DC and AC power

This article deals mainly with the measurement of electrical power, in direct current on the one hand, and for sinusoidal currents and voltages with frequencies between a few hertz and a few kilohertz on the other, frequencies generally encountered in industrial practice.

Very low powers (below 0.1 W) require special techniques and precautions, and are not covered here.

On a power grid, it's very useful to know instantaneous consumption in order to adapt production to requirements and, if necessary, reduce the load imposed on power plants through load shedding.

Power measurements are also necessary for machine testing and, in industry, to check the power absorbed by motors (rolling mills, ventilation units, etc.).

Another problem is that of measuring time-integrated power, i.e. the energy consumed by different subscribers. This latter problem is examined in the articles Electricity metering. AC meters [D 4 952] and Electricity metering. Metering assemblies [D 4 953] in the treatise Electrical Engineering.