Range............................................................................................... 2-4 Power Profile Rating.................................................................................................. 2-4 Power Converter Hardware............................................................................................... 2-5 Ac and Dc Input Devices............................................................................................ 2-6 Dc Link and Dynamic Discharge................................................................................ 2-6 IGBT And IAXS Devices........................................................................................... 2-6 Output Contactor MDA.............................................................................................. 2-7 Output Shunt SHA..................................................................................................... 2-7 Control Electronics Module .............................................................................................. 2-7 TCCB (DS200TCCB) ................................................................................................ 2-8 PSCD (IS200PSCD) .................................................................................................. 2-8 GDDD (IS200GDDD) ............................................................................................... 2-8 PTCT (DS200PTCT) ................................................................................................. 2-8 NTB/3TB (531X305NTB) ......................................................................................... 2-9 LTB (531X307LTB).................................................................................................. 2-9 RTBA (DS200RTBA)................................................................................................ 2-9 ACNA (DS200ACNA) .............................................................................................. 2-9 Inputs and Outputs............................................................................................................ 2-9 Generator Inputs ........................................................................................................ 2-9 4-20 mA Inputs.........................................................................................................2-10 Generator Line Breaker Status...................................................................................2-10 Generator Lock-Out Trip...........................................................................................2-10 Additional I/O...........................................................................................................2-11
GEH-6375A User's Guide
Contents
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Chapter 3 Software System Overview
3-1
Introduction...................................................................................................................... 3-1 Configuration Tools.......................................................................................................... 3-2 Programmer Module......................................................................................................... 3-2 Software Design ........................................................................................................ 3-2 Standard Functions ........................................................................................................... 3-3 Automatic Voltage Regulator (AVR) Ramp................................................................ 3-3 Automatic Voltage Regulator Setpoint ....................................................................... 3-3 Automatic Voltage Regulator..................................................................................... 3-3 Field Regulator (FVR) Ramp ..................................................................................... 3-3 Field Regulator .......................................................................................................... 3-3 Under Excitation Limiter (UEL)................................................................................. 3-4 Over Excitation Limiter (OEL)................................................................................... 3-4 Firing Block............................................................................................................... 3-4
Chapter 4 Software Configuration and Scaling
4-1
Introduction...................................................................................................................... 4-1 Configuration and Scaling Example .................................................................................. 4-2 Example Generator, Exciter, and Regulator ........................................................ ........ 4-3 General Configuration ...................................................................................................... 4-4 Feedback Scaling.............................................................................................................. 4-6 Generator Feedback ................................................................................................... 4-6 Bridge Voltage Feedback ........................................................................................... 4-7 Bridge Current Feedback............................................................................................ 4-8 Feedback Offsets........................................................................................................ 4-8 Instantaneous Overcurrent Trip .................................................................................. 4-9 Regulator Scaling ............................................................................................................. 4-9 Automatic Voltage Regulating System ....................................................................... 4-9 Under Excitation Limiter (UEL)................................................................................4-13 Reactive Current Compensator (RCC).......................................................................4-16 VAR/Power Factor Control.......................................................................................4-17 Field Regulator (FVR) ..............................................................................................4-18 Field Current Regulator (FCR)..................................................................................4-20 Optional Functions Scaling and Configuration..................................................................4-23 Transducer Outputs...................................................................................................4-23 Ground Detector and Diode Fault Monitor.................................................................4-24 Field Thermal Model ................................................................................................4-25
Chapter 5 Startup Checks
5-1
Introduction...................................................................................................................... 5-1 Prestart Checks ................................................................................................................. 5-2 Energization and Simulator Control Checks................................................................ 5-2 Pre-start Power Checks ..................................................................................................... 5-4 Initial Roll Offline Checks ......................................... ....................................................... 5-6 Online Checks .................................................................................................................. 5-7 Operator Interface............................................................................................................. 5-8 Units with Innovation Series Controller...................................................................... 5-8 Units with Discrete Switches and Meters.................................................................... 5-8
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EX2000, PWM Regulator GEH-6375A
Chapter 6 Simulator Scaling and Operation
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Introduction...................................................................................................................... Simulator.......................................................................................................................... Simulator Scaling....................................................................................................... Operation...................................................................................................................
6-1 6-1 6-2 6-4
Glossary of Terms Index
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EX2000, PWM Regulator GEH-6375A
Chapter 1 Overview
Introduction This manual describes the EX2000 Pulse Width Modulated (PWM) digital regulator for brushless generator excitation systems. This is a microprocessor controlled power converter that produces controlled dc output for rotating exciter, brushless generator applications. This manual is intended to a ssist applications and maintenance personnel in understanding the equipment hardware and software. It also provides initial startup information. The manual is organized as follows: Chapter 1 briefly defines the EX2000 PWM regulator with an overview of the hardware and software design. Includes references to other manuals and documents, one-lines and connection diagrams. Its purpose is to present a general product overview for the reader as follows: Section
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System Overview ................................................................................................ 1-2 Product Overview................................................................................................ 1-3 Hardware Design.......................................................................................... 1-3 Power Converter Module........... ................................................................... 1-5 Software Design........................................................................................... 1-6 Human-Machine Interface (HMI) ................................................................. 1-8 Chapter 2 Hardware System Description, contains specific information on system hardware design and purpose, ratings, I/O definition. Chapter 3 Software System Overview, contains specific information on software tools, structure, functions, and one-line representations. Chapter 4 Software Configuration and Scaling , gives examples of the scaling for specific parameters in a generic brushless regulator generator application. Chapter 5 Startup Checks, contains pre-start, startup, and on-line adjustments required during the commissioning of the PWM regulator for a brushless excitation system. Chapter 6 Simulator Scaling and Operation gives example simulator scaling and operation instructions for a typical brushless regulator generator application.
GEH-6375A User's Guide
Chapter 1 Overview
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1-1
System Overview A second power power source is also possible from a dc battery source.
The PWM regulator controls the ac t erminal voltage and/or the reactive volt amperes of the generator by controlling the field of the rotating brushless exciter. Figure 1-1 shows a typical one-line system of a Permanent Magnet Generator (PMG) fed brushless generator generator application. Power Power for the regulator is normally supplied from a PMG driven directly by the main generator field. This can be a single phase or 3 phase PMG. An An alternative method method is to obtain excitation excitation regulator power power from a Power Potential Transformer Transformer (PPT) supplied from an auxiliary bus. This can also be a single or 3-phase supply. The PPT is required to ensure an ungrounded input to the regulator. The control system contains both a generator terminal voltage regulator and an exciter field current regulator. These are known as the automatic or ac regulator and the manual or dc regulator respectively. When operating under control of th e dc regulator, a constant exciter field current is maintained, regardless of the operating operating conditions on the generator terminals. When operating under control of the ac regulator, a constant generator terminal voltage is maintained under varying load conditions. If the gen erator is connected to a large system through a low impedance tie, the generator cannot change the system voltage appreciably. The ac regulator, with very small variations in t erminal voltage, then then controls the reactive volt amperes (Var)s. If the generator is i solated from a system, the ac regulator controls the terminal voltage and the Vars are determined by the load. Most systems operate in a manner that is between these two extremes. That is, both Vars and volts are controlled by the ac regulator. Normal operation is with the ac r egulator in control, with an automatic transfer to the dc regulator in the event of loss of potential transformer feedback feedback as detected through Potential Transformer Failure (PTFD) or PT Undervoltage Detection (PTUV). In the regulator, PT Failure Detection requires two sets of PT inputs. There is automatic tracking between the ac and dc regulators to ensure a bumpless transfer transfer in either direction. A balance signal is available for di splay on the operator station or turbine control interface. A transfer between regulators can be initiated by the operator or, if supplied, by the PT failure detection algorithm. In addition to the reference input to the ac regulator summing junction, a number of both standard and optional inputs are possible.
The regulator includes a Local Area Network Network (LAN) (LAN) and RS-232C interfaces for external communication.
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Chapter 1 Overview
Besides the regulating functions, functions, the excitation excitation system s ystem contains protective limiter functions, startup and shutdown functions, and operator interfaces that are implemented in both h hardware ardware and/or software. The software is accessed via an RS-232C communication link using the GE Controls Systems Toolbox (toolbox). (toolbox). The toolbox toolbox is used to configure and ma intain regulators and exciters. It is Windows®-based and consists of a collection of programs (tools) running under a command shell.
EX2000, PWM Digital Regulator GEH-6375A
Figure 1-1. PMG Brushless Exciter Overview
Product Overview Hardware Design Optional hardware devices are also available, such as 420 mA transducers, PPT, and Field Ground Detector Detector Power Power supplies.
GEH-6375A User's Guide
The regulator hardware consists of a control core and a power power converter section, described in Chapter 2. The controller includes printed wiring boards containing programmable microprocessors microprocessors with with companion circuitry, circuitry, including electricallyelectricallyerasable programmable read-only memory (EEPROM) where the regulator’s system system blockware pattern is stored. The The power converter consists of input disconnects and filters, a dc link with charge control, IGBT devices, devices, output contactor and shunt, and control circuitry. circuitry.
Chapter 1 Overview
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Control Core (Regulator Module) Refer to figures 2-3 and 2-4 in Chapter 2.
The control core is mounted in two board racks on the outside of the core panel and is accessible while the regulator is operating. Also, behind the hinged outer door, several Input/Output (I/O) boards are mounted. The control core consists of all these circuit boards interconnected by ribbon cables and harn esses, which keep wiring to a minimum. Detailed hardware information including fuse and test point information, replacement instructions instructions and board layouts are provided in the r eferenced documents for each of the following following circuit boards. Power Supply and Contactor Driver (PSCD) board creates internal power supplies and redistributes the necessary power supply voltages for the other control core circuit boards. boar ds. An isolated 70 V dc supply is also produced and used for LTB LTB board inputs. The PSCD board also produces the contactor coil voltage for the MDA output and charge control contactor (refer to GEI–100241). Gate Driver and Dynamic Discharge (GDDD) controls the gating of the IGBTs for bridge output and Dynamic Dynamic Discharge Discharge control. It also also isolates and and scales dc output, output, dc link voltage, shunt feedback and h eat sink temperature feedbacks (refer to GEI– 100240).
between control devices and LAN Terminal Board (LTB) provides an interface between external devices such as contactors, relays, indicators, lights, pushbuttons and interlocks (refer to GEI−100022). Microprocessor Microprocessor Application Application Board (TCCB) contains software transducering algorithms that mathematically manipulate manipulate the inputs from the isolation and scaling printed wiring boards. boards. These inputs are analog feedback feedback signals from the the current and voltage transformers, which monitor generator output and line voltage, and from the bridge ac input and and dc output voltages voltages and shunt feedbacks feedbacks (refer to GEI GEI−100163). I/O Terminal Board (NTB/3TB) includes an RS-232C communication port for connecting to a personal computer (PC). The optional field ground detector inputs are connected to the NTB board (refer to GEI–100020). Drive Control and LAN Control Board (LDCC) controls LAN communication and permits operator access and control via the Programmer keypad. It also contains the drive control microprocessor microprocessor which monitors start/stop sequencing, alarms, trips and outer loop regulators and motor control microprocessors microprocessors which monitors the field voltage and current regulators, gating and overcurrent protection (refer to GEI– 100216, for reprogramming the LDCC board refer to GEI −100217). Relay Terminal Board (RTBA) provides seven output relays with form C contacts available for customer use which can be driven from a remote input or directly from the relays on th e LTB board (refer GEI–100167). ARCNET Link (ACNA) board provides the connection point for the ARCNET LAN communications.
