Higher than expected plant voltage

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sii

sii

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My company recently purchased another company and we are in the process of moving some equipment from one of their plants to ours. When I went to the new plant, the first order of business was to disconnect the electrical supply from a machine. When I was doing the live dead live test to ensure I was locking out the proper breaker, I noticed that the L-L voltage was around 498-499 and the L-G was 288-289. I have never seen voltages that high at equipment. Is that typical in some places or just a fluke?
 
sii said:
My company recently purchased another company and we are in the process of moving some equipment from one of their plants to ours. When I went to the new plant, the first order of business was to disconnect the electrical supply from a machine. When I was doing the live dead live test to ensure I was locking out the proper breaker, I noticed that the L-L voltage was around 498-499 and the L-G was 288-289. I have never seen voltages that high at equipment. Is that typical in some places or just a fluke?
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Was going to ask if there was any load but posted at same time.
Sounds like you might have some tap changers to change. I suggest you monitor voltage for 24 hours and get back to us.
 
They have eleven identical, or at least close, machines. Eight of those eleven were running to some extent and while I'm not sure of the load, they all would have a 100 amp main. They also had two of their three 60 hp compressors running and another larger machine that has a 250 amp main. I guess that doesn't tell what the load was other than that I would estimate it to be 80-90% of normal.

As far as monitoring voltage, that won't happen as I'm unlikely to ever return there. Their one-man maintenance staff was calling VFD-driven motors "stepper" motors so I'm guessing they aren't going to be doing any voltage monitoring either.:D I don't even want tell you some of the other things I saw there.
 
I am working on a design in which the client wants to run certain 480-208/120V transformers at their highest tap so the secondary voltage will be approximately 230/133V. The higher voltage will help the efficiency of their IT servers which is the only load from these transformers
I told them that as long as all the equipment/CB's were properly rated, I didn't see a problem. Although I told them that they would need to use a different color scheme per phase and post the identification standard.

So maybe the plant you visited has the voltage up high for a reason?
 
ron said:
Although I told them that they would need to use a different color scheme per phase and post the identification standard
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You may want to rethink that one, your 208 and 230 systems have the same nominal voltage for the purposes of 215.12.

Voltage, Nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.
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sii said:
My company recently purchased another company and we are in the process of moving some equipment from one of their plants to ours. When I went to the new plant, the first order of business was to disconnect the electrical supply from a machine. When I was doing the live dead live test to ensure I was locking out the proper breaker, I noticed that the L-L voltage was around 498-499 and the L-G was 288-289. I have never seen voltages that high at equipment. Is that typical in some places or just a fluke?
Click to expand...

Has the location been an industrial site and electrified since, say, 1890? When I worked for Hecules at their Kenvil plant, they had their own power house at the turn of the last century and operated on 3-phase 500 VAC. Eventually the power house was used to only supply steam plant-wide and they did bring in some 480 service, but many of the larger motors were still 500 volt working off a sub-distribution system in the plant, and you had to be careful what you were replacing where. No fun sending out a 100HP motor to be re-wound for 500 volts!
 
ron said:
So maybe the plant you visited has the voltage up high for a reason?
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I can't imagine what the reason would be. The maintenance guy seemed surprised by it when I told him. My first thought was that I was mistaken but I had two meters with me and both showed the elevated voltage.

I know almost nothing about utility transformers. Would it be possible, in relation to what zog posted, that the transformer is accidentally tapped incorrectly? Or is it possible that it could have been tapped to provide the higher voltage in an attempt to lower current? If so, would that be flawed thinking?

Plant was built in early 80's and is in the Chicago suburbs FWIW.
 
I have seem some plants tap a transformer higher to account for voltage drop during loaded periods only to find that during unloaded periods the voltage rises to 500V or so.

However 500V is within 10% of the nominal 480V value and should be fine for most equipment. IEEE Standard 141 gives a maximum value of 504V for both the service and utility voltage.

Based on this I do not see a problem operating at your indicated voltage but I'd be interested to hear others thoughts and issues such as additional heating of equipment, and effeciency effects.
 
mull982 said:
I have seem some plants tap a transformer higher to account for voltage drop during loaded periods only to find that during unloaded periods the voltage rises to 500V or so.

However 500V is within 10% of the nominal 480V value and should be fine for most equipment. IEEE Standard 141 gives a maximum value of 504V for both the service and utility voltage.

Based on this I do not see a problem operating at your indicated voltage but I'd be interested to hear others thoughts and issues such as additional heating of equipment, and effeciency effects.
Click to expand...

Would have to agree. Tapping the transformer would give that voltage, and it is common to do if the starting of a large motor causes the voltage to dip or causes lights to flicker. Shouldn't be an issue at all when system is loaded. The value of transformer taps is often overlooked.
 
mull982 said:
I have seem some plants tap a transformer higher to account for voltage drop during loaded periods only to find that during unloaded periods the voltage rises to 500V or so.

However 500V is within 10% of the nominal 480V value and should be fine for most equipment. IEEE Standard 141 gives a maximum value of 504V for both the service and utility voltage.

Based on this I do not see a problem operating at your indicated voltage but I'd be interested to hear others thoughts and issues such as additional heating of equipment, and effeciency effects.
Click to expand...

I have seen the same but it came from the primary of the utility. A customer called me about his mfg.plant. He said that during the day the voltage would drop on his 208/120 system in the summer months. After some checking the only conclusion was the poco line that feed his transformers also feed several other businesses and a lot of residential customers. In the afternoon his voltage would drop but as the evening came and businesses closed down and A/C loads decreased his voltage would come back. It was not a significant drop to cause any harm but it was something that had him concerned.
 
I did a few shows in an older part of the Las Vegas convention center. Their nominal 120/208 was actually around 204v unloaded, with a show going it was more like 192-195. They had several handcarts rigged up with a pair of boost 2-3kva transformers if this was a problem.
 
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