Download - Hamza Kazmi (GTE)
Syed Hamza Kazmi
GTE – ElectricalBatch 11
FINAL PRESENTATION
Syed Hamza Kazmi (GTE) 1
Presentation Geography - Comprehensive
Syed Hamza Kazmi (GTE) 2
Technical Overview
• Generators (Operating Modes & Control Mechanism)
Annual Progress Review
• Highlights• Technical Initiatives• Extracurricular Initiatives
Generators Operating Modes & Control Mechanisms
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PRIME MOVER GENERATOR
GOVERNOR AVR
Generator Control Mechanisms
There are two types of controls associated with a generator:a) Governor (controls the MW and frequency)b) AVR (controls the MVAr and Terminal Voltage)
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Mechanical Power Electrical Power
Presentation Geography
• In the next 25 minutes we shall go through the following:
Operating Schemes
• Islanded Operating Scheme• Parallel Operating Scheme
Governor Control
• Droop Mode• Isochronous Mode• Case Studies (Practical Considerations)
Excitation Control
• Fundamentals & Types• Capability Diagrams & V-Curves• Case Studies (Practical Considerations)
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GENERATOR OPERATING SCHEMESBrief description of control modes
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Generator Operating Schemes
A number of Operating Schemes are employed worldwide. Considering FFL’s system, today’s discussion will deal with following schemes only:• Islanded operation with one generator• Islanded operation with multiple generators (parallel)
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GTG A GTG BGTG A
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Operating 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.
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Syed Hamza Kazmi (GTE) 10
Operating 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.
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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)
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GOVERNOR CONTROLModes of Operation, Case Studies and Practical Examples
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Governor Operating Modes
Governor Operation Modes
Isochronous Mode Droop Mode Base load Mode
Governor Droop Mode
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Droop Mode - Introduction
What does a droop of 3, 4 or 5% indicate ?
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The percentage of frequency change required to move a unit from no-load to full load is called Percentage Droop
Droop Mode - Explanation
In 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
%
- Δf / fo
ΔP / Po
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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 Hz
f [%]
60 rpm, 2Hz or 4%
P [%]100%
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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 Hz
f [%]
75 rpm, 2.5Hz or 5%
P [%]100%
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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
37MW 37MW 37MW
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4%4%
f [%]
P [%]100%
RAISE LOWERRAISE
Droop Mode – Case Study
G1max 50 MW
8000 MW 50 Hz
50 Hz
For 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 MW
G2max 50 MW
G3max 50 MW
37 MW
37 MW
37 MW
What 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 studied
5 MW
OPERATOR
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Governor Isochronous Mode
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Isochronous Mode - Explanation
• In 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
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f [Hz]
P [%]100%50%
RAISE LOWER
SP Regulator
RAISE
Isochronous Mode – Case Study
Referring to previous case, with one of the three generators being operated in Isoch mode
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Isoch & Droop Modes - Control principle
A 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
DSP VCE
Governor
Gear Box &
Alternator
Optical or MP EncoderAS
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Isoch & Droop Modes - Control principle
For 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 principle
For Droop Control, the control system is mechanized as
In this case, the VCE is fed back to amplifier’s input as Δ VCE
This addition of Δ VCE compensates for the difference b/w AS and DSP
Hence VCE is minimized and Governor Speed Controller does not change its speed
DSP: Digital Set Point AS: Actual Speed VCE: Velocity Control Error
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Case Study
The Generation system at FFL is currently in Island ModeLet us simplify the generation system by considering GTG-A & GTG-B only
