What Types of motors can be used with variable frequency drives?
The various types of industrial motors that can be used with variable frequency drives are:
Dc motor: dc motors are still in production although the number of active manufacturers has decreased considerably, specifically those that are still manufacturing large dc motors (> 1 MW).
Ac asynchronous squirrel cage motor: This type of motor is the most commonly used motor in industrial processes with variable frequency drives.
Ac asynchronous wound rotor motor: This type of motor was traditionally used in variable frequency drive when the load required a high starting torque and the strength of the power supply network was insufficient to permit Direct On-Line (DOL) starting. Variable speed operation is obtained by varying the effective resistance in the rotor circuit.
Ac synchronous motor with brush less ac or brushed excitation.
Ac synchronous motor with permanent magnet excitation: This type of motor is specifically designed for operation with a variable frequency drive. Synchronous motors are used mainly in the high power ranges to minimize costs by minimizing the current rating of the variable frequency drive and due to the non availability of squirrel cage induction motors.
The most common electrical VFD used in industry today is the variable frequency drive using Voltage Source Inverter (VSI) typology and controlling asynchronous squirrel cage motors.
The power range of VSI types of variable frequency drives extend from fractional kW such as 0,18 kW to 2 000 kW in the low voltage range and from 200 kW through to 30 MW in the medium voltages. The low voltages that are of interest to the local market are the standard IEC (International and Electrotechnical Commission) voltages namely 230 V single-phase, 400 V three-phase, and 690 V three phase, all at the 50 Hz input frequency. To satisfy the 525 V market, variable frequency drives with a rated voltage of 600 V and 690 V are used. At the medium voltage level the voltages of interest are 3 300 V, 6 600 V and 11 000 V. Economics should be the determining factor as to the rated voltage of the drive given the required power rating, although this is not always the case.
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