Industrial Drive Applications Questions and Answers

Answer: A

The slab passes back and forth through the stand, so the drive must motor and brake in both directions and change over in a fraction of a second. Very large low-speed machines with cycloconverter or load commutated inverter supplies are the usual arrangement.

Answer: B

The bite is effectively an impact, and the drive's speed dips sharply until the control recovers it. Overload capability of two or three times rated torque, and a fast current loop, are what make the recovery acceptable.

Answer: C

The strip lengthens as it thins, so each stand must run faster than the one before it in a ratio set by the reduction. Tension between stands is regulated by trimming those ratios, and a loss of coordination breaks the strip.

Answer: D

The sheet is drawn through press, dryer and calender sections whose speeds must be held in exact and adjustable ratio, or the web wrinkles or tears. An electronic line shaft distributing a common position reference is the modern arrangement.

Answer: A

A fraction of a per cent of speed difference stretches the sheet and sets the tension, so the adjustment is fine and the measurement must be finer still. Load cells or dancer rolls close the loop in the more demanding positions.

Answer: B

Constant surface speed and constant tension together mean the torque rises and the angular speed falls in inverse proportion, so the power is nearly constant. Field weakening or the constant-power region of a converter drive suits it exactly.

Answer: C

The kiln turns at a few revolutions a minute while the charge inside it shifts unpredictably, so the torque varies a great deal. Large reduction gearing with an inverter-fed machine, and a standby drive against a stoppage, are standard.

Answer: D

Correct answer: the kiln can be turned slowly during a power failure

A kiln left stationary while hot sags under its own weight and the refractory is destroyed, so it must keep turning even with the supply lost. The auxiliary drive is small, usually fed from a diesel set or a battery, and turns the kiln at a fraction of a revolution a minute until it has cooled.

Answer: A

A drum full of ore and grinding media has to be broken away from rest, and the requirement can be twice the running torque or more. Low-speed synchronous machines on cycloconverters, or geared induction drives with soft starting, are used.

Answer: B

Hoisting and lowering, loaded and empty, cover the whole plane, and a fault in a system carrying people is unacceptable. Redundant brakes, overwind protection and rigorous periodic testing are all statutory rather than optional.