Voltage Balance

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cjbouchard@bergco.com

cjbouchard
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Hello Im working a a step-up transformer 120/208 delta to a 277/480 Y Im getting voltage readings all over the place with 3 different meters none of the reading are good In my opinion L1 250v L2 284v L3 284v secondary . 122Vac L1 L2 L3 solid on the primary. The transformer is mounted inside a shipping container on a metal L shaped plate .
Im stumped at the moment But believe something is going On that is not good For the reason it was hooked up to a new machine and it blew the surge protector right out of it Im trying to determine if the voltage indifference is the problem or there was something wrong with the machine and how much voltage indifference is acceptable.
 
If it's truly a delta primary transformer, you would want to know the line to line primary voltage. You are not using the neutral at the primary.
 
cjbouchard@bergco.com said:
Hello Im working a a step-up transformer 120/208 delta to a 277/480 Y Im getting voltage readings all over the place with 3 different meters none of the reading are good In my opinion L1 250v L2 284v L3 284v secondary . 122Vac L1 L2 L3 solid on the primary.
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What is the voltage line to line A to B, A to C, B to C on the primary? As metioned there is no neutral on the primary of a Delta-Wye transformer. What is the voltage line to line on the secondary?

284V to neutral sounds fine, 250V is low. Could be something simple like a poor connection at one of the lugs.
The transformer is mounted inside a shipping container on a metal L shaped plate
Im stumped at the moment But believe something is going On that is not good For the reason it was hooked up to a new machine and it blew the surge protector right out of it Im trying to determine if the voltage indifference is the problem or there was something wrong with the machine and how much voltage indifference is acceptable.
Click to expand...
What size is the transformer? Is the neutral on the secondary bonded to the case of the transformer or in the first disconnect?

+ or - 10% is generally accepted tolerance for voltage level.
 
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If the line to line voltages are matching, system voltage may vary 10% without much trouble.

If the line to line voltages are not matching, line to line voltage imbalance should not exceed 1% line to line, as 3 ph motor heating increases by 25%. for 3 ph motors connected directly across the line.

The transformer model #, wiring diagram, needs a second look. If it is a standard distribution transformer and reverse fed, the primary would be 208 Y with no neutral connection and the Y centerpoint floating. That would make the secondary 480 V delta, and if the TVSS wants 480 Y, that will probably smoke the TVSS (which is itself Y connected and center grounded).

208 delta primary, 480 / 277 Y secondary is very non standard, but that may be what you need as stated.
 
I think the first order of business here is for the OP to show us the name plate to determine if he actually has a 208 delta to 480Y transformer as he says.
 
ActionDave said:
What is the voltage line to line A to B, A to C, B to C on the primary? As metioned there is no neutral on the primary of a Delta-Wye transformer. What is the voltage line to line on the secondary?

284V to neutral sounds fine, 250V is low. Could be something simple like a poor connection at one of the lugs.

What size is the transformer? Is the neutral on the secondary bonded to the case of the transformer or in the first disconnect?

+ or - 10% is generally accepted tolerance for voltage level.
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No the XO is not grounded to the case Its running a 480 v Stud machine is this where my problem is should i ground the XO to the case even thought Im not using the Neutral?
 
electrofelon said:
This. Is the secondary grounded? If not, you will likely get odd measurements.

Edit: To clarify, Line to XO should all be the same even if ungrounded I meant if measuring line to ground.
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No the secondary XO is floating I was thinking because the mechine Runs on 480 i would not need the Xo connection so my reading where from EGC
AWW this is making sense
 
__dan said:
If the line to line voltages are matching, system voltage may vary 10% without much trouble.

If the line to line voltages are not matching, line to line voltage imbalance should not exceed 1% line to line, as 3 ph motor heating increases by 25%. for 3 ph motors connected directly across the line.

The transformer model #, wiring diagram, needs a second look. If it is a standard distribution transformer and reverse fed, the primary would be 208 Y with no neutral connection and the Y centerpoint floating. That would make the secondary 480 V delta, and if the TVSS wants 480 Y, that will probably smoke the TVSS (which is itself Y connected and center grounded).

208 delta primary, 480 / 277 Y secondary is very non standard, but that may be what you need as stated.
Click to expand...
this is a step up transformer coming off a 120/208 delta primary to a Y 480/277 secondary to feed a 480v stud machine The XO connection is Not used But i did not ground it to the case ,
 
If the secondary X0 is floating, the TVSS is also internally Y connected and grounded (if 3 phase type), so you would be using the MOV's in the TVSS as the system bonding jumper, until they smoke.

The seperately derived 480 / 277 secondary is also a system required to be grounded
 
texie said:
Can you post a pic of the data plate? Your terminology is making me wonder what your transformer is.
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I am with Texie here. Can you show us the xfmr data plate. Your use of the X0 terminology makes me wonder if you are back feeding a step down transformer. If that is the case...
1) Do not ground the X0 terminal.
2) You have the wrong transformer and will continue to harm components on the secondary that expect to be supplied from a Y connected secondary.

All the step up 208D -> 480Y xfmrs I use do not have an X0, they have an H0. If you really see an X0 terminal in yours, please post data about your specific transformer.
This would be a typical wiring diagram of a purpose built transformer, wound for a step up Wye secondary. Note the H0, and lack of X0.

Capture1.JPG
Apologies in advance if you actually have an H0 and are mistakenly referring to it as X0. And if you do have a real step up xfmr with an H0 terminal you should ground that. Without it, any H1,H2 or H3 to Ground voltage readings will be meaningless (like you saw) and, like Dan mentioned, the electronics downstream will be in harm's way.
 
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cjbouchard@bergco.com said:
No the XO is not grounded to the case Its running a 480 v Stud machine is this where my problem is should i ground the XO to the case even thought Im not using the Neutral?
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Wouldn't that be the H-0?

In my opinion, the secondary neutral should be grounded, regardless of the load's need for a neutral.
 
cjbouchard@bergco.com said:
this is a step up transformer coming off a 120/208 delta primary to a Y 480/277 secondary to feed a 480v stud machine The XO connection is Not used But i did not ground it to the case ,
Click to expand...
Are you using X-0 to describe the LV (primary) neutral or the HV (secondary) neutral ?
 
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