We have wired a 3phase 480v Delta to 240 4w delta transformer backfed to up the voltage to 480v from a 3ph 208v highleg panel with nothing connected to X4.

When we turned on the 3 pole beaker it tripped. There are no shorts on the conductors and the transformer ohm reading were consistent

Any ideas what the problem can be?

 

Sparky312...

Providing a sketch would be helpful!

Regards, Phil Corso

 

Please mention, what is the trigger of 3-PH breaker trip...??

What type of electrical relay operated..?

If it is a numerical relay , which triggered the tripping...??

Short CKT / UV / reverse power / Residual voltage.

I think your 280V side short circuit current setting need to be re-evaluated.

Make it at least 7 times of full load current with 50 milli sec delay.

 

Sparky:

If I have interpreted your dilemma correctly, you are trying to feed a 480V, 3-ph, delta-connected load from a 240V, mid-phase-grounded (Hi-Leg) power supply!

The interposing Xfmr is Delta-Delta, wired as hi-leg, but the X4 terminal (presumably used as the mid-phase ground connection) has been isolated! I suggest a simple resistance check to confirm that fact!

Secondly... Barindra raises a very good point. Are you sure the breaker powering the interposing xfmr can handle its inrush-current?

Phil Corso