Testing distribution switchgear for partial discharge

• General correlation between Relative Humidity in substation and presence of Surface PD Activity - 60% RH triggered discharge early stages • Ultrasonic noise level does not continue to increase as equipment progresses towards failure • Level of discharge measured in pC had no discernible rise as it progressed to failure - Quantifying seriousness through ultrasonic level or pC level for surface discharge activity almost impossible • Switching is a critical time - Safety implications