Transformer Tap ????

[adavey]

Do tranformers have multi-taps for variable voltages on the primary side (voltage drop calculated @ approx 30 volts) ???????

The plan is to step down 277/480 - 120/208 3phase utilizing existing wire.

 

[jim dungar]

Most three phase transformer above 15kVA have taps for accomodating voltage drop on the transformer primary supply. The actual number and % change dependeds on the specific transformer. But in general you can adjust for a 5% VD on small transformers and up to 10% on 75kVA and larger units.

 

[adavey]

Thanks Jim. I was looking @ the cutler hammer catalog, but didn't see reference for this. Maybe, I should try another product ??????

 

[bdarnell]

If you are looking at Eaton (Cutler Hammer) this link will probably help:

http://www.eatonelectrical.com/unsecure/cms1/TB00900001E.PDF

It's a big PDF, so I'd download it rather than try to open it from a browser unless you have a super fast connection.

 

[jtester]

Do tranformers have multi-taps for variable voltages on the primary side (voltage drop calculated @ approx 30 volts) ???????

Be careful how you use the taps. If you are planning to compensate for voltage drop as the transformer load increases, taps usually don't work. The problem is that at no load, you have boosted the voltage to high to be acceptable.

Taps work for a steady state low voltage, but not varying one.

Jim T

 

[templdl]

Standard full capacity taps are usually +(2) 2-1/2% abive normal and (4) 2-1/2% bellow normal. +5%, +2-1/2%, 0, -2-1/2%, -5%, -7-1/2%, -10%. Again, these are standard taps but manufacturers often offer a different combination of these taps.
When a transformer is installed the primary voltage available is often lower the the transformer pri. NP voltage. So "bellow" normal taps are provided to match the supply voltage so the the secondary voltage will be correct. If the transformer primary is 480v, a 2-1/2%FCBN tap will correct fort supply voltages 2-1/2% below 480v, etc.
It's not to often that a primary voltage is on the high side.

 

[adavey]

Jester ,

The load should NOT vary very much. This is a temporary (if you call 2 years temporary) install for 4-5 trailers for contractors during construction (AC and Elec. heat are the largest loads). ------- AD