| 摘要 |
<p>PURPOSE:To prevent a malfunction by providing an adding means computing a zero-phase voltage component and first to fourth storage means storing an instantaneous-value data group, a reference storage value and an effective value. CONSTITUTION:The error component of a high-frequency component, a low-frequency component, etc., by noises, etc., is moved by developing an output from an adding circuit 17 to a Fourier series and computing only a commercial- frequency component value. The error component of zero-phase voltage changed by the humidity characteristic difference, etc., of earth capacitances 10a-10c is removed by subtracting the sampling data (a first reference storage value stored in a second storage means 22) of the past (just before the generation of a ground accident) and the effective value (a second reference storage value stored in a fourth storage means 22) of the sampling data from a latest sampling data (an instantaneous-value data group stored in a first storage means 21) and the effective value (an execution value stored in a third storage means 21) of the latest sampling data respectively.</p> |
