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NP Plant Status Update

Syed Hamza KazmiGTE ElectricalBatch 11

FINAL PRESENTATIONSyed Hamza Kazmi (GTE)1

Presentation Geography - ComprehensiveSyed Hamza Kazmi (GTE)2

Generators Operating Modes & Control MechanismsSyed Hamza Kazmi (GTE)3

PRIME MOVERGENERATORGOVERNORAVRGenerator Control MechanismsThere are two types of controls associated with a generator:Governor (controls the MW and frequency)AVR (controls the MVAr and Terminal Voltage)Syed Hamza Kazmi (GTE)4

Mechanical PowerElectrical Power

Presentation GeographyIn the next 25 minutes we shall go through the following:

Syed Hamza Kazmi (GTE)5

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Generator Operating SchemesBrief description of control modesSyed Hamza Kazmi (GTE)6

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Generator Operating SchemesA number of Operating Schemes are employed worldwide. Considering FFLs system, todays discussion will deal with following schemes only:Islanded operation with one generatorIslanded operation with multiple generators (parallel)Syed Hamza Kazmi (GTE)7

GTG AGTG B

GTG A

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Syed Hamza Kazmi (GTE)8Operating Schemes Islanded Operation with Single GTG

Islanded Operation (Single GTG)When operating in isolation, an increase in load will have two effects:Speed (frequency) will initially fall. The speed reduction is detected by the governor, which opens the prime mover fuel valve by the required amount to maintain the required speed (frequency).Voltage will initially fall. The voltage reduction is detected by the AVR which increases the excitation by an amount required to maintain output voltage.

Syed Hamza Kazmi (GTE)9

Syed Hamza Kazmi (GTE)10Operating Schemes Islanded Operation with Multiple Sources

Parallel Operation When a machine operates in parallel with a power system, the voltage and frequency will be fixed mainly by the system. The fuel supply to the prime mover determines the Power which is supplied by the generator and this is controlled by the governor. The generator excitation determines the internal emf of the machine and therefore affects the power factor when the terminal voltage is fixed by the power system. Syed Hamza Kazmi (GTE)11

Points to Remember

In single and parallel operation it is important to realize that PRIME MOVER Active Power (by varying Fuel Supply)EXCITATION Voltage (Islanded Operation) & Voltage + Power Factor or Q of Machine (Parallel Operation)Syed Hamza Kazmi (GTE)12

Governor ControlModes of Operation, Case Studies and Practical ExamplesSyed Hamza Kazmi (GTE)13

Governor Operating Modes

Governor Droop ModeSyed Hamza Kazmi (GTE)15

Droop Mode - Introduction

What does a droop of 3, 4 or 5% indicate ?

Syed Hamza Kazmi (GTE)16The percentage of frequency change required to move a unit from no-load to full load is called Percentage Droop

Droop Mode - ExplanationIn this graph both the frequency (f) and Power (P) are plotted relatively (i.e. in terms of relative ratios)

Vertical axis represents f / fo

Horizontal axis represents P / Po

Hence the final formula for droop becomes:

0.9 o%- f / fo P / PoSyed Hamza Kazmi (GTE)17

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Droop Mode Explanation (Contd)Droop of 4 % :A change in 25% of the rated load of the machine results in a change of 1% in its rated speed (Frequency)A change in 100% of the rated load of the machine results in a change of 4% in its rated speed (Frequency)A 4 % change in frequency, means 50 Hz x 0.04 = 2 Hz or for a 4 pole generator, 1500 rpm x 0.04 = 60 rpm.

50 Hzf [%]

60 rpm, 2Hz or 4%

P [%]100%Syed Hamza Kazmi (GTE)18

Droop Mode Explanation (Contd)Droop of 5 % :A change in 20% of the rated load of the machine results in a change of 1% in its rated speed (Frequency)A change in 100% of the rated load of the machine results in a change of 5% in its rated speed (Frequency)A 5 % change in frequency, means 50 Hz x 0.05 = 2.5 Hz or for a 4 pole generator, 1500 rpm x 0.05 = 75 rpm.

50 Hzf [%]

75 rpm, 2.5Hz or 5%

P [%]100%Syed Hamza Kazmi (GTE)19

Droop Mode Case Study

8000 MW 50 Hz

G1max 50 MW

G2max 50 MW

G3max 50 MW

For our case study, let us consider a grid whose total generating capacity is 8000 MW rated at 50 Hz

An IPP, having three generators of 50 MW each, is synchronized with the grid and are supplying 37 MW each initially

All the 3 generators are operating at droop mode with a droop setting of 4%

Each of the 3 generators will take up 50 / 8000 i.e. 0.625% of any load demand changes that may occur on the grid

For this context, let a load of 5MW be added to the grid.

