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Generator Circuit-Breaker Systems HEC, HGC
Data and Dimensions
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Contents Application Characteristics Modular design concept Equipment options Standards and quality Generator circuit-breaker Disconnector Earthing switch Starting switch Manual short-circuiting connection Short- circuiting- /braking switch Current transformer
3 3 4 5 5 5 8 9 9 9 10 10
Voltage transformer Surge arrester Surge capacitor Terminals Phase enclosure Control and supervision Tests Transport to site Site erection and commissioning Maintenance Technical data and dimensions
11 11 11 12 12 12 13 13 13 13 14
Application The Generator Circuit-Breaker System type HEC and HGC has been developed as a system suitable for application in all types of power plants. The HEC and HGC Generator Circuit -Breaker
System is also suitable for retrofitting in existing power plants, when these are modernised, extended and/o r automated. It is available for both indoor and outdoo r application.
Characteristics • 3-phase system with a SF6 circuit-breaker and disconnector in series with the circuitbreaker, in single-phase enclosures, supplied fully ensembled on a common frame, with operating mechanisms, supervisory and control equipment.
permanent with switch (for braking) or to be mounted manually (for power plant protection setting), current- and voltage transformers, surge capacitors, surge arrester, all integrated and mounted in the phase enclosures, can be provided.
• Additional components as earthing switches, starting switch (for starting of gasturbines), short- circuiting connection either
• The phase distance can be selected to suit the busbar spacing in the power plant.
Standards and quality The Generator Circuit-Breaker System type HEC and HGC fulfil the requirements of all relevant standards, i.e. IEEE (ANSI) Std C37.013 and IEC 60694, IEC 60129, IEC 60044-1/ 2, IEC 60099-4, IEC 60358, IEC 60529, IEC 61166.
ABB High Voltage Technologies Ltd. is continuously endeavoured to improve its qualityassurance-system; this has been recently new assessed by The Swiss Association for Quality and Management Systems with the SQS-certificate ISO 9001 / ISO 14001.
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Modular design concept The standard design includes: • SF6 circuit-breaker and disconnector • Earthing switches on one or both sides • Current transformers on one or both sides with up to three cores per current transformer (depending on the class) • One or two voltage transformers on one or both sides with one or two secondary windings • Starting switch for (reduced voltage) starting the gas turboset via SFC (Static Frequency Converter) • Surge capacitors on both sides.
As required by the plant layout, individual components can be deleted from the standard execution. The standard execution can be extended by t he following optional items: • Short-circuiting connection - either permanently fitted with switch (for braking), or to be manually mounted (for power plant protection setting) • Surge arrester on transformer side.
View into one pole of circuit-breaker type HGC 3
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Equipment options 20 7 9
10
19
15
12
11
G
T
13
16 3
1
2
4
17
14
5 1 2 3, 4 5 7
Generator circuit-breaker Disconnector Earthing switches Starting switch for gas turbines Braking switch (HEC only) or manual short-circuiting connection
9 - 12 13,14 15 16,17 19 20
Volt age transformers Current t ransf orm ers Surge arrester Surge c ap acit ors System enclosure Earthing link
Generator circuit-breaker Interrupting chamber Within the interrupting chamber SF6 gas is used for both arc extinguishing and internal insulation. The external insulation is air. For the interruption a combination of the self-existinguishing and the puffer principle is used, a design optimised to achieve a significant reduction in operating energy. This self-pressurising principle allows high breaking capacities as well as almost overvoltage-free interruption of small (inductive) currents. Separate contact systems for breaking and for continuous current carrying are used. This avoids wear / erosion of the continuous current cont acts and ensures trouble-free current carrying even after a large number of operations.
Interrupting chamber of the circuit-breaker type HEC 3. On the right the terminal is visible, while on the left a concentric ring of spring loaded contact fingers can be seen. This ring forms the fixed contact which accepts the cylindrical moving contact of the disconnector. The circuit-b reaker cont acts are operated by a shaft p assing from below, through the vertical support insulator.
