Motor starting current

[SAkieran]

when sizing cables i looked at in work, i saw starting power factor at 0.3 and motor starting current x 7. i would like to know why this is the case, what losses indicate the 0.3 starting power factor and what losses indicate to multiply the starting current by 7. i have been browsing for an answer but i can't seem to find it. i am sure the answer isn't too complex so any help on an explanation would be appreciated.

 

[rockman7892]

The 0.3 power factor is due to the fact that upon energization of the motor most of the current is reactive current used for magnetizing the windings and establishing a field in the motor and a very little portion of the current is real current used to provide output power from the motor. As the motor increases in speed an and the slip decreases the power factor will increase as the motor becomes more loaded.

The multiplying the current by 7 has to do with the fact that at starting the motor is in a locked rotor condition and has a very low impedance causing the increased current.

 

[SAkieran]

thanks for such a quick reply, helps a lot with the understanding