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Anyone give me idea about motor starting method selection guide by motor power (i.e. 0.75 ~ 200kW 3 phase 440V)?

In generally, starting method will be decided by load type, utility power and etc.
Is it correct that "Soft starter must be selected in case of 75kW over"?

Hyonwoo,

The most important factor to consider when choosing a motor starting method is capacity of the supply system! Or, perhaps, the size of an intervening transformer that reduces supply voltage to utilization voltage!

Horsepower limits are imposed because of constraints normally by the power supplier or utility! As an example, I personally know of a 19,000 Hp machine designed for DOL (Direct-On-Line) starting at 11-kV!

Of course there are some restrictions, that is, excessive voltage-drop might be experienced by other parts of the system! Other times the load is not able to withstand the mechanical stress produced by the rapid acceleration associated with DOL starting.

Who told you that 75-kW machines needed soft-starting? The utility, or a motor starter vendor?

Regards, Phil Corso (cepisicon@aol.com)