Line voltage running high 130v

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ericmccurley

ericmccurley

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Arkansas
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Electrician
I had a call where they had 130v coming off the secondary side of a transformer. I thought at first the secondary side was tapped wrong. When I checked voltage at transformer I had 130v on secondary side and A phase 187v, B phase 290v, C phase 290v. This transformer was fed from a 277v-480v panel. My company pulled me off the job before I could get to the main switch board feeding the 277v panel. Can anyone tell me not what this may be but what is wrong??? Connections are good and transformer was bonded. Please I would like to know what this is because up to this point I’ve never heard of such a thing!
 
ericmccurley said:
I had a call where they had 130v coming off the secondary side of a transformer. I thought at first the secondary side was tapped wrong. When I checked voltage at transformer I had 130v on secondary side and A phase 187v, B phase 290v, C phase 290v. This transformer was fed from a 277v-480v panel. My company pulled me off the job before I could get to the main switch board feeding the 277v panel. Can anyone tell me not what this may be but what is wrong??? Connections are good and transformer was bonded. Please I would like to know what this is because up to this point I’ve never heard of such a thing!
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Typo and A phase should been 287?

Your 277 supply values are about the high end of what is deemed acceptable. Chances are there was not much load on the service at the time this reading was taken and when the load does increase it may drop to more normal levels.

Also if this is a control transformer they tend to run a little higher voltage than power transformers and ~30 when unloaded is fairly common if supply side volts isn't below nominal values.
 
ericmccurley said:
I had a call where they had 130v coming off the secondary side of a transformer. I thought at first the secondary side was tapped wrong. When I checked voltage at transformer I had 130v on secondary side and A phase 187v, B phase 290v, C phase 290v. This transformer was fed from a 277v-480v panel. My company pulled me off the job before I could get to the main switch board feeding the 277v panel. Can anyone tell me not what this may be but what is wrong??? Connections are good and transformer was bonded. Please I would like to know what this is because up to this point I’ve never heard of such a thing!
Click to expand...
ericmccurley said:
I had a call where they had 130v coming off the secondary side of a transformer. I thought at first the secondary side was tapped wrong. When I checked voltage at transformer I had 130v on secondary side and A phase 187v, B phase 290v, C phase 290v. This transformer was fed from a 277v-480v panel. My company pulled me off the job before I could get to the main switch board feeding the 277v panel. Can anyone tell me not what this may be but what is wrong??? Connections are good and transformer was bonded. Please I would like to know what this is because up to this point I’ve never heard of such a thing!
Click to expand...

ericmccurley said:
I had a call where they had 130v coming off the secondary side of a transformer. I thought at first the secondary side was tapped wrong. When I checked voltage at transformer I had 130v on secondary side and A phase 187v, B phase 290v, C phase 290v. This transformer was fed from a 277v-480v panel. My company pulled me off the job before I could get to the main switch board feeding the 277v panel. Can anyone tell me not what this may be but what is wrong??? Connections are good and transformer was bonded. Please I would like to know what this is because up to this point I’ve never heard of such a thing!
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ptonsparky said:
Primary voltages of A, B, C?
Secondary are all 130 to neutral? Three phase?
Picture of the transformer nameplate would be a plus.
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This is my first thread I don't know how to add pics yet sorry. But it is Made by Zinsco. It is a three phase 30kva 480v-208v to 120v. primary diagram is delta and the secondary is Y. If this helps you at all. The co-workers at my company keep on telling me that is was the taps. I wasn't seeing that being the problem. My company pulled me off the job thinking it was the utility transformer. Our utility company said that was not the problem. So I'm sure we could lose this client. Hope this helps and thank you for helping me with this!
 
ericmccurley said:
This is my first thread I don't know how to add pics yet sorry. But it is Made by Zinsco. It is a three phase 30kva 480v-208v to 120v. primary diagram is delta and the secondary is Y. If this helps you at all. The co-workers at my company keep on telling me that is was the taps. I wasn't seeing that being the problem. My company pulled me off the job thinking it was the utility transformer. Our utility company said that was not the problem. So I'm sure we could lose this client. Hope this helps and thank you for helping me with this!
Click to expand...
If it has different input taps that very well could be that wrong ones are in use, but at same time if load is down at the time it may be where desired and will end up being too low when loaded. Not necessarily talking about the secondary load but loading on the 480 volt system may be down raising the main supply volts. Your 290 volt readings suggest that this may be the case and when there is significant load they may drop closer to levels you might be expecting.
 
