frequency control turbine governor droop nerc requirement droop setting and turbine response...

Frequency Control

• Turbine Governor Droop• NERC Requirement• Droop Setting and Turbine Response• Governor underperformance• ERCOT Droop• Size does make a difference

Sydney Niemeyer

• Turbine Governor Droop, Speed Regulation or Speed Error are common terms used in describing a turbine’s response to Changes in Interconnection Frequency (speed).

• Not the same as the “Regulation” Ancillary Service Deployment of ERCOT’s Frequency Control System.

• NERC requires all generators greater than 10 MW’s to have an operating governor.

• Droop distributes Frequency regulation to all generators in the interconnect.

• Recommended droop settings of 4 to 5% with a maximum dead band of +/- 0.036 Hz.

Droop Setting Determines Response• 5% Droop: 100% change in generator output for a 5%

change in Frequency or Speed.– A 5% change in frequency, 60 Hz x 0.05 = 3 Hz or for a

2 pole generator, 3600 rpm x 0.05 = 180 rpm.• 4% Droop: 100% change in generator output for a 4%

change in Frequency or Speed.– A 4% change in frequency, 60 Hz x 0.04 = 2.4 Hz or for

a 2 pole generator, 3600 rpm x 0.04 = 144 rpm.• 4% Droop setting is more sensitive (responsive) than the

5% Droop setting.

Example of Expected Response• 150 MW unit at 5% Droop

– 150 / 3 Hz = 50.00 MW/Hz or in tenths of Hz, 5.00 MW/0.1 Hz

– Frequency change from 60.05 to 59.95 should result in the generator increasing output 5.0 MW’s

• 150 MW unit at 4% Droop– 150 / 2.4 Hz = 62.50 MW/Hz or in tenths of Hz,

6.25 MW/0.1 Hz– Frequency change from 60.05 to 59.95 should

result in the generator increasing output 6.25 MW’s

Expected Governor Response

• 5 % Droop:– Unit Net Capability/30 = MW/0.10 Hz

• 4 % Droop:– Unit Net Capability/24 = MW/0.10 Hz

Turbine Governor Response to Frequency - Max Capability 60 MW

-14.0

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

59.50 59.60 59.70 59.80 59.90 60.00 60.10 60.20 60.30 60.40 60.50

Meg

aw

att

s

-14.0

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

2.0

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6.0

8.0

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14.0

Meg

aw

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5% 4%

4%

4%

5%

5%

Testing Governor Performance

• ERCOT requires off line testing of Steam Turbine governors every 2 years.– Mechanical and Electro hydraulic test forms are in

the Operating Guides.• Combustion Turbines do not have an approved test

procedure.– On Line observation verifies proper performance

for limited frequency range.

59.70

59.72

59.74

59.76

59.78

59.80

59.82

59.84

59.86

59.88

59.90

59.92

59.94

59.96

59.98

60.00

60.02

60.04

60.06

60.08

60.10

7:40 7:45 7:50 7:55 8:00 8:05 8:10 8:15 8:20 8:25 8:30 8:35 8:40

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

Hz 400 MW Unit at 55% Throttle Pressure - Boiler Following

7/18/01

400 MW Unit at 55% Throttle Pressure - Boiler Following

• Base Load with output limited by Exhaust Temperature – Small governor response then reverses and reduces output.

• Pre-Selected Load set-point, limited by Exhaust Temperature – some governor response within Load set-point dead-band.

• Partial Load, not controlling to a load set-point – Full governor response.

