Transformer step-up to step-down setup 3

[joviancw]

I have a transformer setup that has a 3000 kVA 480V Delta to 4160/2400V Wye step-up dry-type transformer hooked up to a 4160V Delta to 480V Wye step down oil type transformer. I believe this configurations is fine but I am getting feedback from the manufacturer that the setup of the step-up transformer should be switched (480V Wye to 4160/2400V Delta instead of a 480V Delta to 4160/2400V Wye). I am fairly sure it doesn't matter but is there a reason why they might suggest the Wye Delta configuration?

Thanks for any insight and help!

 

[oldfieldguy]

Assuming that your 480-volt system feeding the step-up transformer is already grounded, you don't need a grounded LV winding at that point. Providing a grounded HV winding establishes ground reference for voltges on the HV side and assures that in the event of a single ground fault on the HV system, there will be fault-level current drawn from the LV input, for protection. Grounding the other LV winding establish ground reference for the LV equipment fed at that end of your system.

old field guy

 

[joviancw]

Oldfieldguy,

Thanks for the feedback.

Are you saying that the wye-delta configuration is the better way for the step-up? I had thought that the single ground fault detection was better for a wye on the secondary side of the step up.

 

[oldfieldguy]

Delta 480, wye 2400 on the step-up, delta 2400, wye 480 on the step-down, IF the 480 system you're feeding the step-up transformer is already grounded.

old field guy

 

[joviancw]

It is grounded.

Thanks again!

 

[FreddyNurk]

In terms of just stepping the voltage up from one level to another, it doesn't really matter.

In terms of providing an appropriate protection arrangement for the overall system, its very important. oldfieldguy has an accurate summary of being able to detect ground faults on the relevant sections of the network. There is a general expectation, as most people are familiar with step down arrangements, that the delta is always on the high side, as this is what is most commonly found. High side delta is a lot more common as a result, but it doesn't necessarily mean its correct for your application.

 

[LionelHutz]

480V wye source - delta primary - wye secondary - delta primary - wye secondary with the neutral of the wye windings grounded would make sense. Assuming this is a islanded system, nothing else really makes much sense.

 

[iceworm]

I am fairly sure it doesn't matter but is there a reason why they might suggest the Wye Delta configuration?

Yes there is a reason. I've run into it several times. 4160D/480Y is a lot more common and that is what the mfg has on the shelf. Every one I have seen put in, the way the MFG suggested, is because that is all that was available in the required time.

Shame on the mfg for not telling you why.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[waross]

I have seen a lot of wye:delta transformer banks in operation. I have also seen a lot of problems including transformer burn out and equipment damage that were unique to a wye:delta connection. If you avoid a wye:delta you avoid a lot of potential problems.
But most transformers used in industry are step down. Delta:wye works fine.
These will work for step up, but you open the door to the potential issues.
An option may be to use a bank of single phase transformers in delta:wye.

Bill
--------------------
"Why not the best?"
Jimmy Carter