Let 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
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Case 1: Both the GTGs are operated in Isoch mode
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Case 1: Both the GTGs are operated in Isoch mode
Isoch
GTG A
GTG B Isoch
Let us assume our system is stable initially with following characteristics
System: 50 Hz , 15 MWGTG-A: 50 Hz , 15 MWGTG-B: Not in operation
GTG A GTG BF (Hz)
MWGTG B = 0 MWGTG A = 15 MW
System = 15 MW
50 Hz
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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 Power
Case 1: Both the GTGs are operated in Isoch mode
Isoch
GTG A
GTG 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 A
GTG BF (Hz)
MWGTG B = 0 MWGTG A = 20 MW
System = 20 MW
GTG B = 20 MW
GTG A = 0 MW
50 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
Hz
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Case 1: Both the GTGs are operated in Isoch mode
Explanation
Since frequency setting of GTG-B is above System’s frequency, it gains more load and keeps on gaining until System’s 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
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Case 2: Both the GTGs are operated in Droop mode
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Droop
GTG A
GTG B
Droop
Let both the GTGs be operated in DROOP mode (with same Droop setting)
Let us assume our system is stable initially with following characteristics
System: 50 Hz , 30 MWGTG-A: 56 Hz (@ no load) , 18 MWGTG-B: 53 Hz (@ no load) ,12 MW
GTG A GTG BF (Hz)
MWGTG B = 12 MW
GTG A = 18 MW
System = 30 MW
50 Hz
Case 2: Both the GTGs are operated in Droop mode
56 Hz
53 Hz
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Droop
GTG A
GTG B
Droop
Meanwhile, Refrigeration Compressor at NP (1.5 MW) is started As a result the load on both GTGs will increase in equal proportions (b/c of same droop settings)
GTG A GTG BF (Hz)
MWGTG B = 12 MW
GTG A = 18 MW
System = 30 MW
50 Hz
Case 2: Both the GTGs are operated in Droop mode
GTG A = 18.75 MW GTG A = 12.75 MW
System = 31.5 MW
As a result, the overall frequency of the System will decrease to meet load requirement
49.4Hz
Therefore, in order to bring the system back to 50 Hz, operator must raise the ‘no load frequency’ of either one or both the GTGs.
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Case 2: Both the GTGs are operated in Droop mode
Explanation
In this case, an increase in system load will decrease its frequency(operator will have to increase the ‘no load frequency set point’ of either
both GTGs or any one)
While, a decrease in system load will increase its frequency(operator will have to decrease the ‘no load frequency set point’ of either
both GTGs or any one)
Conclusion
Hence, this method of operation is feasible in load stable systems (where load doesn’t vary in large proportions). Otherwise continuous
load monitoring is necessary.
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Case 3: GTG-A in Isoch mode & GTG-B in Droop mode
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Droop
GTG A
GTG B
Isoch
This case is explained using a number of sub-cases
Let us assume our system is stable initially with following attributes
System: 50 Hz , 20 MWGTG-A: 53 Hz (@ no load) , 10 MWGTG-B: 50 Hz (Isoch) , 10 MWGTG A GTG B
F (Hz)
MWGTG B = 10 MW
GTG A = 10 MW
System = 20 MW
50 Hz
53 Hz
Case 3: GTG-B in Isoch mode & GTG-A in Droop mode
Rated Capacity: 20 MW each
NOTE: In each of the following sub-cases, operator is not allowed to change the no load frequency set point of GTG-
A
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Droop
GTG A
GTG B
Isoch
Subcase ‘a’: System load increases by 1.5 MW (NP Refrigeration Compressor starts)
System: 50 Hz , 21.5 MWGTG-A: 53 Hz (@ no load) , 10 MWGTG-B: 50 Hz (Isoch) , 11.5 MW
GTG A GTG BF (Hz)
MWGTG B = 10 MW
GTG A = 10 MW
System = 20 MW
50 Hz
Case 3: GTG-B in Isoch mode & GTG-A in Droop mode
GTG B = 11.5 MW
System = 21.5 MW
Rated Capacity: 20 MW each
Consequence: No action required
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Droop
GTG A
GTG B
Isoch
Subcase ‘b’: System load decreases by 5 MW
System: 50 Hz , 15 MWGTG-A: 53 Hz (@ no load) , 10 MWGTG-B: 50 Hz (Isoch) , 5 MW
GTG A GTG BF (Hz)
MWGTG B = 10 MW
GTG A = 10 MW
System = 20 MW
50 Hz
Case 3: GTG-B in Isoch mode & GTG-A in Droop mode
GTG B = 5 MW
System = 15 MW
Rated Capacity: 20 MW each
Consequence: No action required
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Droop
GTG A
GTG B
Isoch
Subcase ‘c’: System load decreases to 10 MW
System: 50 Hz , 10 MWGTG-A: 53 Hz (@ no load) , 10 MWGTG-B: 50 Hz (Isoch) , 0 MW
GTG A GTG BF (Hz)
MWGTG B = 10 MW
GTG A = 10 MW
System = 20 MW
50 Hz
