Modern motors for modern drives
15 Jan 2000
Despite their increasing popularity, variable speed drives still probably account for only around 10 per cent of the installed base of motors in industry, according to one of the world's largest motor manufacturers, Leroy Somer.
One of the reasons is the inherently limited operation range of existing motors. Standard ac motors can normally operate over a 2:1 speed range without modification. De-rating the motor can offer a 5:1 speed range but reduces the power available from the motor. Another alternative is to force-ventilate the motor, which can extend the speed range to 10:1 but still retains the limited dynamic response of the standard motor.
Modern electronic drives, however, offer a much wider speed range than even 10:1 - a fact that Leroy Somer has acknowledged with the introduction of its new MV motors.
These range from 0.75 to 132kW in 2, 4 and 6 pole versions, and run on 380-415V at 50Hz and 400-460V at 60Hz. Where they differ from standard, general purpose motors is in their electrical and mechanical design.
By increasing the size of the magnetic circuitry in the motor, current density is reduced. This is said to avoid the de-rating that is needed with standard motors and leads to a smaller frame motor with a smaller, less expensive inverter.
In standard form the same size as a standard motor, the MV is also available with an encoder option for operation with flux vector control drives.
