1994 Volume 114 Issue 7-8 Pages 701-707
The networks rely on distant power generation facilities, underground cables and large static capacities. In case of a fault on the lines, this sometimes causes an LC resonance circuit to generate low-frequency harmonics that are approximately twice as high as the fundamental frequency. Such low-frequency harmonics cause the deterioration of distance-measurement accuracy in distance relays. To solve this problem, distance relay based on differential equations are now used as they are affected by the higher harmonics resulting from LC resonance. However, the derivative of current with respect to time (J) is calculated by using a computer, and the accuracy of the computation greatly affects the relay performance. And conventional relays based on differential equations have the limits to detect the corrective impedance, because the term J in differentional equation is poorly computed by harmonics that are higher frequency than the low-frequency harmonics.
By using the high-speed sampling technology, we improve the performance of distance relays based on differential equations.