By sion932 
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The resonant grounding method of power system is a comprehensive technical issue, which is closely related to the reliability of power supply, personal safety, equipment safety, insulation level, overvoltage protection, relay protection, communication interference (electromagnetic environment), and grounding devices of the system.
There are many voltage levels in the power system, and the neutral grounding methods of different rated voltage grids also have their own characteristics. In the medium voltage range below 110kV, China and many other countries’ power grids generally adopt low current grounding method, which is characterized by the self extinguishing of single-phase fault grounding arc. The low current grounding method is ineffective grounding, among which the neutral point resonance (through arc suppression coil) grounding method is the most concerned. There are many technical issues involved in neutral point resonant grounding, and its development and changes have been rapid in recent years. The operating characteristics have also been optimized.
Zero sequence impedance
Zero sequence impedance is a fundamental physical concept in the problem of resonant grounding in power systems. According to circuit theory, the voltage and current of the power grid can be decomposed into three symmetrical systems: positive sequence, negative sequence, and zero sequence. The impedance of the circuit through which the zero sequence current flows is called the zero sequence impedance. The essence of various neutral grounding methods is actually the difference in the magnitude of zero sequence impedance, in other words, the difference in the ratio of zero sequence impedance to the positive sequence impedance of the system.
Neutral point resonant grounding
Generally, grounding the neutral point through an arc suppression coil is called neutral resonant grounding. Although the tuning inductance only varies within a small range, the zero sequence impedance of the system is close to infinity. In general, the arc suppression coil and automatic tracking compensation device in operation often adopt overcompensation operation mode slightly deviating . As the technical term “resonant grounding” is more in line with the actual situation of the neutral point grounded system through the arc suppression coil, the power system with the neutral point grounded through the arc suppression coil is usually referred to as a resonant grounding system.
Non effective grounding of neutral point
This category includes systems where the neutral point is not grounded, resonant grounded, and high resistance grounded, with the condition that the single-phase grounded arc can self extinguish, as well as systems where the neutral point is grounded through medium and low resistance and medium and low reactance, with the condition that the grounded arc cannot self extinguish.
There are two main types of resonant grounding methods in power systems:
Any single-phase grounding arc that can instantly extinguish on its own belongs to the low current grounding method. There are mainly three grounding methods: neutral point resonance (through arc suppression coil) grounding, neutral point non grounding, and neutral point high resistance grounding.
Anyone who needs a circuit breaker to interrupt a single-phase grounding fault belongs to the high current grounding method. There are mainly neutral point direct grounding methods, neutral point low reactance, medium resistance, and low resistance grounding methods.
Application of resonant grounding method in power system
Various grounding methods have been adopted in power systems both domestically and internationally, but overall, the neutral point resonant grounding method has been widely used in medium and high voltage power grids and generator grounding systems both domestically and internationally.