ARC FLASH REVIEW - UPDATES ON ARC FLASH STUDIES AND PROPOSED REVISIONS TO SAFETY STANDARDS

摘要

On April 16, Steve Woodring, chief plant operator at the Harrisonville Wastewater Treatment Plant in Harrisonville, Mo., was working in the plant's main lift station, which contains a split wet well with two submersible dry water pumps. Normally, these pumps take care of the flows to the wet well, but when they get too high, the overflow is directed into a larger pump gallery. On this day, the split wet well was flooded, and one of the two submersible dry pumps was reading inoperable-the monitoring system was keeping the 30-hp variable-frequency drive (VFD) from starting it. While Woodring waited for the pump repair people to arrive, he decided to try to bypass the VFD and engage the pump, running it for a few minutes so he could hook the bail, which had come detached from the rope used to track it, to the boom truck to draw the water down. "The controls on these pumps are extremely touchy," says Woodring. "The slightest bit of moisture or variance in ohm readings will show a problem. It's not uncommon for this system to cry wolf."