transformer voltage ratio

[cmelguet]

Hi,

There is any guideline from ieee or from your experience to set the maximum voltage ratio for a distribution transformer? I need to decide if install a 33 kV / 0.4 kV 2 MVA transformer or run a 4.16 kv cable from a 500 m away substation, and install a 4.16 kV / 0.4 kV 2 mva transformer.

Please advice,

Regards

 

[GuntherA]

33kV to 433/415V is pretty standard for a distribution transformer in Australia. The 33k/433 will likely also be cheaper, smaller and more efficient than the 4.16k/433 as the HV current is a lot lower on the 33kV.
No experience with the cost of cabling for the 500m at the different voltages though so you would have to factor that into your decision making.

 

[PHovnanian]

What are your company/utility plans for the 4.16 kV system? Are you keeping both voltages for the foreseeable future? Or do you have plans to retire the 4.16 kV system?

The definition of 'foreseeable future' would be the present value of the 4.16 kV installation plus the present value of the future event to replace it. If that event is far enough out, its PV approaches zero.

 

[ScottyUK]

A 33kV breaker is significantly more expensive than it's 4160V counterparts and the protection is likely to be more sophisticated and costly. These factors may offset or completely negate the additional cost of 500m of MV cable.

 

[cmelguet]

Scotty you are right,

Actually the feeder in 33 kV is more costly than the 2 MVA transformer. Regards

 

[prc]

Also load losses of 33/0.433 kV and 4.16/0.433 kV transformers will be almost same, infact it may be slightly high for 33/0.433 KV as mean turn dia of HV will be bit more.