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Chapter 1 Overview
EX2000, PWM Digital Regulator GEH-6375A
Figure 1-2. EX2000 Brushless Unit
Power Converter Module The power conversion section consists of an input section, a dc link, and the converter output section. The input section is a 3-phase diode bridge with input filters. The range of the ac input is from 90 V rms up to 275 V rms. Frequency inputs range as high as a n ominal 360 Hz. It can be a single phase or three phase input from a PMG, auxiliary bus or generator terminal fed. An input PPT is not required for the PMG input. A PPT is required for an auxiliary bus or generator terminal feed. An optional voltage doubling feature is available for units requiring higher forcing capability. This circuit is normally powered from the GDDD board but may be powered through the dynamic discharge power source resistor RDS if control power is lost.
An optional backup source from nominal 125 or 250 V dc batteries is filtered, diode isolated and combined with the three-phase diode bridge output. These sources charge the power capacitors through a charge control resistor, RCH, which forms the dc link portion of the power converter module. The dc link is the unregulated source voltage for the control core power supplies and the output power through th e IGBTs. A coarse control of the voltage level of the dc link is provided by the dynamic discharge circuit. This circuit will dissipate excess power from the dc link (possible due to a regeneration effect from the field of the r otating exciter) through the dynamic discharge resistor, RDD. The converter output section takes the dc link source voltage and pulse width modulates it through the IGBT devices. The output voltage i s determined by the following formula: Voutput = Vinput * (time on/(time on + time off))
For more information refer to Chapter 5, Figure 5-1.
where Vinput is the dc link voltage, time-on is the conduction time of the IGBT devices and time-off is the n on-conduction time of the IGBTs. The chopping frequency of the IGBTs is a pproximately 1000 Hz. This output is fed to the rotating exciter field as a regulated voltage or current. A single pole contact from the MDA contactor isolates the regulator from the field. An output shunt monitors the field current.
GEH-6375A User's Guide
Chapter 1 Overview
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Optional Hardware Modules Scaling is provided in the PWM software.
There are a limited number of structured options available with the PWM regulator. Up to four 4-20 mA output transducers are available for customer use. They ar e driven from D/A converters located on the NTB board, and are non-adjustable devices. A 50/60 Hz, 25 kVA Power Potential Transformer (PPT) is available for units that are connected to an auxiliary bus or generator output termina ls. This PPT may or may not be supplied inside the regulator enclosure. Power to the primary should be fused per the application notes found in the control elementary supplied with the equipment. This transformer is sized to supply rated excitation requirements continuously and still be capable of operation at ceiling excitation for a short time. An optional Field Ground Detector Power supply may be supplied for some systems. This power supply provides 24 V control power to the Field monitor unit mounted in the generator exciter housing. A 120 V ac feed is required to power this supply.
Software Design The regulator application software consists of modules (blocks) combined to create the required system functionality. Block definitions and configuration parameters are stored in read-only memory (ROM), while variables are stored in random-access memory (RAM). Microprocessors execute the code. Diagnostic software is transparent to the user. A programmer module with a digital display and keypad allows an operator to request parameter values and self-checks.
Software The exciter application emulates traditional analog controls. It uses an open architecture system, which uses a library of existing software blocks. The blocks individually perform specific functions, such as logical AND gates, proportional integral (PI) regulators, function generators, and signal level detectors. These blocks are tied together in a pattern to implement complex control functions. For example, a control function such as the under-excitation limit (UEL) is included as an ac r egulator input by setting software jumpers in EEPROM. The relevant blockware is enabled by pointing the block inputs to RAM locations where the inputs reside (the UEL requires megawatts, kilovolts and megavars). The UEL output is then pointed to an input of the ac regulator summing junction. The software blocks are sequentially implemented by the block interpreter in an order and execution rate defined in the toolbox. The blockware can be interrogated while running by using the toolbox. The dynamically changing I/O of each block can be observed in operation. This technique is similar to tracing an analog signal by using a voltmeter.
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Chapter 1 Overview
EX2000, PWM Digital Regulator GEH-6375A
AC and DC Regulators The power system stabilizer (PSS) is an optional function.
The ac or automatic regulator and, dc or manual regulator are software functions again emulating traditional analog controls. The ac regulator reference is from a static counter and is compared t o the generator terminal voltage feedback to create an error signal. In a ddition to the reference signal input to the ac regulator summing junction, the following inputs can be used to modify the regulator action.
Alternatively it can be used to provide line drop compensation.
Reactive Current Compensation (RCC): The generator voltage is allowed to vary in order to improve reactive volt amp (VA) sharing between generators connected in parallel. Generator voltage decreases as overexcited reactive current increases, and increases as underexcited r eactive current decreases. Under-excitation Limit (UEL): Under-excited Vars must be limited to prevent heating of the generator iron core and to ensure dynamic stability of the turbine generator. This is done by an under-excitation limiter that takes over when a specified limit curve is reached and prevents operation below this limit. V/Hz: The ratio of generator voltage to frequency (V/Hz) must be limited. This prevents overfluxing the generator and/or line-connected transformers caused by overvoltage operation or under-frequency operation, or a combination of the two. Power System Stabilizer (PSS): The introduction of high g ain, high initial response exciters can cause dynamic stability problems in power systems. The advantage of these exciters is to provide improved transient stability, but this is achieved at the cost of reduced dynamic stability and sustained low frequency oscillations.
The PSS is an optional function.
The PSS is fed with a synthesized speed signal based on the integral of accelerating power. This indicates the rotor deviation from synchronous speed. This signal is conditioned and fed into th e summing junction of the continuously acting ac regulator so that under deviations in machine speed or load, excitation is r egulated as a composite function of voltage and unit speed. The stabilizer therefore produces a damping torque on the generator rotor and consequently increases dynamic stability. Over-excitation Limiter (OEL): It is necessary to limit generator excitation current off-line to prevent overfluxing the generator and connected transformers. Online, it must be limited to prevent field thermal damage. The limiting action is performed by the excitation current regulator. The current regulator takes control of bridge gating if the regulator (automatic or manual) calls for exciter field excitation current in excess of a predetermined pick-up level.
The dc or manual regulator is configured as a field current regulator using shunt feedback and comparing it to the manual regulator static adjust reference. It will maintain a constant exciter field current based on the setpoint adjuster. The online and offline field current regulators are low value gate selected with the inner loop regulator output to select the appropriate firing level for the IGBT bridge.
Scaling It is necessary to scale the software in each exciter for application with a particular generator. The regulators use normalized values of counts to represent one per unit (1 pu). Typically 1 pu equals either 5000 or 20000 counts. This means that the feedback value for a particular variable, such as dc link voltage (VDCLINK = 1 p u) or bridge current (AFFL = 1 pu), must be normalized by using a multiplier to equal the prerequisite value of counts when it is at 1 pu. See Chapter 4 for more details.
GEH-6375A User's Guide
Chapter 1 Overview
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Faults Refer to GEI 100242 for fault codes, interpretation, and troubleshooting. −
The EX2000 exciter has a sophisticated self-diagnostic capability. If a problem occurs, a fault code flashes in the programmer display showing a fault name and number. The fault number also appears on the display on the LDCC in coded form.
Simulator Located within the core software is a sophisticated system simulation program that models the exciter and gen erator behavior. The simulator is activated via a software jumper in EEPROM. The simulator physically operates the field contactors when a start signal is issued to the exciter. If dc link voltage is present, current may flow in the exciter field.
This tool is useful for training, startup, and calibration checkout.
Signals representing the field and the generator feedbacks are simulated in the microprocessor application board (TCCB) and fed to the transducering algorithms, in place of the real feedbacks. Once the exciter is scaled for a particular generator, the simulator uses that scaling. For example, after a successful startup sequence is performed in simulator mode, the operator interface will displays the exciter voltage and current and generator voltage applicable to th at particular unit.
Note Scaling and operation of the simulator is discussed in Chapter 6.
Human-Machine Interface (HMI) Refer to the control elementary supplied with the equipment for further information.
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Chapter 1 Overview
The PWM has a HMI datalink with the turbine controller over the Status_S page for regulator information. Optional interfaces include, discrete switches and meters, direct DCS control through an Innovation Series Controller, or some other device.
EX2000, PWM Digital Regulator GEH-6375A
Chapter 2 Hardware System Description
Introduction This chapter describes the EX2000 PWM regulator hardware structure, and overall operation. When reading these descriptions, refer to Figure 1-2, the specific unit elementary, and the excitation layout diagrams provided with the equipment. Section
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Packaging ........................................................................................................... 2-2 Environmental.............................................................................................. 2-2 Enclosure ..................................................................................................... 2-2 Ratings ............................................................................................................... 2-3 Input Ratings................................................................................................ 2-3 Output Current Rating .................................................................................. 2-4 Voltage Control Range................................................................................. 2-4 Power Profile Rating .................................................................................... 2-4 Power Converter Hardware ................................................................................. 2-5 Ac and Dc Input Devices.............................................................................. 2-6 Dc Link and Dynamic Discharge .................................................................. 2-6 IGBT And IAXS Devices ............................................................................. 2-6 Output Contactor MDA................................................................................ 2-7 Output Shunt SHA ....................................................................................... 2-7 Control Electronics Module................................................................................. 2-7 TCCB (DS200TCCB) .................................................................................. 2-8 PSCD (IS200PSCD)..................................................................................... 2-8 GDDD (IS200GDDD).................................................................................. 2-8 PTCT (DS200PTCT).................................................................................... 2-8 NTB/3TB (531X305NTB)........... ................................................................. 2-9 LTB (531X307LTB) .................................................................................... 2-9 RTBA (DS200RTBA) .................................................................................. 2-9 ACNA (DS200ACNA)................................................................................. 2-9 Inputs and Outputs .............................................................................................. 2-9 Generator Inputs........................................................................................... 2-9 4-20 mA Inputs ...........................................................................................2-10 Generator Line Breaker Status.....................................................................2-10 Generator Lock-Out Trip.............................................................................2-10 Additional I/O.............................................................................................2-11
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Chapter 2 Hardware System Description
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2-1
Packaging GEI-100228 provides information on Receiving, Storing, and Warranty Instructions for DIRECTO-MATIC ® 2000 Equipment. This document should be consulted upon receipt of the regulator. Each regulator will withstand the following environmental conditions without damage or degradation of performance.
