Abstract: Provided is an enhanced switching speed photo-coupler circuit for providing an output signal in response to an isolated input signal. The photocoupler is comprised of a phototransistor which operates in the active region in response to an applied input signal. A switching transistor connected to the output of the phototransistor is turned on when the phototransistor enters the active region. An output signal, measured from the collector of the switching transistor, will change only slightly in comparison with the off state. In one embodiment, a power semiconductor is coupled to the circuit output for enhanced switching speed.

Abstract: Breaker units (3, 4) of three-phases are enclosed in a common container (25). The three-phase breaker units and lead conductors (27a, 28a) connected to both ends of the breaker units are arranged on imaginary straight lines that are in parallel each other nearly passing through vertexes of an equilateral triangle. A common operation unit (7) for driving the three-phase breaker units is accommodated outside the container (25) and juxtaposed at a position opposed to one side (28b-28c) of the equilateral triangle. A zero-phase sequence current transformer (ZCT) is provided surrounding the lead conductors of three phases outside the container.