Wind Generators – Evolving Technology

Transmission Advisory Group

Ray BrownTransmission Manager - Meridian Energy

April 2008

Overview of Presentation

3 Different Wind Farms– 3 Different Technologies

– Te Apiti Wind Farm55 x NEG Micon 1.65MW, Simple Induction

generators (90MW total)

– White Hill Wind Farm29 x Vestas V80 2MW, DFIG (58MW total)

– Project Westwind development62 x Siemens 2.3MW, Full converter output

(142.6MW total)

Overview of Presentation

Disclaimer…

Power system integration capability is improving rapidly as new technologies immerge, however some caution is required in assuming which Wind Turbine Generator (WTG) type will be used in future projects as generators generally choose the (WTG) based on its productivity/cost :economics and robustness. Power systemintegration is generally not the main issue influencing WTG choice.

So we might not always select the best WTGs from a power system integration perspective on future wind farm developments.

Te Apiti – Simple Induction Generators

• Te Apiti first wind farm subjected to grid connected EGR requirements

• 90 MW connected to 110 kV

• NEG Micon Simple Induction Generators (SIG)

Te Apiti – 22kV On Site Reticulation

• 48km of underground cables

• 22kV, XLPE

Te Apiti – 22kV On Site Reticulation

Te Apiti - Substation• 100MVA 22kV / 110kV Transformer• Outdoor capacitor banks

• 22kV indoor SF6 Switchgear• Indoor Statcon

• First such device in NZ

• Power electronic device using Insulated Gate Bipolar Transistors (IGBT)

• Provides reactive power - Voltage support- Fault ride through

• Fast operating (milliseconds)

• Rated ± 9.6MVAr• 8x 1200 kvar units - watercooled, modular

• Water Cooled

Te Apiti - STATCON

Te Apiti - Transmission Line

• Te Apiti to Woodville substation – 110kV, 5km

• Owned by Meridian

• Steel monopoles

• Comms OPGW

Gearbox

Squirrel CageInduction

Generator

Grid

CapacitorBank Capacitor

BankDynamicReactiveSupport

Fixed Speed Induction Generator

e.g. Te Apiti • Inductive ! • Reactive power support Optional (but non-compliant with EGRs if none)• Requires dynamic reactive power support for Low Voltage fault ride thru’ i.e. STATCONs• Somewhat chunky control of reactive power compared to synchronous machines• Provides inertia but no governor control• Provides some damping to synchronous power oscillations

• Few WTG suppliers offer this technology now, but can provide good economic solution

Te Apiti – Simple Induction Generators (SIG)

Te Apiti - Fault Ride Through

• Transpower provided minimum requirements

• Power system fault studies performed by turbine manufactureWoodville 110 kV Point-of-Connection Voltage Profile - Individual 3-phase Grid Faults

(Distribution faults final voltage = 0.95 p.u., Transmission faults final voltage = 0.9 p.u.)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3

Time (sec)

Volta

ge (p

.u.)

Remote, BPE 110 kV - Trip remote (Zone 1)Local 110 kV - Trip WDV(Zone 1), BPE (Zone 2)Remote BPE 110 kV - Trip BPE (Zone 1), WDV (Zone 2)Remote, BPE 220 kV - Trip remote (Zone 1)Remote, BPE 33 kV Feeder (0 Ohm)Remote, BPE 33 kV Feeder (2 Ohm)Remote BPE 33 kV busRemote, WPW 33 kV Feeder (0 Ohm)Remote, WPW 33 kV Feeder (5 Ohm)Remote, WPW 33 kV Bus

Te Apiti - Reactive Power Support

EGR Requirements System Operator Agreed Requirements

Export (Capacitive) 50% (45.4 MVAr) 30% (27 MVAr)

Import (Inductive) 33% (30 MVAr) 33% (30 MVAr)

Te Apiti Reactive Power provided by:

1. Thyristor switched capacitor banks at turbine generator (850kVAr total each WTG)

2. Three substation capacitor banks (9MVAr, 6MVAr, 3MVAr)3. Statcon (8 individual units totalling ± 9.6MVAr)

Wind farm de-rating of 2.5MW for every statcon not in service

EGR Dispensations:Limited Reactive Power Range and No Governors

White Hill

• Deeply embedded large wind farm testing limits of technology (ESR≈1)

• 58 MW connected to 66 kV

• 29 Vestas V80 2 MW DFIGs

• > 70 MW WTG site

• 40 MW GXP 70km away

1. Vestas Latest WTGs

2. 6 MVA STATCON

3. Intertrip

4. Runback

5. Protection Upgrades

6. HED Capacitor Banks

7. Ripple Blocking Filters

8. New line NMA-WIN

9. Connect Redundant HED-WIN line

10. NMA Capacitor Banks

White Hill

220kV 110kV 66kV 33kV

NManapouri 220kV

Heddon Bush

North Makarewa

Go

Monowai

Lumsden

Mossburn

Riversdale

Dipton

Centre Bush

Otautau Winton

Ohai

Orawia

~ White Hill

Te Anau

10

1,2

3,4

5,6

98

White Hill - Substation

Switchroom – 22 kV Switch Board and Control Cabinets

66/22 kV 65 MVA Transformer, T1

WHL – TEA Line Bay & Gantry Structure

Oil Separator & Containment System

WHL – HED Line Bay & Gantry Structure

D-VAR Statcon Modules

NER

MEL

TPCL

White Hill – Transmission Line

GearboxWound Rotor

InductionGenerator

Grid

Partial ScaleFrequency Converter

CapacitorBankDynamic

ReactiveSupport

Doubly Fed Induction Generatore.g. White Hill• Variable Speed (slip -40% to +30%) • Better reactive power, voltage support and fault ride through• Might need some reactive power support for EGR compliance – depends on WTG reactive power range• Might need dynamic reactive power support for LV ride thru’ – depends on system strength• Good control of reactive power similar to synchronous machines – depends on control system• Generally improves power system synchronous stability compared to conventional generators•Theoretically - significant improvements to synchronous stability could be achieved with high spec controls•Governor control dependent on WTG supplier

•White Hill – EGR Governor Dispensations required

White Hill - DFIGs

Good & Bad Days at White Hill

On a bad day......On a good day......

