The Effect of Distributed Generation on Power System Protection

Interconnecting a distributed generation (DG) to an existing distribution system provides various benefits to several entities such as the DG owner, utility and end users. DG provides an improved power quality, higher reliability of the distribution system and covering of peak shaves. Penetration of a DG into an existing distribution system has so many impacts on the system, despite the benefits a DG will provide; it has a negative impact on one of the most important aspects of the system which is the power system protection, and it is a main factor affecting both reliability and stability of the system. DG causes the system to lose its radial power flow, besides the increased fault level of the system caused by the DG. In this thesis, the effect of DG penetration on the short circuit level of the network is investigated through simulating the IEEE 13 bus test feeder using ETAP. The simulation is repeated for nine different cases at which the location of one large DG is changed in six of the cases to study the effect of the distance on the fault level, while the rest of the cases are performed using small decentralised DGs. The result of those three cases at which the DG is decentralised are used to investigate the effect of the generating capacity of the generation unit on the distribution network parameters and on the currents flowing through the laterals of the distribution network. Results are compared to that of the normal case to investigate the impact of the DG on the short circuit currents flowing through different branches of the network to deduce the effect on protective devices.