Industrial Drive Applications Questions and Answers

Answer: C

A pump running flat out around the clock, or a conveyor whose belt speed is fixed by the process, has nothing to gain from a converter beyond a soft start. The duty profile decides, and the dramatic savings come from fluid loads at part flow.

Answer: D

Correct answer: False, since quadrants, accuracy and thermal duty all differ

A drive is specified for a particular load. The quadrants it must work in, the speed and position accuracy required, the duty cycle and the environment all differ between applications, and matching the power rating establishes almost nothing. A drive sized for a fan will not serve a hoist however well its nameplate matches.

Answer: A

The torque-speed requirement determines the machine size, the converter rating and the region of the envelope in use, and everything else follows from it. Ambient and insulation matter, but only once the duty is known.

Answer: B

Correct answer: forced ventilation or a substantially derated machine

A self-ventilated machine has almost no cooling air at standstill while its stator carries full current, so its temperature rises quickly. Either a separately driven blower supplies the air, or the permissible torque is reduced to what the machine can dissipate - and the derating at zero speed is severe.

Answer: C

Certification governs what may be installed, and a cage machine in a flameproof or increased-safety enclosure is the usual choice. Brushgear is exactly what such an area cannot tolerate, and enclosure reduces the rating a given frame can deliver.

Answer: D

Dust blocks fins, blankets surfaces and finds its way into bearings, so a sealed machine with an adequate ingress rating and a maintainable cooling path is essential. Its rating will be lower than an open machine of the same frame size.

Answer: A

Correct answer: the thermal duty of the whole cycle

Each start draws heavy current, and with frequent starts the machine never cools between them. The rating must therefore be based on the equivalent current over the whole cycle, starts and running and rest together, rather than on any one part of it. A machine sized on the running load alone will overheat.

Answer: B

A large link capacitance carries the drive through a few milliseconds, and beyond that the control has to reduce the load rather than trip. Continuous process plant where a trip means hours of lost production is where this matters most.

Answer: C

Washing needs a slow reversing tumble at high torque and spinning needs many hundreds of revolutions a minute at low torque, which is a wide constant-power range. Brushless machines on small inverters have displaced the older brushed universal motor and its gearbox entirely.

Answer: D

Running slowly and continuously is more efficient than switching a fixed-speed compressor on and off, and it holds a steadier temperature. Small permanent magnet machines with sensorless control made it affordable in a mass-market appliance.