Flashover in MCC
Flashover in MCC
(OP)
I maintian a Hammermill that has a control cabinet built in 1960. The supply voltage to the MCC is 500V ungrounded delta. The MCC has a 400A main breaker with 25 #10 AWG conductors per phase on the load side feeding 25 30A G.E. breakers and starters in the same cabinet. The MCC was site built to very slackend standards and the componets are snugly fit with little air space.
The problem is that when a fault occures at any motor feeder we lose 5 or 6 breakers and starters do to flashover. Is the voltage spiking to high for the close coupled components? Could it have somthing to do with the sytem being ungrounded. Any input would be greatly appreciated.
Best Regards,
ASB1
The problem is that when a fault occures at any motor feeder we lose 5 or 6 breakers and starters do to flashover. Is the voltage spiking to high for the close coupled components? Could it have somthing to do with the sytem being ungrounded. Any input would be greatly appreciated.
Best Regards,
ASB1






RE: Flashover in MCC
With the ungrounded system when you get a fault phase to ground voltage rises to the phase to phase voltage on two phases. I would suspect this is the source of the flashover in the MCC when a motor circuit fails. (Leakage ground current flows initiating the flash over) (As noted speculation) A good cleaning may help.
RE: Flashover in MCC
RE: Flashover in MCC
RE: Flashover in MCC
Low-voltage ungrounded-system {transient, oscillatory or steady-state} "neutral shift" outside of nominal ø-ø voltage can be disastrous. One account is 67.115.161.42/dat/beemaIPSH6.doc
Conversion to a high-resistance-grounded system for ungrounded 240-600V distribution may be desirable, and is well documented. An example is John P. Nelson and Pankaj K. Sen, High-Resistance Grounding of Low-Voltage Systems: A Standard for the Petroleum and Chemical Industry, IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 35, NO. 4, JULY/AUGUST 1999
RE: Flashover in MCC
RE: Flashover in MCC
Sounds like you might have to rebuild the unit with better spacings and/or go to a grounded(or resistance-grounded) system.
RE: Flashover in MCC