Single Phasing Event

[WiscElectrician]

Last month we had a single phasing event throughout the campus on our primary side. A few VFD's tripped out, our mechanical equipment without VFD's have phase loss protection and protected themselves properly. The other day though, during the Annual NFPA 25 inspection, we realized that we lost our fire pump controller, more specifically the lead contactor in the pump.

This is a 7 year old Joselyn Clark controller, with two 400A contactors one hooked up to the 65% taps of an autotransformer. Unfortunately for us, Joselyn Clark no longer manufactures pump controllers and the replacement proprietary contactor is now $22,000 for a new one. Needless to say we ordered a newer solid state controller.

Here is my question. How could we have completely melted the plastic seats and scorched the contacts in the contactor during a single phasing event, in a no load condition? The pump was not running during the event. Nobody on the campus believes that the event could have caused the failure, but the pump hasn't ran since it was last checked a month prior and everything was perfect. Also, after the single phasing event, the strip mall across the highway lost multiple pumps/controllers too. Not sure if they failed the same way or not.

Anyone interested in taking a stab at explaining this to me? Hopefully this is the correct thread for this....

 

[Ingenieur]

Pdf of controller schematic?

is it on a generator?

 

[Ingenieur]

Does the system have a jockey pump?
could loss of pressure started the pump?

 

[Jraef]

Does the system have a jockey pump?
could loss of pressure started the pump?

That to me is the most likely scenario. The single phasing event meant that the Jockey Pump didn't turn on and therefor failed to maintain pressure in the standpipe. So eventually the pipe pressure dropped so low that the main Fire Pump attempted to come on, but because there was a single phase condition, it just burned up the contactor.

 

[brian john]

Does the system have a jockey pump?
could loss of pressure started the pump?

I'd put money on that scenario.

 

[WiscElectrician]

Sorry, late to get back with the answers. Had to get back to the pump for the wiring schematics.

As for a jockey pump.. Standard pressure is 175 Jockey on at 165, pump run at 155. Jockey is still actively working just fine even after the event, so a loss of pressure and a pump running scenario couldn't have happened. 1) Fire department would have been on site 2) Room is checked 4-5 times a day by security and would have been noticed.

Key notes: event lasted about 30 minutes; the pump controller is tapped directly off of the utility transformer; the strip mall next to us lost a couple pumps also, according to the fire department it happened during the event also.

Here's a picture of the wiring diagram:

 

[Ingenieur]

How often does the jockey pump cycle to maintain pressure?
shut it off and see how fast it drops to kick on the main pump
I bet it lost >20 psi in less than 30 minutes

no one said the jockey failed
only that upon loss of power (single phasing) it could not run and maintain pressure

this was a very common failure on older controllers when nfpa prohibited single ph lockout relays
they do allow them now

the only way it could fail like that is if the pump tried to run and could not spool up and the contacts cooked due to locked rotor current

 

[Ingenieur]

....

 

[Electric-Light]

3P motor will keep running if it is single phased unless it's loaded enough to stall on 1ph.

A motor can't start on single phase. 1p motors use a capacitator to provide the 2nd phase to start. A 3P motor fed 1P will sit and hum until something trips or burns out.
So the controller must have tried to start it.

 

[Phil Corso]

Wise 'E"

Several questions:

1) How is I/O Circuit-Board powered? Thus, how would it have reacted to single-phasing? Perhaps initiate a false-start!

2) Additional detail on damaged "M" or "AT" contact... any evidence of connected cable or insulation damage? Was cable connection secure?

Regards, Phil Corso