Monitoring of transient overvoltages on the power transformers and shunt reactors - field experience in the Croatian power transmission system

Power transformers and shunt reactors may be subjected to various dielectric stresses such as lightning and switching overvoltages. Since the exposure of equipment to overvoltages during operation and the overvoltage amplitudes are usually unknow, an on-line overvoltage transient recorder is used with the ability to sample, analyze and store transients at transformer terminals in real-time. In this paper, transient overvoltage monitoring system is presented. Overvoltages are measured on the outside measurement terminal of the shunt reactor and transformer bushing. Field experience regarding the application of monitoring system in Croatia is described including different cases of lightning and switching overvoltages. Lightning overvoltages recorded by monitoring system are correlated with data from the lightning location system (LLS). Switching overvoltages recorded on the shunt reactor are compared with numerical simulations in EMTP-RV software. Collected data about overvoltage stresses can be used as the basis for the assessment of the transformer and shunt reactor insulation condition and estimation of health index.