HBR DC brake
A quick reduction of the RPM of a three phase AC motor is always becoming more and more important from technical security and process point of view. Electronic direct current brakes fulfill this function saliently and furthermore can also offer following deploying possibilities
- Quick switch off
- Brake for reduction of cycle times
Against the mechanical ones the electronic brakes show essential advantages like there is no wear and tear and thus are maintenance free. A later assembly may require no constructive changes on the machine. The breaking torque (Breaking current) and the breaking time are customized as per the respective requirements.
Function
A DC is given to the stator winding of the motor after separating the motor form the circuit. The still rotating motor creates a current, which is proportional to the breaking torque. The breaking torque can be set progressively by using the controlling semi conductors and a freewheel diode. A time link is inserted in the breaking device, which switches off the breaking current as per the adjustable time. This avoids that this current flows further on the motor slowed down to standstill and thus avoids the unnecessary heating of the windings.
Controlling the Breaking Devices
Operate the motor on zero-potential to introduce the breaking (K1 falls off). At the same time the locking of the breaking device is removed using the help contact (opener) of K1. The contact 8-9 of the breaking device opens and prohibits the re-switching of the motor contactor K1 M.
The breaking current can be determined using the potentiometers »Rough« and »Fine« for the required breaking effect. Depending upon the size of the motor the breaking is set from delay of 500 ms up to 2,5 s. This ensures a secured reduction of remanence voltage in the motor.
Determining the Breaking current
Following formula can be used for determining the breaking current. Most of the times the best result is derived using the breaking current. This current is in accordance with the 2X rated current of the motor.
IB = k x IN x √tA/tB (A)
IN = Rated current of the motor in ampere
tA = Start up time in seconds
tB = Desired breaking time in seconds
k = Factor (After switching the motor winding)
Normal values for the start up time tA in seconds:
Conveyer belt 20-30
Compressor 10-30
Pump 5-8
Ventilator 20-30
Jaw crusher 30-40
Cement crusher 20-25
