3 Phase Generator Transfer Panel Not Sensing Power Failure

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ptonsparky said:
I don't see that as corner grounded. I think it is floating. No one made the corner ground..
Some one that knows should comment shortly.
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As far as a loss of phase on the primary side, it really doesn't matter if the secondary delta is grounded or floating.
 
If the POCO transformer was delta-wye, then a lost phase on the primary would result in only a single-phase voltage being applied to the primary. As a result, there would just be single-phase output voltages on the wye secondary, with two of the L-N voltages reduced by a factor of 1/2. Also, because the output is single-phase it will have both positive and negative sequence components. Therefore, the loss of a primary phase should be relatively easy to detect.

However, with a wye-wye (Yg-Yg) transformer like the OP has shown, if it has a commonly used 3-legged core then it will regenerate the voltage on the open phase, as is mentioned on pg. 3 of the document at the link below. The figures in the document show that the missing voltage is fully regenerated at no load or a light load, and its voltage drops about 15% relative to the other phases when the transformer is 50% loaded. I think this could make reliable detection of a lost phase using the secondary voltages somewhat challenging. The algorithms listed in Table I on pg.11 of the document as being applicable for detecting a lost phase in a Yg-Yg transformer require measurement of the currents on the primary side of the transformer.
https://selinc.com/api/download/124320

For the OP, how was the presence of a lost phase on the FPL transformer noticed? For example, did the equipment shut down, have alarms, noticeable performance degradation, etc.?
 
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Just to confirm, the phase-loss monitor is on the secondary of the 480/240 transformer? Unless that transformer is fused (not breakers), it would be more reliable on the primary side so it will see the actual utility voltages.
 
zbang said:
Just to confirm, the phase-loss monitor is on the secondary of the 480/240 transformer? Unless that transformer is fused (not breakers), it would be more reliable on the primary side so it will see the actual utility voltages.
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From what I see in the pics of post #19, that is correct. The bottom pic shows the ATS nameplate, and just below the nameplate is the top of the phase loss monitor. On that nameplate next to Voltage it shows 240 which is the normal supply to the ATS. This is the proper place for this monitor since it is part of the transfer scheme that monitors proper voltage to the load and determines whether to start gen and transfer load by the Lake Shore ATS, regardless of what happens to the utility supply (2) transformers upstream.
The configuration is: 500KVA Wye to Wye 12KV- 480V utility transformer to 300KVA Delta to Delta 480V-240V to the L.S. ATS. My question is what happens to the 240 phase to phase voltage at the ATS (phase monitor) when the utility looses a phase.
The voltage measurements in post #19 also tells me that the ATS (and phase monitor) is fed from an ungrounded delta transformer secondary.
 
ptonsparky said:
Synchro's linked paper indicates that voltage will be pretty iffy to monitor from what I got out of it. Better if it's heavily loaded?
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For just a couple of $k, I would put something like a Basler BE1-47N relay on the output of the 500kVA 480V transformer. The relay output would be wired to the ATS input. It could probably be paid for by preventing an hour of downtime or additional time spent problem solving.
 
ptonsparky said:
I don't see that as corner grounded. I think it is floating. No one made the corner ground..
Some one that knows should comment shortly.
Click to expand...
It would come shipped with no bonding jumper installed. If you want a grounded system you ground one of the corners in the field.
 
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