Dielectric loss and capacitance measuring is an important method to check the condition of transformer insulation.The capacitance is also an important auxiliary parameters to judge the winding deformation. From the test principle and the internal structure of transformer

equivalent capacitance was used to analyze a case of abnormal dielectric loss and capacitance for a 220kV transformer

and the reason of abnormal dielectric loss and capatitance date causell by core ungrounling is analyzed.