Environmental Temperature requirements for the regulator should be maintained within the limits in GEI−100228 during transport and handling. Once installed, the operational limits of an ambient temperature of 0 t o +45 °C, outside of the convection cooled cabinet, should be maintained. It is expected that the hottest board entry temperature will be approximately 60 °C allowing the use of 70 °C parts. Maintain 5 to 95% relative humidity with no external temperature or humidity excursions that would produce condensation. The control equipment is also designed to withstand 10 ppb of the following contaminants: •
reactive sulfur
•
reactive chlorine
•
hydrogen sulfide
•
sulfur dioxide
•
chlorine dioxide
•
sulfuric acid
•
hydrochloric acid
•
hydrogen chloride
•
ammonia
Enclosure The standard offering is a NEMA 1 or IP20 equivalent, 90 inches high by 24 inches wide and 20 inches deep. An optional 36 inch wide enclosure is also available. In some instances, just the regulator panel without enclosure will be pr ovided. This panel measures approximately 63 inches high by 17 inches wide by 18.5 inches deep. Other enclosure types are available. The estimated weight is 1200 pounds with NEMA 1 24 inch enclosure, and 900 pounds without enclosure. The estimated watt losses are a maximum 200 watts for all applications.
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Chapter 2 Hardware System Description
EX2000, PWM Digital Regulator GEH-6375A
Ratings Each regulator has a specific output limit rating based on the application of th e regulator and limited by the shunt chosen for the application. The following ratings information is the maximum output of the standard r egulator, using a 25 A shunt. For shunt ratings other than 25 A, the output current limitations will be reduced proportionately. Name plate information should be used for accurate ratings.
Input Ratings The ac input is the primary input power to the brushless regulator. The range of input ac is from 90 V rms up to 27 5 V rms. The ac input may be single or 3-phase. The input ac may be from a permanent magnet generator (PMG), customer supplied auxiliary bus, or bus fed from the generator. The ac source input to the regulator should have an impedance of 6 % nominal based on an estimated 20 A, 10 kVA source.
PMG Input The voltage and frequency for PMG-based input will start from 0 and increase to rated as a function of generator speed. Rated input from the PMG system can be as high as 250 V ac rms / 36 0 Hz. Nominal voltages can be 100 V ac rms up to 250 V ac rms. With overspeed conditions, the maximum is 275 V ac rms / 440 Hz. Since the PMG is ungrounded and only used to source power to the brushless regulator, no input transformer is required. PMG systems on gas turbines will see extended periods of time at < 50 % speed operation on startup. This is due to the purge cycle needed by the gas turbine. Since the PMG may be the only input power to the regulator, the control will initialize at ≤ 60 V ac rms (~50% speed).
Auxiliary Bus Input Auxiliary bus-based systems require an input transformer to isolate the input to th e brushless regulator from the customer power system. This insures that the power source to the brushless regulator is ungrounded. The transformer can be external to the enclosure that houses the brushless r egulator, but will generally be located in the panel. The secondary voltage can range from 90 V ac rms up to a max. 275 V ac rms. Nominal secondary voltages can be 100 V ac rms up to 250 V ac rms. Rated frequency for the auxiliary bus-based systems can be 50 Hz or 60 ±10%.
Bus Feed from the Generator Bus fed-based systems will require an input transformer to isolate the input to the brushless regulator from the power system. This also insures that the power source to the brushless regulator is ungrounded. The transformer will be external to the enclosure that houses the brushless regulator. The secondary voltage can range from 90 V ac rms up to a max. 275 V ac rms. Nominal secondary voltages can be 100 V ac rms up to 250 V ac rms. Rated frequency for the bus feed based systems can be 50 Hz or 60 ±10 %. If a bus fed system is applied on a black-start gas turbine, this input may start at 20 % of rated speed, therefore, the voltage and frequency will start at 20 % of rated.
GEH-6375A User's Guide
Chapter 2 Hardware System Description
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DC Input Power The dc source input power is generally provided from a battery bus. This source is a back up to the primary ac input power source. It can be used as the primary input power for starting black-start turbine generators. The nominal battery bus voltages are based on a 110/125/ 220 / 250 V dc. Therefore, the operating range for the dc input is from 80 V dc up to a max of 290 V dc.
Output Current Rating The bridge is capable of delivering th e following absolute maximum output: •
25 A dc continuously over the specified temperature range
•
40 A dc for 20 s once every 30 minutes after continuous operation at 25 A dc over the specified temperature range.
The PWM bridge is monitored for excessive temperature by a heatsink sensor. Both alarm and trip signals are available.
Voltage Control Range The PWM bridge is capable of t wo-quadrant operation (positive and negative output voltage, positive current). This allows operation near zero voltage. The PWM bridge has two active transistors and will operate in zero vector mode. This will allow the output voltage to be chopped in PWM fashion from +V dc to 0 for positive voltage commands and -V dc to 0 for negative voltage commands. The chopping frequency is approximately 1 kHz. The IGBT bridge does not provide a low impedance path, which would provide rectification when gating is disabled. This prevents runaway conditions known to occur on brushless units having rotating diode failure. The four flyback diode structure provides this inherently.
Power Profile Rating The output power profile is a function of line impedance, line current rating, operating point (I dc and V dc), and capacitor current rating. Peak current is limited by IGBT rating. In general higher current output is available at lower output voltages. Output current (I dc) can be higher than line current rating. The regulator shall be capable of matching the following power profile. The continuous operating area is bounded by the minimum of the capacitor limit, line limit, 25 A dc, or maximum output curve and the x (V dc) and y (I dc) axis. The y-axis shows input line amps (rms), capacitor amps (rms), or output amps (dc) for a given output V dc and I dc. The curve labeled 25 shows rms capacitor current on the y-axis for a given V dc and 25 I dc.
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Chapter 2 Hardware System Description
EX2000, PWM Digital Regulator GEH-6375A
Line and capacitor currents as functions of dc voltage and current 35 at 200 Vdc and 25 Adc line current is 15 Arms
IGBT limit 25Adc
30
cap limit 10 Arms
t n e r r u c ) 25 c d A ( t u p t u 20 o r o , ) s m r
line limit 12.5 Arms maximum output
25 Adc
A ( 15 r o t i c a p a c , 10 ) s m r A ( e n i L
25
at 50 Vdc and 25 Adc capacitor current is 10 Arms
5
0 0
50
100
150 200 Output voltage (Volts dc)
250
300
350
Figure 2-1. Typical Power Profile The curve labeled 25 A dc shows rms line current on the y-axis for a given output V dc and 25 I dc. Negative voltage operation is not shown.
The line limit curve corresponds to given V dc and I dc, which would result in rated line current. The cap limit curve corresponds to given V dc and I dc, which would result in rated capacitor current. The following graph illustrates the various limits.
Power Converter Hardware For the following discussions, use elementary drawing 03A and the panel layout drawings (Figures 2-2 through 2-5) as references. The elementary drawing is typical for all applications. On a requisition basis, the output shunt (SHA), charge resistor (RCH), and dynamic discharge r esistor (RDS) may change. Also, various combinations of the input source power may exist. A single phase PMG with battery backup is assumed.
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Ac and Dc Input Devices The ac input device DSWAC is a 3-phase, 600 V ac, 30A molded case industrial circuit breaker. For single-phase applications, the L1 and L3 connections should be used. The dc input device DSWDC is a two phase, 250 V dc, 30 A molded case industrial circuit breaker. These input devices are mounted at the top of the panel, easily accessible for operation as a disconnect during equipment maintenance or inspection. All of these components are located at the top of the panel, behind the ac and dc disconnects.
The ac input source is filtered by snubber RC networks and rectified by a 3-phase diode bridge (DM1, 2 and 3). The dc output of this bridge charges capacitors C1, C2, C3, and C4, forming the dc link. The dc supply is filtered through inductors (LPDC and LNDC) and battery capacitor C1F. It is then fed directly to the dc link through isolation diode DM4. MOV1 and MOV2 are provided for surge protection.
Dc Link and Dynamic Discharge A charge control resistor (RCH) mounted on the heat sink assembly is provided to limits inrush current during powerup and capacitor charging. The second pole of the MDA contactor controls application or removal of the charge control resistor. The dc link provides the source power for internal board power supplies via cable DCPL to the PSCD board. The control power supply is designed to operate over a range of 60 to 600 V dc on the dc link. Auxiliary diodes DM5 allow stored energy in the exciter to be returned to the dc link when the output contactor MDA opens. Excessive voltage buildup in the dc link during regeneration is controlled through the dynamic discharge circuit. This circuit monitors the level of the dc link and will dissipate energy through the dynamic discharge resistor (RDD) mounted at the top of the panel to prevent overvoltage of the power circuit and board rack supply. The C leg of the 3-phase IGBT pack is controlled by the dynamic discharge circuitry on the GDDD board. An alternate source of power for the discharge circuit is provided through the RDS resistor, also to the GDDD board, in the event that control power is lost. Jumper settings on the GDDD board set the control level of th e dc link by the dynamic discharge circuit.
IGBT And IAXS Devices The dc link also provides th e unregulated power source for the Insulated Gate Bi polar Transistor (IGBT) bridge used to provide the exciter field current. The bridge consists of legs A and B of the 3-phase, 50 A, 1200 V IGBT pack. Only leg A upper and leg B lower IGBT’s are active. Leg A lower and leg B upper are permanently inactive. Controlled by the microprocessor-based digital regulator, the leg A and B are modulated to pulse the dc link supply and feed the resulting output to the field of the rotating brushless exciter. The output voltage is determined by th e following formula: Voutput = Vinput * (time on/(time on + time off))
where Vinput is the dc link voltage, time on is the conduction time of the IGBT devices and time off is the non-conduction time of the IGBTs. The chopping frequency of the IGBTs is approximately 1000 Hz.
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EX2000, PWM Digital Regulator GEH-6375A
The IAXS board provides the connection of the dc link capacitors to the IGBT bridge, dynamic discharge control and gate control from the GDDD board. The IAXS board is also the connection point for the dc output voltage and sensing feedbacks to the control circuitry.
Output Contactor MDA The output contactor MDA is described in GEK −83756. It is a double pole, single throw, 600 V dc, 50 A contactor, isolating the positive leg of the bridge output. The second pole is used to remove the charge control resistor RCH. The power for the contactor coil is provided from the PSCD board. This voltage is only present when the control has been commanded to run. When the dc link voltage is not present, there is no power available to drive this contactor.
Output Shunt SHA The output current is monitored by the control via the 100 MV feedback shunt SHA. The shunt rating is application specific. A range from 1 A to 25 A maximum is possible. The shunt rating must be less than twice the exciter amps full load.