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Mode of operation of the interrupting chamber of the HEC 3-6 circuit-breaker 7 a Circuit-b reaker CLOSED 2
b Initiation of opening movement, (transfer of current from the main contacts to the arcing contacts)
3 4
a 9
6
c Separation of arcing contacts with interruption of small currents supported by puffer action
b
5 1 2 3 9
c
d Separation of arcing contacts with interruption of large currents – supported by the thermal effect of the current arc itself to build up the pressure in the heating volume e Circuit-b reaker OPEN
d 7
6
5
4
e
8
1 2 3 4 5 6 7 8 9
Terminals Cylindrical coil Fixed arcing contact Moving arcing contact Fixed main contact s Moving main contact Puffer Heating volume Gas compart ment
Hydraulic spring drive The hydraulic spring operating mechanism comb ines the advantages of a hydraulic operating mechanism with those of a spring energy storage system. Energy storage is accomplished with the aid of a disk spring assembly, with the advantages of high long-t erm stability, reliability and non-influence of temperature changes. Tripping of the operating mechanism and energy output are based on proven design elements of the hydraulic operating technique, such as control valves and hydraulic cylinders.
High pressure Low pressure
The operating mechanism is based on the so-called differential piston principle (between the larger piston head side area and the smaller piston rod side area). For the closing operation the p iston head side is isolated from the low pressure and simultaneously connected to the high pressure oil volume. As long as the pressure is maintained, the piston remains in the CLOSED position. A pressure controlled mechanical interlock prevents movement of the piston to the OPEN position in case of a pressure drop.
1 Breaker operating rod 2 Energy storage device
Schematic diagram of the hydraulic spring operating mechanism
View of the hydraulic spring op erating mecha- nism with cover removed
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For the opening operation, the piston head side is isolated from the high pressure and simultaneously connected to the low pressure oil volume. The charging state of the spring disk assembly is controlled by switching elements, actuating the pump motor to immediately maintain the oil pressure. For emergency use or maintenance, charging of the spring disk assembly and tripping is possible locally. The fully integrated construction has no hydraulic pipe connections of any kind.
A non-return valve between pump and high-pressure oil volume prevents pressure loss in the event of a pump outage. The hydraulic system is hermetically sealed against atmosphere (no corrosion). The mechanically operated position indicator provides reliable indication of the circuit-breaker position. The drive operates all three breaker poles simultaneously by mechanical linkages, thus keeping the switching time difference between the poles to a minimum.
SF 6 gas density monitoring system The breaking capacity of an SF6 circuit-breaker and the dielectric withstand level across its open contacts is dependent upon the density of the SF6 gas. Under the condition of constant volume the gas density is independent of t he gas temperature, while the pressure varies with the temp erature. It is therefore more practical to measure and use the gas density rather than the pressure for circuitbreaker supervisory purposes.
The functional principle of the density monitor is shown in below diagram. The density monitor op erates according to the reference-volume-density principle. The density of t he gas in the circuit-b reaker chamber is compared with the density of the gas in a sealed reference gas volume. When the gas density drops below the specified value, the density monitor signals the loss of SF6 gas in several steps. It is mounted on t he crankcase of the middle pole. Since the gas volumes of the three breaker poles are connected via the refilling pipe only one SF6 gas density monitor per breaker is required to supervise the gas density.
Schematic diagram of the SF 6 gas density monitor 1 Pressure connection 2 SF 6 gas volume of the circuit- breaker 3 Metallic bellows
4 Reference gas volume 5 Actuating rod 6 Microswit ch
P/t-diagram for SF 6 gas, with operating cha- racteristics of the gas density monitor for the SF 6 circuit-breaker
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Disconnector The switchgear concept provides a disconnector fitted in series with the circuit-breaker. It is placed on the out- going side of c ircuit-breaker and within the same enclosure. The disconnector is a tubular telescopic unit, with the moving contact tube on the circuit-breaker side and the fixed contact on the terminal side. This layout provides easy access and simplifies maintenance. In the open position of the disconnector the isolating air distance can be c learly seen through an inspection window in the cover of the enclosure. The moving contact is motor d riven.
SF6 circuit-breaker pole type HEC 3 and its disconnector, shown installed in its phase enclosure. The disconnector on the left, is shown with its moving contact stopped in an intermediate position between closed and open. The terminals on both ends are formed with silver plated multi contact surfaces to fit the flexible connectors to the bus bars.
