Investigation of resonance overvoltage in the IMB-550 measuring current transformer
To date, considerable statistics of transformer failures in both power and measuring equipment for unknown reasons have been accumulated. This article discusses one of the possible causes of failures occurring in 330-500 kV transformers of the IMB type. At the Itatskaya 1150 kV substation in the SWYD 500 kV, measurements of high-frequency processes that occur at the time of switching circuit breakers and disconnectors were made. Typical waveforms of voltage and current flowing through the current transformer insulation are presented. Analysis of the amplitude-frequency spectrum waveform data showed the presence of components with frequencies from 1.8 to1.9 MHz, which cannot be explained by the commutation process. In addition, experimental studies of transient characteristics of the IMB-550 current transformer were conducted in the laboratory. When transformer windings were exposed to a current rectangular pulse a resonant frequency of 1.4 MHz was obtained. The resonance frequency reduction was caused by the grounding bus inductance which was used in the experiment. The parameters of the transformer primary winding were found. The estimated value of the resonant frequency was 2 MHz. Based on the experiments conducted, it can be stated that resonance voltages are induced in the IMB-550 current transformer caused by switching processes at the substation. That in turn can cause emergency situations.