Trifasic transformers

[olivierm34]

Hi!
I am having an earth leakage in my circuit and I am trying to find where it comes from.

One of the equipment installed is a trifasic transformer (Primary 380V, Secondary 380V, dy1). I begin to make some basic continuity test in order to found some insulation issues.

During that, with the transformer not energized, I discovered that, in the secondary:
- fase X and neutral make continuity
- fase X and fase Y make continuty (X / Y = 1 , 2 or 3)

In the primary, there is the same behaviour (without the neutral obviously)

Is it normal? Somebody can give an explanation?

Regards!

 

[rcwilson]

You have a three-phase transformer, with a delta primary at 380V, 50 Hz and a wye connected secondary at 220V /380V withthe nuetral point of the "Y" secondary grounded to earth.

Your ohmeter reads the DC resistance of the windings, not hte AC impedance of an operating winding.

On the secondary, the three windings are all connected together at the neutral. The ohmeter will read a low resistance between all the windings and the neutral because they are tied togehter.

On the primary, the three windings are connected in a delta (triangle). Each phase winding is connected to one of the other two phase windings at the each end. The ohmeter reads through the transformer windings.

The winding resistance is quite low. You proably can't read it on your meter.

When energized