Auxiliary Power Transformer

[VSilveira]

Are there any special reccomendations to use wye conection instead of delta conection to primary winding of an auxiliary power transformer direct conected to a busbar voltage hidrogenerator ? What happens if I use delta conection ?

 

[bartos]

The delta connection will trap triplen harmonics and isolate the zero sequence current. This may be preferred.

 

[jwerthman]

The delta primary connection is preferred for the reason stated by bartos. However, this is not always possible if the transformer must phase out with another startup or reserve transformer connected to another source. You must determine the necessary phase shift for the auxiliary transformer in order to confirm which connection to use. If a wye primary - wye secondary connection is required for phasing, the primary neutral usually should be ungrounded to provide primary to secondary zero sequence isolation. Depending on the transformer design and the secondary grounding, the wye-wye arrangement may also require a delta-connected tertiary winding for neutral stabilization.

 

[dpc]

Just to add to the issue of phase shift: For a delta-wye transformer, you can get the 30 degree phase shift in either direction. ANSI standard is for low to lag the high, but transformer can be connected such that low leads the high.

This is a common occurrence for standby transformers at power plant that have a station service transformer connected to the generator leads. If both are delta-wye, one of these has to have phase shift reversed.

I'd go with delta-wye if you can work it out.

dpc