Variable-speed control alternative is 'magnetic'
Seattle, Wa. -A sophisticated, magnetic 'coupling' placed between a motor and its driven load enables variable-speed control of ac motors up to 600 hp at 460 V-as well as medium-voltage (4,300 V) motors. The device is not another version of eddy-current control. MagnaDrive Coupling consists of a copper conductor assembly connected to the motor shaft and a precision rotor assembly (containing rare-earth neodymium-iron-boron magnets) connected to the load shaft. Relative motion between the Nd-Fe-B magnets and copper conductors develops a magnetic field that transmits torque through the air gap between the input and output members-although they are not mechani-cally connected. A linear actuator that re-sponds to 4-20 mA process signals controls torque magnitude by adjusting air gap width. MagnaDrive Coupling offers several bene-fits, such as 'soft' start/stop control, elimi-nation of harmonics and coupling-induced vibrations, and insensitivity to input volt-age/power quality. Ownership and mainte-nance costs are said to be lower, compared to a variable-frequency drive. Initial appli-cation successes have been in speed control of pumps, fans, and blowers.