| 摘要 |
<p>PURPOSE:To miniturize a device, to prevent a malfunction and to use the device for an overhead electric wire by providing a current measuring means of an AC electric line on every phase, and also, eliminating an error component caused by a temperature characteristic and the noise of the measuring means. CONSTITUTION:A magnetic field being proportional to a current flowing through electric wires 1a-1c of three phases is induced in annular iron cores 2a-2c, and a light beam which reaches magneto-optical field sensors 5a-5c from light emitting elements 6a-6c is modulated in proportion to the magnetic field, and received 7a-7c. Subsequently, this electric signal is brought to current conversion by signal processing circuits 9a-9c and synthesized by an adding circuit 10, but becomes zero at the stationary time and there is no output from the circuit 10, and at the time of a ground accident, a zero-phase current is made flow, the output of the circuit 10 becomes a value being proportional thereto and the accident can be detected. In this case, an error component based on the difference of a temperature characteristic between each phase is offset by subtracting 11 the corresponding instantaneous data of an n/2 period before from the respective instantaneous value data of sampling data of a prescribed frequency, and an error component caused by a noise is reduced by averaging 11 plural subtraction value data at every electrical angle, and the malfunction can be prevented.</p> |
