| 摘要 |
PURPOSE: To obtain a current-transformer circuit which increases the reliability of an apparatus by a method wherein positive DC power supplies and negative DC power supplies are installed at a plurality of current transformers and the current conduction polarity of a current- transformer primary current is reversed between the current transformers on one side and the current transformers on the other side. CONSTITUTION: A current-transformer circuit differs from conventional current-transformer circuits in such a way that a positive DC power supply 73 and a negative DC power supply 83 which are common to current transformers 611, 621 are installed, that the primary-winding current conduction polarity of the current transformer 621 is reversed with reference to that of the current transformer 611 and that the polarity of the output of the current transformer 621 to be applied to an adder 181 is inverted. When the negative DC power supply is broken down, the same waveform as that of a primary current 111 is detected in the current transformer 611 with reference to the positive-side current of the primary current 111, i.e., the primary-winding current conduction polarity current to L from K of the current transformer 611, but a negative-side current is not detected so as to become zero. The primary- winding current conduction polarity of the current transformer 621 is constituted so as to be opposite to that of the current transformer 611. The same waveform as that of a secondary current 112 is detected with reference to the negative-side current of the secondary current 112, i.e., the primary-winding current conduction polarity current to L from K of the current transformer 621, but a positive-side current is not detected so as to become zero. That is to say, the output, of the adder 181, which has exceeded a prescribed value is obtained. |
