Lightning Protection of 110 kV and 220 kV Transformer Neutral Points in Shenzhen Power Grid

At present, the neutral point of ungrounded transformer in our country is usually protected by gap and/or arrester. The overvoltage including lightning overvoltage and power frequency overvoltage may cause misoperation of protection gap or thermal collapse of arrester, which affects the safe and reliable operation of the system. In recent years, Shenzhen power grid has suffered several faults caused by inappropriate neutral point protection measures or unreasonable parameter configuration of 110kV and 220kV transformers. Therefore, this paper explored two solutions. (1) One is a new lightning protection measure for transformer neutral point. This measure is combined with controllable clearance and metal oxide arrester (MOA). Under lightning overvoltage, the arrester operates. Under power frequency overvoltage, the gap breaks down to protect transformer neutral point insulation and arrester. Such measure can effectively solve the following problems. The arrester is prone to explosion when it operates under power frequency overvoltage. The clearance cannot extinguish arc when it operates under lightning and power frequency overvoltage impulse. The insulation coordination between the clearance and the parallel protection of the arrester is difficult. (2) A new type of relay protection configuration is adopted to avoid possible malfunction of system protection. The above two measures can greatly improve the stability and security of the system, and at the same time, vigorously enhance the level of intelligence of 110 and 220 kV substations, effectively promote the construction of intelligent substations. In the future, more simulation and experimental verification works for the above two measures will be carried out.