Electrical – Is this a ac three phase motor with a dynamic braking control


enter image description here

I am an electrical apprentice and this question popped up on my exam, and then again on an exam under a different topic, and I have to review it.

What type of motor control is this?

note: I received enough answers to the question above. Thank you.

My other question is with regard to the role of the varistor.

Is it to vary the stopping time? If someone would please guide me in the right path, I would be most obliged.

Best Answer

That is a DC "braking" or "DC injection" braking circuit. Such a circuit is often called a dynamic braking or DC dynamic braking, but I think it is preferable just to call it DC braking. That avoids confusion with another type of braking that is called dynamic braking.

The circuit includes a variable resistor that is used to set the DC current applied to the motor windings. The braking current controls the braking torque. See: How much DC voltage is needed to brake a 3 triphasic motor? There is also a timer to limit the time that braking current is applied. Applying braking too long can overheat the motor.