Analysis of Overvoltages on Power Transformer Recorded by Transient Overvoltage Monitoring System

Abstract

In this paper, an on-line transient overvoltage monitoring system (TOMS) for power transformers is used for measurement of overvoltages on the transformer bushing tap. The focus of the paper is on the analysis of transient overvoltages caused by lightning strikes recorded at the terminals of power transformer. Several recorded overvoltages are analyzed and their amplitudes and frequency spectrum are presented and compared with those referring to standard impulse voltages from IEC standard. Collected data include number, peak and duration of recorded transient overvoltages and can be used for the assessment of the transformer insulation condition and estimation of health index. Data recorded by TOMS are also of significant importance since the insulation system of power transformer and other equipment in the substation can be damaged by lightning or switching overvoltages.