- 1). Describe a conventional AC motor. Point out that AC motors are designed to run on the alternating current supplied by power stations for domestic and industrial use. This current travels in a wave-like motion called a "sine wave." The motion is very regular, going through 60 Hz, or wave-like cycles, per second. Conventional AC motors only run at one speed; they cannot run at low speeds without eventual damage.
- 2). Describe an inverter duty motor. Explain that inverter duty motors are AC motors modified to accept AC current that is not always regular. This allows an inverter duty motor to run at different speeds under the control of a variable frequency drive (VFD), also called an adjustable speed drive (ASD).
- 3). Explain the construction characteristics of an inverter duty motor. The windings of an inverter duty motor must be voltage-spike resistant because VFDs produce temporary voltage spikes. Inverter duty motor windings are dipped and baked in premium varnish, accumulating a thick layer of varnish that allows them to tolerate abrupt voltage changes without damage. According to the U.S. Department of Energy, inverter duty motor manufacturing increases the corona inception voltage (CIV) of inverter duty motors, increasing the voltage level at which the motor windings begin to short out, or discharge.
- 4). List applications for inverter duty motors. Inverter duty motors are suited to applications that require variable electric motor speeds or low-speed electric motor operation. For example, crane manufacturers use inverter duty motors, as do industries that employ cooling tower fans that must be operated at low speeds during the winter.
- 5). Point out operational cost differences between AC motors and inverter duty motors. The materials and manufacturing that go into an inverter duty motor lead to higher initial costs when compared to conventional AC motor costs. Long-term reliability, however, outweighs this cost disadvantage if the inverter duty motor serves in an application requiring variable- or low-speed motor operation.
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