What Happened to My Transformers?

What's the voltage across the damaged transformer, Guv? <cough>

it should be 380V!

What is connected to the secondaries ? and how ?

The 2 phase transformer is without neutral ?

Please note that the 2 phase output (of the inputs at 90 deg) and 1 phase output- will have phase shift.

in the secondaries i have electric bulbs at 24 v

the primary coil of the 2 phase transformer is powered by 2 different phases of 220V each one, deg at 120. so between them i have 380 V, the power supply for this type of transformer. at output, at secondary coil have only 24 V what powers a number of 3 electric bulb. so, the two phase transformer is without neutral.

As CJ said and as i meant in the prev post- do not interconnect the secondaries of the two transformers, since it will cause a high secondary recirculation between them and that will kill the weaker one.

If the secondaries are isolated, then it is defective transformer.

the secondaries were not interconnected between them. thank you for the answer!

It doesn't sound as though you did anything wrong (assuming you have a 380Y220 supply), so most likely it was just a defective transformer. It happens...

the 2 phase transformer was verified before use. thank you for your answer!

If the transformer primaries were as stated, then they were connected correctly since it appears you have a 380/220 Wye system. You don't say where you are at, but I can assume also you have a 50 Hz system. Keep n mind the output 24 v of the two transformers can not be interconnected.

Assuming the transformers were in good condition, and ok for 50 Hz operation, we need to know what connections were made on the secondary side of each transformer. Were the secondaries interconnected? Are these auto transformers? Did you earth any of the secondary lines?

This information will help very much with your question. CJM

It is proper to call the transformer that you are calling a "2 phase transformer", a single phase one. Both of these transformers are single phase units.

N. of LX,

In IEC world, they call 2 wires of a 3 phase system "2-phase". They apparently never heard of the kind of true 2-phase we have (had) in North America where the phases are 90 deg. out.

Took me a while to figure that out.

jraef; where do they use this 90 degree 2 phase you talk about? perry

Really... interesting. Thanks for the heads up.

Can anyone else from the IEC sphere of influence comment? Why would you refer to this as a "2 phase" transformer.

true! i live in Europe.

this transformer is powered at 380 V. i live in Romania (east-Europe) and here from 2 different phases i have 380 V. the secondaries were not interconnected. thank you for your answer!

The 2 phase transformer got overloaded. The cause is that the load was unbalanced. If you analyze the 3 phase wave form diagram and the way you conected the transformers it can be seen that at a particular time, the current flows from L2 to L1 and also from N to L1. this overloads the 2 phase transformer because its winding has to carry an excess current given by N-L1. Te solution would have been to connect the 1 phase transformer between L3 and N.

it's possible! i thought to that myself but i did not find in any book for electric engineering something to use as an explanation. thank you for your answer!

Simple, BLOWN UP SIR!

Another minor error noticed. The phase-phase rated voltage in Romania is 400V, and phase-ground is 230V. I live there too. It should also be taken into consideration.