Comparing Gas Call Rates of Various SF6 Circuit Breaker Models

To focus further on gas calls, EPRI analyzed work orders to calculate the annual average gas call values of various SF6 breaker families as shown in Figure 2-6.

Annual Average Gas Call is calculated for each breaker using up to the last 10 years of maintenance history. Similar to the Annual Average CM discussed before, Annual Average Gas Call is calculated by summing the gas call counts for each breaker and averaging it annually by dividing by the number of years of recorded history. Annual Average Gas Call for breaker = (Number of Gas Calls incurred by breaker)/ (Number of Years over which work order histories were observed)

The table includes the percentage of breakers with gas calls. This is calculated for each model group by dividing the number of breakers in the group that have incurred at least one gas call corrective maintenance in the recorder history period by the total number of breakers in the group. As Figure 2-6 reveals, there are significant differences in average annual gas calls among the different breaker families. The ABB-PM, Siemens-TCP and GE-HVB have higher gas call work orders than the other three types and, even though the average ages of the Siemens and GE breakers are similar (24 and 28 years), there is a significant difference in the percentage of breakers with gas calls—62% of the GE breakers versus 27% of the Siemens breakers.

This type of representation allows “apple-to-apple” comparisons of gas breaker families with a single metric, the Annual Average Gas Call. The data can also be represented with a utility view to show which utilities have higher values in order to draw additional comparisons and inferences.