Hello.
I bought today a transformer which was used in an UPS. I do not know the power of this transformer, all I know is that is has 2 high current windings of 15.5V, 2 low current of 27V, and 3 windings for 230V connections marked with 0V, 196V, 225V, 252V. The person said that the transformer was taken from a new UPS which had a problem at the PCB.
The problem is that the person from which I bought the transformer has inverted the label on the primary side of the transformer and the 0V standed for 27V and I connected the 230Vac mains to 27V and 0V. After this, I plugged the power cord and nothing happened, but after this I plugged the cord the second time and some smoke comed up from the transformer and I saw some sparks.
A few hours later, I managed to find the problem and I powered correctly the transformer. Now the transformer works good, but I checked with load only the primary and de 15.5V secondary. The 27V secondaries were only measured and they are approximately 27Vac each.

Are there any problems that can appear, for example after this error could the isolation between the primary and secondary to be affected ?

I am very sorry and I feel very bad for happening this things but I did not knew that the label was inverted.

 

... interesting.
Are you able to correctly designate the wire pairs on the secondary and primary side ... Try to draw a diagram ... especially of the wire pairs that are possibly damaged. Using your best guess, test the continuity of the wire pairs ... post the diagram here. ... in order to understand what is going on.

 

I uploaded the diagram. The affected pair is one of the 27V secondaries. I do not know which of 27V secondaries.
I measured both of the 27V secondaries and they are having about 27Vac. But I do not know which primary socket I used when I measured the 27V secondary.
On the diagram, I am not sure if there are 2 secondaries in series or if there is only one secondary with median socket. Also, on the diagram I forgot to draw the iron core.

 

Are you able to measure resistance values of the 27-0-27 coil? If there is no damage from the previously mentioned overvoltage, then you should measure two relatively equal resistance values for each 0-27 coil connection .... Be sure the AC power is disconnected when measuring resistances.

 

1. I measured 1.2 ohms resistance on each 27V secondary. So 1.2 ohms on one 27V secondary and 1.2 ohms on the other 27V secondary.

2. If there are any problems regarding the 27V secondaries, could those problems affect the primary or the 15.5V secondary ?

 

The only method of confidently testing transformer performance is to apply the rated voltage and amperage to the primary side and measure the voltage and amperage on the secondary side using an appropriate load. The product of volts * amps on the primary side must equal the product of volts*amps on the secondary side.
Transformers are typically rated in terms of VA ... Volt Amps, rather than watts.

If the transformer VA rating is not known, then at least check to see that for an input test current and voltage on the primary side, an equivalent V*A product is available on one or both of the secondary circuits, each measured individually, not at the same time.