PURPOSE: To prevent excessive equipment investment by calculating the electrical amount such as voltage or current in each feeder section and produced an alarm when the electrical amount exceeds over a predetermined value, and modifying the configuration of the distribution system such that the electrical amount is settled to a predetermined value.

CONSTITUTION: Feeder current, i.e., current flowing through a circuit breaker 1a, is calculated based on the overall impedance of feeder connected with the circuit breaker 1a and the voltage of substation bus. Furthermore, current flowing through a feeder section is calculated based on the voltage drop across the impedance in the feeder section. Voltage at the end of the feeder is also calculated. Electrical amount such as the bank capacity or the distribution line loss is operated through CPU 12 in a configuration design supporter 200 and the operation results are displayed on a CRT display section 14. The operated electrical amounts are compared with values preset in a memory 16, and when they exceed over predetermined values an alarm is produced to prompt a configuration designer to modify the distribution system configuration or the wire size.