Droop Underperformance due to Unit Control Mode – Combustion Turbine

Control Mode of Combustion Turbine May Limit Governor Response

3600 RPM ReferenceActual Shaft Speed

Exhaust Temperature Limit

Pre-Select Load Set-point Generator Output MW

Fuel Control Valve

FSR - Full Speed Regulation

Speed Error

Pre-Select Control Mode

Droop Setting

Combustion Turbine in Pre-Select Mode – Limited Governor Response

Combustion Turbine in Partial Load Mode – Full Governor Response

59.80

59.82

59.84

59.86

59.88

59.90

59.92

59.94

59.96

59.98

60.00

60.02

60.04

60.06

60.08

60.10

17:40 17:45 17:50 17:55 18:00 18:05 18:10 18:15 18:20 18:25 18:30 18:35 18:40

0

4

8

12

16

20

24

28

32

36

40

44

48

52

56

60

Hz GBY 82

7/18/02 Unknown External Unit Trip

GBY 82

QSE - REI

0.00Performance at Point BGreater than 0.64 = Passing

59.80

59.82

59.84

59.86

59.88

59.90

59.92

59.94

59.96

59.98

60.00

60.02

60.04

60.06

60.08

60.10

17:40 17:45 17:50 17:55 18:00 18:05 18:10 18:15 18:20 18:25 18:30 18:35 18:40

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

Hz SJS 1

7/18/02 Unknown External Unit Trip

SJS 1QSE - REI

-0.03

59.80

59.82

59.84

59.86

59.88

59.90

59.92

59.94

59.96

59.98

60.00

60.02

60.04

60.06

60.08

60.10

19:50 19:55 20:00 20:05 20:10 20:15 20:20 20:25 20:30 20:35 20:40 20:45 20:50

65

66

67

68

69

70

71

72

73

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75

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80

Hz SJS 2

7/16/02 Unknown External Unit Trip

SJS 2QSE - REI

0.02

ERCOT System Droop

• Unit mix determines Frequency Response– Possible Combination

% ResponseMW Droop MW/0.1 Hz

Nuclear 4700 100 0Wind 200 100 0

Combined Cycle CT 6000 55 19Solid Fuel Fully Loaded 11300 51 38

Steam Turbine 12000 6.2 390

Total 34200 13.89 446Spinning 3000

Total On-Line Capacity 37200

ERCOT Load Contributes to System Droop

• As Frequency decreases, load decreases. As Frequency increases, load increases.– Droop contribution of load 0.266 %/MW of ERCOT Load,

in MW/0.1 Hz.• 34,700 MW Load x 0.00266 = 92.3 MW/0.1Hz.

– Total ERCOT Droop includes Turbine droop and Load droop.

• 446 + 92.3 = 538.3 MW/0.1Hz.– For a disturbance of 1250 MW’s and a system response

of 538.3 MW/0.1 Hz, System Frequency would decline by 0.2322 Hz. If starting at 60.00, would result in a minimum frequency of 59.7678 Hz.

ERCOT Load Change vs. Frequency Change

0

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800

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Frequency Change

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20000

25000

30000

35000

40000

45000

50000

55000

20,000 MW Load

55,000 MW Load

ERCOT’s Future Droop?

• What will the future unit mix be?– 2000 MW’s of Wind Generation?– Combined Cycle Combustion Turbines want to be

100% loaded on Temperature Control.• What governor response the turbines don’t provide,

the load will (at the expense of larger frequency deviations).

Increasing Wind & Combined Cycle Generation

% ResponseMW Droop MW/0.1 Hz

Nuclear 4700 100 0Wind 1200 100 0

Combined Cycle CT 12000 55 37Solid Fuel Fully Loaded 11300 51 38

Steam Turbine 5000 6.2 202

Total 34200 22.43 276Spinning 3000

Total On-Line Capacity 37200

• Changing the unit mix changes minimum frequency for the same event.– Droop contribution of load 0.266 %/MW of ERCOT Load,

in MW/0.1 Hz.• 34,700 MW Load x 0.00266 = 92.3 MW/0.1Hz.

– Total ERCOT Droop includes Turbine droop and Load droop.

• 276 + 92.3 = 368.3 MW/0.1Hz.– For a disturbance of 1250 MW’s and a system response

of 368.3 MW/0.1 Hz, System Frequency would decline by 0.3394 Hz. If starting at 60.00, would result in a minimum frequency of 59.6606 Hz.

ERCOT System Droop

Firm Load Shedding

• 59.30 Hz – Trips 5% Firm Load• 58.90 Hz – Trips 10% Firm Load• 58.50 Hz – Trips 10% Firm Load

Size Does Make a Difference

• Eastern Interconnect and Western Interconnect Frequency is much more stable than ERCOT’s.

• Based on 2001 Peak Planning Data and Load’s contribution to System Droop:– East 527,000 MW 1370 MW’s/0.1 Hz– West 132,492 MW 344 MW’s/0.1 Hz– ERCOT 53,391 MW 139 MW’s/0.1 Hz

Plot-0

1/31/02 05:17:05 AM 1/31/02 06:17:05 AM60.00 Min(s)

ICCP .HLPFREQ .AV

MAN .MANSYSFREQ .AV

Keystone.KY0 NRRW FREQ .AV

59.95

60

60.05

59.9

60.160.003

59.993

59.963

ICCP .HLPFREQ .AV

MAN .MANSYSFREQ .AV

Keystone.KY0 NRRW FREQ .AV

ERCOT

WEST

EAST

Interconnection

Frequency

ERCOT

EAST

WEST