Utility Outage with 3000A Main Breaker Trip

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jeremysterling

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Location
Austin, TX
Hey all,

I'm back in the service department just in time to be on call for the holiday's weekend. Late Friday night, customer calls with Tier 4 power system on genset after utility loss (presumably from lightning). I discover 3000A main tripped. In previous utility outages this main has not tripped.

Inside the cabinet, there is a phase loss monitor relay. The button on the upper right was popped out, so I reset it. After poking around to rule out any other causes, I assumed that the breaker tripped on phase loss. My service manager donned a flash suit and reset the breaker, and, after the programmed delay, the ATS switched to normal and shut down the genset (happy ending):).

Was my assumption that the breaker tripped on phase loss correct?

How come previous utility outages have not affected this breaker?

Would it be because typical outages involve all three phases and on perhaps on this occasion only one phase was lost? Is that how the phase loss monitor relay operates?

Happy Labor Day!

Jeremy
 
I am not a big proponent of Phase loss at the main. IMO a facility (depending on the type of facility) is better served by placing phase loss at the loads that need phase protection, in lieu of dumping the complete service.

The ITI relay in your picture has adjustable time delay. Picking a time delay setting to minimize nuisance tripping versus frying equipment from single phasing is always a toss up.
 
Ragin Cajun said:
Not unusual for an outage to start as single phase, thus phase loss taking it out. Gotta love trip annunciators!
RC
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Unfortunately, no trip annunciator. The ATS does, however, annunciate "no normal" or something to that effect. Are you suggesting that a trip annunciator should be installed?

brian john said:
I am not a big proponent of Phase loss at the main. IMO a facility (depending on the type of facility) is better served by placing phase loss at the loads that need phase protection, in lieu of dumping the complete service.
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Even if on an ATS?

brian john said:
The ITI relay in your picture has adjustable time delay. Picking a time delay setting to minimize nuisance tripping versus frying equipment from single phasing is always a toss up.
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Thanks for the input and info. I live fairly close, and the genset has a big tank. I would rather respond at 2am to a nuisance trip than try to explain the time delay that allowed single phasing to fry equipment.

Do the big UPS's handle single phasing OK?
 
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My response included SITE SPECIFIC
(depending on the type of facility)
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. Typically we see these in almost all new office buildings. These buildings have generators for EM lighting, life safety. elevators and fire pumps. To dump a building like this in the middle of the day for single phasing iIMO is a poor design.
 
brian john said:
My response included SITE SPECIFIC . Typically we see these in almost all new office buildings. These buildings have generators for EM lighting, life safety. elevators and fire pumps. To dump a building like this in the middle of the day for single phasing iIMO is a poor design.
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My Original Post specified Tier Four. What is your opinion on Mains with phase loss relays in Tier Four data center applications?
 
I've wondered if there are any graphs or curves showing how much voltage unbalance a motor can stand for how long before it starts to be a concern. I know it depends on loading of the motor...

I'm ok with phase loss protection at the main as long as a time delay is included that will greatly reduce nuisance tripping due to events on the utility. I am guessing cost is a big reason why folks use one at the main instead of one at every piece of equipment. There are definately cases where having protection at the individual equipment is preferred...a data center comes to mind as one of these cases.:)
 
jeremysterling said:
My Original Post specified Tier Four. What is your opinion on Mains with phase loss relays in Tier Four data center applications?
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For a Tier 4 Data Center you want to know if the Utility has lost a phase asap in order to switch to generator mode in an orderly fashion. I'd suggest a couple cycles to ensure that it's a true Utility phase loss.

There's no urgency to do it within a subcycle timeframe because critical loads will have switched to their alternate source, with at least 4-5 seconds of coverage.

Utility phase loss is a pretty significant event for a Utility provider - meaning that it's not something they take lightly - at least not when providing primary (MV) power for a Data Center. And a Tier 4 Data Center is well equipped to exist on Generation - and therefore switches to that Mode without hesitation.

John M
 
If the electrical design incorporates a transfer switches in lieu of a circuit breaker transfer scheme, I see no reason to have phase loss at the mains.

The system is set up for automatic operation, loss of power will be handled by the ATS and when normal has returned and is stable based upon time frames the end user has set all will automatically re-transfer. If you want to hold the ATS in emergency position this can also be addressed without affecting the position of the utility main.

And the major factor in all this is what the designer feels is best. As a field tech we can always second guess the design engineer, but he/she may have more insight to local issues that may affect design than someone walking onto a job for the first time, or answering a question on a forum.
 
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jeremysterling said:
My Original Post specified Tier Four. What is your opinion on Mains with phase loss relays in Tier Four data center applications?
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I may have misinterpreted your question in my last post.

I agree that main breakers in panels shouldn't necessarily have single-phase detection.

My comment was in reference to Utility incoming service. It's our experience that we want to know if the Service has lost a phase, at which point the Tier 4 system would immediately go to backup power until the proper Utility service is restored. This would typically be detected by a 47 negative sequence overvoltage relay, that would initiate the disconnect from the Utility source, and the subsequent transfer to backup power.

John M
 
brian john said:
If the electrical design incorporates a transfer switches in lieu of a circuit breaker transfer scheme, I see no reason to have phase loss at the mains.

The system is set up for automatic operation, loss of power will be handled by the ATS and when normal has returned and is stable based upon time frames the end user has set all will automatically re-transfer. If you want to hold the ATS in emergency position this can also be addressed without affecting the position of the utility main.

And the major factor in all this is what the designer feels is best. As a field tech we can always second guess the design engineer, but he/she may have more insight to local issues that may affect design than someone walking onto a job for the first time, or answering a question on a forum.
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I try to "always second guess the design engineer.":grin:

I appreciate the wisdom in what you write here. After all is written and read here; no recommendations will be proffered, nor any changes made to gear. Just Q&A on a forum.

I am very interested in the design ideas presented. I need to get back in school and do some studying.

Thank you all for your expert commentary, esp, "If the electrical design incorporates a transfer switches in lieu of a circuit breaker transfer scheme, I see no reason to have phase loss at the mains."

Jeremy
 
Its Not a Main "Breaker"

Its Not a Main "Breaker"

Based on the picture, the 3000 Amp Main is a fused High Pressue Switch and not a circuit breaker. The switch has a shunt trip that allows the phase loss monitor or a ground fault detector to trip open the main.

Is it possible that the phase loss detector is monitoring power on the LOAD side of the siwtch to trip the switch if one of the fuses blows, single-phasing the whole facility?
 
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