Xxx Source Starter

[TCE]

I undertand that different reduced starters are constant voltage or constant impedence or constant current starters, but what I don't understand is how that affects the motors current and torque. Best I can figure is that a constant impedence starter means that if you reduce the voltage the current also reduces. I need to understand the same for all three type of starters.

[marke]

Hello TCE

 

Welcome to the forum.

 

At any time during the start, the torque produced by the motor is a function of the full voltage torque at that speed, and the square of the current being used to start the motor.

 

The motor has an impedance which is a function of the motor design and the speed of the rotor.

 

If you reduce the voltage applied to the motor, you will reduce the current. (I = V/Z)

 

If you apply a constant reduced voltage to the motor during start, you can easily calculate the start current and torque curves from the full voltage curves.

Likewise, if you apply a constant current start to the motor, you can also calculate the start torque curves from the full voltage current and torque curves. With a constant current start, the terminal voltage, is a function of the start current and the motor impedance which rises as the motor increases in speed.

 

If you apply a constant impedance starter, then the voltage at the motor terminals at any speed is going to be a function of your starter impedance and the motor impedance which is a function of motor speed. As the motor accelerates, the motor impedance increases, so the motor terminal voltage increases.

 

Best regards,