Case 3: GTG-B in Isoch mode & GTG-A in Droop mode
GTG B = 0 MW
System = 10 MW
Consequence: No load ‘f’ set-point of GTG-A should be decreased
Rated Capacity: 20 MW each
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Droop
GTG A
GTG B
Isoch
Subcase ‘d’: System load decreases to 5 MW
System: >50 Hz , 5 MWGTG-A: 53 Hz (@ no load) , 5 MWGTG-B: 50 Hz (Isoch) , 0 MW
GTG A GTG BF (Hz)
MWGTG B = 10 MW
GTG A = 10 MW
System = 20 MW
50 Hz
Case 3: GTG-B in Isoch mode & GTG-A in Droop mode
GTG B = 0 MW
System = 5 MW
GTG A = 5 MW
51.5HzConsequence: No load ‘f’ set-point of GTG-A should be decreased
Rated Capacity: 20 MW each
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Droop
GTG A
GTG B
Isoch
Subcase ‘e’: System load increases to 40 MW
System: < 50 Hz , 40 MWGTG-A: 56 Hz (@ no load) , 14 MWGTG-B: 50 Hz (Isoch) , 26 MW
GTG A GTG BF (Hz)
MWGTG B = 10 MW
GTG A = 10 MW
System = 20 MW
50 Hz
Case 3: GTG-B in Isoch mode & GTG-A in Droop mode
GTG B = 26 MW
System = 40 MW
After crossing rated capacity
GTG A = 14 MW
< 50 Hz
Consequence: No load ‘f’ set-point of GTG-A should be increased
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Explanation
In this case, an increase in system load will not affect system frequency (The GTG running in Isoch mode provides the additional load without
affecting the frequency of system – if load change is with in prescribed limit)
While, a decrease in system load will not affect system frequency either(The GTG running in Isoch mode reduces its own fed load without affecting
the frequency of system – if load change is with in prescribed limit)
If load changes are not in ‘Prescribed Limits’, operator will have to step in and increase or decrease the ‘No load frequency set point’ of droop GTG
Conclusion
Hence, this method of operation is feasible in all systems running in Island mode. Isochronous GTG serves as the Swing Generator.
Case 3: GTG-B in Isoch mode & GTG-A in Droop mode
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EXCITATION CONTROLControl Functions, Types, Capability Curves & Case Study
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Functions of Excitation Systems
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The basic functions of an excitation system are• To provide direct current to the synchronous generator field winding• To perform control and protective functions essential to the satisfactory
operation of the power system
Performance Requirements of AVR
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These control and protective functions include:
Secondary Functions of AVR
Generator Considerations(Follow Capability Curve,
Maintain V/Hz ratio)
System Considerations(Ensure System stability)
Brushless Excitation System
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AVR Operation Principle
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The line voltage (provided by VT) is compared to a Reference Voltage.
The difference (error) signal is amplified and then used to control the output of a thyristor rectifier
This rectifier supplies a portion of the PMG output to the exciter field
Load Increment:
If Generator Load is increased, Terminal voltage drops.
Error Signal is amplified, which causes an increase in exciter field current
This results in an increased Main Field Current
Hence, Generator Voltage is restored.
Conversely, Load Reduction will lead to actuation of Opposite series of steps
Vt
AVR Operation Principle – Parallel Scheme
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The discussed AVR principle is relevant for Islanded Operation with singular source or even multiple sources
But for Parallel operation (especially with Infinite Bus), Terminal Voltage is not influenced by the Generator’s Excitation.
Instead, Excitation now determines the Reactive Power developed by the Generator
ConsequencesSystem Voltage Excitation
CurrentReactive Power
Consequence
Vsys < Vref Increased by AVR Excessive Lagging Q
Excessive Rotor Heating
Vsys > Vref Decreased by AVR Excessive Leading Q
Generator Pole Slipping (Asynchronism)
AVR Operation Principle - QCC
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Hence to overcome this problem, the AVR Voltage Control System is modified using QCC (Quadrature Current Compensation)
This compensation replicates the ‘frequency/MW’ relation for ‘Voltage/MVAr’
Note: QCC Schematic Diagram and Operation Principle can be discussed in detail if required*
QCC Operation (Islanded Scheme with Multiple Machines)
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The mentioned system has 3 Generators which share Total Load VArs on QCC Principle
In this example, machines A and B have identical droop and at a particular line voltage will supply equal VARs.
