Transformer

Yes And no reason (if it was not to be I could have given a reason but for Yes what is the reason ? Except the two sides voltage ratings should be equal. eg 220/12 V transformer can be used to step up 220 V from 12 V or step down from 220V to 12 V , provided the load KVA in both cases are maintained with respect to transformer KVA rating. However obviously you can not use ti to step up from 220 V to 4 KV (220*220/12) - the insulation will fail. For 12 to 0.65V, (12*12/220), the magnetising flux may be too weak. As far it is 220/12V and corresponding voltages are on pri and secondary, which side is load and which is source doesn't matter. But you can not go too far away from ratings in either directions and finally take care of VA or KVA ratings (as the case may be)

I don't agree.

If you have an ideal transformer you could use it to increase and to lower the voltage.

But in real, transformers have looses, the heat produced by the copper wires will always in you disadvantage.

So when designing a transformer, they output voltage is chosen higher to compensate the voltage losses (ie the internal impedance)

If you interchange your transformer you will need a bigger input voltage to compensate these voltage loss on the original output stage.

A transformer designed for feeding with 400 volt and giving out 230 volt. If you interchange this transformer and feed it with 230V you will only get out 370 volt at the 400volt connections.

Theoretically and in reality, this can be done. We have tried this setup in our sister utility company and it works.

The thing to watch out for when applying this scheme is to properly size the surge arresters so when there is reverse power flow, the arresters will not fail.

How did you size your arresters on the 11 kV side? Did you based it on the 11kV line configuration? Or did you based it on the primary delta configuration of the Dyn11 transformer? How did you connect it? Wye or delta?

In our case, our 69 kV line supplying power through the Dyn1 69kV/13.8kV power transformer is using 4-wire wye configuration. Normally, we use 3 units, 60 kV, 48kV MCOV arresters and connected it wye on the delta side of the power transformer and 3 units 12 kV 10.2 kV MCOV connected in wye on the 13.8 kV side.

Now, if we install the above transformer with the power flow from 13.8kV to 69kV step-up, the 60 kV arresters connected in wye will now be subjected to line-to-line voltage surges through the delta. The arresters will most likely fail since originally they were sized based on the line to ground configuration and not line-to-line.

[Our colleagues in our sister utility company, experimented on this and each time the power transformer (Dyn1) was energize at the wye side, the 60 kV arresters at the delta side all failed.]

In this case, the more appropriate size would now be 90 or a 96 rated kV arrester and connected in delta.

To complicate matters, let's say our Dyn1 transformer will be used to step up and step down power at anytime depending on the power flow direction. In this case we have 2 options:

1. On the delta side, we will install 3 units 90 or 96 kV connected in delta and inside this delta, we will also connect 3 units of 60 kV arresters arrange in wye configuration. In this arrangement, we will be assured that whichever direction is the power flowing our arresters will be able to perform effectively without failing.

2. On the delta side, we will use the 3 units 60 kV arresters and connect them in wye. Additionally, between the star point of the wye arrangement and the ground connection, we will install another surge arrester rated accordingly. This 4th arrester will be the one to dissipate the added voltage surge when there is a reverse power flow.

For option 2, you may use the ABB guide in sizing the 4th arrester. Or you may refer to the IEEE surge arrester standard.

Hope you find this useful.

I do this routinely, although I use 3-winding units with a grounded zigzag tertiary. At one of our power stations, several of the generators connect directly to 13.8KV distribution buses. When the generators are not in service, the 69Δ/13.8x7.97Y KV transformer steps down to supply the load on the distribution bus. When the generator is on-line, the transformer steps up to send excess power to the transmission system. The losses in either direction are marginally greater than a transformer designed for single use, but that cost is greatly outweighed by the capital outlay for 2 separate units (1 generator step-up and 1 distribution step-down).

The grounded ZZ winding creates an artificial ground to allow the delta-connected high voltage side see phase to ground faults on the distribution side.

FOR DIFFERENT VOLTAGE GENERATION POWER STATION INTER COONECTING TRANSFOMER BETWWEN TWO SWITHC YARD IS USED FOR EITHER SIDE TO WORK AS PRIMARY AND SECONDARY.

WHILE PRCURING NEW POWER TRANSFORMER IT NEEDS TO BE SPECIIFED FOR TAKING CARE OF DESIGN

nascon