| 摘要 |
PURPOSE:To simplify the circuit configuration of a controller for circuit breakers and suppress the manufacturing cost of the controller by eliminating the need of output level adjusting work and reducing the number of required analog circuit elements by performing over current protecting operations requiring an inverse time lag characteristic through digital operation. CONSTITUTION:An A/D converter 36 samples analog voltage signals from burden circuits 29a and 29c, converts the sampled signals into digital voltage signals, and inputs the digital signals to a microcomputer(MC) 37. The MC 37 selects the maximum load currents out of those indicated by the digital signals based on a preset program and executes arithmetic operation on the effective values of the maximum load currents and level discrimination on each phase load current value indicated by the effective values. When the MC 37 detects the presence of a fault current from the level-discriminated results, turns on a thyristor 38 and causes a tripping device 39 to open a main circuit contact 22 by outputting a trigger pulse after performing inverse time lagging operations corresponding to the magnitude of the fault current. |
