1000va transformer

[jerkynumber7]

Hello, I'm having some issues with an Acme Electric transformer. It seemed to be bad in an existing piece of HVAC equipment, after replacement it still had the same issue on the secondary. The feed is good, seemingly. The power for the transformer is a 2 pole 480 volt from a 3 phase 480 volt delta circuit for the unit and the secondary should be a 2 pole 240 volt. However, upon measuring the secondary it reads 150 volt leg to ground and 85 volt leg to ground. Phase to phase is 240. Is this a grounding/neutral issue? There is no center point terminal for neutral on the secondary. From the initial contractor install, years ago, it has worked fine. Could it be something back feeding from down stream? There have been some recent installments of power analyzers and conditioning equipment in the building, which coincidentally, were done right before this interruption occurred. That may be of no concern though. Thanks for any help on this.

 

[charlie b]

If there is no grounded neutral on the secondary, the voltage from either leg to ground is a random number that has no meaning. Is the equipment working properly? What went wrong that caused you to be called in to investigate?

 

[winnie]

As described, the transformer secondary is ungrounded. Phase to ground measurements are thus meaningless, and depend on leakage current and meter impedance.

If you measure with a low impedance meter such as a 'wiggy', you will probably get 0V to ground on both terminals.

Unless there is a problem you are trying to diagnose, the values you measured don't themselves indicate a problem

 

[Jpflex]

There is no center point terminal for neutral on the secondary.

If you need 120 volts and the transformer secondary is a 2 wire tap 240 volts phase to phase, has no center neutral secondary tap, then it seems this transformer is wrong or not meant for your application. How it worked before I do not know unless the input primary taps were tapped for higher voltage input than actual utility voltage

There is also a possibility of unbalance on the 3 phase lines causing voltage differences?

 

[jerkynumber7]

Thank you all for your responses. At the moment, no, the equipment is said to not be working properly and was before on the same transformer. That's why I was called to look at it. I'm not sure if they are needing 120 volt all the sudden where they didn't before, components get added all the time so it's possible, if so then I would need to get a different transformer. I will dig deeper and see what I come up with, thanks very much for all of your help.

 

[infinity]

Do you have a part number for the transformer. The secondary doesn't have 4 leads, X1-X4? That would be typcial for a small transformer. You would splice X2 and X3 together and ground that junction point to the transformer case.

 

[ptonsparky]

Voltage Leg to Earth (Ground) means nothing if the system is not grounded. Bond as suggested.

 

[jerkynumber7]

Yes, the secondary has four terminals and and the 2,3 are joined but I don't have it to case though.

 

[infinity]

Yes, the secondary has four terminals and and the 2,3 are joined but I don't have it to case though.

It should be bonded to the case. Since it's 1000 VA it will not require a GEC to an electrode. Once bonded your voltages to ground will be 120 and 120 on each leg.

 

[ptonsparky]

Bonding it may not fix anything, unless you have 120V controls utilized from each leg of the secondary.
Do you need 240v secondary from the transformer?
If your controls are only 120v, rewire the transformer to 120v secondary only.

 

[infinity]

Bonding it may not fix anything, unless you have 120V controls utilized from each leg of the secondary.
Do you need 240v secondary from the transformer?
If your controls are only 120v, rewire the transformer to 120v secondary only.

I believe that the OP stated that the original transformer had a 240 volt output which is what he needs he does not need 120 volts. The issue is that the 240 volt transformer secondary is not grounded.

 

[ptonsparky]

I believe that the OP stated that the original transformer had a 240 volt output which is what he needs he does not need 120 volts. The issue is that the 240 volt transformer secondary is not grounded.

I agree.
His voltage readings are because the transformer secondary is not grounded. Grounding may not solve his problem, other than blowing a fuse and making troubleshooting a bit more convenient by process of elimination.

 

[jerkynumber7]

Thank you everyone for your responses. As it turns out the problem was something they had hooked up in the room. The original transformer works again after we took everything new out of the room. The room is running fine and has dropped temp from 70 to -20 degrees in less than two hours, it must have been one of the components I mentioned before that they had just added recently. I did learn a few things from this page though, thanks for that.

 

[ptonsparky]

Thank you everyone for your responses. As it turns out the problem was something they had hooked up in the room. The original transformer works again after we took everything new out of the room. The room is running fine and has dropped temp from 70 to -20 degrees in less than two hours, it must have been one of the components I mentioned before that they had just added recently. I did learn a few things from this page though, thanks for that.

Thank you for returning.
It is frustrating for us, at least me, sometimes when we have no feedback.

 

[jerkynumber7]

Yes sir, I could understand that.