Isolated Phase Bus Project

Southwest Kansas

A power generating station located in Southwest Kansas that was preparing to come back online from a scheduled six-week outage. During startup testing of the isolated phase bus duct, ‘B’ phase experienced a failed megger test. Following the failed megger, the plant performed high potential testing which also failed. The operators had neither the time nor expertise to identify what was causing the issue much less fix it. The plant was scheduled to go back online, and they simply were not ready.

Immediately a call was placed to Powell Electrical Systems, Delta Unibus Division to take advantage of its Repair Replacement and Refurbishment bus program. As a key piece of the program, our team was dispatched within hours to the site to arrive the next day, Friday at 7:30 a.m. Although the power generating station’s bus was not a Powell designed bus, our team was well equipped to address the issue.

After assessing the test conditions and work completed by the owner, the step was to inspect all the insulators on the B Phase. Once removed, the gaskets were inspected and discovered that many had been twisted during insulation, causing damage to the gasket.

Indication of water ingress was additionally found at the top of one of the insulators. The culprit in this situation was that the bolt holes had rusted, leading to additional corrosion. Finally, an inspection of the outer shell was conducted in order to check for cracks or other issues, and none were identified. The team now knew what the root causes of the problems were, and they would lay out a game plan to solve them.

The gaskets discovered were either wiped clean and re-installed or replaced completely. The nature of the gaskets was determined to be a very likely source of the water ingress found at the bottom of one of the insulator and at the top of the other. SE Energy recommended installing additional drains at the low point in the bus in the area of the first broken insulator on all phases. In order to clean up the water ingress evidence and establish a baseline for future inspections, SE Energy vacuumed and hand-wiped the B phase at the point where the water ingress had been previously detected in order to establish a baseline for future inspections. Additionally, a visual inspection was conducted on the outdoor bellows which revealed that they were in fact near the end of their functional life.

Our team addressed the immediate issues the plant was having which caused the failed high potential testing in order to safely return the unit to service. However, additional corrective actions would need to be taken during the next scheduled outage prevent further failures. The first recommendation was to replace all the insulator gaskets and stainless steel mounting hardware. Additionally, the power plant operators were instructed to inspect and hand wipe all the remaining insulators and the inside of the Isophase shell. New low point drains should be fabricated and installed at specific locations where the problems were detected. The rubber expansion bellows would need to be replaced in-kind along with the door gaskets and hardware both at the GSU and the generator.