One depends on the actual design of the transformer, but the other does not. All transformers are rated at full load. So a transformer designed for volts in and volts out will read a higher output voltage when lightly loaded. This is related to the losses that chuckey mentioned. If you connect the transformer backwards, the "loss budget" is working in reverse, so you would have to put more than volts in to get volts out. The other problem concerns "full" load rating.
If a transformer is wound with the primary on the inside and the secondary on the outside, all flux generated by the primary cuts wires in the secondary through one path or another. If you reverse the connections, some of the flux lines on your new primary propagate out into space, coupling no energy to the new secondary.
Thus you have to derate the transformer by some percent; exact value determined by experiment. The short answer is yes, it will work in the general case. Just make sure your transformer is rated significantly higher than the actual anticipated load. Is the motor demanding 3x start current and grinding up over a second period every 30 seconds?
Are you using across-the-line starting? One way to find out, is to hook it up, shoot it, and the motor case, with an IR thermometer, and start it up, let it run under average load, and log temperature rise It might result to a shift in phase which is critical in parallel operation.
If it is a standalone transformer, I see no problem except for the tap changer operation and grounding. If the transformer has a neutral ground at the secondary and a delta connection at the primary, reversing the transformer connection will result to grounding of the transformer at the primary.
This will result to ungrounded secondary which might be an issue to your system. The conclusion is to check first its application prior to its connection. Typical step down transformers have vector group of Dy1 or Dy If you use it as step-up transformer in parallel operation with other step-up transformers with typical vector group of Yd1 or Yd11, then you are paralleling a Dy1 or Dy11 to either Yd1 or Yd11 transformer.
If it belongs to the same vector group like Dy1 and Yd1 , then you'll have no problem. But if you parallel a Dy1 to a Yd11, then you'll have a phase difference resulting to circulating current.
So you should check first the vector group of the step-down transformer that is intended for step-up application if to be operated in parallel with the existing step-up transformers. Could you explain the difference related the leakage flux of the primary winding through the core limb compaired with the step up transformer? The step up transformer is exciting and the step down transformer is no exciting.
The former increased the no-load losses, noise level, temperature mainly when the the impedance is too much big. It's an odd application. I have never heard of someone reversing a large 3MVA 11kv distribution transformer.
Is this related to a solar grid tie application? Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Use step down transformer as step up transformers Ask Question. Asked 4 years, 11 months ago.
Active 3 years, 6 months ago. Viewed 13k times. Pallab Pallab 21 1 1 gold badge 1 1 silver badge 2 2 bronze badges. Either terminal can be N or L Just like isolation transformers.
I've no idea about 3-phase transformers but I think the same thing applies for them as well. Add a comment.
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