Arc-Transformer Unbalance

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Thread Starter

paru

We have a transformer for electric arc furnace 45MVA, 30Kv/1000v. The secondary is connected to the heating electrodes through bus bar, which is water cooled. And this bus bar is supported on some insulators for all three phases.

My problem is that when one day I checked open ckt voltage at secondary, it was 600/900/1000v with phase to phase in three phases.

What may be the reasons for this voltage imbalance?
 
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Phil Corso, PE

Responding to Paru's 07-Jun-08 (00:26)... here are a few questions to start:

1) Did you confirm unbalanced readings by means of a second volt-meter?

2)While taking the ph-to-ph measurements did you observe current in the 30kV primary?

3) Had a recent ratio-test be carried out?

4) Have fixed primary taps been checked?

5) Has movable primary tap drive been checked checked?

Regards, Phil Corso ([email protected])
 
Phil Corso wrote:
>1) Did you confirm unbalanced readings
>by means of a second volt-meter?

Answer: We checked it with multimeter in both phase to phase and phase to ground with same result.

Phil Corso wrote:
>2)While taking the ph-to-ph
>measurements did you observe current in
>the 30kV primary?

Answer: no we have not seen that so far.

Phil Corso wrote:
>3) Had a recent ratio-test be carried
>out?

Answer: no

Phil Corso wrote:
>4) Have fixed primary taps been
>checked?

Answer: problem is same on all taps.

Phil Corso wrote:
>5) Has movable primary tap drive been
>checked checked?

Answer: maintenace of tap changer is done after every 6 months.
 
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Phil Corso, PE

Pare, see my reply to Paru. However, in your case I suspect a change of phase-to-earth capacitance in the busbar coolant system!

Regards, Phil C.
 
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Phil Corso, PE

Paru... there is a simple test that can be carried out to determine where the insulation weakness is in the 1000V system. If you are interested contact me!

Regards,
Phil C.
 
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