Dynamic braking and DC braking are the standard methods of stopping industrial AC motors for bringing it to rest. Stopping motors on time is as much important as running it. The conventional braking methods by using mechanical brakes has been supplemented by the introduction of electronic brakes that use electric current to accomplish the task of braking to slow down and stop running motors. There may be several reasons to use brakes on motors – to clear the press, to change tools or even the manufacturing process might require intermittent running and stopping of motors. The control mechanism of AC motors that is required to maintain accurate torque and speed is achieved by using soft starters but it cannot help in slowing down motors and eventually stopping it.
Importance of stopping motors
Motors are meant to drive equipments and machineries and stopping should not be an issue because switching off the power supply to the motor is an easy way to stop it. But this kind of gradual stopping may not always be suitable for the intended use of motors. When a motor is stopped, the stopping operation is completed in two steps – firstly the motor is slowed down and then finally it comes to rest. The time taken by a motor to come to rest could be a few seconds but allowing this time can become a hindrance in the operating process of machineries. The time that is wasted in stopping motors can increase the downtime of the production process that actually translates to monetary losses if the operation involves intermittent starting and stopping of motors. This issue has been perfectly addressed by the DC injection braking system that can bring AC motors to a halt almost instantly.
Working modality of DC injection brakes
In this method of braking, as soon as the AC motor is switched off, a controlled DC voltage is injected into the motor winding and it provides a braking force that stops the rotation of the rotor. The AC power that is received from the mains is converted to DC voltage that flows into the motor winding. The problems of wear and tear that is associated with mechanical braking is eliminated in this electronic braking system as there is no frictional force used in bringing the motor to rest.
Used along with regenerative braking
A lot of heat is generated when DC injection brake is used to stop an AC motor and this heat cannot escape to the outside it can be a cause of wearing out of motors. To prevent it, regenerative brakes are used to prevent overheating of motors. The regenerative brakes slow down the motors before the action of DC injection brake can stop it completely. The spinning rotor and load supply the dynamic energy that is required for regenerative braking which is then converted to electrical energy that is fed into the power line of the DC injection braking system.
The DC injection braking system can be automated by including it into the circuit that drives motors.