During electricity generation, transformation, distribution and consumption, distortions of voltage and current sinusoidal signals occur. Most consumers are non-linear, and a significant content of higher harmonics emerges when they are connected to the supply grid. The algorithms of modern electricity meters take into account most of higher harmonics, whilst with some fallibilities. However, when supply voltage and current have the same amplitude and a various harmonic composition, the readings of electricity meters can vary greatly. This article describes how the harmonic composition of supply voltage and current affects the readings of electricity metering devices. The analysed ratios do not depend on the amplitude of supply voltage.

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