Characterization of transformer FRA signature under various winding faults

Abstract

Frequency response analysis (FRA) is gaining global popularity in detecting power transformer winding and core deformations due to the development of FRA test equipment. However, because FRA relies on graphical analysis, interpretation of its signatures is still a very specialized area that calls for skillful personnel to detect the sort and likely place of the fault as so far, there is no reliable standard code for FRA signature classification and quantification. This paper aims to initiate the establishment of standard codes for FRA signature interpretation through comprehensive simulation analysis on a detailed transformer distributed parameters-based model. Various mechanical faults such as axial displacement, buckling stress, disk space variation and bushing fault are simulated on the model to study its impact on the FRA signature. The main contribution of this paper is the comprehensive table it presents for FRA signature sensitivity to winding and core deformations that can be used for classification and quantification of the transformer FRA signature.

A Review of Frequency Response Analysis Methods for Power Transformer Diagnostics

“…The faults simulated by using the transformer model shown in Figure 1 were loss of clamping pressure, inter-disk fault, HV bushing fault, axial displacement fault, leakage fault, and short circuit fault [15]. This allows the identification of the problem inside the transformer and helps in establishing a standard code for FRA signature interpretation [15].…”

“…This will increase the conductivity because of the reduction in dielectric thickness between the winding layers. This type of fault can be simulated by increasing the value of the shunt conductance (Gsh) [15].…”

“…In [15], it was assumed that the HV and LV windings consisted of ten disks. Each disk comprises series resistance (R s ) and inductance (L s ) shunted by a capacitor (C sh ) and a conductance (G sh ).…”

“…In this test, the input signal should be supplied at the HV terminal and measured at the LV terminal [10]. In addition to winding, the FRA may also be applied to transformer bushing to check its condition [15].…”

“…The insulation between the HV/LV winding and ground is represented by capacitance (Cg) and dielectric conductance (G) as shown in Figure 1. Moreover, transformer bushing was simulated using model shown in Figure 2 [15]. In [7], the bushing model of the basic structural unit used was in the form of the series of capacitors and resistors.…”