New India Brake Motors are offered for various applications requiring almost instantaneous stopping of the driven load. These motors are offered in frame sizes 63 to 225m. their operations is of 'fail safe' type. i.e. the brake is applied, when, power to the motor is switched off, or, if power failure occurs.
Construction
A Brake Motor is an integral combination of an A.C. induction motor and a disc type, fail safe, electromagnetic brake unit. It consists of the following:
- A.C.Induction motor
- Encapsulated brake coil housed in the non-driving end End-shield.
- Brake liner attached to the armature disc at its interface with the cooling fan
- Cooling fan.
- The rectifier unit is provided inside the Terminal Box. It converts A.C. supply into D.C supply for Brake coils.
Operation
Under no power condition Brake springs keep the Brake Liner pressed against the cooling fan. This prevents rotor shaft rotation, because, the fan is keyed to it. When power is switched on, the Brake coil gets energised by the Rectifier unit. It instantly attracts armature disc by overcoming the spring force. This action results in releasing of the fan allowing the rotor to rotate freely. When power fails or when it is switched off, the Brake coil gets de-energised. This results in the spring pressing the brake liner against cooling fan by returning armature disc to its original position. This causes almost instantaneous braking of rotor. Fail safe condition is thus ensured.
For applications, where total load stopping time is not very critical, A.C. side interruption can be used. However, for applications, where faster braking is required, D.C. side interruption should be used. This entails additional contactors interlocking with main contactor.