Burned switchgear enclosure bolts

[maxyn]

Recently, we noticed 2 bolts of our 12kV Ring Main Unit switchgear enclosure were totally burned that left 2 empty burned holes. Also, we found that the earthing/grounding connection of the switchgear and the 3 core power cable armor was missing. Additionally, a fault occured along the line which this RMU was connected. To make matters interesting a fire occurred on the accumulated combustible garbage around the equipment. My question is - Was the fire could have been possibly caused by the burnt/melted bolts that fell on the garbage near the RMU? Was the fault the cause of the burned bolts?

 

[desertfox]

Hi

Some photographs would help, that said if the bolts were loose at the time of the fault then a lot of heat would be generated which could lead to a fire from the loose joint sparking etc.

From my time in switchgear design I seem to remember that bolt tightness was supposed to be checked periodically in accordance with the maintenance manuals supplied with the equipment, any idea if this was done?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[jraef]

Enclosure bolts or bus bar bolts?

Pure speculation:
If it was enclosure bolts, the removal of the ground wire could have lead to an arc forming from some conducting component seeking ground, and found the bolts because they were extending into the air spaces ever so slightly more than anything else. Once an arc started, it's conceivable that it burned right through one bolt until it fell out, then to the other bolt because it too was the shortest distance.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[maxyn]

The photo shows on the right side the bolt hole and below that is where the rivet was supposed to be.

 

[maxyn]

Please take note that this RMU is continuing to operate after the incident up to this day. Interrupting medium of transformer feeder breaker is vacuum but surrounded by SF6. Busbar and 2 incomer line feeder switches are immersed in SF6 also.

 

[prc]

Normally such burn out of bolts is due to current flow through them. When there is a gasket on the flange the only path for current to pass on is through bolts. If the bolts are of stainless steel,chances of burn out are more as resistivity of stainless steel is 5 times more than steel.