Switching operations in a high voltage substation correlated with overvoltages generated in the low voltage internal service network

Due to problems caused to electronic devices, fed by 220 V auxiliary circuit in a 400 kV substation of the Greek HV interconnected system, extensive measurements of overvoltages have been performed, correlated with the timing of switching operations in the primary circuit of 400 kV. The investigated cases were the opening of incoming circuit breaker, the closing of coupling circuit breaker between busbars, the opening and closing of the circuit breaker of a reactor and the simultaneous opening of two coupling circuit breakers. The waveforms of the overvoltages recorded between phase and neutral had duration of about 100-200 /spl mu/s and a decaying oscillation of about 500 kHz, while their crest values were up to 6.4 kV. The overvoltages recorded between neutral and earth had values only up to 200 V.