Copy of Control Gas Turbine Power Output in Conjuction With Grid Frequency

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CONTROL GAS TURBINE POWER OUTPUT CONTROL IN CONJUCTION WITH GRID FREQUENCE 

INTRODUCTION

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GAS TURBINE LOAD COMMANDS

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SPEED/LOAD CONTROL COMMANDS

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GOVERNOR COMMANDS



FUEL STROKE REFERENCE



POWER PLANT PROBLEM PROBLEM AND THE TH E SOLUTION

INTRODUCTION  

General Electric gas turbine MS9001FA uses MARKVI/e to control the turbine from stand still to base load

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From SS (0 rpm) to T.G(6 rpm) » T.G motor

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From T.G (6 rpm) to Purge(699 rpm) » LCI system is ON

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From Purge(699 Purge(699 rpm) to 400 rpm rpm » LCI LCI system is OFF

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From (400 rpm) to fire (435 rpm) rpm) » LCI system is ON

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From fire (435 rpm) to FSNL, SYNC(3000 rpm) » LCI system is ON + FIRE LCI system is OFF at 2730 rpm , acceleration control control FSRACC

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From SYNC(3000 rpm) to part load » load control FSRN

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At base load » temp control FSRT

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INTRODUCTION

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GAS TURBINE LOAD COMMANDS

G A S TUR B INE L OA D C O MMA ND S 

SPINNING RESERVE

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LOAD SELECTION PRE SELECT LOAD BASE LOAD PEAK LOAD

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SPINNING RESERVE

In the absence of having selected either of the commands listed below 1. PRE SELECT 2. BASE 3. PEAK 

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If the gas turbine is started in AUTO with automatic synchronization selected at the generator panel, the unit will automatically load to a point known as SPINNING RESERVE

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The unit will remain at SPINNING RESERVE until another load command is given or until a RAISE or LOWER load command is given

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SPINNING RESERVE is a site± adjustable setting determined by control constant LK90SPIN.

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PRESELECTED LOAD

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 When PRESELECTED LOAD is selected, the unit will automatically load or unload at the automatic loading rate until the preselected load output is attained

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The preselected load is a megawatt setting that is site adjustable by changing control constant LK90PSEL

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Once the preselected load level is attained, fuel flow will be controlled to maintain that megawatt output until another load command is given or until a RAISE or LOWER load command is given

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BASE LOAD

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 When BASE LOAD is selected, the unit will load (or unload from PEAK) at the normal loading rate until the unit goes on exhaust temperature control

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at this point, the unit is at its nominal rated power out-put for the ambient conditions

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 When the unit is on exhaust temperature control, fuel flow is regulated to provide the maximum power for the ambient conditions without over firing the machine

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It is important to note that as ambient conditions change, primarily compressor inlet temperature, the unit's power output will change

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Once at BASE LOAD, the unit will remain there until another load command is given or a LOWER load command is given

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 After selecting BASE LOAD, the automatic loading or unloading of the unit may be aborted by giving a RAISE or LOWER load command

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PEAK LOAD

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PEAK LOAD is an option and, when selected, the unit will load at the normal loading rate until the unit goes on peak exhaust temperature control

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Similar to operation on BASE, as ambient conditions change, primarily compressor inlet temperature, the unit's power output will change

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 When operating on PEAK, the unit is operating at a firing temperature above its design limit unit output is increased with a consequent reduction in the machine's maintenance intervals  A rule of thumb is one hour of PEAK operation is equivalent to six hours of BASE operation Once at PEAK LOAD, the unit will remain there until another load command is given or a LOWER load command is given  After selecting PEAK LOAD, the automatic loading or unloading of the unit may be aborted by giving a RAISE or LOWER load command.

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INTRODUCTION



GAS TURBINE LOAD COMMANDS



SPEED/LOAD CONTROL COMMANDS

 S P E E D/LOA D C ONTR OL C OMMA NDS 

SPEED/LOAD CONTROL

RAISE L OWER 

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RAISE SPEED/LOAD

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 When selected, a RAISE command will increment the turbine speed reference TNR 

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 With the generator breaker open, selecting RAISE will increase the unit's speed

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 With the generator breaker closed and the unit on droop control, selecting RAISE will increase the unit's load

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Selecting RAISE is the manual means of increasing the unit's speed or load

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LOWER SPEED/LOAD

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 When selected, a LOWER command will decrement the turbine speed reference TNR 

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 With the generator breaker open, selecting LOWER will de-crease the unit's speed

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 With the generator breaker closed and the unit on droop control, selecting LOWER will decrease the unit's load

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Selecting LOWER is the manual means of decreasing the unit's speed or load

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INTRODUCTION



GAS TURBINE LOAD COMMANDS



SPEED/LOAD CONTROL COMMANDS



GOVERNOR COMMANDS

GOVERNOR COMMANDS 

GOVERNOR 

DROOP ISOCH

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ISOCHRONOUS GOVERNOR 

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Isochronous Speed Control is a form of governor control that is used when a gas turbine is applied on an isolated system where its speed is not dictated by the system

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The isochronous governor set point is fixed at 100% speed

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the speed signal is compared with the speed reference signal and the error is fed through a proportional and integral speed controller

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 As long as a difference between signals exists, the isochronous speed control algorithm  will continue to increase or decrease FSR until there is no error signal. This is a fast acting system which continuously adjusts FSR to hold turbine speed constant in spite of load changes Only one unit can be under isochronous speed control at a time. Otherwise, the separate integral actions will interact, leading to load swings between all units in the isochronous mode.

