Industrial Drive Applications Questions and Answers

Answer: C

The profile is designed for the depth, the payload and the comfort of the people carried, with the stopping distance verified against the headgear clearance. Automatic winders follow it under control rather than leaving it to the driver.

Answer: D

Correct answer: an active load component from gravity

Gravity acts on the material whether or not the belt is moving, and it acts in one direction only - downhill. That makes it an active load, capable of driving the belt as well as opposing it, which is why an inclined conveyor needs a holdback and why a downhill one needs regenerative capability.

Answer: A

Starting a loaded belt abruptly sends a wave down it that can spill material or break the splices, and several drive stations along the route must take equal shares. Converter drives with a common torque reference solve both problems.

Answer: B

Correct answer: hold, raise and lower the load under control

A hoist must motor to raise, brake regeneratively to lower a load that would otherwise run away, and hold the load stationary against gravity. That is four-quadrant operation with a genuine holding requirement, and it is why hoist drives are among the most demanding on a plant.

Answer: C

The load on its rope is a pendulum whose period depends on the rope length, and accelerating in a pattern matched to that period leaves it hanging still. It saves the operator a great deal of time spent waiting for the swing to die.

Answer: D

Correct answer: accurate stopping with comfortable acceleration

Two requirements govern a lift and neither is speed. The car must stop level with the floor, or the doors cannot open safely, and the acceleration and jerk must stay within what passengers tolerate. Maximum acceleration would be neither comfortable nor, given the stopping accuracy required, faster overall.

Answer: A

Balancing at half load makes the drive's duty roughly symmetrical between a full car going up and an empty one coming down, which halves the machine rating needed. The drive still has to work in all four quadrants as the load varies.

Answer: B

Those are the cases in which the load overhauls the counterweight, so the machine restrains rather than drives it. Recovering that energy rather than dumping it in a resistor is now common in tall buildings with many lifts.

Answer: C

Correct answer: a compact gearless permanent magnet machine in the shaft

The permanent magnet machine gives enough torque at low speed to drive the sheave directly, so the gearbox disappears and the whole machine becomes small enough to fit within the shaft. That removes the motor room above the building, which is the point of the arrangement.

Answer: D

Large diameters are cut slowly at high torque and small ones quickly at low torque, which is the constant-power envelope exactly. Gearing extends the range at the bottom where the converter alone cannot supply the torque.