The operating mechanism is a compact sub-assembly, including the motor, auxilary switch, reduction gear box and coupling flanges in one unit. Key locking in the positions “Close” and “ Open” is a standard facility. An additional locking prevents motor operation while the disconnector is being manually operated. Mechanically driven position indicator is provided in a readily visible position and a crank handle is provided for manual operation. The yellow sticker shows t he different operation modes of the key locking sche- me of the individual motor operating me- chanisms, which all of them operate in the same way. Besides the drive of the circuit-breaker, other operating me- chanisms, as for disconnector, earthing switch, starting switch are shown. The operating mechanisms for disconnector and all switches are identical. They incorporate a driving moto r and gearing, a mechanical semaphore, key locking and an electrical auxilary switch.
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Earthing switch The earthing switch c an be provided on either one or both sides of the system. The switch and its connections are designed for protective earthing purposes, i.e. it is rated for t he full fault current but has no current making or continuous carrying capacity. Design is of a blade type with the hinge point connected to the enclosure and the fixed contact to the current path. The earthing connection is made via the system enclosure, which is earthed at one end to the busbar enclosure. The moving contact is motor driven.
Starting switch The starting switch can be provided on the generator side of the system. The starting switch and it s connections have been designed for the voltage, current and current-duration occurring during the SFC (Static Frequency Converter) start-up period of the gas turboset. The design is of a blade type with the fixed contact s at the current path and the hinge point isolated f rom the enclosure. High voltage cables can be connected to this. The moving contact is motor driven.
Breaker type HEC Earthing switch or starting switch shown in closed position.
Manual short-circuiting connection The manual short-circuiting connection can be provided for the use between the circuit-breaker and the disconnector of the system. This arrangement has been designed for installations where the short-circuiting facility is only rarely used. The short-circuiting connection is built for the voltage, current and current duration occurring during the testing and adjustment of the power plant protection system. The cover of each of the phase enclosures has to be removed to allow t he fitting of t he short-circuiting b usbars.
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Short-circuiting-/ braking switch The short-c ircuiting-/braking switc h (HEC 3-6 only) can be provided between the circuitbreaker and the disconnector of the system. The short-circuiting-/braking switch and its connect ion between phases have been developed to expedite the testing and adjustment of the pow er plant protection system, respectively for the use as an electrical brake to shut-down the generator set. Closure of the switch establishes an unearthed three phase short-circuit, which then can be switched to t he generator terminals by closure of the circuit-breaker. The design of the switch is of a sliding type with the moving cont act isolated from the enclosure and the fixed contact connected to the current path. The actual short-circuiting connection between the phases is established external to the enclosure and being insulated from the enclosure (2000V), and is protected against inadvertently t ouching. The moving contact is motor d riven. As an additional feature, a link can be provided with which the short-circuit connection can be connected to the phase enclosure i.e., to earth. This link can only be fitted manually.
Braking switch contacts - shown in closed position - establish via integra- ted buses a connection between the three phases. Braking switch and bus is isolated from t he enclosure. The contacts of the braking switch are normally motor operated, but can also be operated by m eans of a hand crank. The operating mechanism is mounted on the braking switch housing.
Current transformer A ring core current transformer can be provided on either one or both sides of the b reaker system. Depending on the class up to three cores per current transformer can be accommodated, depending on o utput and class required. The secondary windings are permanently wired back to terminal blocks in the control cubicle.
Ring core current transformers with up to 3 cores per transformer can be mounted at each end of each phase enclosure.
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Voltage transformer Single-phase, cast resin voltage transformers can be provided on either one or both sides of the breaker system. Up to tw o voltage transformers can be fitted at each side and each voltage transformer can be supplied with one or t wo secondary windings, depending on the c lass and output power required. The secondary windings are permanently wired back to terminal blocks in the control cub icle.
Surge arrester A surge arrester can be fitted on the transformer side, to provide protection for transformer and generator against overvoltages. Standard is an ABB metal-oxide surge arrester of the POLIM range with silicon housing. Metal-oxide resistors have a highly non-linear resistance characteristic. At service voltage a predominantly capacitive current of
