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 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 Presentation overview Introduction and background Simulation setup Electronic voltage regulators Reactive power control modification Conclusions
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 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 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 DG integration constraints Maximum DG size limited by a 3% RVC and voltage headroom, depending on the connection point
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 Simulation setup - Solar profile Necessary to simulate both a sunny and cloudy day
10 Generation Increase on Distribution Feeders using Electronic Voltage Regulators
11 EVR options DEVR CEVR
12 Penetration increase VR EVR Series EVR
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.] 1.075 1.05 1.025 td VR CEVR DEVR 1 0 60 120 180 240 Time [s]
EVR results 14 24. 19. 14. 9.6 4.8-0.0 1.08 1.05 1.03 1.00 0.98 0.95 24. 19. 14. 9.6 4.8-0.0 16.0 9.60 3.20-3.20-9.60-16.0 MV-BB T4 T4-1 T10 Capacitor tap position VR tap position OLTC tap position Time[h] Time[h] 24. 19. 14. 9.6 4.8-0.0 1.08 1.05 1.03 1.00 0.98 0.95 24. 19. 14. 9.6 4.8-0.0 16.0 9.60 3.20-3.20-9.60-16.0 MV-BB T4 T4-1 T10 Capacitor tap position DEVR tap position OLTC tap position Time[h] Time[h]
EVR results 15 24. 19. 14. 9.6 4.8-0.0 1.08 1.05 1.03 1.00 0.98 0.95 24. 19. 14. 9.6 4.8-0.0 16.0 9.60 3.20-3.20-9.60-16.0 MV-BB T4 T4-1 T10 Capacitor tap position VR tap position OLTC tap position Time[h] Time[h] 24. 19. 14. 9.6 4.8-0.0 1.08 1.05 1.03 1.00 0.98 0.95 24. 19. 14. 9.6 4.8-0.0 16.0 9.60 3.20-3.20-9.60-16.0 MV-BB T4 T4-1 T10 Capacitor tap position Time[h] Time[h] CEVR tap position OLTC tap position
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 T10 1 3310 OV 1.07 2.6 2648 N/A 52 1.1 1.1 1.23 2 665 RVC 1.07 3 1990 N/A 40 1.11 1.12 1.48 3 300 RVC 1.06 3 2147 N/A 24 0.65 0.74 1.44 4 945 OV 1.07 4.7 2240 N/A 34 0.3 0.67 0.78 Case P DG Limiting V max RVC E loss Increase Tap Voltage fluctuation [%] [kw] factor [p.u.] [%] [kwh] DG [%] changes T4 T4-1 T10 1 3400 OV 1.07 2.6 2646 3 162 1.15 0.8 0.92 2 790 OV 1.07 0.9 1903 19 172 1.26 0.91 1.18 3 450 RVC 1.06 3 1977 50 104 0.81 0.8 1.56 4 945 OV 1.07 4.65 2225 0 90 0.67 0.87 1.17 Case P DG Limiting V max RVC E loss Increase Tap Voltage fluctuation [%] [kw] factor [p.u.] [%] [kwh] DG [%] changes T4 T4-1 T10 1 3400 OV 1.07 2.6 2694 3 167 1.11 0.22 0.34 2 790 OV 1.07 1 1877 19 184 1.15 0.22 0.53 3 460 RVC 1.06 3 1940 53 132 0.82 0.2 1.14 4 945 OV 1.07 3.42 2194 0 108 0.67 0.2 0.57
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 Local Reactive Power Droop Control Modification for Distributed Generators
19 Reactive power control Reactive power control can help to reduce the voltage change caused by an active power change
20 Droop control Q DG V ref V m P r tan r
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 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 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 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 0.13 0.68 0.77 1.21 2 34 2 2130 15 5% droop CPF 0.975 0.12 0.55 0.62 1.04 2 24 2 2167-1167 2.5% droop 0.11 0.58 0.65 1.08 2 26 2 2111 1326 AS 1.1% droop 0.12 0.46 0.5 0.84 2 22 2 2126 33 AS 2.5% droop CPF 0.975 AS 2.5% droop CPF 0.9875 AS 1.1% droop CPF 0.9875 0.13 0.5 0.55 0.93 2 22 2 2192-2166 0.13 0.51 0.57 0.96 2 24 2 2172-1577 0.13 0.42 0.46 0.79 2 20 2 2165-1452
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 Thank you Jonathan Nye nyejm@eskom.co.za