Design Of Reforming Low Resistance Ground System Of 220kV Transformer Substation Scheme

The neutral grounding mode of the power grid covers a wide range, which has different affects on power system reliability, insulation level of equipment, high-voltage circuit breakers and other electrics options, relay protections and system stability. Along with the sustainable development of national economy, the scale of overall power grid is increasing quickly and power cables are employed largely in urban power grids, which make the system capacitive current grow significantly and threat the operation of power system's safety. These problems have been reflected the overall power system steady operation. So there is necessity for power system to select the right neutral grounding way to meet the demand of power system.First of all, this paper investigated different kinds of factors which influencing the neutral grounded operation mode, and analyzed in detail the characteristics of neutral ungrounded, neutral directly grounded, neutral grounded through low resistance and neutral grounded through arc suppression coil. From different aspects analyze the advantages and disadvantages for the four situations respectively and particularly. Only acknowledging the basic conditions of neutral grounding, it can be well to analyze the specific neutral grounding situation.Then put forward the arc suppression coil and small resistance grounding mode, analyze its working principle and illustrate the two different operation modes under the permanent fault and transient fault. Analyze the advantages of arc suppression coil and small resistance grounding mode combining the features of small resistance grounding and grounding by arc-suppression-coil.Next, according to the actual situation of the 220kV substation, modify its grounding system. Understanding the operating characteristics of the neutral grounding mode, Take the arc suppression coil and small resistance grounding mode instead of grounding by arc-suppression-coil, including the choice of neutral point grounding resistance, circuit breaker and overhead line, protection setting and so on.Finally, this article established the 220kV substation simulation model, using RTDS real-time digital simulator to simulate system operation state under different fault conditions. Analyze the simulation results to prove the arc suppression coil and small resistance grounding mode could increase the active component of fault current and facilitate protection device fast and exact tripping.