Hi,

Basically what are the assumptions that should be taken in consideration when sizing auto-transformer starter example for a 185 k W 3 phase 400 V application.

Bob

Autotransformers designed for motor starting are typically sized specifically for a given motor by the transformer mfgr. If you are planning on using an off-th-shelf autotransformer that is for a distribution load, I have no idea.

Example: http://www.olsun.com/sm2.html (sorry, I only have references for US mfgrs.)

Thanks jraef. However, I wish to know how to size auto-transformer for starting of an induction motor.

Bob

Hello Bob,

When selecting/sizing an auto-transformer starter the following should be considered.

Motor nameplate kW and Amps
Which voltage tapping will best suit the load
What is the anticipate voltage tapping
Number of starts ie equally spaced and consequtive
Ambient temperature

Once those details are known provide them to the aut-transformer manuacturer and they will design/build a transforemr to suit your application.

Alternative, standard transformers are available from a variety of different suppliers (or at least they are in Australia anyway). These are normally designed for 3, 10 or 30 starts per hour with each start cycle not exceeding 10 seconds.

I hope the above helps.

Regards,
GGOSS