Dc chokes are often used to reduce ac motor-drive harmonics. Although they operate effectively when the motor is at full load, under partial loads, they don’t fully saturate, meaning they don’t generate enough inductance to sufficiently filter harmonics. Swinging chokes solve the dilemma by saturating gradually across the face of a specially designed airgap. Even at partial load, corresponding to low current, there’s enough inductance in the saturated portion of the airgap/core to reduce harmonics by 30%. As current (load) increases, the saturated region of iron expands; harmonics continue to be filtered without a corresponding increase in energy-wasting heat.