Relaxation studies on power equipment

This paper describes a method of studying and modeling the dielectric relaxation for stationary power apparatus in an interconnected network to get the necessary aging indicators. The polarization phenomenon was studied using Recovery Voltage (RVM) and Polarization Current (PCM) Measurements on individual power apparatus and on network with other connected apparatus. Because of dielectric absorption in composite insulation, all RVM responses showed a single peak response and the response was linear with charging voltage. PCM decreased monotonically with a sudden drop in the initial period and after 100 s, it decreased very slowly and the response was linear with charging voltage. The responses were analyzed by modeling the dielectric function as an exponential function and as two-time dependent fractional power law function to determine suitable aging parameters. Exponential function model was found to fit both responses to get an equivalent electrical circuit of the system. Interrelation of RVM and PCM was established in most of the cases. Predicted dielectric response function for generator was more linear with time than for transformers and cable. In the frequency plane, it was found to have distinct regions of relaxation spectrum. Studies indicated that the parameters of fit for RVM response with each charging period differed from all RVM responses.