Question

Explain the circuit breakers reclosing and relaying issues while interconnecting the DG sources to the power network.

Answer 1

Actually the existing grid system is very much efficient and robust. The existing grid system is run by the power generated by the conventional energy sources like thermal, gas and nuclear etc. But, due to rapid growth in the population, there is a shortage of power. This is met by using the power generated from the non-conventional energy resources (Distributed Generation(DG)) like hydal(water), wind etc. It is easy to utilize the power generated from the non conventional energy resources but the problem is that, inorder to interconnect the existing system with non conventional energy system. Many problems will occur due to the integration of both rhe systems.

The major problem here is, in the existing system the power flow is single directional i.e., uni directional and in DGsystem the power flow is bidirectional. The main protection required in the power system is the over current protection. Fast acting relay system is used for protection of over currents. The relays are operated with coordination. I.e., a main or primary relay is operated with the coordination with secondary relays. The over current sensing is mainly done by sensing the short circuit current sensing. So due to the bi directional power flow in the DG system, the circuit breakers reclosing and relaying issues arises.

If at all there is higher current (short circuit current) in the conductors, the relay will sense and activate the circuit brealers in the uni directional system. So, relay circuit breaker coordination is effective but in integration of DG system due to bidirectional system this coordination is failed. Here in integration of existing and DG system, the main problems are the fuse recloser coordination mismatch, false tripping etc.