High voltage circuit breakers are a critical power grid asset for system switching and protection, particularly EHV (extra high voltage) assets. These critical assets are a significant investment for grid owners. Keeping these assets reliable and making them last longer will lower the total cost of ownership. Preventive maintenance is the key to achieving these two goals. There are five preventive maintenance steps we recommend you implement into your yearly maintenance plan (if you are not already exercising) for high voltage circuit breakers.
First and foremost, check the moving components of your circuit breaker – the interrupter (contacts) and mechanism. These two components are subject to the most wear and possible changes in performance over time. The contacts which are responsible for carrying current when the breaker is closed are checked by timing the breaker and verifying it is operating within the parameters set in the manufacturer’s instruction book. Changes in breaker timing from the last inspection or deviations from the instruction book parameters indicates a need for maintenance. Mechanisms are the other critical moving component. Moving parts need to be greased regularly, oil levels should be checked (if applicable), and springs should be checked (if applicable). Changes in operation could indicate a loss of energy, “sticking” components, or other problem. A properly operating mechanism is necessary for a breaker to meet proper operating velocity when performing switching operations.
Second, and just as important, check the SF6 gas integrity yearly. An analysis of SF6 gas is an excellent indicator of breaker health. Is the gas pure, does it have low or no moisture, and does it not contain decomposition particles? SF6 gas with a high moisture level, for instance could be an indicator of a leak in the breaker. According to John Dalton’s partial pressure law, the breaker will equalize itself with the ambient air. This means, as SF6 gas leaks out, ambient air enters the breaker, inducing moisture to the breaker as well. This moisture will cause corrosion inside the breaker. Have high levels of SO2 or other contaminants been found during SF6 analysis? These other contaminants carry their own risks which reduce reliability and must be addressed through proper maintenance.
Third, check all heaters. Tank heaters keep SF6 from liquefying at cold temperatures. It’s necessary that SF6 stay in a gaseous state to maintain its integrity and dielectric strength to safely extinguish the interrupting arc. Mechanism and control cabinet heaters keep the temperature inside the cabinet ten degrees warmer than the ambient temperature. They also prevent condensation in high humidity areas. This inhibits corrosion from building up on control cabinet components or mechanism components. Once corroded they will not operate.
Fourth, perform a site condition assessment by subject matter experts – this will either be inhouse experts that know your equipment thoroughly or OEM experts with both a depth and breadth of knowledge. A site condition assessment is more than a walk through of your substation to confirm what equipment is rusted and what is still new and shiny. Subject matter experts know where to look, how to look for leading indicators, such as equipment operations, bushing indications, et cetera.
Fifth, download and review monitoring device data, if applicable. Often data from monitoring devices is not used or is under used. Data may be indicating trends that are not realizable with inspections done at a specific slice of time. OEM’s are very good at deciphering what the data means. What is good data, what is bad data, and what is my equipment telling me? Sometimes data will be aggregated and compared to benchmarks to get a holistic picture of asset health. Other times, pieces of data are enough to indicate asset health. Every asset and its application is unique, making the evaluation unique as well.
Preventive maintenance plays a key role in maintaining equipment reliability and lowering the total cost of ownership. A small investment in yearly diagnostic maintenance will help you verify healthy assets and determine asserts that have or are developing issues which must be addressed through more traditional maintenance methods to maintain overall system reliability.
If you would like to learn about more about a high voltage topic, you may be interested in the HV Education Series. Click here to register. On Sept 14, aging infrastructure and reliability will be covered in our Customer Education Webinar Click here to register.. On Sep 23 and Nov 17 circuit breaker and mechanism maintenance will be covered in our HV products training webinars Click here to register.
For questions or more information, or if you need assistance with any of the preventive maintenance steps covered above, contact firstname.lastname@example.org