2009 Volume 129 Issue 3 Pages 428-436
In Japan, operational principles from the mechanical-type era, such as the directional ground relay (DG) and overcurrent relay (OC), are still used without modification for the protection of distribution lines. We are now facing various problems, such as ground faults with high fault resistance in systems isolated from the ground.
A new operational principle to solve the above problems is summarized below.
·A fault is simulated by replacing a branched distribution line with a one-section single distribution line, in which loads are concentrated at its terminals.
·Lines with a one-line to ground fault are detected on the basis of the relationship between the fault-phase voltage E before the fault and the fault current using Ho and Thevenin's theorem.
·Faults are assumed to occur at both terminals in the section. If the signs of the obtained fault reactance Xf at the two terminals are opposite, it is judged that a fault point where Xf = 0 holds exists within the section.
As a result of the simulation using the program we developed, it was confirmed that no errors in the detection of the internal and external ground faults with a high fault resistance of 0-30kΩ were observed.