Power measurement by the hook-on method

THE hook-on method is here defined as the measurement of an electrical quantity, where the current component of such measurement is obtained by encirclement of the current-carrying conductor by a removable magnetic structure. This magnetic structure is thereby subjected to a magnetomotive force, which is a unique function of the current and provides a magnetic flux for a secondary winding or an instrument mechanism. Available self-contained instruments are limited to current measurement. Interest in extending this measurement method to active and reactive power has resulted in the development of the self-contained hook-on wattmeter, illustrated in Figure 1. It was necessary that this instrument meet exacting requirements as to weight, simplicity of operation, and range of full-scale capacities (3 to 300 kw).