Braking Resistors

Listing ID #3745204

When an induction motor’s rotor is turning slower than the synchronous speed set by the drive’s output power, the motor is transforming electrical energy obtained from the drive into mechanical energy available at the drive shaft of the motor. This process is referred to as motoring. When the rotor is turning faster than the synchronous speed set by the drive’s output power, the motor is transforming mechanical energy available at the drive shaft of the motor into electrical energy that can be transferred back to the drive. This process is referred to as regeneration. Most AC PWM drives convert AC power from the fixed frequency utility grid into DC power by means of a diode rectifier bridge or controlled SCR bridge before it is inverted into variable frequency AC power. Diode and SCR bridges are cost effective, but can only handle power in the motoring direction. Therefore, if the motor is regenerating, the bridge cannot conduct the necessary negative DC current, the DC bus voltage will increase and cause an overvoltage fault at the drive. More complex bridge configurations use SCRs or transistors that can transform DC regenerative electrical power into fixed frequency utility electrical energy. This process is known as line regeneration. A more cost effective solution can be provided by allowing the drive to feed the regenerated electrical power to a resistor which transforms it into thermal energy. This process is referred to as dynamic braking.