Condition Assessment of Generator Insulation using Diagnostic Tests

Generator is a critical asset in the power system. The reliable operation of a generator mostly depends on the condition of stator winding insulation; hence, performing a periodic diagnostic test and finding a health index of generator insulation has become mandatory. In this paper, effort has been made to compute a health index of generator winding insulation using a scoring and weighting method. Three levels of score are assigned against each dielectric diagnostic test conducted on a stator winding. The score is given after framing an acceptance criteria referring relevant standards. The weight of each test is calculated using analytical hierarchy process. Diagnostic test used for this approach includes insulation resistance, polarization index, dissipation factor (tan delta) test, capacitance test, DC ramp test, and partial discharge test. Visual inspection of a stator winding is also included. The test results of 12 in-service hydro generators with class F insulation, commissioned between 1999 and 2006 in Bhutan are applied in the study. After computing a health index, it is concluded that the condition of winding insulation in all 12 hydro generators arc remaining satisfactory.