generator voltages

[jcole]

Hello guys and gals.

We recently had standby generator installed for one of our pumping stations. It is a 480/277Y system. I noticed today that the phase to neutral voltages were:

l1 to n- 300
l2 to n- 380
l3 to n- 380

I assume that it has been like this since it was installed. Its not really that big of a deal because we dont have any 277 loads. I was just curious of why and how to correct just in case we add 277 loads.

Thanks for all replies.

 

[dkarst]

Hello guys and gals.

We recently had standby generator installed for one of our pumping stations. It is a 480/277Y system. I noticed today that the phase to neutral voltages were:

l1 to n- 300
l2 to n- 380
l3 to n- 380

I assume that it has been like this since it was installed. Its not really that big of a deal because we dont have any 277 loads. I was just curious of why and how to correct just in case we add 277 loads.

Thanks for all replies.

If your line to neutral voltages are that high, the line-line voltages will be high. Do you have 480 loads connected and what is the line-line voltage with load?
Typically, the field excitation is used to vary voltage but more details would be needed.

 

[Pierre C Belarge]

What is the voltage reading of the normal power from the utility?

If the voltage is too high, it can be corrected by the generator people. It should not be too difficult to change.

 

[nakulak]

whoever did the startup on the genset should have checked the generator output. did you do an acceptance test or commissioning test for it ? Hopefully its under warranty, as Pierre indicated.

 

[steve66]

Any chance you one of the meter probes was on an open or ungrounded connection? Or could the meter have an open fuse?

I'm thinking you might be reading a ghost voltage. Those readings seem too far away from normal to keep the smoke in the wires.

(Unless maybe you are not testing it under load?)

Steve

 

[don_resqcapt19]

What is the line to line voltage from the generator? How many poles in the transfer switch?

 

[jim dungar]

Need all the voltage readings
Generator
L1-L2
L2-L3
L3-L1
L1-N
L2-N
L3-N
L1-G
L2-G
L3-G
N-G

Are these measurements taken at the generator terminations with the transfer switch open? It is possible that the neutral-ground bonding is not present except when the transfer switch is in the 'generator position'.

 

[jcole]

Sorry it took so long to get back.

The line to line voltages are reading 480v from generator. I dont think its the meters because they read correctly when utility power is measured.

This meter is before the main on an mcc. The ats is before the meter.

It seems the neutral bus on mcc and neutral from gen are not terminated together correctly. Or they would be at same potential. Correct?

I havent really had time to look in to it yet. Just looking for ideas for when I do.

 

[jcole]

The meter is part of the metering section of the mcc. Not a multimeter that I am using.

I am not sure if the ats switches the neutral or not.

Ill get back with you when I know more about the system.

Thanks for the replies.

 

[zbang]

Really depends on where the neutral you're measuring is. If it's -really- the generators, then something is weird 'cause you can't get 380 L-N if the L-L is 480. OTOH, if the generator's neutral is not bonded at all, and you're not measuring to it, the readings could be all over the place. Sounds like it genny is installed as an ungrounded system.

 

[Pierre C Belarge]

Really depends on where the neutral you're measuring is. If it's -really- the generators, then something is weird 'cause you can't get 380 L-N if the L-L is 480. OTOH, if the generator's neutral is not bonded at all, and you're not measuring to it, the readings could be all over the place. Sounds like it genny is installed as an ungrounded system.

I am not as surprised today, as I used to be in the past. There are too many who do not check the neutral setup of the generator. And there are those who do not know what to do with it anyway.
Based on the OP's posts, this is the first item I would check. Also, knowing how many poles the transfer switch has is important.

 

[jcole]

Its a 3pole ats. Does not switch neutral.

 

[don_resqcapt19]

Its a 3pole ats. Does not switch neutral.

Then the neutral of the generator is not bonded to ground. When you are running on generator power you are on an ungrounded system.

 

[jcole]

Then the neutral of the generator is not bonded to ground. When you are running on generator power you are on an ungrounded system.

So what you saying is the neutral is not connected to earth or are you saying that there is no system bonding jumper connecting the egc to neutral?

 

[zbang]

Sounds as if the generator's neutral lead is not connected to anything, but since it's a 3-pole transfer switch, it should be connected to the "system" neutral (ref previous topics on generator grounding).

 

[don_resqcapt19]

So what you saying is the neutral is not connected to earth or are you saying that there is no system bonding jumper connecting the egc to neutral?

The neutral is not connected to earth and there is no neutral connection to the EGC. It is an ungrounded system.