Transformer Copper Losses

Assuming you are transformer manufacture.

4000 KVA 3 phase at 415 Volts calculates to 5,565 amps.

Low voltage winding should be either strip or transposed.

Did you use strip conductor or transpose the winding?

Copper loss test also measures the loss in the shorting conductors. Were shorting conductors large and short?

If you are not the manufacture, what does the manufacture say?

I am the designer and my LV winding is layer strip . The winding is in three layers with 16 flat and 16 over conductors and transposition is in the middle of second layer only.size of lv conductor is 5.0*9.5/5.6*10.1

Not sure of your description of secondary.

Things that you could check are

Skin depth: The conductor should not be over one skin depth thick.

Skin depth in inches=2.6/square root of frequency. Have not heard of any other transformer designer using skin depth, but I have had good luck using it.

The width of the strip winding and the wire winding should be approximately the same width. I prefer using a single conductor strip winding (if practical) that is slightly longer than the wire winding.

There could be a problem with your transposing. There was a story of a winding with three conductors. When only the outside conductors were transposed there was excessive loss. When all three conductors were transposed, the loss was as expected.

Good Luck

Carl

Thinking it over, there are some other things you can do.

Check copper loss on all tap positions. You may be surprised.

You should be using a stainless steel or plastic plate where the low voltage bushings exit the tank and also between the low voltage bushings.

If possible view the oil while performing copper loss tests. Check for unusual oil activity.

Let us know what the problem is.

SS plate is used on both sides i.e LT and HT bushing side.