Phase loss detection

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texie

Senior Member
Location
Fort Collins, Colorado
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Electrician, Contractor, Inspector
I have a situation with a customer that has had issues with loss of 1 phase on primary side of the 500 KVA POCO owned transformer that serves only them. This has happened 4 times in 3 years due to storms. The service is 208/120Y, 4000 amp protected by a SQD Powerpact breaker. I'm wondering about the wisdom of adding a phase loss kit to the breaker to open it on phase loss. Or would it be better to add shunt trip and use a stand alone phase loss detector. Does anyone have have any opinions about the reliability of phase loss detectors on the secondary of a transformer to detect a phase loss on the primary side?
 
texie said:
I have a situation with a customer that has had issues with loss of 1 phase on primary side of the 500 KVA POCO owned transformer that serves only them. This has happened 4 times in 3 years due to storms. The service is 208/120Y, 4000 amp protected by a SQD Powerpact breaker. I'm wondering about the wisdom of adding a phase loss kit to the breaker to open it on phase loss. Or would it be better to add shunt trip and use a stand alone phase loss detector. Does anyone have have any opinions about the reliability of phase loss detectors on the secondary of a transformer to detect a phase loss on the primary side?
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Personally I wold go with a system voltage monitor that would monitor not only the voltage but for loss of phase. I remember that Westinghouse used to have what they called an SVM which would do the job.
But then how would you reliably trip the breaker if it so happens that the phase that is lost provides the power to trip the shunt trip?
You could use a capacitive trip device (CTD) where a capacitor stores enough energy in order to trip a suitably matched shunt trip installed in the breaker or use an undervoltage release in the breaker that would trip when the UVR looses power. You would connect the UVR in series with a N/C contact in a loss of phase device which upon a loss of phase would openthe N/C contact dreopping out the power to the UVR tripping the breaker.
Loss of phase devices are often used with a N/C contact in series with the motor control coil circuit droppinout the contactor when there is a loss of phase.
 
We install things like templdl describe, all of the time.

We use a phase monitor from Taylor (http://www.taylorphaseguard.com/) and a capacitor trip from Sure-trip.
Your phase monitor contacts can be gotten so that they trip under all conditions including a total power loss (a real nuisance during a storm) or just for undervoltage and a 'single' phase loss (their PNDRLV is our preference).
 
Thanks for the help. My experience has been that all phase loss monitors are not created equal. I'm familar with the one mentioned, but have not used it myself. Will it operate reliably when the phase loss is on the primary side?
 
You need low voltage and phase unbalance sensing if you are trying to protect against a phase loss on the primary of a transformer.
 
jim dungar said:
You need low voltage and phase unbalance sensing if you are trying to protect against a phase loss on the primary of a transformer.
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Jim doesn't Square D have a micro logic unit for under voltage and shunt trip and or phase balance monitoring for the R frame which I think is 250 amps to 3000 amps, not sure which frame covers a 4000 amp? might be the best route to take if so? either way he will still need a shunt trip and cap/battery supply to trip the shunt trip unit even with a third party unit.
 
hurk27 said:
Jim doesn't Square D have a micro logic unit for under voltage and shunt trip and or phase balance monitoring for the R frame which I think is 250 amps to 3000 amps, not sure which frame covers a 4000 amp? might be the best route to take if so? either way he will still need a shunt trip and cap/battery supply to trip the shunt trip unit even with a third party unit.
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I believe there is and as part of my question, I'm wondering if a stand alone device is better and use it to shunt trip breaker (shunt trip would have to be added to the breaker) or do as you describe and do it all in the breaker. This is a situation that was brought up over a year ago and the customer sheved it for various reasons at that time and now wants to revisit it. I have not had a chance yet to get out the file to get the exact size and model of the Powerlogic breaker that is there. Either way it is going to require a shut down and mod to the breaker to add phase loss/undervoltage and/or shunt trip to the breaker.
 
texie said:
I believe there is and as part of my question, I'm wondering if a stand alone device is better and use it to shunt trip breaker (shunt trip would have to be added to the breaker) or do as you describe and do it all in the breaker. This is a situation that was brought up over a year ago and the customer sheved it for various reasons at that time and now wants to revisit it. I have not had a chance yet to get out the file to get the exact size and model of the Powerlogic breaker that is there. Either way it is going to require a shut down and mod to the breaker to add phase loss/undervoltage and/or shunt trip to the breaker.
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Remember that simply adding a ST to a breaker isn't going to necessarily guarantee that you will be able to trip the breaker. Please don't loose sight of the fact that you always must have a voltage available be able to assure that you can trigger the shunt trip no matter which phase is lost.
 
hurk27 said:
Jim doesn't Square D have a micro logic unit for under voltage and shunt trip and or phase balance monitoring for the R frame which I think is 250 amps to 3000 amps, not sure which frame covers a 4000 amp? might be the best route to take if so? either way he will still need a shunt trip and cap/battery supply to trip the shunt trip unit even with a third party unit.
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From what I know about their product offering R frame breakers go to 2500A, and NW go up from there. But, regardless, there is no 'internal' sensing circutis which I would trust for this type of protective relaying. In my opinion 'power monitoring' and 'power relaying' should be done by dedicated components.
 
We have installed, Time Mark, Taylor, ITI (Instrument Transformer) But recently switched to the Basler. We find the Basle cost effective and reliable. For a cap trip I like the ITI.
 
Doesn't someone make a loss-of-phase system that is powered by a 3-phase rectifier; so if any one phase was hot, there was trip power? This strikes me as so obvious there must be either something I don't see....or they exist in spades...
 
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