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DROOP GOVERNOR 

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If the entire grid system tends to be overloaded, grid frequency (or speed) will decrease and cause an FSR increase in proportion to the droop setting

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 A drop in electrical grid frequency indicates that the power generation capability is less the load demand in the grid. and conversely 

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 A droop governor response used to help maintain an electrical grid at constant frequency.

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Droop speed control is a proportional control, changing called for fuel f low (FSR) in proportion to the difference between actual turbine speed and the speed reference  Any change in actual speed (grid frequency) will cause inversely proportional change in unit load

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If all units have the same droop, all will share a load increase equally 

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Load sharing and system stability are the main advantages of this method of speed control

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Standard GE droop is 4.0%

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Constant settable droop speed/load control

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Constant settable droop speed/load control represent a method of formulating the gas turbine response as a function of the unit power output.

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This method of speed/load control is applied to units where the fuel stroke reference is not predicable due to 1. varying fuel heating values 2. or where fuel is switched between different combustion system injection nozzles

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Typical droop constant for POWER STATION 1 =0.0146 POWER STATION OLD 2 = 0.0163 POWER STATION NEW 2= 0.01488

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Constant settable droop anti windup

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Some protection is provided if P2 pressure begins to decrease

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later the load will start to drop off and the speed error will respond by requesting more fuel flow and the until SRV if fully open.

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If speed error tn_err > 0.7% + tnh > 99.5 % + L52GX = 1 for 5 sec

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Thin a lower signal “DWARTT TOO LOW TO SUPPORT TNR, TNR_LOWER ” is given and break any base load or preselect load

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INTRODUCTION



GAS TURBINE LOAD COMMANDS



SPEED/LOAD CONTROL COMMANDS



GOVERNOR COMMANDS



FUEL STROKE REFERENCE

F UE L S TOK E R E F E R NC E  

 

FSR

(FSR) is determined by the turbine parameter (speed, temperature, and so on) calling for the least fuel. FSR calculation occurs in the main processor, then is transmitted to the servo valve cards on the backplane of the control module. The Stop/Speed Ratio valve (SRV) and the Gas Control Valve (GCV) work in conjunction to regulate the total fuel flow delivered to the gas turbine. The GCV controls the desired fuel flow in response to a control system fuel command, Fuel Stroke Reference (FSR) from the SPEEDTRONIC ™ panel.

The called–for–speed, TNR, 

determines the load of the turbine. The range for generator drive turbines is normally from 95% (min.) to 107% (max.) speed. The start –up speed reference is 100.3% and is preset when a “START” signal is given.

Speed/Load Reference FSRN 

The speed control software will change FSR in proportion to the difference between the actual turbine generator speed (TNH) and the called–for speed reference (TNR).

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By closing the generator breaker and raising TNR via raise/lower, the error between speed and reference is increased. This error is multiplied by again constant

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FSRN is used at part load

Important Equations 

DWATT * 0.0164 = DWDROOP

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TNR –DWDROOP = TNRL

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TNHSYS = COMPLICATED = TNH , FILTERED + RATE CONTROLLED + STEP ADDER + CURVE

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ERROR = TNRL – TNHSYS

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THIS ERROR INDICATES CHANGE IN GRID FEQUENCY OR IN THE OUTPUT POWER

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FSRN = FSR + TN_ERR

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TN_ERR = ERROR + DEADBAND

 DEADBAND

= 0 OR 0.02

 DEADBAND

= TNKEDB

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INTRODUCTION



GAS TURBINE LOAD COMMANDS



SPEED/LOAD CONTROL COMMANDS



GOVERNOR COMMANDS



FUEL STROKE REFERENCE



POWER PLANT PROBLEM AND THE SOLUTION

 P OWE R P L A NT P R OB L E M

TNKEDB AT TNKEDB = 0.02 

There will be an error dead band between TNRL which represent load (MW)and TNHSYS which represent grid frequency

 This

will lead to variation in MW with frequency within the 0.02 error dead band

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TNKEDB = 0.02 AT

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UNIT ONLINE = 1 MASTER PROTECTIVE SIGNAL = 1

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LIMITED FREQUENCY SENSITIVE MODE L83LFL_MODE = 0

 POWE R PLA NT S OLUTION   CHANGE

THE VALUE OF

LIMITED FREQUENCY SENSITIVE MODE L83LFL_MODE  FROM

0 » 1