Electrical stresses on circuit-breaker voltage grading capacitors caused by unequal voltage sharing during switching operations

✍ Scribed by Paul Coventry; Magne Runde

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 117 KB
• Volume: 21
• Category: Article
• ISSN: 1430-144X
• DOI: 10.1002/etep.426

✦ Synopsis

In recent years, a number of disruptive dielectric failures of unknown cause have occurred on grading capacitors installed on circuit-breakers switching shunt reactors. In an attempt to clarify the origin of these failures, the electrical stresses to which the grading capacitors are subjected in service have been studied. Following initial studies, attention was focused on the first parallel circuit, i.e., the circuit consisting of the grading capacitor and the associated interrupter. It is proposed that the observed failures can be explained by unequal voltage sharing under switching operations, where one interrupter of a pole prestrikes or reignites momentarily before the other interrupter(s) of the same pole. Simulations show that under worstcase conditions, the voltage across one grading capacitor of a pair may then approach a value of 1.5 times the source voltage in the case of a prestrike and three times the source voltage in the case of a reignition. These are substantial dielectric stresses as they correspond to three and six times the stationary voltage across the capacitor. Measurements of voltages and currents inside the first parallel circuit would be very helpful in a further investigation of these phenomena.