In the electric power system,whether the neutral points of generators and transformers are grounded or not involves multiple aspects such as technology,economy,and safety,making it a comprehensive issue.Neutral points grounded through arc suppression coils(also known as non-effective grounding)are classified as small grounding current systems in China based on the current during single-phase grounding faults in the system.According to relevant regulations in China,in 3~10kV power systems,if the capacitive current during single-phase grounding exceeds 30A;or in 35~60kV power systems,if the capacitive current during single-phase grounding exceeds 10A,the neutral point in the system should be grounded through an arc suppression coil.Arc suppression coils have been applied for more than 100 years,and operational experience in medium-voltage power systems shows that grounding the neutral point through an arc suppression coil has significant advantages.
Most of the urban power grids and medium-voltage systems of factories and mining enterprises in China are neutral ungrounded(i.e.,low-current grounded)systems.When a single-phase grounding occurs in such systems,the power grid can still operate with faults.However,with the development of society and economy,transmission cables have been extensively laid and applied,leading to a significant increase in grounding capacitive current during single-phase grounding faults.If the grounding arc develops into intermittent extinction and reignition,it can cause arc grounding overvoltage,endangering the insulation of electrical equipment and posing great harm to power supply and consumption equipment.If the grounding arc cannot be reliably extinguished,it will quickly develop into a phase-to-phase short circuit,causing line tripping and power supply interruption.
One of the methods to prevent this hazard is to connect a reactor in series between the neutral point and the ground.This reactor is commonly referred to as an arc suppression coil.It can effectively reduce the grounding current,thereby achieving the purpose of automatically extinguishing the arc.
The tuning-tap type arc suppression coil is currently one of the international mainstream design schemes,with particularly prominent application in Germany(the world's first arc suppression coil was installed and put into operation at the generator neutral point of the Pleidelsheim power plant in Germany in 1917,invented by German scientist W.Petersen).
