Industrial Drive Applications Questions and Answers

Answer: C

A broken web wraps itself round the cylinders within a fraction of a second, so the stop has to be immediate and coordinated across every unit. Braking capability on every section is therefore part of the specification.

Answer: D

Correct answer: A fire pump held at rest and run at full speed on demand

A fire pump runs only in an emergency and then at full output, so there is no part-load operation from which to save energy and no process variable to control. Its requirements are reliability and starting on demand, which a direct-on-line starter serves better than a converter.

Answer: A

Correct answer: A test dynamometer loading an engine

A dynamometer must absorb power from the engine under test, which is generating, and must also motor the engine to start it and to test its friction - in both directions of rotation for some machines. That is the full four quadrants, and few applications need them so plainly.

Answer: B

Everything about the machine and converter rating follows from that curve, because it says what has to be delivered and where. The other three are constraints on the equipment rather than statements of what the load demands.

Answer: C

Correct answer: motors in a single direction and never brakes

One-quadrant operation means positive torque at positive speed only: the drive supplies power in one direction and never absorbs it. Adding braking in the same direction makes it two-quadrant, and adding the reverse direction makes it four - the count following from which combinations of torque and speed sign occur.

Answer: D

Correct answer: the load curve, the quadrants, the accuracy and the environment

Choosing a drive means matching it to the whole application: how the torque varies with speed, which quadrants are needed, what accuracy the process requires, and what the surroundings will do to the equipment. Any one of those considered alone gives the wrong answer, and the converter’s price is usually the least of them.

Answer: A

Continuous process plant loses far more in lost production than the cost of a spare converter or a second drive train. Hot-swappable modules, monitored cooling and planned capacitor replacement all follow from that arithmetic.

Answer: B

Fans and electrolytic capacitors are the wear-out items, and both age faster when hot, so a clean heatsink in a cool cabinet buys years of life. Performance features have nothing to do with how long the drive will last.

Answer: C

Correct answer: preconfigured with the parameter set of the installed unit

A drive out of the box carries default parameters and will not run the machine correctly. Configuring the spare in advance and keeping its parameter set current turns a replacement into a matter of minutes rather than of commissioning, which is the whole reason for holding a spare on a critical application.

Answer: D

Windings designed for a sinusoidal supply may not withstand the inverter's fast edges, and a self-ventilated machine cools poorly at low speed. Inverter-duty windings, output filters and a torque derating curve are the three remedies.