What kind of power?

[PowrJim24]

I'm trying to determine if I have a wye or a delta connection for our 240/3/60 and 460/3/60 service at our business. The service to the building is 240/3/60. The 460/3/60 service is created by a big transformer, powered by 240/3/60.

There are three wires coming from the 240/3/60 disconnect switch. The voltage is 190 between the 1st wire and ground, 309 between the 2nd wire and ground and 360 between the third wire and ground. Between any of the two, the voltage is 240V. Any ideas what kind of connection this is?

There are three wires coming from the 460/3/60 disconnect switch. The voltage is 491 between the 1st wire and ground, 498 between the 2nd wire and ground and 498 between the third wire and ground. Between any of the two, the voltage is 498V. Any ideas what kind of connection this is?

 

[davidbeach]

If there are three wires coming out of a black box, it is impossible to make measurements to determine whether the connection in the box is wye or delta. Delta and wye equivalents can be developed for any possible condition on three wires.

 

[Skogsgurra]

While davidbeach is correct in a text-book sense, the configuration sometimes can be derived from the different phase-gnd voltages.

In your case, the voltages measured do not correspond to any known (to me) configuration. So, it is probably a delta with floating or impedance ground. Try loading one of those phase-gnd voltages and see if it is highly load sensitive. If so, you have an ungrounded system. could be delta or wye. Impossible to say.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[davidbeach]

You will also have a bit better luck if you can measure all voltages simultaneously.

 

[waross]

I agree with David and Gunnar. But, 240V is more commonly seen as a delta connection. It is often derived from three 240 volt transformers. The common wye voltage is 208 volts. It is often derived from three 120 volt transformers.
Also, your system seems to be ungrounded. The NEC allowed ungrounded delta systems, but has for many years demanded that wye systems at that voltage level be grounded.
You can't tell but I would bet on ungrounded delta for the 240 volt system.
The 480/498 system, 480 volts is common to both wye and delta so you can't tell from the information given.
Look for a nameplate on the transformer if possible.

Bill
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"Why not the best?"
Jimmy Carter

 

[burnt2x]

Tried calculating from the figures posted and found out the figures do not exactly display a perfect ungrounded system!
davidbeach is correct in saying meaured voltages were not measured simultaneously. Phasors indicate ground reference way outside of the power polygon (assuming delta config) resulting to a larger than nominal voltage of about 360 and 309 V (as posted).

 

[jghrist]

My guess is that the 240 volt system is delta because you get much different voltages to ground. On a delta system, the phase voltage to ground depends on the phase capacitance to ground which can be highly variable. Also, as Bill said, 240 volt three phase is most commonly from a delta transformer connection (139 volts to neutral is uncommon).

The voltages to ground and line-to-line on the 460 volt switch do not make sense. If you have 498 volts between phases, you will not have 491+ volts to ground on every phase.

 

[ruggedscot]

What type of meter are you using ? If you are using a old analogue this may have the effect of loading up the transformer.

Id look to see what you get to ground use a couple of lamps in series say 4 110v lamps from phase to ground and see if they light. still cant get the 498v to ground though maybe your tranny is running with the wrong tappings or at the start of a long run?

rugged