The discharge coil of 35kV 1 M 312 shunt capacitor bank at a 500kV substation was cracked during operation

It is found through the inspection that the top of discharge coil is blasted and arc fusion isbetween electrostatic screen on both ends. It is also found through inspection and test analysis that there isdisplacement between the two windings of the burst discharge coil and the insulation defects between thesemiconductor layer and the core. Based on the insulation test of remaining 35 units discharging coil

thepartial discharge of two units is found to exceed the standard and one unit with more serious problem is dis-assembled and porosity is existed between the inter layers of two sections of winding of the discharge coil. Itis confirmed through analysis that the discharge and the burst discharge coil has the common problem

theinsulation layer porosity defect due to weak production process is the roof of discharge burst and excessivepartial discharge. The effective measures for checking the internal insulation situation of discharge coil is tostrengthen the partial discharge test of the discharge coil.