Field Investigations into the Factors Governing the Severity of Prestriking Transients

Steep-fronted surges are a major cause of insulation failure in motor windings. These surges are produced by switching operations and will vary depending upon the type of system and type of circuit-breaker. Results of investigations carried out at a number of installations are described. The prime objective of these investigations was to determine the nature and severity of the switching transients produced during circuit-breaker closing operations and the variation of these transients with system parameters and type of circuit-breaker. Techniques used during these investigations, including on-site synthetic testing methods, will also be described. The value of these techniques in evaluating system characteristics will be demonstrated.