substation HV Disconnect Failures

[mosesnbklyn]

thread238-410869

Had an engineering manager tell me they are concerned vertical end break switches (VEB) may fail by closing after being opened to isolate equipment for work. I would agree that double-end break (DEB) are generally more reliable/robust.

I have seen switches that failed due to flash-over/arcing on the insulators (DEB), mounted high up on 65ft towers, and I can assume debris build-up and over-heating in the contacts sometimes happens, but never failing closed while in the open position. Has anyone come across this above situation?


PE/IEEE-SM

 

[stevenal]

You linked a thread discussing MODs. Are your disconnects motor operated?
We try to have vertical disconnects oriented so that gravity helps to hold the de-energized blade open when in the open position. Always de-couple motors and apply locks that prevent closing prior to testing, grounding and commencing work.

 

[crshears]

My former utility used the verbal terminology of "check open and leaning back" in these cases, and the expectation was that when the switch was being serviced Electrical Maintenance would adjust the trunnions and/or other appropriate parts of the switch operating mechanism so that this position was obtainable through normal operation of both motorized and manually operated disconnects. Switching agents would sometimes have to request an additional close, then open operation via motor to get the blades to lean back; sometimes the S/A would have to decouple the motor and close the blades to 80° or so, then as quickly as possible open the switch so as to impart just enough momentum to the switch blades to get them to travel past plumb.

If a switch would only go to plumb [ 90° ], it was still permitted to use it as an isolating device but this condition had to be noted on the "safety precautions" section of the pertinent work protection documentation.

If not even a full 90° condition could be obtained, it was prohibited to use that device as an isolating point until the zone encompassing the jaw side of the switch had been isolated under work protection and the switch in question had been securely tied open by crews working aloft.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[mosesnbklyn]

Yes thanks guys. motor operated ~MOD or ~MOAB switches

P.E. / IEEE Senior Member