i am t man in fl and recent weeks have had several pmh 9 sw gear with 1 and 2 runs of 1000 feeds and 1-2 out bound 1/0 or 4/0 runs looped and rad run . only 1 with cap bank on the the gear no lightning and no animal or water in gear but gear all of sudden the gear gose to ground and burns insides only .some to shows ckt operates or just call of tx fire by public, but no outage when arrived on scene some show fault on 1 or more phases but no outage and the fire inside has melted fuses but no faults on cables down stream cannot find see a pin point a cause that matches each one like a baord or mach. error in gear it still opens /close normaly epoxelators that isolate bus in gear to containated or damaged other than after the fire . need some insight or feed back [ voltage 7620 /13k ]
biff was there load on the switch gear when it faulted? depending on the length of the conducter run some really strange things happen with induction and capacidence with no load.we've had brand new installs done with three phase underground that when they energized the cable with no load the cables faulted. they dug it all up and laid new cable and it blew again. had everyone scratching their heads.
The phenomenon of Ferroresonance is the occurrence of an unstable high voltage, typically on 3 phase electrical systems which only occurs under specific conditions. The nature of the overvoltage can cause the failure of equipment.
Ferroresonance occurs when an unloaded 3-phase system consisting of an inductive and a capacitive component is interrupted by single phase means. In practice this is typical of a high voltage electrical distribution network of transformers (inductive component) and power cables (capacitive component). If such a network has no load and the applied voltage is then interrupted on a single phase, a ferroresonance may be observed. If the remaining phases are not interrupted and the phenomenon continues, overvoltage can lead to the breakdown of insulation in connected components resulting in failure.
The phenomenon can be avoided by maintaining a minimal load on the circuit or by interrupting the applied voltage by a 3-phase interrupting device such as a ganged (3 pole) circuit breaker
Weve had numerous PMH-9 switch cabs fail. All relatively new in service, within 3 years, and we were told we were running too many amps thru this 600 amp gear...which we found out we were. The s&c reps looked the cabs over and said that was the only problem. Then we started to have failures well under rated amperages on circuits that have never been overloaded and the s&c reps do not know or will not admit to any issues. The gear itself heats up so much that the plastic snuffer devices at the top of the gangs melts and will not allow the blades to operate so when you throw the gang the spring pressure breaks the switch...be carefull brothers
we were told to watch out for some spray on tar crap on the inside of the top that is supossed to stop condensation that may come un-glued and fall on the buss work and go boom.