Four Quadrant Operation (Cont.)
- Speed torque curve of the hoist is represented by vertical
line passing through two quadrants. Loaded hoist characteristics
in first and fourth and unloaded in second and third quadrants.
- In the first quadrant the load torque acts in the opposite
direction to that of rotation. Hence to drive the loaded
hoist up, the motor developed torque must be in the direction
of the rotation or must be positive. The power will also
be positive so, this quadrant is known as ‘forward
motoring quadrant’.
- The hoisting up of the unloaded cage is represented in
the second quadrant. As the counterweight is heavier than
the empty cage, the speed at which hoist moves upwards may
reach a very high value. To avoid this, the motor torque
must act in the opposite direction of rotation or motor
torque must be negative. The power will be negative though
the speed is positive, so this quadrant is known as ‘forward
braking quadrant’.
- The third quadrant represents the downward motion of
the empty cage. Downward journey will be opposed by torque
due to counterweight and friction at the transmitting parts,
move cage downwards the motor torque should must be in the
direction of the rotation. Electric machine acts as a motor
but in the reverse direction compared to first quadrant.
The torque is negative as speed is increased I the negative
direction, but the power is positive, this quadrant is known
as ‘Reverse motoring quadrant’.
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