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
Contents 1. Local and system level impact of windpower 2 2. Di t ib ti Distribution feeder voltage profile f d lt fil 3. Voltage control actuators 4. 4 Voltage control sensors V lt t l 5. Control scheme 6 6. E ON test case E.ON test case 7. Conclusions Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Wind turbine generator technologies • Induction generator • Doubly-fed induction generator • Full-scale converter Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Local level impact of windpower • Risk of island operation at distribution level – Anti-island protection A ti i l d t ti • Power quality – Harmonics, voltage dips H i lt di • 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
System level impact of windpower • Variable generation Variable generation – Balancing • Non-synchronous generators displace synchronous generators Non synchronous generators displace synchronous generators Load Load-windpower Load-windpower – Reduced inertia (Johan Björnstedt) (J h Bjö t dt) 50 49.5 f [Hz] 49 48.5 0 10 20 30 40 50 time [s] Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Fault behavior of windpower • SG instability related to critical clearing angle • Induction generator instability related to critical clearing speed I d ti t i t bilit l t d t iti l l i d – Notion of ”Rotor speed stability” proposed • Calculation of fault currents from DFIG (Francesco Sulla) ( ) Phase current for DFIG at three-phase short-circuit 8 6 (pu) 4 4 I a ( 2 0 0 0.05 0.1 0.15 0.2 0.25 0 (O Samuelsson and S Lindahl ”On Speed Stability ” IEEE Transactions of (O. Samuelsson and S. Lindahl. On Speed Stability, IEEE Transactions of Power Systems, Vol. 20, No. 2, pp 1179-1180, 2005) Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
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
Voltage profile along a feeder Voltage limits L Load only d l Generation only Load and generation Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Voltage-constrained windpower capacity • Worst cases with tap changer control – Maximum generation at minimum load M i ti t i i l d – Minimum generation at maximum load Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Change in voltage magnitude along line R R P P X X Q Q line r line r V R I X I line line p line q V • At transmission level reactive power controls voltage • At distribution level Q normally required to be zero • Draw Q should be possible with power electronics Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Medium Voltage lines R L C X/R Line type [ Ω /km] [mH/km] [ μ F/km] Cable AXCEL 95mm 2 0.320 0.35 0.21 0.34 Cable AXCEL 150mm 2 0.206 0.32 0.24 0.49 OHL FeAl 99 0.336 1.085 0.0061 1.01 OHL F Al 157 OHL FeAl 157 0 214 0.214 1 036 1.036 0.0061 0 0061 1 52 1.52 AXCEL 95mm 2 8km FeAl 99mm 2 8km Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Network losses AXCEL 95mm 2 8km AXCEL 95mm 2 8km FeAl 99mm 2 8km FeAl 99mm 2 8km Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
How frequent is maximum generation? • Some curtailment of active power is reasonable Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Use all actuators in a coordinated way • On-load Tap Changer • ± 9 steps 1.67 % each → ± 15 % in entire network ± 9 t ± 15 % i 1 67 % h ti t k • 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
Voltage requirements • EN 50160 – Voltage quality at customer side V lt lit t t id – +/- 10 % for 95 % of a week with 10 min RMS values Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
New electricity meters can report voltage • Remote reading of energy once a month since July 2009 – Urban: PLC, ZigBee U b PLC Zi B – Rural: GPRS • Additional features Additi l f t – Voltage limit violation alarms – Operate main breaker Operate main breaker – Control output Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
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
Heuristic algorithm uses incremental control Heuristic algorithm uses incremental control Delay until Start next step V limit no violation ? yes yes Priority scheduler no no Priority yes yes OLTC on Done? controller OLTC? no no no yes yes Priority Q controller Done? on Q? no no yes yes Priority P controller Done? on P? on P? no Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Result indicators • Installed MW windpower • Delivered and curtailed MWh windpower D li d d t il d MWh i d • Tap operations • Losses in MWh • Losses in MWh Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
E.ON test case Feeder Load Existing WT New WT [MW] [MW] [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 0.0 6 6 1 9 1.9 0 0 3 0 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
E.ON test case • 130/20 kV E.ON substation • 8 feeders 8 f d • 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
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
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 Voltage at node with highest voltage Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
E.ON test case voltages with new control Voltage at substation busbar Voltage at node with lowest voltage Voltage at node with highest voltage Voltage at node with highest voltage Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
E.ON test case results MWh MWh 10000 150 8000 100 6000 4000 4000 50 2000 0 0 Transferred energy gy Losses Losses MWh 150 300 250 100 100 200 200 150 50 100 50 0 0 0 0 Tap changer operations Curtailed Energy Local OLTC, existing windpower OLTC with EM, PF=1 Local OLTC, PF=1 O C O OLTC with EM, PF=0.89 C Local OLTC, PF var OLTC with EM, PF var Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
E.ON test case economic analysis • Costs for tap operations – Maintenance costs M i t t • Costs for network losses – MWh price at NordPool MWh i t N dP l • 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
E.ON test case economic results 30000 € 25000 20000 15000 10000 5000 0 Curtailment Losses Tap changer Total operations L Local OLTC, PF = 1 l OLTC PF 1 L Local OLTC, var PF l OLTC PF Coordinated OLTC, PF = 1 Coordinated OLTC, PF = 0.89 Coordinated OLTC, var PF Lund University / LTH/ Measurement Technology and Industrial Electrical Engineering/ IEA
Recommend
More recommend
