Loss of Critical Load

[gftt]

We had a MGE Comet UPS unit, 125 kVA, loaded to 43.5 kVA (small motors, controls, etc.) that dropped off line. The bypass breaker tripped (thermal 200 Amp frame) and critical load was dropped. The fault codes in the UPS indicated an inverter fault, rectifier fault, and thermal overload. The theory from the UPS technician is the main invert fan failed causing the UPS to overheat, but didn't have an explaination of why the bypass breaker tripped. Anyone have any thoughts or similar problems?

 

[dpc]

Bypass breaker may have tripped on instantaneous at the moment of transfer. If the running motors had become slightly out of phase with the system, but still excited, an out-of-phase condition could have existed. Or some other transient condition caused the breaker to trip.

 

[itsmoked]

If the bypass had any GFI aspect perhaps the fan failed to ground.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com