830 volts from a 480 volt delta bank?

[Endrid Cold]

Today I was investigating an electric meter with no display at a pumping station near our flood walls. It’s a 3 wire 480v UNGROUNDED delta bank. I checked voltage in the secondary side of the PT (metering transformer) and read 15 volts. When I checked the primary side of the PT I read 830v. That seemed impossible. I followed the lines feeding the bank back to the pole the primary tap was on. I noticed 2 cut out fuses on the pole were hanging open. So, only one phase was being delivered to the delta bank feeding the pumping station. How is one phase of a 480v system delivering 830v? And, is it a coincidence that the 830v I’m measuring is equal to 480v multiplied by 1.732, the square root of 3?
Tomorrow I’ll get a serviceman to close those 2 cutout fuses for me and see if the voltages normalize. Also a good chance my PT’s are ruined.

 

[augie47]

Were you measuring from phase to ground ??

 

[paulengr]

On a delta system there is no intentional connection to ground. And you had an isolated conductor. So up by the transformer the fields from the primary side can easily inductively or capacitively induce just about any voltage. Get a meter with “low Z” input or the fluke stray voltage eliminator and check again.

 

[petersonra]

with an open circuit like that it could read just about anything.

 

[LarryFine]

I'm betting you have a grounded phase.

 

[ptonsparky]

Last time that happened to me, the POCO was almost there with a new transformer before I could get my tools picked up.

 

[jim dungar]

I'm betting you have a grounded phase.

That would fix the L-G voltage at the L-L value.

Ungrounded systems can easily see 2x L-L voltage during some fault conditions, which is one of the reasons they are not usually employed.