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Voltage control in distribution networks with windpower networks - - PowerPoint PPT Presentation

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Voltage control in distribution networks with windpower networks with windpower Olof Samuelsson Div. of Industrial Electrical Engineering and Automation Lund University Lund University / LTH/ Measurement Technology and Industrial Electrical

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SLIDE 1

Voltage control in distribution networks with windpower networks with windpower

Olof Samuelsson

  • Div. of Industrial Electrical Engineering and Automation

Lund University

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 2

Contents

1. Local and system level impact of windpower 2 Di t ib ti f d lt fil 2. Distribution feeder voltage profile 3. Voltage control actuators 4 V lt t l 4. Voltage control sensors 5. Control scheme 6 E ON test case 6. E.ON test case 7. Conclusions

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 3

Wind turbine generator technologies

  • Induction generator
  • Doubly-fed induction generator
  • Full-scale converter

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 4

Local level impact of windpower

  • Risk of island operation at distribution level

A ti i l d t ti – Anti-island protection

  • Power quality

H i lt di – Harmonics, voltage dips

  • New fault current situation

Fault current contribution – Fault current contribution

  • New power flow situation (Ingmar Leiße)

Overvoltage may limit connected capacity – Overvoltage may limit connected capacity – Losses

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 5

System level impact of windpower

  • Variable generation

Variable generation – Balancing

  • Non-synchronous generators displace synchronous generators

Non synchronous generators displace synchronous generators

Load-windpower Load

– Reduced inertia  (J h Bjö t dt)

Load-windpower

(Johan Björnstedt)

50 49 49.5 f [Hz]

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

10 20 30 40 50 48.5 time [s]

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SLIDE 6

Fault behavior of windpower

  • SG instability related to critical clearing angle

I d ti t i t bilit l t d t iti l l i d

  • Induction generator instability related to critical clearing speed

– Notion of ”Rotor speed stability” proposed

  • Calculation of fault currents from DFIG

(Francesco Sulla) ( )

4 6 8 (pu) Phase current for DFIG at three-phase short-circuit 0.05 0.1 0.15 0.2 0.25 2 4 Ia (

(O Samuelsson and S Lindahl ”On Speed Stability ” IEEE Transactions of

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

(O. Samuelsson and S. Lindahl. On Speed Stability, IEEE Transactions of Power Systems, Vol. 20, No. 2, pp 1179-1180, 2005)

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SLIDE 7

Voltage: Generic network with tap changer

  • 130/10 kV substation

with OLTC

  • 3 feeders
  • 3 feeders
  • 16 nodes
  • Load: 5 MW
  • Generation: 7 2 MW

Generation: 7.2 MW

  • Length: 28 km

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 8

Voltage profile along a feeder

Voltage limits L d l Load only Generation only Load and generation

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 9

Voltage-constrained windpower capacity

  • Worst cases with tap changer control

M i ti t i i l d – Maximum generation at minimum load – Minimum generation at maximum load

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 10

Change in voltage magnitude along line

Q X P R V Q X P R I X I R V

r line r line q line p line line

    

  • At transmission level reactive power controls voltage
  • At distribution level Q normally required to be zero

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

  • Draw Q should be possible with power electronics
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SLIDE 11

Medium Voltage lines

Line type

R [Ω/km] L [mH/km] C [μF/km] X/R Cable AXCEL 95mm2 0.320 0.35 0.21 0.34 Cable AXCEL 150mm2 0.206 0.32 0.24 0.49 OHL FeAl 99 0.336 1.085 0.0061 1.01 OHL F Al 157 0 214 1 036 0 0061 1 52 OHL FeAl 157 0.214 1.036 0.0061 1.52

AXCEL 95mm2 8km FeAl 99mm2 8km

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 12

Network losses

AXCEL 95mm2 8km FeAl 99mm2 8km AXCEL 95mm2 8km FeAl 99mm2 8km

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 13

How frequent is maximum generation?

