Industrial Drive Applications Questions and Answers

Answer: C

Cycling wastes energy in unloaded running and in the pressure band it needs, whereas a variable-speed machine sits at whatever speed the demand requires. On a plant with a widely varying air demand the saving is substantial.

Answer: D

Hundreds of metres of cable reflect the inverter's switching edges and can nearly double the voltage at the machine terminals. An output filter or an inverter-duty winding is essential, and the cable's own charging current has to be allowed for as well.

Answer: A

Getting a heavy train moving needs torque, and cruising needs speed at whatever torque the resistance demands, which is the two-region envelope exactly. The dc series machine's characteristic suited it naturally and the converter now provides it deliberately.

Answer: B

Cage or magnet machines with no commutator withstand the environment and need almost no maintenance, and the converter gives whatever characteristic is wanted. Resistance-controlled dc traction survives only on older stock.

Answer: C

Comparing the speeds of the axles reveals the one that has broken adhesion, and backing off its torque lets it recover within a fraction of a second. Independent control of each axle is one of the advantages of individual inverter drives.

Answer: D

The available power rises steeply with wind speed, and the rotor is held at the tip speed ratio that extracts the most from it, which means variable-speed operation. Above rated wind the blades are pitched to shed the surplus.

Answer: A

Aerodynamic efficiency peaks at one ratio of blade tip speed to wind speed, and tracking it across the wind range recovers several per cent more energy over a year. Pitch control still handles the region above rated wind.

Answer: B

A converter of perhaps a third of the machine rating gives a useful speed range, which is a large saving on a multi-megawatt machine. Full converter arrangements have since gained ground because they ride through network faults more gracefully.

Answer: C

At a few tens of revolutions a minute the machine needs a great many poles and is correspondingly large in diameter, but the gearbox that most often fails is gone. Permanent magnet excitation keeps the diameter within reason.

Answer: D

The end effector's accuracy depends on every joint, and lost motion anywhere in the train shows up directly as error. Harmonic or cycloidal gearing with magnet servo machines and high-resolution feedback is the standard arrangement.