Powerhouse Iso-Phase Bus Incident Analysis & Repair
A hydroelectric plant’s generating unit experienced a relay trip for undervoltage and investigations discovered A-phase of the isolated-phase bus had a high-resistance connection on the flexible strap connectors at the power transformer causing excessive heat and melting the bus bar connector. PPE was engaged to correct the discrepancy due to our company’s flexibility in action and purchasing. Time was a critical factor in this project and the client determined that repairing the bus bar was the most efficient and economical solution to get the unit back online. PPE removed and transported the bus bar section to our facility in Sacramento to crate and ship for repair. Following the repair, PPE assisted in reinstallation of the bus bar and coordinated on-site silver-plating and hi-pot testing of the repaired section. After conducting a root cause investigation and relay settings analysis, PPE reenabled the neutral overvoltage element in the relay and third-harmonic profiling was performed on unit startup to develop settings for the third-harmonic differential element in the future. The unit was returned to service eight days following authorization to perform work, two days sooner than the timeframe specified by the client.
- Root Cause Investigation
- Relay Settings Analysis
- Relay Settings Development
The iso-phase bus bar as-found during the investigation of the relay operation. Discoloration, smoke, melting, and metal spray resulting from the excessive heat caused by the high-resistance connection.