Control Electronics Module The control electronics module contains powerful programmable microprocessors with companion circuitry, including EEPROM, to process the application software. It is a module assembly that is located on the front door assembly of the power conversion module. Elementary diagram sheet A04 and Figure 2-7 shows the connections of the various boards in the control module. This control module assembly contains the main processor board (LDCC), microprocessor application board (TCCB), power supply and contactor driver board (PSCD), and the gate driver board (GDDD). These boards are interconnected through ribbon cables. Each board has a unique GEI, which documents the hardware layouts, test points, fuses and other information for each individual board. These are referenced in Chapter 1. The LAN and Drive Control board (LDCC), which is the main processor board, provides the IGBT gating circuit control and regulator functions including: The LDCC board also contains both isolated and non-isolated circuits for communication inputs to the exciter's controller. The LED display and keypad programmer is on this board.
•
automatic voltage regulator
•
field current regulator
•
field current limit regulator
•
volts/hertz limit regulator
•
reactive current compensation
•
under-excitation limit regulator
Optional functions include: • •
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VAR/power factor regulator power system stabilizer
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TCCB (DS200TCCB) The microprocessor application board (TCCB) is essentially a transducer board. The isolated and scaled generator PT and CT signals are fed from the PTCT board to the TCCB board. The TCCB uses voltage controlled oscillators (VCOs) to transform the analog voltage signals into digital signals. Software transducers process the voltage and current signals and then calculate generator data. This information is passed to the LDCC control processors for use by the regulators. The regulator simulation software also resides in the TCCB.
PSCD (IS200PSCD) The Power Supply and Contactor Driver board (PSCD) is powered from the dc link through stab-on terminals DCPL1 (+) and DCPL2 (-). The control operates from 80 400 V dc as nominal range inputs. Transient operation to 600 V dc is possible during maximum operation of the dynamic discharge. This board produces control power for distribution to the other control module boards. The main supply produces ±24 V, ±15 V, and +5 V for control boards (LDCC and TCCB) A 17.7 V ac squarewave is distributed through high frequency transformers to the gate driver and LTB inputs power supplies. Auxiliary to the main supply are supplies for generating isolated 70 V dc (sufficient to power 13 LUP inputs ) and an isolated SHVI/SHVM power for future applications. The contactor control power supply from the PSCD board is sized to deliver up to 0.75 A dc. Power is taken directly from the dc link and converted to 105 V dc by a buck converter. The enable of the MDA contactor is through an optically coupled signal, which is logically in parallel with the coil of K1. Relay K1 is driven from the LDCC board when the control is commanded to run. Relay K86 is used as the controls permissive to run and emergency stop. Dropping out K86 will immediately stop the regulator. Coil voltage is from the 70 V dc power supply on the PSCD board.
GDDD (IS200GDDD) The Gate Driver and Dynamic Discharge board (GDDD) provides the interface isolation between the IGBTs and the main processor firing circuits. Dynamic discharge circuit control is implemented on the GDDD board as well as the gating circuits for the A and B leg active IGBTs. This board also provides the instrumentation of the r egulator. Output dc voltage, dc link voltage, shunt current mV input, and th e heat sink thermistor input are processed on the GDDD board and sent to the LDCC processors for use by the regulators.
PTCT (DS200PTCT) The Potential Transformer Current Transformer (PTCT) board isolates and scales th e voltage and current signals from the PTs and CTs. It also provides auxiliary inputs and outputs for either low voltage (± 10 V dc) or 4-20 mA current signals. Secondaries of the isolation transformers are passed to the TCCB board through the JKK ribbon connector.
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EX2000, PWM Digital Regulator GEH-6375A
NTB/3TB (531X305NTB) The NTB/3TB serves as a general purpose terminal connection board. Connections are made as an interface between the control core and other devices. Th e RS-232C serial port is located on this board. When supplied, the field ground detection inputs from the ground detector receiver are connected to the auxiliary VCO inputs on the NTB/3TB board.
LTB (531X307LTB) The LAN Terminal Board (LTB) is an I/O termination board that serves as an interface between the control core and other devices. Ribbon cable RPL allows software variables pointed to the seven low voltage, low current, form C LTB output relays to control higher voltage, higher current, form C RTBA board relays. Jumper settings on the RTBA board determine if the LTB relays or external connections operate the RTBA relays. The eight LTB (or LUP) inputs are connected to the LDCC board through 8PL for use by the regulator controls.
RTBA (DS200RTBA) The Relay Terminal Board (RTBA) board contains seven form C, DPDT relays that can be software driven via the LTB pilot relays or externally driven. The relay contact outputs are used for external customer interface. Each relay contains an LED that indicates when the relay is energized.
ACNA (DS200ACNA) The Status_S data link connection to the turbine controller is made on the ACNA board.
The ARCNET Board (ACNA) serves as the connection for the ARCNET data link for the regulator. Termination is made using co-axial cable. Each ACNA can terminate two co-axial cables.
Inputs and Outputs The regulator has a limited amount of hard inputs and outputs (I/O) that can be supported. For most applications, these are to be conducted over the Status_S data link. The following sections define the minimum I/O that must be supported.
Generator Inputs Potential Transformer Inputs Up to three sets of 3-phase PT inputs are supported. These inputs are a nominal 120 V secondary with software adjustments available for other nominal secondary voltages. The inputs are less than a 10 VA burden on the PT inputs. The first two PT sets are used to supply generator line voltage feedback information to the automatic (ac) regulator for control of the generator output voltage. The first PT set is used for generator control. The second set is used for PT failure detection and can be configured for control should the first set fail. These inputs also supply speed/frequency feedback information for the regulators, limiters, and protection functions, including the optional Power System Stabilizer (PSS).
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Optional PT isolation switches for all three three sets of inputs may be supplied.
The third set of 3-phase PT inputs provides line side voltage and is used by the control for an optional voltage matching feature. These connections are made directly to the PTCT board.
Current Transformer Inputs Optional CT isolation shorting switches switches for each phase input may be supplied. supplied.
One set of 2-phase CT inputs is supported. Phase A and phase C currents are required by the r egulator. These CTs supply generator line current feedback information for use by regulator, limiters, and metering functions in the brushless regulator control, including the optional Power Power System Stabilizer (PSS). The inputs require a nominal 5 A secondary CT input. Software adjustments are available down to a nominal 3 A secondary input. The CT burden is less than 1 VA per phase. These connections are made directly to the PTCT board.
4-20 mA Inputs Optionally, Optionally, the regulator r egulator can support two 4 to 20 mA inputs for signals used to modify the overexcitation limiter/protection limiter/protection based on the cooling of the generator. On air cooled generators this input is proportional to the cooling air temperature for the generator. On hydrogen cooled generators this input is based on hydrogen pressure of the generator.
Generator Line Breaker Status One form A contact input from the generator output circuit breaker is used by control, limiter, and protection functions. This contact is connected to an LTB input. The contact may be powered using the 70 V dc supply from the PSCD board.
Generator Lock-Out Trip One form A (closed when r eset) contact input from a customer trip relay (86G typically) is supported for an external trip of the excitation control system. This contact must be powered from the 70 V dc power supply on the PSCD board.
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EX2000, PWM Digital Regulator GE G EH-6375A
Additional I/O In addition to the I/O listed above, Table 2-1 lists minimum inputs and outputs that are supported.
Note Not all applications will require each of the contact I/O or 4-20 m A inputs or outputs listed. Refer to the job specific elementary for those supplied. Table 2-1 Minimum Inputs and Outputs supported Input/Output
Description
Input Regulator On / Off (Closed = Regulator On)
Used to start and stop the brushless regulator.
Input Regulator Selector AC/DC (Closed = AC )
Used to select the controlling regulator, auto (ac) or manual (dc).
Input Regulator Raise (Close = Raise)
Interfaces to the active regulator’s reference adjuster, ac or dc, and raises the setpoint.
Input Regulator Lower (Close = Lower)
Interfaces to the active regulator’s reference adjuster, ac or dc, and lowers the setpoint.
Input PSS Enable/Off (Closed = Enable)
Allows the PSS control control to operate if minimum minimum load permissives are reached.
Input Status of Control Output Contactor
Used to monitor the status of the MDA contactor.
Output Exciter Alarm (30EX)
Provides a global exciter trouble alarm for customer annunciation.
Output Protective Transfer to dc Regulator / Transfer Regulator alarm (60EX)
Provides an indication of an automatic transfer to manual regulator.
Output Re Regulator On
Provides an an indication that the regulator is operating
Output Exciter Trip Request (94EX)
Request from the regulator to immediately trip the generator. Usually directed to the 86G device.
Output Exciter Field Ground Alarm/Trip Alarm/Trip (64FA (64FA or 64FT) 64FT)
Can be either an alarm or trip contact depending on customer preference.
The voltage inputs supported are: •
Input from Exciter Field Ground Detector Alarm (+ 24 V)
•
Input from Exciter Field Field Ground Detector Detector Malfunction (+24 V)
•
Input from Exciter Field Groun Ground d Detector Diode Fault (+24 V)
Up to four 4 to 20 mA outputs are also supported. These outputs are provided through the digital to analog converters on the NTB/3TB board. They are software configurable. Typical uses are regulator output voltage, regulator output current, and regulator balance.
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• •
Figure 2-2. 2-2. Mechanical Layout
Note This layout is not certified for construction .
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EX2000, PWM Digital Regulator GE G EH-6375A
Figure 2-3. Front View
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• •
) Figure 2-4. Front View (Door Removed
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EX2000, PWM Digital Regulator GEH-6375A
Figure 2-5. Bridge Components
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• •
Figure 2-6. Bridge Components (Isometric)
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EX2000, PWM Digital Regulator GEH-6375A
TO TURBINE CONTROL OPERATOR INTERFACE METER DRIVER OUTPUTS QTY (4) 1PL
3PL, 2PL
MICROPROCESSOR APPLICATION BOARD
MAIN PROCESSOR BOARD
2PL
LDCC
GDPL, PPL
GATE DRIVER AND DYNAMIC DISCHARGE BOARD
POWER SUPPLY AND CONTACTOR DRIVER BOARD PSCD
TCCB
GDDD
DCPL, MDPL
JKK
CPL
GPL, 8PL 4 PL, 2PL
IOPL, 8PL PTCT BOARD
ARCPL
ARCNET BOARD AC INPUT
ACNA
POWER CONVERTER MODULE (IGBT) DC INPUT 3 PHASE VOLTAGE SENSING INPUT
2 PHASE CURRENT SENSING INPUT DC OUTPUT TO EXCITER FIELD
RPL
LTB
CONTACT INPUTS/OUTPUTS
RTBA
CONTACT OUTPUTS
NTB/3TB
CONTACT INPUTS
RS232 PORT
WORK STATION
Figure 2-7. Typical Connection Diagram
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• •
Notes
2-18
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Chapter 2 Hardware System Description
EX2000, PWM Digital Regulator GEH-6375A
Chapter 3 Software System Overview
Introduction The regulator uses microprocessor-based software that includes adjustable parameters. These parameters perform many functions once controlled through adjustable hardware and software combinations. The parameters are modified to customize the regulator to the specific hardware and application. They also enable field and maintenance personnel to fine tune the regulator for optimal performance. Use the Control System Toolbox (toolbox) and LDCC board programmer to make software adjustments. Section
Page
Configuration Tools ............................................................................................ 3-2 Programmer Module ........................................................................................... 3-2 Software Design........................................................................................... 3-2 Standard Functions................. ............................................................................. 3-3 Automatic Voltage Regulator (AVR) Ramp............................ ............... ....... 3-3 Automatic Voltage Regulator Setpoint....................... ............................. ...... 3-3 Automatic Voltage Regulator ....................................................................... 3-3 Field Regulator (FVR) Ramp........................................................................ 3-3 Field Regulator..................... ........................................................................ 3-3 Under Excitation Limiter (UEL) ................................................................... 3-4 Over Excitation Limiter (OEL)..................................................................... 3-4 Firing Block ................................................................................................. 3-4
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Configuration Tools The toolbox is used to configure, maintain, and fine tune the regulator. It in cludes an extensive database of definitions, accessed and manipulated using menu driven selections. Additionally, the toolbox can graphically display the exciter's program logic on the computer screen. By viewing the logic flow, you can better understand and manipulate the exciter's adjustable values. The toolbox is used at the factory to initially configure and test the systems. At the customer site, it enables GE field engineers and other trained personnel to troubleshoot, fine-tune, and maintain the in stalled regulator. Optional tool based modules provide real display of control variables and communications data. Refer to GEH−6404 for more information and PC requirements.
