When i disconnected the supply of the three phase induction motor (wound rotor), If i connected capacitors or resistor across the stator terminal, would there be any braking in motor?

 

Based on the fact that the three phase wound motor acts just like the normal three phase motor connecting a capacitor across the terminal of the motor will not change the velocity of the motor when the motor is de-energised. The capacitor is normally connected across the motor to correct the powerfactor of the motor, and in a lot of ways it prevents sparking at the controller contacts. Putting a ressistor will not brake the motor.

What you can use to brake the motor is a VFD or variable frequency drive, which induces a dc voltage into the motor for braking purpose. So in that sense you would not need a motor brake that you would have to buy separate and apart from the motor. I have used the method and it works quite efficiently. And one of the fact that you can think of the process of dynamic braking which the vfd utilizes.

 

Responding to Neevarp's query...

The short answer is yes. However, the effectiveness of a capacitor for braking under conditions you specify is questionable.

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"Motion: Braking 3ph Induction Motor"

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected]) {[email protected]}

 

A Variable speed drive with suitably rated dynamic braking unit is the solution when you could have a mains failure and still require to stop the motor under control. The drive should have the "Mains Ride-Through" feature which will make it regenerate energy from the motor to maintain the dc link healthy. However, you will not necessarily be able to make a long stopping ramp - the stopping time will depend on the motor/load inertia.