Reliable System, Dependable Energy
Properly Working Equipment Helps Provide Reliable Power to Our Member-Consumers and Helps Limit Power Outages
At Stearns Electric Association, it is our mission to provide members with affordable and reliable energy. To do this, we work hard to maintain our equipment.
Each winter, Stearns Electric repairs and refurbishes a portion of our oil circuit reclosers (OCRs) to ensure they are in good working order.
Operations Supervisor and Operations Specialist, Glen Kemper and Bryan Berg, with assistance from Cooperative line workers, complete the annual OCR project throughout January and February.
“An OCR is an automatic high voltage switch similar to a household circuit breaker. It shuts off electric power when a short circuit fault occurs out on the power line. Short circuit faults are caused by lightning, fallen tree branches, animal contact or other catastrophic events,” Berg described. “The main functions of an OCR are circuit protection, safety to the public, mitigation of property damage and limiting the number of members affected by a power outage.”
The OCR senses fault current or short circuits out on the main power line distribution circuitry. For example, during stormy weather when there are high winds or thunderstorms, you may notice that your power blinks off and on. Those blinks are typically a result of the OCR sensing a fault caused by lightning strikes or tree branches. The faults cause the OCR to open momentarily, resulting in a short duration power outage of normally 10 seconds or less.
“A lightning strike will generally only cause the OCR to open momentarily one time, causing one blink, then it will reclose automatically and power will be restored without further interruption,” he explained. “However, a tree branch across a power line may cause the OCR to open and reclose up to three times, causing three blinks as the OCR attempts to burn off or clear the branch causing the fault. If the fault (tree branch) is not cleared after the third operation, it will remain open and not reclose, causing a power outage. It is then imperative to call out a line crew to find the cause of the fault (tree branch) and manually reset the OCR to restore power to the affected members.”
Stearns Electric has over 800 OCR breakers throughout our distribution system. Each year, the OCR project team refurbishes approximately 110 of those breakers.
“The breakers are full of oil. After so many years, the oil breaks down and the arcing inside causes carbon build-up which can flashover, potentially causing outages for members,” Berg said. Older OCR models have non-vacuum breakers that are serviced every three years. The newer models have vacuum breakers that prevent arcing in the oil, so those are serviced every seven years.
The line workers remove and replace the OCR breakers with previously refurbished ones and then bring them back to the shop to be repaired by Berg and Kemper. Each OCR takes approximately an hour and a half for a full renewal.
Berg detailed the steps of the project. “We’ll first open the breaker to remove the old oil, then we clean the contacts inside the OCR. Next, we insert new gaskets and seals and flush everything out before adding the new oil. We retest the OCR for proper function and finally repaint the exterior of the OCR.”
When the OCRs are ready for their final testing, they are hooked up to a Multi-Amp Oil Circuit Recloser Tester. The Multi-Amp OCR Tester indicates the number of trip outs, or times the OCR opens and closes, as well as the time curve at each trip. To perform accurately, the breaker needs to trip out four times within the time curve parameters. He explained that during the testing phase they partner with the Cooperative’s engineers to determine the correct time curves for each trip out, which helps guarantee the best functionality. Once they are accurate, the OCRs can be used for operations back in the field.
“The annual OCR project is imperative to make sure our breakers are working properly,” Berg concluded. “This not only protects the system from fault current but also, and most importantly, provides safety to our member-consumers.”