Study on the Triggered Discharge Characteristics of Sphere Gaps for Protecting Transformer Neutral Point

Matching surge arrester with spark sphere gap switches can effectively limit the overvoltage of grounded transformer neutral points and protect the transformer neutral insulation. To better select suitable spark sphere gap switches for different types of surge arresters, this paper has studied the working characteristics of spark sphere gap switches. Designing and manufacturing a 125 mm diameter spark sphere gap switch, which was used to test, in order to get the triggered and natural discharge characteristics of this type gap switch. According to the test data, analysing the effect pattern of the main gap distance on the working voltage range of the 125 mm diameter spark sphere gap switch. Its maximum working voltage range 108.5kV were obtained when the main gap distance was 94mm, at this time the upper and lower limits of the working voltage were 196.5kV and 88.5kV. A finite element simulation model of the studied switch was constructed, and the electric field distribution pattern of the 125 mm diameter spark sphere gap switch when got the maximum range of the working voltage was obtained. The upper and lower limits of the working voltage and the main gap distances of the spark sphere gap switches with 85mm, 105mm, 125mm, 145mm, 165mm, 185mm and 200mm diameters when got the maximum range of the working voltage were obtained from the simulation, along with the relationships between the sphere diameter and the upper and lower limits of the working voltage, and the main gap distances were obtained from fitting. The selection of protection sphere gap electrode diameters and main electrode distances for different types of surge arresters used for protecting ungrounded transformer neutral points in 110 kV and 220 kV systems was achieved.