Location Makara/Terawhiti, WellingtonSize 142.6 MW, 573 GWhTurbines 62 x Siemens S82 2.3MWStage Civil works

Commis-sioning

Late 2008 - mid 2009

Tx 2×110kV Tees to CPK-WIL B

Westwind

Gearbox Generator ?Grid

Full ScaleFrequency Converter

Full Scale Frequency Converter

CapacitorBank ?

e.g. Westwind• Variable Speed, gearbox optional, speed variability depends on WTG• Reactive power, voltage support and ride through can be superior to conventional generators• Synchronous condenser option possible (at no / high wind) - depends on WTG• Might need minimal capacitor banks for EGR compliance – depends on WTG reactive power range• Better than conventional generators re ride through – e.g. simulations suggest WWD should survive

>1 sec 3phase fault zero impedance on 110 kV transformer connection. Special protection needed to trip off WTGs when required e.g. auto-reclose events (conventional generators can not ride through auto-reclose on their grid connection)

• Very fast voltage support – similar to STATCONs (better than conventional generators)• Theoretically - Large improvement to power system synchronous stability compared to conventional

generators (extent of support depends on wind farm control system)• Good control of reactive power similar to synchronous machines – depends on control system• Governor control and frequency support dependent on WTG supplier

Westwind – Full Converter Output

West Wind – EGR Compliance

Westwind Reactive Power to be provided by:

1. Wind Turbine Generators2. Two substation capacitor banks (2 × 10 Mvar?) for compliance only

• Note there are outstanding questions on whether a STATCON will be needed instead to ensure dynamic stability between the HVDC non-linear control response and the WTG non-linear control response, so we are holding off ordering the capacitors. However this is a special case because of the HVDC’s proximity. Normally no STATCON would be needed with this WTG technology

Governor and Frequency Response?• May be fully EGR compliant ….

• No dispensations sought• Ability to provide Ancillary Services?

Westwind - Power Quality Requirementsand Over Voltage Events Ride Through Under Voltage

(WWD must ride through these faults)

Westwind – Preliminary Power Quality Results

Low Voltage Fault – Test extreme (power system protections disabled) case to test the performance of the WTGs.

(Actual zero voltage faults will clear within approximately 200 ms)

Zero volts for 1.5s on wind farm 110 kV connection. Conventional generators would trip well before this. Westwind simulations suggest ride through with no issues.Special Protections (intertrips) are being installed to ensure the appropriate half of WWD trips quickly on spur line faults as we do not want WWD to feed into Central Park while disconnected from Wilton d i l

Westwind – Potential Synchronous Compensate Mode ??

Real Fault Scenario1) Haywards 220 kV Fault2) West Wind 33 kV voltage ramps up quickly due to WTG reactive power support3) This improves the Wellington 110 kV voltages

Wind Technology Is New and Is Still Changing !• Unconventional - Potential Effects:

– Engineers need re-educating e.g. short circuit contribution, no sync checks …– Low voltage ride thru’ can be miserable (SIG WTGs), but can be better than

conventional generators (full converter output WTGs). e.g. may need intertrips to ensure WTGs trip when required.

– Low frequency ride through similar to international grid codes but not the SI standard

– Voltage control OK if EGR compliant, and can be slower/faster than conventional generators

– Frequency support – the next challenge. Theoretically can be better than conventional generators (faster). Good support needs wind spill (similar to CCGTs)

– Generally improves dynamic and transient stability e.g. Hayes. – Can provide STATCON-like support i.e. better than SVCs and potentially better

than conventional generators– Market signals required if penetration levels high if frequency support procured

for wind. Wind may provide its own frequency support in the future if penetration high and signals correct.

Where to next with wind?

– Better Forecasting!– Improved diversity of fuel source– Better understanding of output variability (630 MW Hayes!? and its

effects)– Fast Governor control (hopefully on MEL’s next wind farm – Mill Creek?)– Wind farms provide frequency support services – Power boost from full power?– Power System Stabilisers ??? – Storage – when high penetration levels require wind spill, it might

become economic to store energy rather than spill it

– Some of these will need market rule changes and tools?

Conclusion

Continuing development in wind turbine technology and performance is demonstrating that the often pessimistic predictions associated with aspects of integrating wind generation into the power system can be largely disregarded.

Studies:

• Are based on the most basic technology

• Pessimistic performance assumptions

• Focus on negative impacts

• Do not identify the possible benefits

Wind technology is likely to surpass conventional generator power system performance in the future.

(for discussion if time)

• What is the highest penetration level for wind in NZ

• The engineering answer is we could supply 100% of NZ'selectricity needs from wind and existing renewables. The technology is coming available to do this.

– Germany is discussing the ability to go 100% renewable and they do not have a hydro base like NZ

– But - not economic (e.g. storage, lower tier wind sites) &,– insufficient consentable sites

• Future generation development will include a number of competing technologies, not just wind.

Wind Integration in NZ

Discussion?