3 Phase High Leg Delta System Voltage Issues

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LMACKEY

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Santa Rosa, CA
Hello All,

I am running into some voltage fluctuation issues with a 3 phase system at a winery that I am working at. There is a High Leg Delta transformer supplying the service and feeds from the meter/main approximately 400 feet down a hill to a shop that, when the lights (20A circuit) are turned on the "A" phase drops to around 100V to ground and the "C" phase spikes to around 140V to ground. There are multiple in ground boxes along the way to the barn (which other than lighting, has no load) and I have checked all the terminations including the neutrals and see no issues. When trying to simulate this issue at the main the voltage in fine. I have disconnected the connections up to the point of the last section of feeders from the last box inline to the main (less than 100 feet from the main) and I still have the issue when a small load is applied. Is this a utility transformer issue? If so, why do I not see the voltage issues at the main? I understand with the distance there is voltage drop to consider, but the feeders are sized correctly so I am just a little baffled. Any input to help would be appreciated! I do know the utility transformer supplying the system is tapped and feeding another high leg service onsite. Possible termination issues within the utility transformer? Thanks in advance for the help!

Note: I do know the feeders were grabbed by a backhoe a few years back and "supposedly" re-pulled\repaired, but the extent of the repair is a little vague.

Lauren Mackey
Electrician/JFW
 
The symptoms of one leg reducing the voltage to neutral while the other leg increases the voltage to neutral, with the sum remaining unchanged or only slightly changed, is a clear indication of a high resistance somewhere in the neutral path. Disconnecting the feed completely and measuring neutral ohms from point of use to wherever the voltage remains constant is one way to troubleshoot.
If the entire facility is affected, the problem may be in the meter socket, main panel, or POCO service wiring. This could include the connections to the service transformer center tap.
It does not appear that the neutral is completely open though.
 
Thanks for the confirmation Gold. My thoughts are that when the backhoe pulled the cables, the insulation and possibly the the neutral wire itself may have been compromised inside the conduit. The only neutral terminations I cannot check is the the meter, the utility enclosure, and the transformer, but all other terminations are tight. I will do a resistance test on the neutral and see what I come up with. PG&E is on their way to check their side. Thanks for the input!:cool:
 
LMACKEY said:
Thanks for the confirmation Gold. My thoughts are that when the backhoe pulled the cables, the insulation and possibly the the neutral wire itself may have been compromised inside the conduit. The only neutral terminations I cannot check is the the meter, the utility enclosure, and the transformer, but all other terminations are tight. I will do a resistance test on the neutral and see what I come up with. PG&E is on their way to check their side. Thanks for the input!:cool:
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You are welcome. Damaged insulation without damage (direct or through corrosion) to the wire itself will not cause high neutral resistance.
When POCO checks, make sure they put a large load (e.g. Beast Of Burden device) on one side of the 120/240 only. Then they can check voltages.
 
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