Four Quadrant operation and Speed-Torque conventions

Figure showing the operation of hoist in loaded and unloaded condition Where T denotes motor torque T1 denote load torque Third arrow represents speed Arrows along border indicate direction of motion.

Components of hoist : 1. Cage for carrying load in upward or downward direction or lateral movement. 2. Counter weight where in it is assumed that the weight of empty cage is lesser than the counter weight but loaded cage is heavier than the counter weight. 3. Upward motion is considered as forward motion. Associated torques and the quadrants 1. The torques associated with empty cage is the difference of torques due to counter weight and empty hoist. Essentially in quadrant II and quadrant III. 2. The torques associated with loaded cage is the difference of torques due to loaded hoist and counter weight. Essentially in quadrant I and quadrant IV.

Conventions of Speed & Torque: 1 Conventions of Speed & Torque: 1. Motor speed is positive when rotation is in forward direction. 2. Loads involving up and down motion upward motion is considered as forward motion. 3. Reversible drives forwards direction is arbitrary. Speed in reverse direction is considered as negative. 4. Generating acceleration positive motor torque. 5. Motor has motoring and breaking mode of operation. Motoring action electrical energy converted into mechanical and mechanical into electrical in breaking operation. 6. Power developed by motor is the product of speed and torque. P= ώ(speed) X T(torque)------------equ.1 7. load torque graphs are shown in the figure torque line in quadrants II and III are for empty hoist torque line in quadrants I and IV are for loaded hoist.

From the figure 1st Quadrant Operation: ( hoist loaded and moving upwards) Speed is in forward direction so it is positive. Torque is also positive because it is giving the necessary acceleration. Hence as per equation 1 power is positive. Load torque T1 is in the downward direction. The machine runs as motor supplying the necessary mechanical power. Hence the operation in this quadrant is called forward motoring. 2nd Quadrant Operation: ( hoist unloaded or empty cage and moving upwards) Speed is in forward direction so it is positive. Torque is negative because it is giving the necessary deceleration. Hence as per equation 1 power is negative. Load torque T1 is in the downward direction because weight of counter weight is more than empty cage. The machine works under breaking operation opposing the motion. Hence the operation in this quadrant is called forward breaking.

From the figure 3rd Quadrant Operation: (hoist unloaded or empty cage and moving downwards) Speed is in reverse direction so it is negative. Torque is negative because here torque is being applied to accelerate in reverse direction which is nothing but deceleration. Hence as per equation 1 power is positive. Load torque T1 is in the downward direction. The machine runs as motor supplying the necessary mechanical power. Hence the operation in this quadrant is called reverse motoring. 4th Quadrant Operation: (hoist loaded and moving downwards) Speed is in reverse direction so it is negative. Torque is positive because it is being applied to produce the deceleration and is in forward direction giving the necessary deceleration. Load torque T1 is in the downward direction because weight of loaded cage is more than counter weight. The machine works under breaking operation opposing the motion. Hence as per equation 1 power is negative. Hence the operation in this quadrant is called reverse breaking.