Comparison testing of an adjustable-speed permanent-magnet eddy-current coupling

The paper describes the physical construction, basic principles of operation, and a series of comparison tests conducted on an adjustable speed coupling system (ASCS) and a low voltage variable-frequency drive (VFD). These systems have been tested at three different ratings (50 hp, 100 hp, and 200 hp) driving load profiles representing both fans and pumps. The ASCS employs high energy-product neodymium/iron/boron (NeFeB) permanent magnets which act on steel-backed copper discs to provide torque transfer from motor to load without mechanical contact. The slip that occurs between the motor and load shafts can be changed by adjustment of the mechanical clearance of the magnets and the copper discs, Thus, a form of speed control for the load is affected for a system driven by a constant frequency induction motor. The test results compare the energy savings potentials of the VFD and the ASCS and the merits and disadvantages of the two systems related to motor operation and power system connection issues.