Generation Increase on Distribution Feeders using Electronic Voltage Regulators

Transcription

1 1 Generation Increase on Distribution Feeders using Electronic Voltage Regulators Jonathan Nye University of Stellenbosch, South Africa Co-authors: Dr J Beukes and M Bello

2 2 Local Reactive Power Droop Control Modification for Distributed Generators Jonathan Nye University of Stellenbosch, South Africa Co-authors: Dr J Beukes and M Bello

3 3 Presentation overview Introduction and background Simulation setup Electronic voltage regulators Reactive power control modification Conclusions

4 4 Background South Africa aims to have 8.4 GW of PV by 2030 (Currently total generation is 44GW) Many generation applications on MV feeders Distribution feeders were designed for one way power flow In South Africa there are many long, weak networks so penetration levels are limited

5 5 Generation on MV feeders On distribution feeders with voltage regulators, renewable generation can increase the maintenance requirements and costs for the utilities Voltage on MV can vary to +-5% of nominal Ensure losses are kept to a minimum What can be done to limit voltage variations caused by DG?

6 6 DG integration constraints The maximum unit size is limited to a RVC level of 3% Voltage rise above the maximum voltage at the substation, during low load, is limited to 2% for PV Current carrying capacity of the power lines is limited by their thermal rating

7 7 DG integration constraints Maximum DG size limited by a 3% RVC and voltage headroom, depending on the connection point

8 8 Simulation setup Test network 30 km in length, 2.5 MW peak load, 0.5 MW minimum load A VR at 12 km, fixed and switched shunt capacitors at 15 km and 21 km respectively Generator location and number of generators is varied

9 9 Simulation setup - Solar profile Necessary to simulate both a sunny and cloudy day

10 10 Generation Increase on Distribution Feeders using Electronic Voltage Regulators

11 11 EVR options DEVR CEVR

12 12 Penetration increase VR EVR Series EVR

13 13 EVR operation EVRs respond almost instantaneously to a change in voltage Help prevent under voltages if all generators on a feeder trip Voltage [p.u.] td VR CEVR DEVR Time [s]

14 EVR results MV-BB T4 T4-1 T10 Capacitor tap position VR tap position OLTC tap position Time[h] Time[h] MV-BB T4 T4-1 T10 Capacitor tap position DEVR tap position OLTC tap position Time[h] Time[h]

15 EVR results MV-BB T4 T4-1 T10 Capacitor tap position VR tap position OLTC tap position Time[h] Time[h] MV-BB T4 T4-1 T10 Capacitor tap position Time[h] Time[h] CEVR tap position OLTC tap position

16 16 EVR results VR DEVR CEVR Case P DG Limiting V max RVC E loss Increase Tap Voltage fluctuation [%] [kw] factor [p.u.] [%] [kwh] DG [%] changes T4 T4-1 T OV N/A RVC N/A RVC N/A OV N/A Case P DG Limiting V max RVC E loss Increase Tap Voltage fluctuation [%] [kw] factor [p.u.] [%] [kwh] DG [%] changes T4 T4-1 T OV OV RVC OV Case P DG Limiting V max RVC E loss Increase Tap Voltage fluctuation [%] [kw] factor [p.u.] [%] [kwh] DG [%] changes T4 T4-1 T OV OV RVC OV

17 17 Conclusions EVR reduced the voltage variations EVR solves the problem of increased wear on tap changers EVR allows for up to 50% more generation to be connected far from the substation

18 18 Local Reactive Power Droop Control Modification for Distributed Generators

19 19 Reactive power control Reactive power control can help to reduce the voltage change caused by an active power change

20 20 Droop control Q DG V ref V m P r tan r

21 21 Limitations of droop P [MW] 3 km from S/S Q [MVAr] Time [h] P [MW] 30 km from S/S Q [MVAr] Time [h]

22 22 RPC modifications Adapt the droop setpoint voltage to the current network operating conditions Decrease the droop coefficient Utilise a combination of droop and CPF control V V QDG PDG.tan P tan m ref set r r CPF Droop

23 23 RPC modification results P [MW] 3 km from S/S Q [MVAr] Time [h] P [MW] 30 km from S/S Q [MVAr] Time [h]

24 24 RPC modification results Total generation configuration Average voltage fluctuation [%] Tap changes E loss MV BB T4 T4-1 T10 OLTC VR Cap [kwh] Q gen [kvar h] AS 5% droop unity % droop CPF % droop AS 1.1% droop AS 2.5% droop CPF AS 2.5% droop CPF AS 1.1% droop CPF

25 25 Conclusions RPC reduced the voltage variations Adaptive droop control reduces the number of tap changes and lowers the losses when compared to CPF control Allows for droop control with a small droop coefficient to be effective over wide operating range

26 26 Thank you Jonathan Nye