Digitally measuring electrical energy consumption

A method and apparatus for digitally measuring electrical energy consumption from a transmission line (11,12,13) carrying alternating current. Instead of actually measuring current from a transmission line conductor, the time derivative of the magnetic field induced by current flowing in the conductor is measured, thereby obtaining a reading which is proportional to the time derivative of the current flow. Using an appropriate microcomputer (30), the time derivative of the magnetic field is represented with an algorithmic series for expressing cyclic phenomena, such as a Fourier series of low order. An approximation of the power consumption is then computed by converting the time derivative of the current as expressed in the algorithmic series and a voltage measurement from the conductor to a power reading, and successive power readings are summed to obtain a number proportional to the energy consumption. Even harmonics and high frequency harmonics may be eliminated in the algorithmic expression of the current derivative to further simplify computer computations and required hardware, and the magnetic rate of change pickup (16,17) and the voltage pickup (23) are preferably filtered to remove unwanted noise.