Lets examine what happens next

5 MW

37MW37MW37MWSyed Hamza Kazmi (GTE)20

4%

4%f [%]P [%]100%

RAISELOWER

RAISEDroop Mode Case Study G1max 50 MW

8000 MW 50 Hz

50 HzFor any demand load, each generator must increase 50 MW / 8000 MW = 0.625% = 0.00625 of that demand

For 5 MW increase in demandG1 = 0.00625 x 5 MW = 0.03125 MW 37.03125 MWG2 = 0.00625 x (5- 0.03125) MW = 0.03105 MW 37.03105 MWG3 = 0.00625 x (5- 0.03125- 0.03105) MW = 0.03086 MW 37.03086 MWG2max 50 MW

G3max 50 MW

37 MW37 MW37 MWWhat happens to frequency ?50 Hz - (0.04 x 50 Hz x 5 MW / 8000 MW) = 49.9987 Hz

How? Lets revisit the formula we just studied5 MW

OPERATORSyed Hamza Kazmi (GTE)21

Governor Isochronous ModeSyed Hamza Kazmi (GTE)22

Isochronous Mode - ExplanationIn this mode, the speed of governor (also frequency) remains constant regardless of any change in the load.Also called Frequency Control Mode or Swing Generator Mode

A system running in Islanded Scheme is required to run at least one of its Generators on Isochronous mode

Syed Hamza Kazmi (GTE)23

f [Hz]P [%]100%50%

RAISELOWERSP Regulator

RAISE

Isochronous Mode Case StudyReferring to previous case, with one of the three generators being operated in Isoch modeSyed Hamza Kazmi (GTE)24

Isoch & Droop Modes - Control principleA generator that can be operated in both Isoch and droop modes necessarily incorporates a feedback control system

Take a look at these 3 abbreviations first:

DSP: Digital Set Point (for speed of governor)AS: Actual Speed (of governor)VCE: Velocity Control Error where, VCE= AS DSP(difference b/w Actual and Set speed of governor)

Shaft RotatesTurbine Fuel Adjust

DSPVCE

GovernorGear Box &Alternator Optical or MP EncoderASSyed Hamza Kazmi (GTE)25

Isoch & Droop Modes - Control principleFor Isoch Control, the control system is mechanized as:

DSP: Digital Set Point AS: Actual Speed VCE: Velocity Control Error

The circle represents an amplifier

It amplifies the Error (VCE = AS DSP) and sends it to the governor speed controller

Greater the Error, Greater the change in speed of governor

Hence, AS recurs to DSP Syed Hamza Kazmi (GTE)26

Isoch & Droop Modes - Control principleFor Droop Control, the control system is mechanized as

In this case, the VCE is fed back to amplifiers input as VCE

This addition of VCE compensates for the difference b/w AS and DSP

Hence VCE is minimized and Governor Speed Controller does not change its speedDSP: Digital Set Point AS: Actual Speed VCE: Velocity Control Error

Syed Hamza Kazmi (GTE)27

Case StudyThe Generation system at FFL is currently in Island ModeLet us simplify the generation system by considering GTG-A & GTG-B onlyLet the GTGs be rated to a capacity of 20 MW each which accounts to a total generation capacity of 40 MW (considering STG is not being operated)We shall discuss the following 3 cases:

Case 1: Both the GTGs are operated in Isoch modeCase 2: Both the GTGs are operated in Droop modeCase 3: GTG-A in Isoch mode & GTG-B in Droop mode

Syed Hamza Kazmi (GTE)28

Case 1: Both the GTGs are operated in Isoch modeSyed Hamza Kazmi (GTE)29

Case 1: Both the GTGs are operated in Isoch mode Isoch

GTG AGTG B Isoch

Let us assume our system is stable initially with following characteristicsSystem: 50 Hz , 15 MWGTG-A: 50 Hz , 15 MWGTG-B: Not in operationGTG AGTG BF (Hz)MWGTG B = 0 MWGTG A = 15 MWSystem = 15 MW50 HzSyed Hamza Kazmi (GTE)30

Hence Finally,GTG-A: 50 Hz, 0 MWGTG-B: 50.1 Hz, 20 MWSystem: 50.1 Hz, 20 MW

In fact, GTG-A will finally trip on Reverse PowerCase 1: Both the GTGs are operated in Isoch mode Isoch

GTG AGTG B Isoch

Now the system load gradually increases to 20 MW. Hence GTG-B is brought in service to share load with GTG-A

GTG AGTG BF (Hz)MWGTG B = 0 MWGTG A = 20 MWSystem = 20 MWGTG B = 20 MWGTG A = 0 MW50 Hz

When GTG-B is about to be synched with the systemSystem: 50 Hz , 20 MWGTG-A: 50 Hz , 20 MWGTG-B: 50.1 Hz 50.1 HzSyed Hamza Kazmi (GTE)31

Case 1: Both the GTGs are operated in Isoch mode

Explanation Since frequency setting of GTG-B is above Systems frequency, it gains more load and keeps on gaining until Systems frequency becomes equal to GTG-B(which happens when GTG-B serves the entire load of the System)

Consecutively, GTG-A will loose its entire load while GTG-B begins to feed the entire load. (GTG-A may reach the point of Reverse Power Trip as well)

Conclusion

Since the frequency of the Incoming generator will be greater than that of the system (for synchronism), this method of operation is strictly unfeasible Syed Hamza Kazmi (GTE)32

Case 2: Both the GTGs are operated in Droop modeSyed Hamza Kazmi (GTE)33