Programmer Module The regulator includes a programmer module with a 16-character digital display and an alphanumeric keypad. It functions as an operator interface for software adjustments and diagnostic testing when the toolbox is n ot available.
Note Permanent changes made using the programmer module must also be made in the toolbox to keep them up to date with the exciter's software configuration. Get contact information from GEI−100242. Refer to GEI −100242 for more information on the programmer module.
Software Design The exciter application consists of functional software modules (blocks) combined to perform to system requirements. Block definitions and configuration parameters are stored in read-only memory (ROM), while variables are stored in random-access memory (RAM). Microcontrollers execute the code. The exciter application emulates traditional analog controls. The software uses an open architecture system, which uses a library of existing software blocks. The blocks individually perform specific functions, such as logical AND gates, proportional integral (PI) regulators, function generators, and signal level detectors. These blocks are tied together in a pattern to implement complex control systems. For example, a control function such as the under-excitation limit (UEL) is included as an ac regulator input by setting software jumpers in EEPROM. The relevant blockware is enabled by pointing the block inputs to RAM locations where the inputs reside (the UEL requires megawatts, kilovolts and megavars). The UEL output is then pointed to an input of the ac regulator summing junction. This technique is similar to tracing an analog signal by using a voltmeter.
3-2
• •
The software blocks are sequentially implemented by the block in terpreter in an order and execution rate d efined in the toolbox. The blockware can be interrogated while running by using the toolbox. The dynamically changing I/O of each block can be observed in operation.
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EX2000, PWM Digital Regulator GEH-6375A
Standard Functions These inputs and outputs can be monitored through the toolbox.
Table 3-1 is a description of the inputs and outputs for the more significant blocks used in the exciter. Also, the significant adjustments of those functional blocks are described as adjustable constants. These constants represent limits, gains, and setpoints. They are functionally equivalent to potentiometers or other discrete adjustment devices used in previous excitation systems.
Automatic Voltage Regulator (AVR) Ramp The AVR ramp block accepts an input from the operator through the Status-S page for auto regulator raise or lower. The reference then ramps at a predetermined rate, within an upper and lower limit (usually 0.9 to 1.1 pu terminal V). The output can be preset to a value upon startup. Automatic tracking of the AVR track value is performed when operating in manual regulator (refer to Figure 3-2).
Automatic Voltage Regulator Setpoint The AVR setpoint block sums the output from the reactive current compensation (RCC), AVR ramp, UEL output, and power system stabilizer (PSS) output. This sum is compared to the V/Hz reference in a minimum select block and then passed through a high limiter as the AVR output signal. By selecting a negative or positive gain, line-drop or droop compensation mode may be selected on the RCC. An auto/manual command by the operator generates auto active or manual active status indicators. A PT failure can also select manual (refer to Figure 3-3).
Automatic Voltage Regulator The AVR block combines the AVR setpoint with the n egative generator terminal volts to provide an error signal. This is passed through to the automatic regulator proportional and integral gain sub-blocks, and then passes through the auto regulator limits to the manual voltage regulator (refer to Figure 3-4). The auto regulator is modeled by the following transfer function: AVR out = AVR error (Kp + KI)/S
Field Regulator (FVR) Ramp The FVR ramp block accepts an input from the operator through the Status-S page for manual regulator raise or lower. The reference then r amps at a predetermined rate within an upper and lower limit (usually 0.7 pu VFNL to 1.2 pu VFFL). The output can be preset to a value upon startup. When in auto regulator mode, the FVR ramp tracks the value of exciter field current (IFE) (refer to Figure 3-5).
Field Regulator The exciter field regulator is configured as a current regulator. The reference input to the FVR is from either the manual r egulator ramp block or the AVR. When fed from the AVR, the field regulator is used a s an inner loop. A bridge firing enabled signal is also provided to keep the exciter turned off until bridge firing is enabled (refer to Figure 3-6).
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Under Excitation Limiter (UEL) The UEL blocks accept watts and volts as inputs and calculates a VAR reference. Using a table lookup, which approximates the underexcited capability of the generator, the Var reference is then compared to the actual unit Vars to develop a Var error signal. The error signal is then passed through a proportional and integral regulator sub-block to keep the ma chine within its underexcited capability (refer to Figure 3-7).
Over Excitation Limiter (OEL) A cool down function is also supplied to simulate cooling of the field after an overexcitation condition.
The alternate current regulator is initially enabled. If the signal level detect looking at exciter field current or either of the inverse time protection blocks activate, the alternate field current regulator is disabled and the primary current regulator setpoints are active. The output of either th e alternate or primary field current regulator is fed to the firing block where a minimum select with the field regulator firing command is performed (refer to Figure 3-8).
Firing Block The firing block accepts the field current reference and the field voltage reference and then selects the least of the two. This signal is passed on to the bridge only if the instantaneous overcurrent or the stop commands are not a ctivated. If either of these are active, the firing signal is a preset retard limit (refer to Figure 3-9).
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EX2000, PWM Digital Regulator GEH-6375A
Table 3-1. Standard Software Functions Function
Inputs
Adjustable Constants
Outputs
AVR Ramp
Auto Increase (RF1@IN) Auto Decrease (RF1@DC) Manual Active (RF1@VE) Go to Preset (RF1@3E) Track Enable(RF1@T2) Track Value(RF1@2E)
High limit (RF1THO) Low limit (FR1TLO) Ramp rate (RF1NRT) Preset value (RF1@T3) Track lag (RF1WLG)
Reference out
AVR Setpoint
Frequency (ASP@FQ) React. Cur.(ASP@IQ) REF Out (ASP@RO) UEL Out (ASP@UE) PSS Out (ASP@PV) Auto/Man (ASP@AC) Extra Input (ASP@EX) PT Fail (ASP@PT) Gen Volts (ASP@VM) PSS Armed (ASP@PC) Gen Watts (ASP@WT) PT Fail Reset (ASP@PR)
ASP Limit High (ASPHLM) V/Hz Gain (ASPVHZ) RCC Gain (ASPRCC) PSS High Watt (ASPHIW) PSS Low Watts (ASPLOW)
AVR Ref Auto Active Man Active PSS Active V/Hz Active UEL Active Setpoint In Limit Latched PT Fail
FCR
FCR Setpoint FCR@SP FCR Enable FCR@EN FCR Alternate Setpoint FCA@SP FCR Alternate Enable EFA@EN
FCR Prop Gain (RGKC0) FCR Integral Gain (IRWIC0) Alt FCR Prop Gain (IRGKA0) Alt FCR Integral Gain (IRWIA0)
FCR Output ILOP0
AVR
Generator Volts (AVR@FB) FVR Output (AVR@TV) AVR Ref (AVR@SP) Manual Active (AVR@TC) Bridge Fire Enabled (AVR@ZC)
High Limit (AVRPLM) Low Limit (AVRNLM) Prop. Gain (AVRPGN) Integral Gain (AVRIGN) Tracking Gain (AVRTGN)
AVR Out AVR In Limit AVR Error
FVR Ramp
Manual Increase (SS) Manual Decrease (SS) Auto Active (RF2@2E) Go To Preset (RF2@3E)
High limit (RF2TH0) Low limit (RF2THL) Ramp rate (RF2NRT) Preset value (RF2@T3)
Reference Out
FVR
Field Current (IFE) AVR Out (EFR@TV) FVR Ref (EFR@SP) Auto Active (EFR@EN) Bridge Fire Enabled (MPWRENAB)
FVR Turn Off (FLDZVL) Tracking Gain (FLDTGO) Proportional Gain (FLDPGO) Integral Gain (FLDIGO)
FVR Out
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Table 3-1. Standard Software Functions - Continued
3-6
• •
Function
Inputs
Adjustable Constants
Outputs
UEL
Watts (RA1@I1) Gen. Volts(@INPUT) Vars (R2@FBO)
Vars Ref. 0 (FGENYO) Watts Ref. 1 (FGENX1) Vars Ref. 1 (FGENY1) Watts Ref. 2 (FGENX2) Vars Ref. 2 (FGENY2) Watts Ref. 3 (FGENX3) Vars Ref. 3 (FGENY3) Watts Ref. 4 (FGENX4) Vars Ref. 4 (FGENY4) Prop. Gain KP (R2KFBO) Integral Gain KI (R2WI_0) High Limit (R2LMPO) Low Limit (R2LMNO)
UEL Output
OEL
Field Current (CURRENT)
High Limit (CRLMHI) 2 Low Limit (I tAFL) FCR Preset (PIT@RS) Inst. Overcur. Lim (PITPU) IIT Limit (PITLM) FCR Pos. Limit (FCRPLM) 2 IIT Cooling Mult. (I tCMT)
Firing Block
FVR Out FCR Out IOC Active Start/Stop
Retard Limit
Chapter 3 Software System Overview
OEL Act (FLDMOD) IIT Acc (PITIACCM)
Firing Code
EX2000, PWM Digital Regulator GEH-6375A
EXVMAG
AUTO AUTO/MAN SELECT LOGIC
PT FAIL DETECT MAN
EXXMAG
VAR/PF CONTROL, POWER SYSTEM STABILIZER AND PT FAIL DETECTION ARE OPTIONAL. ALL OTHER FUNCTIONS SHOWN ARE STANDARD.
