Abstract
In order to test the hot-line insulation of low-voltage house wiring, we usually measure the earth leakage current with a clamp-type current transformer (CT) through which a bunch of main line (two wire line) is placed at the service entrance. In this method, however, the measured value includes not only the effective component to be measured, but also the inductive components of the current due to the capacitance of house wiring to the earth and the load current. Generally, the effective component is small compared to the sum of the inductive component. Therefore, in order to obtain correct measured values, it is essential to develop a technique to remove these inductive components.In order to remove the inductive component due to the load current, we have developed a bypass function element (hereinafter called as breaker attachment) that is applied to a circuit braker equipped at service entrance or branch points. As for the removal of the capasitive current to the earth, the DFT method has been introduced to the measurement using the so-called hyperbolic function method that was developed before. This hot-line insulation measurenent equipment is capabable of measuring the insulation measurement of 10 MΩ within the error of less than ± 5% under the conditions of load current of 10A and capacitance to the earth of 0.08 μF.
