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Download Dynamic Braking of Induction Motors
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Transcript
Dynamic Braking of Induction Motors • Slow down a machine by converting kinetic energy stored in the rotating mass to heat energy in the rotor and/or stator windings. • Switch the motor from the line to a braking circuit that causes the motor to behave as a generator with a connected load. ECE 441 1 Dynamic Braking of Induction Motors • Methods of braking include DC Injection and Capacitive braking. • Note that there is no “holding” torque at the end of the braking period – need a mechanical brake to hold the shaft. ECE 441 2 DC Injection Method ECE 441 3 DC Injection Method • Disconnect the motor from the line and supply a DC source to any two terminals of the stator through a current-limiting resistance. • The DC voltage sets up a stationary magnetic field that generates a voltage in the rotor windings, dissipating energy as I2R losses, slowing the motor. ECE 441 4 Capacitor Braking Method ECE 441 5 Capacitor Braking Method • Disconnect the motor from the line and connect a capacitor bank to the stator terminals. • Motor behaves as a self-excited induction generator. • Rotational energy is dissipated as I2R losses in the rotor and stator windings. • Increase the effect by adding resistor load. ECE 441 6