  • Some curtailment of active power is reasonable

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 14

Use all actuators in a coordinated way

  • On-load Tap Changer

± 9 t 1 67 % h ±15 % i ti t k

  • ± 9 steps 1.67 % each → ±15 % in entire network
  • Reactive Power
  • Local effect
  • Local effect
  • But increases line currents and thus losses
  • PF=0 89 or variable
  • PF=0.89 or variable
  • Active Power Curtailment
  • Root cause – always works

Root cause always works

  • But reduces income to generator owner

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 15

Voltage requirements

  • EN 50160

V lt lit t t id – Voltage quality at customer side – +/- 10 % for 95 % of a week with 10 min RMS values

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 16

New electricity meters can report voltage

  • Remote reading of energy once a month since July 2009

U b PLC Zi B – Urban: PLC, ZigBee – Rural: GPRS Additi l f t

  • Additional features

– Voltage limit violation alarms Operate main breaker – Operate main breaker – Control output

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 17

Proposed control structure

130 kV line 20 kV line 0 4 kV li 0.4 kV line Control and communication Distributed Generation Load Load

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 18

Heuristic algorithm uses incremental control Heuristic algorithm uses incremental control

Delay until next step Start

yes

V limit violation ?

no no yes

Priority scheduler

no

Done? Priority

  • n

OLTC? OLTC controller

no yes yes

Done? Priority

  • n Q?

Q controller

no yes yes no

Done? Priority

  • n P?

P controller

no yes yes no Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

  • n P?

no

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SLIDE 19

Result indicators

  • Installed MW windpower

D li d d t il d MWh i d

  • Delivered and curtailed MWh windpower
  • Tap operations
  • Losses in MWh
  • Losses in MWh

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 20

E.ON test case

Feeder Load [MW] Existing WT [MW] New WT [MW] 1 5.8 0.7 0.0 2 0.0 9.0 0.0 3 5.1 0.0 0.0 4 1.7 0.9 6.0 5 4.0 0.0 6 1 9 3 0 6 1.9 3.0 7 5.3 1.4 13.0 8 4.2 0.8 3.0 ∑ 28.0 12.8 25.0

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 21

E.ON test case

  • 130/20 kV E.ON substation

8 f d

  • 8 feeders
  • 3 substations 20/10 kV
  • ~250 Medium Voltage nodes
  • ~250 Medium Voltage nodes
  • ~170 substations 20/0.4 kV
  • Load between 5 MW and 28 MW

Load between 5 MW and 28 MW

  • Windpower 13 MW installed and 25 MW to be added

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 22

E.ON load and generation profiles

Total active power load (measured) Total active power generation (measured values upscaled)

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 23

E.ON test case voltages with only tap changer

Voltage at substation busbar with normal setpoint Voltage at node with lowest voltage Voltage at node with highest voltage

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

Voltage at node with highest voltage

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SLIDE 24

E.ON test case voltages with new control

Voltage at substation busbar Voltage at node with lowest voltage Voltage at node with highest voltage

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

Voltage at node with highest voltage

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SLIDE 25

E.ON test case results

MWh MWh

4000 6000 8000 10000 100 150 2000 4000 Transferred energy 50 Losses gy Losses 200 250 300

MWh

100 150 50 100 150 200 50 100 Curtailed Energy Tap changer operations

Local OLTC, existing windpower O C OLTC with EM, PF=1 O C

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

Local OLTC, PF=1 Local OLTC, PF var OLTC with EM, PF=0.89 OLTC with EM, PF var

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SLIDE 26

E.ON test case economic analysis

  • Costs for tap operations

M i t t – Maintenance costs

  • Costs for network losses

MWh i t N dP l – MWh price at NordPool

  • Costs for active power curtailment

MWh price at NordPool – MWh price at NordPool – Electricity certificates

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 27

E.ON test case economic results

30000 € 20000 25000 10000 15000 5000 Curtailment Losses Tap changer

  • perations

Total L l OLTC PF 1 L l OLTC PF Local OLTC, PF = 1 Local OLTC, var PF Coordinated OLTC, PF = 1 Coordinated OLTC, PF = 0.89 Coordinated OLTC, var PF

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA

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SLIDE 28

Conclusions

  • Increase of windpower capacity without reinforcement

12 8 MW 25 MW (14 3 MW) 37 8 MW (27 1 MW)

  • 12.8 MW + 25 MW (14.3 MW) = 37.8 MW (27.1 MW)

→ increase of windpower 75 % additional, 40 % total E i l b fit f di t d OLTC d i bl PF

  • Economical benefits from coordinated OLTC and variable PF
  • Energy values critically depends on profiles
  • Use of electricity meters feasible
  • Alarms difficult and discrete control not optimum
  • Alarms difficult and discrete control not optimum
  • Voltage magnitude and some continuous control better

Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA