| 摘要 |
PROBLEM TO BE SOLVED: To use a resistor with a small rated power, reduce the dimensions of a circuit structure and detect a current with high accuracy, even if the current to be detected is small. SOLUTION: At least main circuit contacts 1 (1a-1c) and 2 (2a-2c), a tripping device 14, current transformers 3 (3a-3c), rectifying circuits 4 (4a-4c), a voltage transforming unit T which transforms the voltages of the outputs of the current transformers 3 by using resistance elements, signal amplifying units 9 (9a-9c) for voltage transformation signals, a digital conversion unit 12A, a CPU unit 12C which controls the tripping device 14 according to the digital signals, a characteristics setting unit 15 for time limiting characteristics and a power supply unit 5 are provided. The voltage transforming unit T has 1st resistive elements A (7a-7c) and 2nd resistance elements B (8a-8c) and switching devices 6 (6a-6c), which switch connections between the 1st and 2nd resistive elements A and B according to the detected current values of the current transformers 3 which are under the control of the CPU unit 12C to change the resultant resistance values.
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