OVERCURRENT PREVENTING METHOD FOR NEUTRAL LINE IN THREE-PHASE FOUR-WIRE DISTRIBUTION SYSTEM

摘要

PURPOSE:To prevent overcurrent in the neutral line by connecting a three-phase active filter between a power source and a load and eliminating three-phase a harmonic current flowing through the active filter. CONSTITUTION:An active filter AF is arranged for each trunk line of distribution system or the output bus from a transformer Tr. The gate turn-OFF thyristor in the three-phase bridge circuit of the active filter AF is controlled to maintain the current flowing through a DC reactor DL constant so as to feed a harmonic current IM to the distribution system. Consequently, the harmonic current is eliminated from the neutral line thus eliminating the unbalanced current in the neutral line. As a result, it appears as if only a balanced load is connected to a three-phase four-wire distribution system thus causing no overheat due to the overcurrent flowing through the neutral line nor burning due to overheat.