Current static watt-hour meters: critical combined core current transformers and direct current test

摘要

In many countries, electronic Watt-hour meters must be designed to meet the criteria of the international standard IEC 62053-21. Since late 2006, the further developed standard EN 50470-3 applies for evaluating the conformity of revenue meters in the European Community. B oth standards require the meters' current inputs to be tolerant to direct current (DC). Although typical meters do not take this into account when measuring power, it may be superposed on the alternating current (AC) to be measured, and may not overload the current input or distort the measuring signal. The standards stipulate a test in which a rectified sin current of a value that is unusually high for a household (I{sub}(max)/√2) is applied to the meters. Current half waves and voltage are thus in phase. The meters must measure the exact product of the 50 Hz voltage and 50 Hz components in the half-wave current. The DC components and the harmonics in the half-wave current lead to no relevant power component in the product calculation.