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## Main Question or Discussion Point

Friend gave me this task he had back in school to calculate the necessary amperage for a fuse that is put in series with one of the phases for a 3 phase induction motor.

I could calculate the working current of the motor from the rated kW and cos voltage/current angle, but I couldn't figure out how to calculate the starting current.

The parameters are as such , motor is put in a 3 phase delta (triangle) connection, supply voltage 380v, motor rated power 9.4Kw, power coefficient is 0,91cos.

From this I took 9.4kW and expressed that as 9400w which I divided by the power coefficient times voltage, I got 27.18 amps, the total current consumed, divide that by 3 as each phase uses one third of the current and I got 9.06 amps as the working current for a phase.

Obviously I could crudely take those 9 amps and multiply them by about 7 (times the nominal current for an induction motor at startup) but the task gives additional data, so my question then is using this additional data is it possible to determine the starting current and how?

additional data: mechanic efficiency = 0.98

Kp=Ip/In = 5 (really don't know what this means)

and lastly lower case alpha α = 2.0

thanks.

I could calculate the working current of the motor from the rated kW and cos voltage/current angle, but I couldn't figure out how to calculate the starting current.

The parameters are as such , motor is put in a 3 phase delta (triangle) connection, supply voltage 380v, motor rated power 9.4Kw, power coefficient is 0,91cos.

From this I took 9.4kW and expressed that as 9400w which I divided by the power coefficient times voltage, I got 27.18 amps, the total current consumed, divide that by 3 as each phase uses one third of the current and I got 9.06 amps as the working current for a phase.

Obviously I could crudely take those 9 amps and multiply them by about 7 (times the nominal current for an induction motor at startup) but the task gives additional data, so my question then is using this additional data is it possible to determine the starting current and how?

additional data: mechanic efficiency = 0.98

Kp=Ip/In = 5 (really don't know what this means)

and lastly lower case alpha α = 2.0

thanks.