Dear sir(s),

Please tell what shall be effects of paralleling two transformers having different vector groups from the same source. Can transformer having 180 degrees out of phase be connected? Can we assume that only circulating currents shall flow?

Please suggest.

 

Responding to Anonymous' Feb 24, 12:33am query... some, but not all, different vector group transformers can be paralleled!

The answer is simple, but implementation isn't. The usual parameters to determine circulating current are voltage-ratio, turns-ratio, impedance, polarity, pri-sec displacement angle, and sequence. So, if circulating
current causes little worry, internal changes (if required) are feasible, and external terminal-to-bus changes are feasible, then, different vector-group transformers can be paralleled!

The second part is not clear... Do you mean pri-sec displacement is 180°

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

 

Transformers are in parallel operation if they are connected in parallel on at least two sides. A distinction is made between busbar interconnection and network interconnection. The following conditions must be satisfidied in order to avoid dangerous transient currents:

1. vector group should have the same phase angle number; terminals of the same designation must be connected together on HV and LV sides; Exception: Phase angle numbers 5 and 11 (There is a table for these two connections, if you want e=it ask me)

2. the ratios should be as similar as possible

3. approximately the same impedance voltages uk. Maximium permissible discrepancies +-10%. In event of larger differences, an inductance (reactor) can be connected ahead of the transformer with lower impedance voltage.

4. rated output ratio smaller than 3:1.

For any further information
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