L10

Distributed generation– impact on the power system

Wind power

Overview • • • • • • •

Microturbine

What is DG? Power quality Power balance and markets Dispatch and frequency control Requirements on future DG units Protection Island operation Olof Samuelsson, IEA, LTH

What is DG?

Impact of DG on power system

• Distributed Generation – – – –

• Power Quality - at each unit

Power production in distribution network Usually small-scale Often but not necessarily renewable Single windpower units and small-scale Combined Heat and Power (CHP)

• Wind farms Windpower 2001

– Centralized generation – not DG – Results here still apply Olof Samuelsson, IEA, LTH

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– Starting and stopping – Flicker from tower shadow effect

• Power balance - at large penetration – Non dispatchable, ”must run” units – Uncontrolled, negative loads – Wind power production hard to predict

• Protection - of network and units 3

Olof Samuelsson, IEA, LTH

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Power Quality

Power balance and markets • Main market

• Power Quality - at each unit

– 1 h, 24 h ahead, predicted load

– Starting and stopping – Flicker from tower shadow effect

• Balance market – <1h, 1 h ahead – Actual load

• Control market – 0h, 24 h ahead – Automatic frequency control – Reserve capacity for outages

Olof Samuelsson, IEA, LTH

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Load in western Denmark

Olof Samuelsson, IEA, LTH

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Operation of CHP units 1

48 weeks

• Heat demand – Heat primary product – Electric power byproduct

1 week

• CHP unit schedule

winter

– Heat production follows temperature – Power production non-dispatchable

summer

• Load is predictable, error few % Olof Samuelsson, IEA, LTH

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Olof Samuelsson, IEA, LTH

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Operation of CHP units 2

Operation of wind power plants 1

• Heat accumulators introduced

• Operated for max output

– Heat can be produced at any time – Eltra tariff controls power production

– Production extremely weather bound

• Shutdown at maximum wind speed

Real data from E.ON [Leonhard]

Olof Samuelsson, IEA, LTH

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Operation of wind power plants 2

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Power balance and dispatch • With dispatchable plants

• Wind variations

– Dispatch equals predicted load – Control reserves to handle error – Export/import usually planned

– Faster than load variations – More irregular than load variations

• Wind prediction difficult

• With DG added

– Large prediction errors in MW or h

– Tariff makes CHP predictable – Control reserves to handle wind+error – Export/import at surplus/lack of power – Transmission capacity may be limited

• Increased need for regulating power – ≥20% of installed windpower (DK) – Units must run on part load Olof Samuelsson, IEA, LTH

Olof Samuelsson, IEA, LTH

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Olof Samuelsson, IEA, LTH

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Eltra example: Low wind

Eltra example: High wind

Central units CHP Wind

Central units CHP Wind

Export Wind

Export Wind

Load Load-wind

Load Load-wind

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Svenska Kraftnät

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Frequency dynamics

• 10 TWh goal 2015 gives 4000 MW • 4000 MW windpower – 2000 MW regulating capacity needed

• If in the North – Transmission system must be reinforced – Doubles transmission tariff

• If in the South – No system reinforcement necessary Feedforward control Olof Samuelsson, IEA, LTH

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Feedback control Olof Samuelsson, IEA, LTH

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Frequency dynamics with DG

Balance responsibility • Transmission system operator – Svenska Kraftnät, Eltra, E.ON

• More difficult with windpower – Load minus windpower to be balanced – Windpower replaces thermal units – Fewer units must do more!

• New requirements on DG units

• Wind varies faster than load

– More like conventional plants

– Reduced frequency quality expected Olof Samuelsson, IEA, LTH

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Olof Samuelsson, IEA, LTH

Requirements: Tripping

Extreme voltage protection Voltage/%

• Low penetration: Tripping local issue

• AMP

120

– Enables automatic reclosing – Network owner issues requirements – Sensitive protection good

– 2001 – Recommendation – Trip delay

106

• High penetration: Tripping system issue – TSO requires generator capacity on-line – TSO issues requirements – Sensitive protection not good Olof Samuelsson, IEA, LTH

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90 80

• Svenska Kraftnät – 2002 – Requirement – Stay on-line

25 0.2 0.25 19

0.75

60

t/s Continuous Olof Samuelsson, IEA, LTH

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Extreme frequency protection Frequency/Hz

• AMP

55

– 2001 – Recommendation – Trip delay

Reduced output 51

• Svenska Kraftnät – 2002 – Requirement – Stay on-line

49 48 47.5

Requirements: Control

95% of rated 0.5 s

• MW output reduction to 20% maximum – In 2 s (Eltra) and 5 s (Svenska Kraftnät)

• Windfarm participation in f control – All (Eltra) and >20 MW (Svenska Kraftnät)

• Manual control of windfarms >20 MW – Real/reactive power (Svenska Kraftnät) – On-line/off-line (Svenska Kraftnät)

t/s >30 min Continuous Olof Samuelsson, IEA, LTH

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Requirements: Communications

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The wind farm at Horns rev

”…is a power station with obligations to the power system” (Eltra) …is designed to meet Eltra requirements Olof Samuelsson, IEA, LTH

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Olof Samuelsson, IEA, LTH

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Control reserves imply part load

Network protection • Today

• Hydro power units on part load – Maximum efficiency well below max output – Perfect as control reserve

• Thermal units on part load

– Radial single fault current infeed – Nondirectional protection, fuses

• With DG – Multiple fault current infeed – Directional protection needed – Also with meshed distribution network

– Maximum efficiency near max output

• Wind power units on part load – Energy lost – avoid!

• Island operation – Low fault currents

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Island operation

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Active network • Today: Top-down

• Ultimate challenge

– Generation and control in transmission

– All system functions needed

• Bottom-up instead

• Control

– Generation and control in distribution

– Power balance and frequency control – Voltage control

• Designed for island operation – Normal situation – Connection with other islands – Automation and power electronics – Market functions

• Protection • Supervision – Automation replaces control centres Olof Samuelsson, IEA, LTH

Olof Samuelsson, IEA, LTH

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Olof Samuelsson, IEA, LTH

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Conclusions • Power Quality • DG affects power balance – Weather important factor – Transmission critical – TSO requirements on DG

• Protection revised • Island operation a challenge • Alternative network design Olof Samuelsson, IEA, LTH

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