strange voltages with 480Y

[bsaint]

So our laser cell is coming off a 480Y transformer.

Voltages to ground are 483, 22, 508.

Voltages leg to leg are 488.

Whats the story with the funky voltages to ground? Someone said they might have a "floating ground"

Its not causing any issues BUT at a different time of day it will read 277 leg(x) to ground. Other times it reads the above voltage.

 

[jkwilson]

Is the neutral wired or virtual? I've seen really strange things happen on systems with a virtual neutral and really unbalanced loads.

 

[bsaint]

I do not know if its "virtual" or even what that means. I am not a power electrician.

 

[rockwithjason]

is the center of the wye grounded? if not then the voltages will shift depending on what load is connected to what phases at that time. sometimes a transformer will be grounded thru an inductor, a resistor or a grounding transformer to limit fault currents. this is done mostly done in high energy applications like power plants where they don't want to risk any damage to the equipment due to a fault current.

more on virtual grounds here

http://en.wikipedia.org/wiki/Virtual_ground

 

[bsaint]

The other issue is our competitor also has lasers in the same facility and this caused tons of issues and they had to add wye to delta isolation transformers.

I asked the building electricians if the wye is grounded and they said of course. Which makes sense because BANKS of lights would turn off throughout the day.

 

[bsaint]

They have a lot of electric ovens...

 

[rockwithjason]

The other issue is our competitor also has lasers in the same facility and this caused tons of issues and they had to add wye to delta isolation transformers.

I asked the building electricians if the wye is grounded and they said of course. Which makes sense because BANKS of lights would turn off throughout the day.

i was under the impression that the wye was on the secondary side or load side of the system. if the delta is feeding the load then that might change things depending on if the delta is grounded or not. from the measurements you posted i would guess that the delta is ungrounded. i am not following you on the lights going out so i have no idea about that.

 

[JoeFin]

You sure you have a Y connected transformer ?

Your utility feeding the transformer most certainly will be a ungrounded Delta, probably 12Kv or 4160v primary.

.... OK - I figured it out - your measuring an unloaded transformer at the transformer. Put some load on it and get back to us with the measurements

 

[Jarcese]

It looks like you have a delta service, not wye. If you ground one leg of delta, you will get similar readings. Without that ground you will still read 277 on each leg to ground, even if the secondary side is not grounded and lacks a neutral. With a ground you read 480 to ground on two and zero on the grounded leg to ground.

Just because you have lights doesn't mean it's not delta. You can have 480v lighting or another transformer in the building.

 

[rockwithjason]

My guess is that the facility has isolation transformers for their laser equipment

 

[bsaint]

Okay that makes sense.

 

[Jarcese]

You may want to check if that ground is intentional or not. You either have a corner grounded delta service or a delta service with a ground fault. If it's the latter, then the ground should be cleared.