Pump Department Manager

Welcome to CR4.

Yes... but I would not. Why... the 480V primary of the transformer is more than likely a delta winding and as such there would be no way to ground the pump other than using a zig zag transformer (or courner grounding it - which can be problematic) to "create" a neutral point to ground the 480V side.

Which means if you do not add the zig zag you would need to add special ground indication equipment that would drive up the cost where it may be cheaper getting a proper 240V primary (delta) to 480V secondary (wye) so you can ground it properly.

Thanks North of 60. Do you have any idea where i can get such an animal.

Most suppliers are quoting me the reverse of what you say I need.

I appreciate the help and expertise.

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The problem with listening to what suppliers tell you is that... they often times tell you that you need just what they happen to have on their shelves.

Why bother with the transformer at all? What keeps you from supplying 480 directly?

If the transformer is being dedicated to just running one motor then you may be able to cheat a bit on the install by not having any current protection on the secondary and only having it on the primary by setting it up in an autotransformer configuration where each phase has a physical connection between the primary and the secondary.

"I know nothing about transformers", or motors or electricity!

Do you really need a transformer at all?

Virtually all of the 460/480V motors I've worked on in the 1-30hp range have two sets of windings, which can be connected in series for 480V or in parallel for 240V. Both wiring schemes are normally shown on the nameplate of the motor.

The attached happens to be from a half hp motor, but the wiring is identical for a 10 hp motor.

It's not very clear, so here's an enlargement of the connections:

Apart from the answers already supplied, there are other considerations involved:-

1. The secondary will be a lower impedance winding than the primary, and inrush magnetising current when using it as a primary winding will be much greater and could cause overcurrent problems. For example, a transformer designed for step down operation that draws 100 primary amps full load will draw close to 10 times that when first energised. Connect it as step up and the inrush current can be in the multiple thousands of amps and easily exceed the secondary (now primary) maximum by a magnitude of 30 or more. You can expect to let the smoke out.

2. Transformers are generally produced with compensated windings to allow for voltage drop when under full load, reversing the windings will cause this compensation to also be reversed and thus the voltage drop will be doubled rather than removed.

3. Many smaller transformers have an over-temperature disconnect embedded in the primary winding, this will be ineffective in disconnecting the supply if the primary is now used as the secondary.

4. Transformers are generally designed to operate at close to core saturation in order to save metal and produce high efficiency. Reversing the windings can result in over magnetisation, a resultant deformation of the output wave shape and accelerated heating of the core.

If you decide to try this, don't connect the (now primary) star point to any earthing conductor or to the transformer frame. For the (now secondary) delta winding, do as has been advised or, provided you have only one item connected to the device, treat it as an isolated supply.

Theoretically yes but in practical application it's rarely a problem. Especially so on sub 100's of KVA transformers such as he would be using.

To run a 10 HP submersible pump a fully isolated 10 KVA transformer would be more than enough. Using a auto transformer configured one 5 KVA would still be more than sufficient.

As for experience I have worked at places that had portable 20 - 30 KVA units that were nothing more than common 460:230 step down units wired in reverse for powering 480 VAC devices we had to repair.

Who said it was submersible?

Not that it maters greatly, except if the motor gets fried.

Nobody. I just tossed it in there to see if anyone actually ever reads my posts. So many threads have other posts that tend to give me a very strong suspicion that very few people actually read anything I or anyone else ever posts.

So true! I have the impression that only a _small minority of original posters ever come back to tell us whether the problem was solved or not.

Upon a visit to my companies new facility, before the slab was poured, I noticed only one 4' conduit run. I contacted the electrical contractor and asked how he proposed to provide the 400 amp 480v power as stipulated. He explained "With a transformer, from 208 to 480." I remarked that we did not have the floor space it would require and that merely energising the transformer would drop the whole building. A call to a ComEd engineer confirmed this. The correct system required a larger primary underground feed (distance 350 yards), to a dedicated pad mounted transformer and a dedicated conduit run to a disconnect dedicated to the pump test panel. Luckily we had caught this before the slab was poured. These comments give illustration to the fact that, in my experience with product support (Submersible pumps) the number of repair facilities with sufficient power, through out the U.S. is limited.

You should never let the brakeman drive the train.

Unless it is company policy.

Tell that to the engineer who is descending a 6% grade with a big load; the brakeman can make the engineer cry for his mama without much drama.

In reality, the brakeman is obsolete. Air brakes have rendered them an unnecessary expense.

OK, I get the idea. Thank you all for your posts. I am just going to change out the

motor and controls to save myself and my client a lot of problems in the future.

By the way, it is a submersible motor.

Tim