Mike Dolt Enterprises
Mike Dolt Enterprises
User: wiigelec, Location: Red Desert
Asked on: Saturday, March 26, 2011 at 10:44 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:21 am EDT
Question: Working on a near total outage in one of our large plants in order to upgrade DCS. After upgrade in process of bringing plant back up, testing equipment, interlocks, etc. Walk into control room and ask if there is anything they need us to look at and the entire plant suddenly goes dark.To make a long story short, "Breaker Closed" lightbulb on Cutler-Hammer 1200A 480V breaker was burned out and being replaced. Apparently the lamp is in parallel with the NO trip coil contacts and is a high impedance lamp. Replacement lamp was incorrect impedance and shunted trip contacts tripping the breaker which fed the lighting transformers for the plant. Good news is we found a UPS (dead battery holder) that was no good. Talk about exciting...
Summary
During a plant outage for DCS upgrades, a burned-out "Breaker Closed" lightbulb on a Cutler-Hammer breaker caused a plant-wide power outage.
Cause
The original lightbulb was a high-impedance lamp connected in parallel with the normally open (NO) trip coil contacts. Replacing the bulb with an incorrect impedance shunted the trip contacts, tripping the breaker feeding the plant's lighting transformers.
Impact
Plant-wide power outage Discovery of a malfunctioning UPS
Lessons Learned: Ensure that replacement lightbulbs for electrical devices have the correct impedance. Regularly inspect and maintain electrical systems to identify potential issues.* Identify critical equipment that should be backed up by UPS or other power sources. Flag for review