delta / star connection of the transformer

[mazona]

hello...

 

why do we always connect the tranformer as follows:

 

incoming feeder ---------------delta / star --------------outgoing

transformer

[RalphChristie]

It is not necessarily connected delta/star. You can use different connections, but each has some advantages and disadvantages. However, on distribution transformers, the most common connection is delta/star.

 

See:

http://www.beckwithelectric.com/powerlines...erlines-37.html

for the pros and cons of the different transformer connections.

 

Also, regulation state that every electrical system rated at greater than 50V shall be connected to ground, how that earth connection is to be made differs between HV and LV systems. LV systems (LV is between 50V and 1000V) must be solidly earthed. It is the easiest to earth a star LV-side.

 

Normally bigger transformers (66kV and higher) are star/delta. The reason for this is cost. The higher the voltage, the more insulation you have to use. (more insulation is higher costs) If you use a star primary, you can degrade the insulation towards the neutral-point, thus using less insulation.

 

Hope it answers your question.

 

Regards

Ralph