PURPOSE: To facilitate the detection of a troubled section without recurrence of troubles in case a trouble occurs to open a breaker by a measurement of electricity and a specified computation with a measurement controller connected to the side of a distribution line in a breaker.

CONSTITUTION: Breakers 100 and 200 for distribution lines are connected to the power supply end of distrubition lines 10W13 and 20W23 and section switch devices 111W113 and 211W213 are connected thereto to divide the distribution line. Fixed value impedance 11RW113R and 211RW213R are provided on a bypass of a main circit of the section switch devices. Measuring switch devices 110 and 210 are connected to the side of the distribution line of the breaker. In case any trouble in the distribution line causes to work the breaker, the measuring switch devices are opened or closed sequentially measure to phases of the lines and current and voltage signals between the phases whereby an impedance is obtained. The measured impedance and the fixed value impedance are used to calculte the number of sections, which will be displayed as required. This enables a quick detection of the troubled section easily without recurrance of troubles.