Tapchanger condition monitoring and protection systems

The author describes a scheme which utilizes a current transformer (CT) fitted to the diverter switch of an on-load tapchanger (OLTC) to monitor current passing through the transitional resistors of the tapchanger during a tap-change. The output waveform from the CT is digitized, analysed and compared with previous as well as ideal `normal´ waveforms. From this comparison, any gradual deterioration of the waveforms and thus operation of the switch can be seen. Also any drastic changes from the normal can be detected and acted upon. All analysis programs and resulting information are stored on a computer