Resonant grounding system

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The system in which the neutral point is grounded through an arc suppression coil is also known as a resonant grounding system. After connecting the arc suppression coil between the neutral point of the system and the ground, the grounding current at the grounding point can be reduced when a single-phase grounding fault occurs. An arc suppression coil is an inductive coil with an iron core, which has a low resistance and a high reactance. The iron core of the arc suppression coil has a gap and is filled with insulating cardboard to avoid saturation. Its coil has a tap that can adjust the number of turns to change the magnitude of its reactance. 

(1) When the neutral point is grounded through the arc suppression coil in normal operation, the potential of the neutral point is zero, and there is no voltage across the arc suppression coil, so no current passes through the arc suppression coil. When a metallic grounding occurs in a certain phase, there will be an inductive current flowing through the arc suppression coil, compensating for the single-phase grounding current. If the number of turns of the arc suppression coil is appropriately selected, the inductive current of the arc suppression coil can be roughly equal to the grounding capacitance current, which can make the current flowing through the grounding fault very small, thereby reducing the harm of the arc. 

(2) A system where the neutral point is grounded through an arc suppression coil,. When a phase is completely grounded, the voltage change is exactly the same as that of a neutral ungrounded system. The voltage between the fault and the ground becomes zero, and the voltage between the non fault and the ground increases by times. The insulation level of each phase to the ground is designed according to the line voltage, because the line voltage does not change and does not affect the user’s work. It can continue to operate for 2 hHVHIPOTs. The on duty personnel should search for the fault as soon as possible and eliminate it.

Principle of resonant grounding system

Electromagnetic voltage transformers in low current grounding systems may cause ferromagnetic resonance overvoltage during single-phase arc grounding faults or excitation during closing charging when the bus is unloaded or there are few outgoing lines. On the basis of analyzing the mechanism of single-phase arc grounding overvoltage and ferromagnetic resonance in low current grounding systems, this paper compares and analyzes commonly used harmonic elimination measures, and points out the issues that should be noted during use. 

Resonant grounding system device

The portable grounding alarm device for neutral point resonant grounding system has achieved results in the maintenance and upkeep of the original Minde power grid in the past few years using live working methods. This method has been increasingly widely used in both indoor installations and outdoor power transmission lines. The first issue involved here is the development of new process technologies and working methods. 

Resonant grounding system resonant grounding method

Identify the issues with the outdated turn control arc suppression coils used in ungrounded or resonant grounded systems in China’s medium voltage power grid. How to correctly determine the grounding method of medium voltage power grid is a problem related to the development direction, and a technical analysis of the principle and application of neutral point resonant grounding method is conducted. The domestically produced automatic tracking compensation arc suppression system and its device have been successfully developed, filling the domestic gap. This system completely overcomes the shortcomings of old-fashioned arc suppression coils and is an ideal grounding method for China’s medium voltage power grid.