hi
i have a transformer with 33kv/440v ,30MVA rating?
I found open circuit voltage 435,415,400v at secondary.What may be the reason for this unbalance?

 

Badri,

Please provide more details.

Regards,
[email protected]

 

Sounds to me like you either have a poor bond with the xformer. Is the ground lead pulled in the same conduit as the 3~ coming in? If so remove it temporarily and replace xformer bond(to xformer frame), then apply main(s) voltage. Check the voltage at the secondary. Doing this will bring the xformer back into "balance". If it does you will need to pull a seperate ground for the xformer, as you could have the potential to have a floating neutral.

 

Your transformer may have an ungrounded DELTA connection. The phase voltages will not be balanced due to unequal impedances from line to ground. We have installed Phaseback EMTVSS units to keep phases balanced to ground. The website is:
http://www.applied-energy.us

Or simply call Dan @ 989-790-1441

 

Responding to jaibadri's query... to start:

1) Supply voltage may be unbalanced?
2) Primary taps may be improperly set?
3) What are secondary-to-neutral voltages?

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected]) {[email protected]}

 

Hi, have you checked that the supply voltage on the primary might be unbalanced too? Unbalance is produced is mostly to monophase loads conected unevenly along the transmission line. It is very rare that transformer windings derate differently so check monophase loads and cable lenghts at both sides of the transformer, its more likely that something of the sort is wrecking regulation.

 

its a furnace transformer with 10 taps and voltage is from 250 to 400v.phase to phase voltage dont have very much variation but phase to ground,one phase has nearly 30volts difference whereas other phases have same voltage wrt ground.

 

Responding to Anonymous' Tue, Aug 3, 7:29pm comment:

The data you provided indicates that items 1) & 2) of my response can probably be ignored. However, you still haven't supplied answers to item 3) nor an answer to William Hinton's Jun, 11:04 pm query.

Because the system is large (30 MVA) the secondary distribution should be investigated:

4) Is the secondary distribution busbar or cable? Please provide dimensions as to quantity, size, and lengths used for the three phase circuits, the neutral circuit. and the ground return path, if provided!

5) What is the secondary connection... Wye? Or Delta?

6) How is it grounded... via the star-point if wye-connected? Or, if delta connected, via one secondary terminal being intentionally grounded?

7) Does the annealing furnace process involve a cooling bath?

8) Can you provide provide primary and secondary current values?

9) A Single-Line Diagram or sketch showing major parameters would be extremely helpful!

10) What is the connection between the problem you describe and the topic "Motion?"

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])