V/HZ EXVFREQ
ARM PSS
Pa
ZERO LEVEL
EXCITER FIELD
+
+
REGULATOR
+
PI
+ +
CONTROL
REG. SETPOINT
+
RAISE
EXVARS
LOWER
AUTO REGULATOR
EXWATTS
VAR /PF
MAN
VOLTAGE LIMIT
PSS
EXWATTS
RAISE
AUTO REG
-
PI
-
LOW VALUE GATE
-
IFE
EXVMAG
BRIDGE FIRING
SETPOINT
LOWER
SPARE
HIGH SP
FCR@SP
PI
LOW SP
1177S
EXWATTS IFE EXVARS
UEL
I*T LIM RUNNING
EXVMAG OFFLINE
FCA@SP
ONLINE
EXIREAC
RCC
AND
52G
SLD1
Figure 3-1. Software Overview
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Figure 3-2. Automatic Voltage Regulator (AVR) Ramp
] ] ]
]
]
]
+ ]
]
+
] ]
-
]
+ +
]
+ + ]
]
] ]
] ]
]
Figure 3-3. Automatic Voltage Regulator (AVR) Setpoint
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) Figure 3-4. Automatic Voltage Regulator (AVR
Figure 3-5. Field Voltage Reg (FVR) Ramp
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) Figure 3-6. Field Regulator (FVR
Figure 3-7. Under-Excitation Limit (UEL )
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EX2000, PWM Digital Regulator GEH-6375A
Figure 3-8. Over Excitation Limit (OEL )
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Figure 3-9. Firing Block
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EX2000, PWM Digital Regulator GEH-6375A
Chapter 4 Software Configuration and Scaling
Introduction This chapter gives examples of the scaling for specific parameters in a generic brushless regulator generator application. Section
Page
Configuration and Scaling Example................ ..................................................... 4-2 Example Generator, Exciter, and Regulator.................. ............... .................. 4-3 General Configuration ......................................................................................... 4-4 Feedback Scaling ................................................................................................ 4-6 Generator Feedback................ ...................................................................... 4-6 Bridge Voltage Feedback..................... ......................................................... 4-7 Bridge Current Feedback .............................................................................. 4-8 Feedback Offsets.......................................................................................... 4-8 Instantaneous Overcurrent Trip............ ......................................................... 4-9 Regulator Scaling................................................................................................ 4-9 Automatic Voltage Regulating System.................................. ........................ 4-9 Under Excitation Limiter (UEL) ..................................................................4-13 Reactive Current Compensator (RCC) ............................ ............................. 4-16 VAR/Power Factor Control .........................................................................4-17 Field Regulator (FVR).................................................................................4-18 Field Current Regulator (FCR) ....................................................................4-20 Optional Functions Scaling and Configuration....................................................4-23 Transducer Outputs .....................................................................................4-23 Ground Detector and Diode Fault Monitor...................................................4-24 Field Thermal Model...................................................................................4-25 The software to configure various regulators, metering, and protective functions within the regulator operates on a count system representing actual feedback values. These feedbacks are generated by current transformers, voltage transformers, and dc shunts. The signals may pass through isolators and amplifiers. These analog signals are transformed to digital signals by voltage controlled oscillators.
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The regulator controls use standard normalized values to represent the variable being monitored or regulated. This enables the use of software that, to a large extent, is not application dependent. For example, the automatic voltage regulator (AVR) controls the generator terminal voltage based on a setpoint chosen by the operator. For any machine, 1 per unit (or rated terminal voltage) is defined within the AVR to be 20000 counts. If the operator chooses to set the terminal voltage at rated then the reference to the AVR is 2 0000 counts. The voltage feedback counts are compared to this reference to generate an error signal and the appropriate control action takes place to maintain the feedback counts at 20000. The actual generator terminal voltage being regulated is n ot referenced at this control level. It is therefore necessary to ensure that the feedback counts seen by the regulators are adjusted to provide the standard n umber of counts when the generator is operating at rated. This is r eferred to as scaling. An EX2000 system can be constructed several ways to accommodate customer system requirements. For example, the regulator can be fed from the permanent magnet generator or from an auxiliary bus. It can be a brushless regulator or an SCT control winding regulator. The controls are set to match the hardware used. This is known as configuration.
Configuration and Scaling Example The following section shows how scaling is performed using example generator data. The example system is configured as a brushless exciter regulator fed from a PMG with a 125 V dc battery backup. There is also a single set of generator potential transformers (PT)s and no line PTs. The scaling may not apply to all EX2000 applications. Contact GE Industrial Systems before changing any EE values.
Note Operating data from the generator field is not readily available to the regulator. The generator information listed is critical to the overall operation and performance of the regulator and excitation system. Assumptions made in the AVR and exciter field regulators are based upon the available generator data.
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EX2000, PWM Digital Regulator GEH-6375A
Example Generator, Exciter, and Regulator Generator Data KVA
100000
Frequency
60 Hz
Volts
13800
PF
0.85
Cold Gas Temperature
40 °C
Rated Stator Amps
4184
Amps Field No Load
313
Amps Field Air Gap
281
Amps Field Full Load
846
Amps Field Ceiling
1360
Field Open Circuit Time Constant (T'do)
5.615 sec
Field Open Circuit Subtransient (T’’do)
0.022 sec
Field Winding Resistance
0.199 ohms at 25 °C
Volts Field Full Load
136
Station battery volts
125 V dc
PT Ratio
14400/120
Current Transformer (CT) Ratio
8000/5
Exciter Data kW
268
Volts
300
Rated Exciter Output Amps
893
Amps Field Air Gap (exciter)
1.712
Amps Field No Load (exciter)
3.52
Amps Field Synch Imp.(exciter)
6.236
Amps Field Full Load (exciter)
9.54
Amps Field Ceiling (exciter)
15.45
Exciter Time Constant (T'do)
0.35 sec
Field Winding Resistance (exciter)
4.871 ohms at 25 °C
Regulator Data
GEH-6375A User's Guide
DC shunt
10 A = 100 mV
Dynamic Discharge Resistor
17.0 ohms
Dynamic Discharge Resistor Rated Amps
6.0 A
Charge Control Resistor
2.0 ohms
Voltage Doubling
No
DC Link Expected Volts from PMG
137
Maximum Expected DC Link Volts
360
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General Configuration Throughout this example, the software nomenclature is defined as follows: EE.XXXX (ABCDEF)
where XXXX represents the software address location and ABCDEF represents the software address name. There are many parameters that are set in the regulator that are not di scussed in this manual. Many of them are used to set up configurable parameters such as the Status_S data link, communication, and so on. These are fixed parameters such as baud rates, display, configuration, and keypad configuration for all applications and should not be changed or need changing on any requisition.
Note If any parameters not discussed in this document are in question, contact the product service group of GE Industrial Systems or the local GE service organization for advice. The following list are general configuration adjustable parameters (EEPROM) used to direct signals and h elp make the configurable blockware function as a brushless regulator.
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Generator Model Jumper EE.3850 (GMJMPR) EE.3850.1
Used to simulate PT failure in simulator mode. Normally set to 0.
EE.3850.2
Selects slip source for Power System Stabilizer (PSS) The example has no PSS
EE.3850.3
Selects extra PT source for calculation of PT failure. Can only be from PTCT board for regulator. Set to (0).
EE.3850.4
Generator model type. Can be static (0) or rotating (1). Brushless regulator is rotating.
EE.3850.5
Selects 50 Hz (1) or 60 Hz (0) system for simulator and normal operation. Example is 60 Hz.
EE.3850.6
Selects terminal (0) or separately fed (1) inputs for bridge. The regulator is separately fed.
EE.3850.7
Selects whether the extra PT is used for calculations if a PT failure is detected. (1) is yes, (0) is no. No PT failure detection available in the example.
EE.3850.8
Selects location of extra PT input. Line side (1) of 52G breaker or generator side (0). Example does not have extra PT input.
EE.3850.9
Select if PT failure detection is always (0) or only with 52G closed (1). No PT fail detection in example system. Set to zero.
EE.3850.10
Use maximum of PT feedbacks for calculations. (1) is yes, (0) is no. No for example.
EE.3850.11
Adjusts simulator for 60 Hz (0) or 50 Hz (1)
EE.3850.12
Sets LOE calculation for high gain (rev. G1B) PTCT board for LOE calculations. All new regulators use high gain PTCT inputs. Set to (1)
EE.3850.13
Adjusts PTCT board inputs for Rev. A (0) or Rev. B (1) board.
Configuration Jumper EE.589 (ECNFIG) EE.589.0
Selects IFG feedback to be from SHPL on GDDD (1), IA2PL from GDDD (2) or none (0). Set to 1.
EE.589.2
Selects IFE feedback to be from SHPL on GDDD (1), IA2PL from GDDD (2) or none (0). Set to 1.
EE.589.4
Selects VFG to be from APL/BPL on GDDD board (1), IA1PL on GDDD board (2) or none (0). Set to 0.
EE.589.6
Selects VFE to be from APL/BPL on GDDD board (1), IA1PL on GDDD board (2) or none (0). Set to 1.
EE.589.8
Selects field regulator feedback to be either VFG (0), VFE (1), IFG (2) or IFE (3). For current regulator set to 3.
EE.589.10
Selects source for Var.105 to be either IFG (0) or IFE (1). Set to 1 for the regulator.
Other general configuration parameters important to the operation of a regulator
GEH-6375A User's Guide
EE.550
Identifies product type, for hardware select 84.
EE.556
Identifies hardware feedback board, select GDDD board 2.
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Feedback Scaling As a brushless regulator, there are a limited number of feedback signals from the generator available. These are p otential transformers and current transformers monitoring the stator output, a shunt feed back from the exciter field, and exciter field voltage. Main generator field current and voltage are n ot commonly available for display or control on a brushless generator. The following sections describe common feedback signals and scaling.
Generator Feedback The PT and CT signals to the regulator are isolated by the PTCT board. The voltage signals generated by the PTCT are sent to the TCCB transducer board. Here voltage controlled oscillators (VCO) translate the analog signals into digital counts. The PTCT board will accept one set of 3-phase CT inputs from the main generator stator current transformers. These CTs must have a nominal 5 A secondary and phase A and C are required for correct operation of the regulators. Phase B CT input is not required and not used by the controls. EE.3840 CT_ADJ is used to account for off nominal CTs. The scaling for this EE setting is calculated as equal to 20480/(actual 1 pu CT secondary amps) For the example generator data: EE.3840 = 20480/(4184*5/8000) = 7832
The PTCT board also accepts up to three sets of generator voltage transformer inputs. These inputs are 3-phase inputs with a nominal secondary voltage of 120 V ac. Two of the inputs are for generator voltage before the synchronizing breaker. These two PT inputs should both be on the same side of the generator step up transformer. The third input can be used for a line side of the synchronizing breaker voltage input. The scaling for this EE setting is calculated as equal to 491520/(actual 1 pu PT secondary volts) For the example generator data: EE.3841 = 491520/(13800*120/14400) = 4274
Potential Transformer Failure Detector (PFTD) Operation In the example system only one set of PT inputs are specified. The second set of generator side PT’s can be used for an optional Potential Transformer Failure Detection (PTFD) function. The generator PTFD operates by comparing the sum of the absolute counts for V12 and V23 signals (generator PT signals) with the sum of the absolute counts representing the extra PT input signals VX12 an d VX23. The 1 pu secondary voltages from these two sources depends on the transformer ratios used. A scale factor PTFDSC EE.3835 is used to null the signal difference that could exist. The resulting magnitude difference is filtered and the absolute value is compared to the failure detection level set by EE.3837 PTFDVL. Under normal conditions the difference between the two sums should be approximately zero. If this absolute difference is greater than the value set by PTFDVL EE.3837 then a PT FAIL FLT.488 is generated and VAR.1183 EXVPTL becomes true. This variable is sent to the excitation autosetpoint block input ASP@PT and, if true, forces a latched transfer to the manual regulator.
