Rochester Gas & Electric (RG&E), a subsidiary of Iberdrola USA, requires an extremely reliable infrastructure to provide electricity to more than 367,000 customers and gas to more than 303,000 customers, all from nine counties around Rochester, New York, U.S. In addition, limited operation and maintenance budgets influence maintenance intervals, which, ultimately, affect overall asset reliability.

Of particular importance is a cross-state 345-kV line connecting RG&E to New York Power Authority. To enhance the reliability of that transmission corridor, RG&E sought to equip its type PMI (gas-pressure-interrupter, multiple-tank, independent pole-operated) capacitor bank breakers with real-time remote condition monitoring. With the latest monitoring technology, RG&E was able to institute proactive, rather than reactive, maintenance practices.

RG&E wanted to record all trip and close operations, as well as the timing statistics, of these highly critical circuit breakers. In addition, RG&E had limited to no Ethernet communications at remote substations, which posed a major challenge. The fleet of breakers RG&E wanted to increase the reliability of included 121-kV and 362-kV type PMI sulfur hexafluoride (SF6) capacitor bank breakers.

Monitoring

By installing equipment monitoring packages directly connected to the circuit breaker, myriad breaker statuses and performance parameters can be determined. The required device and sensors are capable of monitoring the interrupter wear, SF6 gas integrity, leakage rate, mechanical integrity of the entire breaker, trip/close conditions, mechanism charging system and the control cabinet heating system. Examples of issues the monitoring device is capable of detecting include a long reaction time for one or all of the poles, fault current interruption with a subsequent increase in calculated interrupter wear and slow SF6 gas-leak detection.

By measuring specific areas of the breaker, the monitoring system alerts RG&E to conditions that may compromise the operation of the breaker before a failure occurs. With the utility being advised when maintenance is required, RG&E no longer needs to perform time- or use-based maintenance.

Time-based maintenance is performed every 10 years regardless of the load the breaker has handled or the number of times the breaker has switched in and out of the line. Use-based maintenance is performed after a certain number of switching operations has occurred at a particular current load. For example, an overhaul may be performed after six switches at 63 kA or 10,000 switches at 3 kA. In condition-based maintenance, a service crew is only sent to the site when a warning alarm states that the breaker requires maintenance of some kind. Performing condition-based maintenance will eliminate unnecessary downtime and save money on unnecessary overhauls.

With condition-based maintenance, repairmen arrive at the substation fully prepared with all parts and equipment because they completely understand the issue. Fully understanding the problem ahead of time also minimizes the in-field repair time because diagnostics can be performed prior to mobilization of the service engineers. Prioritization of the needed repairs will further reduce outages, maintenance times and costs.

The monitoring device also helps RG&E to be more environmentally friendly. With early leak detection, the leak is repaired much more rapidly, which releases less SF6 into the atmosphere. SF6 is a greenhouse gas that is 22,800 times stronger than carbon dioxide. RG&E also reduces cost on SF6 gas purchases by minimizing the amount of gas that needs to be replaced in a leaking breaker.