Quick questions on DC and AC motors for lifting: HSC Engineering Studies Lifting Devices

2short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What are dC motors?

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DC motor torque is proportional to armature current; speed is proportional to applied voltage. They give excellent low-speed torque and are easy to control with simple electronics. The disadvantage is brush wear (typical replacement every 2000 to 5000 hours).

What is variable-speed drives (VSDs)?

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A VSD (also called variable-frequency drive, VFD, or inverter) electronically synthesises a three-phase AC waveform at a controllable frequency and voltage. By varying the supply frequency, the VSD changes the synchronous speed of the motor and so the operating speed. The volts-per-hertz ratio is held roughly constant to keep the magnetic flux constant.

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