Online Monitoring of Power Transformers Using Impulse Frequency Response Analysis

With the recent development in smart grid systems, there is now a growing interest in the development of on-line monitoring techniques. This is to reduce the maintenance costs as well as minimizing the probability of unexpected outages, or potentially to prevent catastrophic failures in the electrical network. Monitoring of power transformers is essential for utilities as they are a critical asset within the network. Frequency response analysis (FRA) is a technique used to diagnose the mechanical integrity of a transformer winding; such diagnostic tools can be of enormous value for condition monitoring of power transformers. Over the past couple of decades, FRA has been utilized as an offline diagnosis method. Now there has been attention and interest to switch from offline to online FRA measurement techniques and recent literature shows there is an increasing research interest in this area. This paper proposes a bushing tap signal injection technique, which has the potential to be developed for in-service monitoring of power transformers. The proposed method uses an impulse as an input excitation signal. Signal injection and measurement are accomplished through high frequency CTs as an interface tool with the transformer bushing tap. FFT signal processing is used to obtain the frequency domain response. Bushing models were developed and experiments implementing the proposed approach were conducted. A single-phase 22kV/110V voltage transformer was used to study the feasibility of the proposed method.