* A motor operate in 2 modes – Motoring and braking
* Motoring - electrical energy to mechanical energy, support its motion.
* (generator) braking – mech energy to electrical energy, oppose the motion.
* Motor can provide motoring & braking for both forward & reverse direction.
* Power developed by a motor is given by the product of speed & torque.
* Quadrant I – Power +ve, m/c working as a motor, supplying mech energy. So called “forward motoring”
* Quadrant II – Power –ve, m/c works under braking opposing the motion. So called “forward braking”
* Quadrant III & IV – reverse motoring and braking.
Operation of hoist in four quadrants
* Direction of motor & load torques and direction of speed are marked by arrows.
* A hoist consists of a rope wound on a drum coupled to a motor shaft. One end of a rope is tied to a cage which is used for transporting material. Other end of the rope has a counter weight.
* Weight of the counter weight chosen higher than the weight of an empty case but lower than a fully loaded cage.
* Load torque TL2 in quadrants I & IV represent speed torque charal of the loaded hoist. This torque is the diff. of torques due to loaded hoist & counter weight.
* Load torque TL2 in quadrants II & III is the speed-torque charal of an empty hoist. This torque is due to the diff in torque of counter weight & empty hoist. This is –ve because the counter weight is always higher than the empty cage.
* The quadrant I operation – hoist requires the movement of the cage upward, which corresponds to the +ve motor speed which is in CCW (counter clockwise) direction. It will be obtained if motor produce +ve torque in CCW direction equal to TL. Since developed power is +ve, this is forward motoring operation.
* Quadrant IV operation is obtained when a loaded cage is lowered. Since the weight of the loaded cage is > the counter weight. In order to limit the speed of the cage within a safe value, motor must produce a +ve torque T = TL2 in anti clockwise direction. Both power & speed are –ve, drive is in reverse braking.
* Quadrant II is obtained when an empty cage is moved up since a counter weight is heavier than a empty cage, it is able to pull it up. In order to limit the speed to safety value, motor must produce braking torque = TL2 in clockwise direction. Since speed is +ve, developed power is, -ve. It is forward breaking operation.
Quadrant III – empty cage is lowered since empty cage weight is < counter weight motor produce a torque in clockwise direction. Since speed is –ve & developed power is +ve, this is reverse motoring operation.