Machine C has less droop and will therefore supply more VARs than A or B, at the same line voltage
Practical ExperimentComprehensive Governor & Excitation
Response
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Comprehensive Governor & Excitation Behavior
The test presented to explain this behavior was practically conducted on 8th May 2010.The system was initially running with following attributes:
GTG-A’s MW and MVAr outputs were varied and comprehensive system response was analyzed
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GTG A GTG B
Pa=8.5 MW Qa=5 MVAr p.f=0.86 Pb=8.5 MW Qb=5 MVAr p.f=0.86
Pt=17 MWQt=10 MVArp.f=0.86
Isoch ModeDroop Mode
Varied using Governor set-point
Varied using AVR QCC set-point
Comprehensive Governor & Excitation Behavior
Manual Action 1:• Pa decreased only (using droop set-point of GTG-A)• Qa not changed (i.e. AVR QCC set-point not disturbed)
Automatic Result:– Pb increased (Isochronous operation)– Qb not changed
– Hence, • P.F. of GTG-A = Decreased (because Pa/Qa ratio decreased)• P.F. of GTG-B= Increased (because Pb/Qb Ratio increased)
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GTG A GTG B
Comprehensive Governor & Excitation Behavior
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Ptot Qtot P Q p.f P Q p.fMW MVAR MW MVAR --- MW MVAR ---
17 10 8.5 5 0.86 8.5 5 0.86
Action 1 Pa Decreased Manually* Pb Increased Automatically
17 10 6 5 0.77 11 5 0.91
Action 2 Qa Decreased Manually** Qb Increased Automatically
17 10 6 3.529 0.86 11 6.471 0.86
Action 3 Pa Increased Manually* Pb decreased Automatically
17 10 8.5 3.529 0.92 8.5 6.471 0.80
Action 4 Qa Increased Manually** Qb decreased Automatically
17 10 8.5 5 0.86 8.5 5 0.86
GTG-A GTG-B
* performed using droop set-point** performed using AVR QCC set-point
Explanation through V-Curve (for GTG-A only)
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Action-1
Action-2
Action-3
Action-4
CAPABILITY CURVEGenerator Limitations,
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Capability Diagram of Generator
This diagram determines the limitations of a generator’s output.• Following Constraints define the entire limitation:
– Current heating of the stator (armature).– Power Output of the prime mover.– Current heating of the rotor (field).– Stability of the rotor angle.
Capability Diagram of GTGs
Stator Current Limit
Rotor Current Limit
Rotor Stability Limit
Capability Diagram (Explanation)
P (p.u.)
Q (p.u.)Lagging QLeading Q
Constraint # 1:STATOR CURRENT
1.0
1.5
1.0 1.0 O
VI
Stator HeatingMVA Limit
Ø
P (p.u.)
Q (p.u.)Lagging QLeading Q
Constraint # 2:Prime Mover Output1.5
O
1.0
1.0 1.0
Max MW Output
Arbitrary Operating Point
Capability Diagram of Generator
P (p.u.)
Q (p.u.)Lagging QLeading Q
Constraint # 3:ROTOR CURRENT
(Generated Voltage)Eg α Rotor Current
1.5
O
1.0
1.0 1.0
VIEg V / Xs
Sq(V) / Xsᵟ
Capability Diagram of Generator
IXsEg
V
OXL
OXM
Note: Xd of GTGs is 2.13 p.u. This determines the position of this point
P (p.u.)
Q (p.u.)Lagging QLeading Q
Constraint # 4:STABILITY OF THE ROTOR1.5
O
1.0
1.0 1.0
Capability Diagram of Generator
UEL
UEM
Theoretical Stability Limit
P (p.u.)
Q (p.u.)Lagging QLeading Q
1.5
O
1.0
1.0 1.0
Capability Diagram of Generator
OXL
OXM
UEL
UEM
Theoretical Stability Limit
Max MW Output
Queries?
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Thank you !
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