Question

1. A renewable energy system delivers 120 kW of three-phase power at 400 V (line-line) to a load with a 0.9 lagging power factor. If each power line has a resistance of R = 0.03 Ω and reactance of X = 0.04 Ω, determine the sending end voltage (line-line) of the three-phase power line connected to the renewable energy system for supplying power to the load.
2. A network service operator found that the voltage rise in a network due to distributed generation is a growing concern. Suggest ways to mitigate this problem.

Answer 1

Rejx = 0.03 e30.04 = 0.05 53.13 Sending End Receiving end 400 -6 I Receiving End Power / ph = = Current 120 - 40 kw 3 Vph Iph as P 90x103 w Iph= a0810 X 0.9 13 400 192.45 fen - 192.48 / aston 192.45 -25.84€ A 400 13 Vs = Sending End Voltage VR2 Receiving End Voltage Vs = Vet fpn Z + 192-45%-25.84 5/-25.84.00.03 8400.05/53-13 = 230.94 € 9.6225/27-29 239.49&J 4.411 = 239.53/11055 Sending End Line Voltage = 239.534 3 - 1414.87 V

. The voltage rise can be mitigated through the following approaches: • Resistance reduction approach • Reactive power compensation approach • Coordinated voltage control approach

1 Resistance reduction approach If the amount of the connected DG to a DS system is constant it is known that the worst case voltage rise which consider maximum DG penetration, is directly proportional to the the resistance of the line. Therefore, if the resistance of the line is reduced, the voltage rise on the DS will also be be reduced. The resistance of a line can be reduced by increasing the conductor size

.2 Reactive power compensation approach. The amount of reactive power that can be imported generally depends on the parameters of the generators. Typically, a synchronous generator can import power at a 0.95 power factor whereas a wind turbine with uncompensated induction generator can import power at around a 0.9 power factor..We can use a switched capacitor bank or other form of reactive power compensation to restore the system voltages.

3 Coordinated voltage control approach In conventional passive distribution network, it is common practice to maintain the primary DS above the nominal voltage to ensure that the system voltages remain within the specified −6% voltage limit as the voltage drops This can easily be done by using OLTC connected to the system in short distribution system but in case of long distribution system which includes many distribution transformers it may be impractical. However, in more complex network, the value of this voltage, and the corresponding tap position of the OLTC, would have to be optimized.