Burnt Shunt Coil on ACB

[raehanar]

The following complaint was received from a client of mine who has a newspaper printing press.

When checking the main power panel during a power outage, the maintenance crew found one of the sub ACBs (800A, 55kA, 3-Pole) have been tripped and the shunt coil had been burnt. There is an Earth Fault Relay (EFR) connected to the shunt which had been tripped, which in turn caused the shunt to trip. The EFR was not damaged during this incident. Only the shunt appears to be burnt. None of the connecting terminals seemed to be damaged by heat.

This draw-out ACB was installed recently to an older panel with the necessary bus bar and panel modifications.

The system operated normally when the it was being commissioned and no problems were to be found. There is an identical EFR + ACB set operating in the same panel serving a different set of loads, and no problems were found on that either.

Any help on the possible causes for this incident would be much appreciated.

http://files.engineering.com/getfil...4f-8e6f-2c5876f4d4ae&file=20141220_153428.jpg

 

[ScottyUK]

Typical damage for a stuck breaker, or a breaker where the shunt release wasn't correctly installed. The trip coil is supplied current until it is cut off by the opening of the breaker, so if the breaker doesn't open the coil burns out. Equally if the coil isn't correctly located then it won't trip the breaker with the same outcome for the coil. Check your commissioning and maintenance records?

 

[sibeen]

Yep, with Scotty on this one. A shunt coil isn't long time rated and should have an auxiliary in front of it so when the breaker opens current to the shunt coil is interrupted.

 

[raehanar]

Thank you all. It was a found to be a fault in the control wiring.