Control.com - Nerds in Control

Dear Sir,

We have tested a 690v (3ph)/230 (1ph) 5KVA Transformer in our company. We had tested the voltage changes in the secondary winding (230V) by removing the supply of the one phase in the primary. The result is given below...

Primary                   Secondary

****************************************

1.Removed R Phase         195V

2.Removed Y Phase         25V

3.Removed B Phase         195V

The secondary voltage is only 25V when we are removing the Y phase... what may be the reason? Any idea?

3 phase to single phase, this is not a normal Delta to Star transformer. It probably has coils
R - Y and B - Y, so when you remove the Y phase the circut is through 2 coils in series from R - B. Are there any capacitors in the circuit?

Regards,
Roy

It is common in some outlying areas to use 2 single phases with a tied common as 3 phase.

If you put a scope on the 3 signals you will see that the 2 phases are not truly 120 degrees apart from each other.

Check voltage to ground also as it is common to do this with a center tied to ground.

Responding to Ranjith’s 26-Apr-08 (23:49) query… yes, it is possible to obtain a single-phase output from a three-phase supply. Three of the transformer arrangements that could provide a 1-phase secondary from a 3-phase primary are:

o Two single-phase transformers.

o Three single-phase transformers.

o A single 3-phase transformer, D-d or Y-d

However, success with any of the arrangements listed above is very dependent on the leakage reactances of the transformer, core-construction, the ability to reverse individual coil polarity, and access to the terminal-pairs associated with individual primary and secondary coils.

If you want additional detail, please provide:

a) The primary and secondary currents for the conditions you outlined!

b) If possible, the number of leads involved!

c) The approximate size of the enclosure!

d) Confirmation that the secondary is a sine-wave?

Regards, Phil Corso (cepsicon@aol.com)

On Apr 26, 2008 11:49 pm, Ranjith wrote:
We have tested a 690v (3ph)/230 (1ph) 5KVA Transformer in our company. We had tested the voltage changes in the secondary winding (230V) by removing the supply of the one phase in the primary. The result is given below...

Primary                   Secondary

****************************************

1.Removed R Phase         195V

2.Removed Y Phase         25V

3.Removed B Phase         195V

The secondary voltage is only 25V when we are removing the Y phase... what may be the reason? Any idea?