Any input (primary side) voltage readings?
What time of Day?
Size of facility running or setting idol.
Morning utility usually runs high.
As mentioned a load, tap can result in these numbers
"The co-workers at my company keep on telling me that is was the taps."
Before you re-tap gather all information.
Think about as a whole, look and listen as well while you there. Don,t get a single line of focus.
something as easy as I usually cant park here because the lot is always full.
On larger facility's look and see if the capacitor bank is open or shut on the pole as you drive in if there is one.
The call was for high voltage to ground and what prompted the call in the first place. Maintenance addressing an issue?

Just some food for thought.
Ask questions from whom ever was sent out after you and use it as a learning experience, I would fr sure.
Have them explain there finding for future calls.
 
kwired said:
If it has different input taps that very well could be that wrong ones are in use, but at same time if load is down at the time it may be where desired and will end up being too low when loaded. Not necessarily talking about the secondary load but loading on the 480 volt system may be down raising the main supply volts. Your 290 volt readings suggest that this may be the case and when there is significant load they may drop closer to levels you might be expecting.
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So if the secondary is retapped then it could fix the problem? But at the same time if we did that wouldn't the secondary voltage drop to low once the primary side has a heavy load applied?
 
ericmccurley said:
So if the secondary is retapped then it could fix the problem? But at the same time if we did that wouldn't the secondary voltage drop to low once the primary side has a heavy load applied?
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Also, how would you go about finding the right taps to retap to? I know this sounds like a dumb question. But the last time I did anything with 480v transformer it was in school.
 
kwired said:
If it has different input taps that very well could be that wrong ones are in use, but at same time if load is down at the time it may be where desired and will end up being too low when loaded. Not necessarily talking about the secondary load but loading on the 480 volt system may be down raising the main supply volts. Your 290 volt readings suggest that this may be the case and when there is significant load they may drop closer to levels you might be expecting.
Click to expand...
How can a load increase affect the line voltage by dropping it on that circuit?
 
ericmccurley said:
How can a load increase affect the line voltage by dropping it on that circuit?
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The source as well as the conductors between the source and whatever point you are interested in all have resistance/impedance. More load you apply the more voltage will drop. Larger than needed source or larger than needed conductors just need even more load on them before the results become significant.

If you have a production facility and come take voltage measurements on a "down day" they likely will tend to be higher than on a day with normal production levels, simply because there is less current being drawn and less voltage drop across the source as well as less voltage drop on service and feeder conductors. Individual branch circuits still in operation, (not all items necessarily go down on a down day) might still see some voltage drop that you don't see elsewhere at that time.

So to have 480 to 120 transformer you have a 4 to 1 turns ratio. But lets say on a down day the load is low enough the actual primary volts goes up to 520 then the secondary will increase proportionally to 130.

On top of that say the normal loading brings the incoming 480 down to 465 then the secondary volts will drop to 116.25. But depending on how much load is on that 120 volt side it could drop even further just because of impedance in the secondary and the secondary conductors.

Selecting a tap to use on the primary of said transformer can bring output volts up or down (you usually have 5% change between each possible tap configuration) But keep in mind you should probably select a tap based on where the loading conditions are the most prevalent. Because it will still go up and down as loading conditions change, and is still effected by any change in incoming primary voltage as well. Often in a production situation if the 480 volt loads are decreased significantly so will a lot of the loads on the secondary, simply because production levels changed, so over compensating on tap setting can put you at pretty high voltage on the secondary when overall load levels are low.
 
The presence of Zinsco means it’s an older system. If the primary was Delta and ungrounded, as was common years ago, then measuring Line to Ground on the primary side would give you meaningless values as you would be measuring capacitive voltages. Always measure primary voltages Line to Line.
 
ericmccurley said:
When I checked voltage at transformer I had 130v on secondary side and A phase 187v, B phase 290v, C phase 290v. This transformer was fed from a 277v-480v panel.
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I bet the secondary of the transformer has become un-grounded somehow.
If it was a primary voltage problem and you had 130 to neutral on each phase phase to phase would be 225.
Whats the system supposed to be normally? 220Y127 is a standard system some places.
 
tortuga said:
I bet the secondary of the transformer has become un-grounded somehow.
If it was a primary voltage problem and you had 130 to neutral on each phase phase to phase would be 225.
Whats the system supposed to be normally? 220Y127 is a standard system some places.
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It apparently was a 480/277 main supply from what was mentioned in OP. What was never clarified was if this was a single phase, three phase or if it was multiwire secondary, or if it were a control transformer in some piece of equipment - which often will have somewhat high secondary voltage especially when unloaded.
 
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