Managing a Power System with 40% Wind

Dr Alan RogersEirGrid

Outline

• Current Situation• Case study: August 26th 2009 > 40% Wind• Power System Stability• System Stability Tools• Conclusions

Current Status

• Oct 2009: 1119MW of wind generation connected• End of 2009: 1250MW installed• End of 2010: 1600MW installed

• Minimum Generation (August 2009): 1632MW exported• Expected Winter Peak Load 2009: 4750MW• Current Maximum Wind Generation: 999MW

• Rapidly moving towards:– 50% instantaneous wind penetration

– 33% capacity penetration (Installed Wind MW / Peak MW)

Maximum Percentage Wind during 2009

Hourly Wind Variability

Increased Wind needs more flexible conventional plant

Maximum Hourly Change in Wind MW vs Maximum Wind

-500.0

-400.0

-300.0

-200.0

-100.0

0.0

100.0

200.0

300.0

400.0

0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0

Wind / MW

MW

/ h

ou

r

On this day, wind peaked at 750MW and dropped by 370MW in one hour

Case StudyAugust 26th 2009 3:45am > 40% Wind

• Wind generation now regularly exceeds 40% of demand• Highest wind penetration in the world on a synchronous system• Occurs during night valleys, when demand is at its lowest• Conventional Generation Dispatch must be carefully managed

– Geographical spread of generation for voltage control– Certain amount of flexible plant to cope with sudden changes in wind

(e.g. hydro)– Large machines to provide inertia, synchronizing torque, and short-

circuit power

• Approximate Dispatch on August 26th:– 870MW Wind– 850MW Large conventional machines at minimum load– 200MW Peat / Hydro / Small-scale Gas

Change in Dispatch from Low to High Wind

0

200

400

600

800

1000

1200

1400

MW

Large Conventional Small Conventional Wind Generation

Night Valley Dispatches: Aug 14th (Low Wind) vs Aug 26th (High Wind)

Calm

Windy1 x MP min HNC min2 x TB min HN2 minPBCCGT min 3 x TH pumping

Case Study – Control Issues

• Wind generation peaked at 880MW on August 26th

• 30MW of non-firm wind was curtailed in South-West• NCC expected severe contingencies in North-West, so SONI agreed to

import 20MW at both Strabane and Enniskillen to alleviate contingencies

Night Valley Frequency TracesAug 26 & Sep 30

49.98

50

50.02

50.04

50.06

50.08

50.1

50.12

1 3601

Time (seconds)

Fre

qu

en

cy

(H

z)

High Wind

Low Wind

Normal fluctuations in demand cause frequency jitter

Wind MW fluctuations make jitter amplitude larger PQ issue / freq control issue

Power System Stability

Power System Stability

Rotor-angleStability

VoltageStability

FrequencyStability

Transient Stability

Small-signal

Stability

MVAr Balance

Tap-changerActions

Short-term

Long-term

System Stability Tools• Online Wind Security Assessment Tool (WSAT) in development:

Real-time Analysis (every 30mins)

– Transient Stability Analysis – Full Dynamic Simulation• Faults at every bus / Tripping of large machines / Relay Actions• Does the system remain as one synchronous area?• Do any machines trip unexpectedly?

– Voltage Stability Analysis (Margin to Voltage Collapse / N-1 Contingencies)

• Voltages in range / Overloads / Voltage Collapse

– Frequency Stability• How low will frequency go / frequency recovery / system inertia ?

• Damping Monitor Relay

– Analyzing low frequency modes 0.001Hz – 99Hz

– Oscillatory Events / Magnitudes / Damping / Duration

– Any systemic change in behaviour with high wind penetration?

System Security: August 26th

• Voltage Security Assessment – extra 500MW wind could be accomodated before voltage collapse / unsolved loadflow

– Yellow region means secure but with some overloads if certain lines trip

• Transient Security Assessment showed that a large generator trip would cause a frequency drop to about 49.3 Hz

– This is normal. No other problems were flagged

• No stability problem with 40% instantaneous wind during SNV as far as we can tell

– Key limitations: Thermal Limits / Conventional Plant Constraints

643.4 843.4 1043.4 1443.4 1843.4 2243.4 2643.4 Wind

Conclusions

• 40% instantaneous wind becoming more common• Change in Dispatch / System Behaviour

– Flexible Generation Requirements– Extensive dynamic simulations required

• Power System Stability Tools– WSAT– Damping Monitor

• 2020: 37% Average Wind Energy– Very high instantaneous penetration in theory (70/80%)– Careful study of stability limits will be required

Possible 2020 Fuel Mix

Fuel Mix 2020

15%

5%

1%

36%

37%

2%1%

2%1%

Coal

Peat

Oil

Gas

Wind

Hydro

Pumped Hydro

Wave/Tidal

Biomass