It uses induced electrical eddy currents in a clutch plate assembly to change pump speed by varying the torque created by the motor. Electrical eddy currents are circular electrical currents set up in an electrically conductive material such as copper or aluminum when a magnet is passed over the material. Magnetic clutches and high strength permanent magnets are used to induce these currents. Adjusting the distance between the magnets on the pump and copper disks attached to the motor varies the amount of torque transferred to the pump. The advantages of the ASCS PLUS compared to a VFD include ruggedness, reduced affects on the power grid, and increased motor life.
Shaft alignment is also less critical because of the air gap between the two sets of disks.
Because the ASCS PLUS is a mechanical device, it does not induce harmonics on the power grid, something of great concern to electric utilities. Electrical harmonics on the power grid increase costs and can cause problems. Because of this, some electric utilities are requiring the use of more expensive VFD motors with filtering devices that produce smaller harmonic currents. Harmonics can also reduce motor life unless a more expensive VFD rated motor is used. While MagnaDrive made the first ASCS PLUS for horizontal applications, it recently installed two vertical units on 75 and 125 horsepower chilled water pumps in the Washington Mutual Building in downtown Seattle.