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The PTFD can be disabled offline by setting EE.3850.9 GMJMPR.9 equal to 1. The PTFD detector can be tested using the simulator by setting GMJMPR.1 equal to 1 to simulate loss of V12 PT signal. Setting EE.3850.9 GMJMPR.7 equal to 1, the extra set of PTs can be used for all calculations downstream from the PT failure detector software.
PTFD Scaling Parameter PTFDSC EE.3835, PT failure scale adjust, is used to null any signal difference existing between V and X PTs. If a second PT for failure detection were supplied, then set EE.3835 = 4096 * (1 pu V PT secondary volts/1 pu X PT secondary volts). In most cases, the second set of PT inputs would be the same secondary as the first and the default value of 4096 would be used
PTFD Detection Level The failure detection level is set using PTFDVL EE.3837. It is typically set to approximately 50% of nominal (120 V) PT signal (loss of half the voltage of one phase). For the example system, EE.3837 = 0.5 * 2048 * (115/120) = 981. In the formula, 2048 represents a complete loss of a PT signal and 115 is the actual 1 pu PT secondary volts. A PT failure detection causes automatic transfer to the field (or manual) regulator. This regulator controls field current level and does n ot look at generator terminal voltage. This is the only fault that initiates automatic transfer to the manual regulator. It is not possible to transfer back to the AVR until this latching fault is cleared. The operator interface should indicate when a PTFD has occurred. A r eset signal must be sent to reset the PTFD. A soft reset of the core is necessary to clear the fault display from the LDCC board once the PT feedback problem is fixed.
P.T.U.V. If a second set of generator PTs is not provided then the PTFD scheme described above can not be used. In this case the PTFD function is disabled by setting EE.3837 to 65,535 and protection is provided by pointing ASP@PT at VAR.1182 EXPTUV. In the event of loss of one phase or complete loss of generator voltage signal as measured by the TCCB board, and after a time delay specified in EE.3834 PTFDT1. EXPTUV will become true, forcing the control into manual regulator mode.
Bridge Voltage Feedback The bridge (regulator) dc output voltage feedback signal is fed via APL-5 and BPL-6 from the IAXS board to the GDDD board. A voltage controlled oscillator on the GDDD board converts this analog signal to a frequency and digital counts. JP1 on the GDDD board is set per the maximum expected dc link voltage. For units n ot employing the voltage doubling feature of the r egulator, this is normally 640 or 360 volts. The example system does not u se voltage doubling. The dc link voltage feedback signal is fed to the GDDD board via the DCPL -1 and 2 connections on the IAXS board. Again, JP2 on the GDDD board is set to the maximum expected DC link voltage.
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EE.612 VDCMAX sets the 1 pu count level (20000) equal to 360 or 604 volts for scaling of both the DC link voltage and DC output voltage. JP3 on the GDDD board sets the operation level of th e dynamic discharge firing circuit. The selection of JP3 is also based upon the maximum expected dc link voltage. JP1, 2 and 3 on the GDDD board should all be set to the same settings.
Bridge Current Feedback The regulator field current feedback signal is from shunt SHA and is fed to the GDDD board via connections SHPL-1 and -2. This input is scaled using EE.1505 CFISF0. This trims the gain of the VCO to achieve 5000 counts at 1 pu bridge current. The scaling for this EE setting is calculated as EE.1505 = 32768*(shunt rating)/(regulator amps field full load). For the sample system, the shunt rating = 10 A for 100 mV. The exciter AFFL rating is 9.54 A. Set EE.1505 = 32768 *(10)/(9.54) = 34348
Feedback Offsets Due to the tolerance limits of the op-amps and VCOs that provide the feedbacks, it is possible that positive or negative offsets may occur with zero signal feedback. The actual offsets produced are dependent on the actual hardware and must therefore be zeroed at startup. The bridge output voltage, dc link voltage and shunt feedback are adjustable using the following feedback offsets: EE.1508 VF1OF0 is used to zero the VFB1 bridge voltage feedback offset. With no bridge output, variable 1014 should be read using diagnostic test 31. This count value multiplied by the constant -1141 and divided by the scale factor value in EE.612 VDCMAX then becomes the value in EE.1508.
For example, with power on the bridge but the bridge not firing, monitor VAR.1014 (assuming VFE is the selected feedback) for any zero offset. Assume the offset found was approximately 80 counts. Set EE.1508 = (80*-1141)/360 = -253. Enter this value and continue to monitor VAR.1014 to verify that the offset is now zero. EE.1510 CF1OF0 is used to zero the CFB1 bridge current feedback offset. With no bridge output, variable 1016 should be read using diagnostic test 31. This count value multiplied by the constant 21475 an d divided by the scale factor value in EE.1505 CFS1F0 then becomes the value in EE.1510.
For example, with power on the bridge but the bridge not firing, monitor VAR.1016 (assuming IFE is the selected feedback) for any zero offset. Assume the offset found was approximately -100 counts. Set EE.1510 = (-100*21475)/34348 = -62. Enter this value and continue to monitor VAR.1014 to verify that the offset is now zero. EE.1513 VDCOF0 is used to zero the dc link voltage feedback offset. Since dc link voltage is required for control power, this offset mu st be made with dc link voltage present. VAR.1018 should be read using diagnostic test 31. The dc link voltage should be read on the IAXS board connection points PL and NL. This measured voltage will then be converted to counts. The converted measured counts minus the count value in VAR.1018 then becomes the value in EE.1513.
For example, with power on the bridge but the bridge not firing, monitor VAR.1018. Assume it is 7825 counts. Then assume the measured value of the dc link is 137 volts. Converting the measured voltage to counts gives 137/360 * 20000 equals 7611. Set EE.1513 = (7611-7825) = -213 counts. Enter this value and continue to monitor VAR.1018 to verify that the offset is now zero.
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Instantaneous Overcurrent Trip An instantaneous overcurrent trip occurs if the bridge current, as monitored by SHPL (CFB1), exceeds the threshold set by EE.1518 IOCTRO where 5000 counts = 1 pu. Set EE.1518 = 25000 (5 pu).
Regulator Scaling There are several regulators and limiters available in the regulator. The applicable one-line or system ordering documents will detail whether or n ot all or any of these are supplied on a given requisition. Generally the AVR, FVR, and OEL regulators are supplied as standard. The UEL, RCC, and V/Hz limiters are also generally standard features. PSS and VAR/PF controllers are typically supplied a s options.
Automatic Voltage Regulating System The primary purpose of the automatic voltage regulator (AVR) is to control the generator terminal voltage according to a chosen reference. The terminal voltage can then be modified by vari ous limiter and regulator functions.
AVR Operation. The regulator is designed to be started in AVR. The exciter can be started in AVR mode with the generator operating from 20 t o 100 Hz. To prevent in itial overshoot, the integrator is held at th e preset value until 95% voltage i s obtained. For a normal bandwidth AVR, this also means forcing the regulator to its maximum output until 95% of terminal voltage is reached. If the speed of the generator is below rated when the regulator is started, the V/Hz limiter will hold down the terminal voltage and regulator output such that the volts per hertz ratio specified in the AVR controls is maintained.
REF1 Operation The selected (unmodified) reference originates in th e INC/DEC reference block REF1 (see Figure 3-2). The initial reference used in th e regulator is a preset value normally set for 1 pu generator voltage. The REF1 output tracks this value when a start is given to the regulator. During this initial operation the RAISE and LOWER controls are ignored. Once the startup operation is complete, the reference can be changed by selecting RAISE or LOWER from the operator station with the regulator in AUTO regulator. When offline, selecting RAISE or LOWER controls the generator terminal voltage over a range set in REF1 (and the autosetpoint block). This range is n ormally ±10% of rated terminal voltage. When online, selecting RAISE or LOWER increases or decreases the generator terminal reactive voltage and/or the power output of th e generator. The more stiff the connection to the power system (lower impedance tie) the less the generator terminal voltage is a ble to change. An optional volt ampere reactive/power factor (VAR/PF) controller can also control the output of the REF1 block. While under control of the VAR/PF controller, the slew rate of REF1 is slowed to an alternate ramp rate, and the operator RAISE/LOWER inputs are ignored.
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When the exciter is operating in manual, the autosetpoint reference REF1 tracks a value representing the sum of ASP@VM (normally generator voltage) and the reactive current compensation signal. While REF1 is tracking this value, the INC/DEC commands from the operator station are ignored in the REF1 block. The output of REF1 in VAR.282 REF1OUT0 is passed to the autosetpoint block (EXASP).
REF1 Scaling and Configuration REF1 tracks target RF1@T3 EE.3402 without delay during startup. It is normally pointed to a value of 20000 counts for 1 pu generator voltage. For 1 pu generator voltage set EE.3402 = 19. During startup, a quick store register can be used to preset the terminal voltage to a value other than rated. This register can contain a count value representing the desired preset voltage. RF1@T3 should then be pointed to this address. For example, during startup, if the desired preset voltage is 12.5 kV on a 13.8 kV machine, the reference preset counts required is 12.5/13.8 * 20000 = 18116 counts. Quickstore EE.95, currently an unused register, can be used to store this value. Then, point EE.3402 (RF1@T3) to EE.95 instead of the normal EE.19 location. The range of the AVR is set using EE.3414 RF1TH0 (upper limit) and EE.3412 RF1TL0 (lower limit). Set this to provide a range of ± 10% of rated generator voltage. Set EE.3414 = 18000 and EE.3412 = 22000. To select the ramp rate of the AVR set EE.3400.6 = 0 for a normal INC/DEC scale control setting of 1/10 bits/sec. The time to ramp across the AVR range is set by the normal INC/DEC rate EE.3421 RF1NRT. The range of the AVR = (22000-18000) = 4000. The desired time to cover this range is 60 seconds taking into account the setting of EE.3400.6. Set EE.3421 = (4000/60) *10 = 667.
Autosetpoint Block The selected reference from REF1 enters the autosetpoint block (EXASP) as the main auto reference setpoint. This reference can now be modified in the autosetpoint block by various standard and optional regulators and limiters. In addition to the REF1 input the ASP block receives feedback variables for reactive current, generator terminal voltage, generator frequency, the output of the under excitation limiter, and generator real power if a power system stabilizer (PSS) is used (see Figure 3-3). Automatic regulation is enabled through the operator station or the A/M selector button on the LDCC board programmer keypad. When auto is active, VAR.953 ASPAUTOA will be true. The ASP block also has an input from the PTFD (or PTUV). When a PT failure is detected, regulation is switched to the MVR. ASPAUTOA becomes false and remains latched in that state until the PT feedback problem is corrected, the core is soft reset, and the PTFD reset button on the operator station is pushed to permit selection of AUTO operation. Configuration jumper EE.589 selections can disabled the PTFD while off-line. The ASP block contains a summing junction, minimum value gate, and a positive output limiter. The summing junction adds the output of REF1, the UEL regulator output, the PSS regulator output (if present), and an extra input ASP@EX. This extra input can be used to insert a test signal. The RCC compensation signal is subtracted in the summing junction.
