Gas-insulated switchgear (GIS) circuit breakers (CBs) with a closing resistor are characterized by structural complexity and a high failure rate. The auxiliary contact of the closing resistor may bounce during the closing process of the GIS CB. The bounce of the closing resistor contacts may cause arc restriking between the auxiliary contacts and aggravate the ablation of the contacts. Moreover, the auxiliary contact bounce may lead to the breakdown of the main break, resulting in high transient voltage and threatening the equipment insulation. Therefore, monitoring and evaluating the bounce of the auxiliary contact of the closing resistor is crucial.

In this paper, the closing process of a CB with a closing resistor and the bounce of the auxiliary contacts were analyzed. Then, a method for monitoring and diagnosing the bounce condition of the auxiliary contact of the closing resistor according to the transient voltage during the closing process was proposed. An ultrawide-frequency-band sensing technology for transient voltage detection was introduced, and an online transient voltage-monitoring system based on the voltage divider sensing technology was realized. The effective measurement bandwidth of this system is 10 Hz-100 MHz. Two CBs (with and without a closing resistor) were used to charge the same gas insulated line (GIL), and the transient voltage during the CB closing process was monitored.

The transient voltage and closing resistor contact bounce during the closing of two CBs were analyzed and compared, and the following conclusions were obtained. During the closing process of the CB without a closing resistor, the excited transient voltage contained rich high-frequency components. During the closing process of the CB with a closing resistor, two types of transient voltages (type Ⅰ and Ⅱ) were generated. Type Ⅰ did not contain any high-frequency components, and type Ⅱ was similar to the voltage generated during the closing process of the CB without a closing resistor. The type Ⅰ voltage was induced by the breakdown between the auxiliary contacts, and the type Ⅱ voltage was generated by the breakdown between the main contacts during the bounce of the auxiliary contacts. Through the online monitoring of the transient voltage during the CB closing process, the bounce of the auxiliary contacts and the breakdown voltage of the main break were analyzed, and the time interval between the first breakdown of auxiliary contacts and arc extinction after the bounce was proposed to characterize the bounce condition of the auxiliary contacts.

Owing to the existence of a closing resistor, there is a difference between the transient voltages generated by the breakdown of the auxiliary break and the main break. During the closing process of the CB with a closing resistor, the breakdown occurred in the main break, indicating that the auxiliary contact bounced and that the closing resistor did not function. Therefore, through analysis of the moment at which the second type of transient voltage appears during the closing process of CBs with a closing resistor, the online monitoring and diagnosis of the bounce condition of the closing resistor contact could be realized. The results of this study can guide the effective monitoring and evaluation of the operating condition of CBs and provide a reference for the design and online monitoring of CBs with closing resistors.