Detection of winding inter-turn faults
Detection based on frequency response analysis – Part II
1. Methodology for detection of fault using SFRA – circuit modelling During the occurrence of the fault, the resonant frequencies and impedance of the winding are subjected to change depending on the percentage and location of the fault. Equivalent circuit of continuous disc transformer winding is shown in Fig. 1.
Physical dimension data of winding has been collected and winding parameters are extracted using finite element method (FEM) before actual modelling
In previous works  an algorithm for locating inter-disc faults in 22 kV continuous disc winding has been developed, which is based on FRA for determining the extent and detection of the fault. In the present study, the similar algorithm is extended to detect the inter-turn fault in the continuous disc winding and layer windings. The impedance of the healthy ZHealthy winding and faulty ZFaulty winding at their corresponding first resonant frequency frh1 is taken as a reference point. The impedance characteristics of winding is obtained by performing FRA. The measured impedance of the winding is analysed for detecting the fault. A factor relating impedance of the healthy winding ZHealthy and faulty impedance ZFaulty at frh1 is defined as Fault Factor.
For detecting an inter-turn fault, impedance characteristics are used by comparing the impedance magnitude in a healthy winding and when an inter-turn fault occurrs. A low percentage of interturn fault is created in the winding such as 8.33 %, 4.44 % and 2.22 %. An inter turn fault of 8.33 % indicates 15 turns are shortcircuited in a single disc, i.e. short circuit is created in the equivalent circuit of transformer winding model in Pspice circuit simulation software package.
From the simulation results, impedance of the healthy and faulty winding at the first resonant frequency of the healthy winding frh1 are noted as ZHealthy and ZFaulty respectively. The impedance magnitude of the healthy winding ZHealthy at first resonant frequency frh1 that is 1.4791 MHz is considered as a reference point and the impedance magnitude of the faulty winding ZFaulty is compared with that of first resonance frequency of healthy winding and the fault factor is calculated and this factor can be used to detect the fault.