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The output of the summing junction feeds a minimum value gate where it is compared with a V/Hz limit signal proportional to the generator frequency by an amount set in EE.3789 ASPVHZ. The minimum of these two references is used as the reference sent to th e regulator. The maximum output is limited to a value set in EE.3790 ASPHLM. If the reference used by the regulator is th e V/Hz limit and the exciter is in auto, then VAR.958 ASPVHZA is set true and an indication is given that the exciter is in V/Hz limit. If a positive value is input to the summing junction from the UEL and the exciter is in auto, then VAR.959 ASPUELA is set true and an indication is given that the exciter is in UEL. The output of the AVR setpoint block VAR.158 ASPAVRSP is sent to the AVR block as the regulator reference signal.
Autosetpoint Block Scaling and Configuration For the example system the V/Hz limiter will be set to 110%. Set EE.3789, the V/Hz gain, to 282 (256 = unity). For 50 Hz a pplications, multiply EE.3789 by 6/5. The ASP High Limit is set in EE.3790 ASPHLM. This is generally set for 110% of rated or 22000 counts. For 50 Hz applications, multiply EE.3790 by 6/5.
Automatic Voltage Regulator (AVR) Block The AVR is a proportional plus integral r egulator that compares the generator terminal voltage feedback (derived from the V12 and V23 generator PT signals) with a reference from the auto setpoint block to produce an error signal. This error signal, VAR.156 AVRERROR, is fed to the PI regulator. If the regulator is in automatic regulator, the output of the AVR, AVROP VAR.157 is then fed to the inner loop field regulator. The AVR output is limited to approximately 2 pu field current so that it does not overdrive the exciter. The output of the AVR is passed through the field regulator to cancel the impact of th e additional time constant of the rotating exciter. By doing this, the calculations and settings of the various regulator limiters, (UEL, V/Hz, OEL) can be set using the same rules as a terminal fed or bus fed excitation system. Tuning of regulators in the field is thus minimized. The AVR is preconditioned to a value corresponding to AFNL at startup. The initial value of AFNL used could be a n estimated value. After the initial startup, when a precise value of firing command counts for AFNL is known, the preconditioning value stored in EE.92 can be adjusted accordingly. When the precondition input AVR@ZC is true, the AVR output follows the preconditioning value AVR@ZV. If AVRJMP.0 = 1 the integrator continues to follow AVR@ZC until AVRERROR is less than 5% (1000 counts on a 20000 base). If, in addition to AVRJMP.0 = 1, AVRJMP.1 also = 1 then the output of the AVR is forced to maximum as set in EE.3772 AVRPLM until the AVRERROR is less than 1000 counts. If the exciter is in MANUAL (ASPMANUA true), the AVR tracks the output of the field regulator FLOPO VAR.1004. The AVR integrator has anti-windup protection that zeros the error feeding the integral gain if either:
GEH-6375A User's Guide
a.
The output is in positive limit or if the regulator is in FCR and the error signal feeding the regulator is positive.
b.
The AVR output is in negative limit or in full retard and the error signal feeding the regulator is negative.
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AVR Scaling and Configuration The AVR response is not set for optimum speed, but for acceptable performance without risking instability due to local mode oscillations. This setting is considered to be a normal bandwidth regulator. A high bandwidth regulator is used when a high gain fast response AVR is required. The example assumes a normal bandwidth regulator. If a high bandwidth regulator is chosen, then the high bandwidth settings for the UEL regulator should be used also. AVRJMP EE.3759.0 is set to 1 for AVR output to follow AVR@ZC until regulator error is less than 1000 counts. Set at 1 for a high bandwidth exciter also. EE.3759.1 is set to 1 on a normal bandwidth exciter to hold AVROP in ceiling until AVRERROR is less than 1000 counts. Set to zero for a high bandwidth exciter. AVRPLM EE.3772 is the positive limit for AVR output. Normally set to 10000, which is approximately 2 pu current for the exciter field. AVRNLM EE.3773 is the negative limit for AVR output. Set to 0. AVRTGN EE.3770 is the AVR tracking gain. This sets the time delay for the AVR to track the output of the field regulator while in manual regulator. Set EE.3770 = 5 (where 100 = 1 rad/sec) for a 20 second tracking filter. The following is an example of setting the AVR regulator for an regulator with normal bandwidth. Prior to startup, the AVR output is preset to the no load exciter field current level. This effectively wipes out overshoot problems when starting in the automatic regulator. VR@ZV EE.3764 points to EE.92. In EE.92, the RUN2RF storage register stores the firing command count value necessary to produce 80% exciter AFNL. In the example, exciter AFNL was 3.52 A dc. Set RUN2RF EE.92 to a FIRCMD = 0.8 * AFNL* 5000/AFFL = 0.8*3.52*5000/9.54 = 1476
AVR Proportional Gain The proportional gain of the PI regulator is set as follows: 1.
Determine the transient gain requirements of the system.
2.
Calculate the proportional gain, which is directly proportional to the transient gain. For the normal bandwidth regulator, set the transient gain to 4*T'do (the open circuit field time constant) with 20 as a default minimum for new gas and steam applications. A high bandwidth regulator should be set for a transient gain of 100.
From the transfer function of a brushless regulator, the relationship between proportional and transient gains is: Transient gain = (Kp*20000 * K ex*AFFLex) / (VFAGgen*5000) where K ex is the gain of the exciter. The gain of the exciter is calculated as the (voltage out/current in) or ((VFFL gen at 100 C - VFNLgen at 100 C) / (AFFLex - AFNLex)). For the example system, K ex is calculated to be (216-80.13)/(9.54-3.52) = 22.51.
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VFAGgen is the air gap voltage, which is determined by reading IFAG from the machine estimated air gap line at 1 pu armature voltage. The example generator has IFAG of 281 A dc. The rated field resistance Rf@rated temp is defined as 100 C. The Rf@100C was not given and is therefore extrapolated from Rf@125C to give Rf@100C = .256 ohms. VFAG = .256 * 281 = 72 V dc. Solving for Kp gives Kp = (transient gain * VFAG gen*5000) / (20000 * K ex*AFFLex) = (20*72*5000) / (20000*22.51*9.54) = 1.67. Set AVRPGN EE.3769 = 1.67 * 256 (where 256 = unity) = 429
Integral Gain Set Kp/Ki = 1 for a lead time constant of 1 sec. For the example Ki = Kp = 1.67 Set AVRIGN EE.3771 = 1.67 * 100 (where 100 = 1 rad/sec) = 167
Under Excitation Limiter (UEL) The two basic problems with operating a generator in the underexcited region of the capability curve are stator end iron h eating and generator steady state stability limit. Stray flux in the end turn region of a high speed steam or gas turbine driven generator can cause large losses in the core end iron during underexcited operation. The steady state power stability limit indicates the maximum real power that can be delivered at constant field voltage. The effect of the h igh initial response AVR is to substantially increase the steady state stability limit. The generator must be constrained to operate in the underexcited region in an area where the unit would be stable if a transfer were made to the field regulator. The thermal limit is usually more restrictive than the power stability limit. The default scaling of the UEL curve described is based on the generator capability curve. The intent is to protect the generator from end iron heating effects by setting the UEL approximately 10% above the underexcited reactive capability curve. The 10% is chosen to give sufficient safety margin. The stability limit is a function of th e network to which the generator is connected. The customer is responsible for system stability protection settings. If the customer supplies UEL curve points, enter those values instead of th e values from the method described.
UEL Operation This section describes the UEL operation, which is performed by a combination of standard blocks (see Figure 3-7). The capability of a generator when plotted on a reactive power versus real power plot changes as t erminal voltage changes. This means that a number of curves a re required to provide protection over the normal 10% terminal voltage range permitted by the AVR. If the real and reactive power signals are normalized by dividing by the square of the terminal voltage then the capability of the generator becomes a single curve. The generator watts signal is first normalized by dividing by the square of the filtered voltage signal. The resulting normalized power is then filtered and absoluted. This value is fed to the function generator block where the normalized pu UEL curve has been entered. The output of the function generator block is the UEL curve point corresponding to that value of generator r eal power output. This value then becomes the UEL limit allowed.
GEH-6375A User's Guide
Chapter 4 Software Configuration and Scaling
4-13
• •
This UEL limit as read from the curve is normalized Vars and must be m ultiplied by the square of the filtered voltage signal to produce a Var reference for the proportional plus integral regulator. The PI regulator is enabled by an AND gate if 52G is closed and the AVR is in control. It compares measured generator Vars feedback quantity with a reference limit derived from the UEL curve to generate an error signal that feeds the r egulator. The output of the PI regulator block is fed to a limiter set to allow only positive outputs. This value is then fed to the excitation autosetpoint block ASP@UE input. It is added to the existing AVR setpoint to produce an increase in the excitation level sufficient to prevent the excitation decreasing below the level corresponding to the UEL limit curve chosen.
UEL Scaling and Configuration Configuring and scaling the UEL function involves setting the PI regulator for proper gain and time constants. It also includes setting the UEL curve based on the generator capability curve. The UEL limiter uses process regulator #1. This is a proportional plus integral regulator. A PI regulator has the form: Kp + Ki/s where Kp = proportional gain and Ki = integral gain (rads/sec). Only two sets of adjustments for the UEL regulator are necessary. One for exciters using a normal bandwidth AVR and one for those customers requiring a higher bandwidth, such as a fast response/high gain AVR. The default setting is normal bandwidth. The recommended settings are as follows: Normal
High
EE.5899 = 200
(Ki = 2 rads/sec)
EE.5899 = 200
(Ki = 2 rads/sec)
EE.5900 = 819
(Kp = 3.2)
EE.5900 = 410
(Kp = 1.6)
Note Two EEPROM values are set because the command and feedback gain s are independently adjustable. Steady state stability of the UEL can be verified by operating the generator at various power levels then slowly lowering the excitation to drive the generator into the limit curve. Dynamic closed loop response can then be verified by stepping the AVR setpoint using the excitation autosetpoint block extra input ASP@EX. A step of 1 or 2% is sufficient. If it is not permissible to drive the generator into its true limit curve then the curve could be reset at a safer level and the testing performed using this curve.
UEL Curve The UEL limit curve is obtained by using a general purpose background function generator block. This is a five point piecewise linear function generator. The function is flat to the left of Y0, the first point, and to the right of Y4, the last point. The X coordinates must be monotonically increasing X0
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