Research On Anti-interference In Secondary Circuit Of Substations

The secondary circuit of substations is in a strong electromagnetic environment. Because of the secondary circuit in DC system being interfered, there are many trip accidents happened in power grid without any fault in recent years. This phenomenon has seriously affected the safety and the reliability of power system. Thus, it is necessary to research the anti-interference of secondary circuit in substation.According to the coupling mode, interference is classified into five kinds: the capacitive coupling interference , the inductive coupling interference , the electromagnetic radiant interference, the interference caused by the ground potential difference and the interference caused by the secondary circuit itself. Analyzing the source and the interfere process of these five interference and discussing it, it is easy to find that the interference mainly has an effect on the electronic transformer and intelligent circuit breaker controller in digital substation.The equivalent circuit of the fault making secondary circuit is simulated on the basis of the analysis of the trip accidents without any fault especially the fault data of the 500kV Liaocheng station. According to analyze the simulation of the DC system grounding, DC system connect to AC220V and AC connect to DC system fault, the probability of trip accident that with the larger stray capacitance, the probability get larger is obtained.Analyze the substation's stray capacitance and its influence on the secondary circuit and obtain the action scope of the stray capacity. The stray capacity is related to cable's length, temperature, frequence and humidity in substation's environment with hardened cement, soil, atmosphere dielectric. With longer cable, larger humidity and lower frequence, the stray capacity get larger.Anti-interference methods are proposed according to the interference offered above, including the restraint of every coupling, substation grounding and the optimization of cables. Study the intermediate relaying action experiments of different protecting manufacturers' circuit breaker controller. The reliability of the trip relaying action is improved by adding a resistance parallel to trip circuit.