For example, a four-zone phase and ground mho distance relay requires 24 comparators. These relays typically have 5 to 36 legs, each usually between 5 and 10 km (3.1 and 6.2 miles) long, though sometimes as long as 16 km (9.9 mi). Which means if the distance Relay senses Impedance less than 25.62 Ohm then it will pick-up for Zone-2. The number of relay elements required for complete schemes is usually quite large. The balance 20 to 30% is given as tolerance in order to avoid the relay overreaching due to various errors introduced in measurements if the relay were set at 100% . The idea behind a CCVT is to use ... A distance relay relies on accurate voltage and current Let us consider the following 20 kV power system in figure 4 (taken from [1] and modified). Distance relays are generally used for phase-fault primary and back-up protection on subtransmission lines, and on transmission lines where high-speed automatic reclosing is not necessary to maintain stability and where the short time delay for end-zone faults can be tolerated. One approach to making a distance relay with a … Unlike over current relays distance relays achieve selectivity on the basis of impedance rather than current. Uniquely, a distance relay measures th e apparent im pedance derived from locally measured current and voltage. In this way, it is a more sophisticated form of fault detection than simple overcurrent (e.g. Long-distance relays have become increasingly popular with runners of all skill levels. This paper provides guidelines for setting distance relays ap-plied directly on a power transformer and for applications of relays to a line on which transformers are connected. Where high-speed automatic reclosing is not necessary to maintain stability. Short time delay for fault is permitted. This is because they are more cost -effective than wire- wound potential devices rated for full system voltage. inrush. Long-distance relays. of distance along a transmission line, which explains the name applied to this group of relays. A form of protection against faults on long-distance power lines is called distance relaying, so named because it is actually able to estimate the physical distance between the relay’s sensing transformers (PTs and CTs) and the location of the fault. Distance relaying generally used when. 50 or 51 relay). THE IMPEDANCE-TYPE DISTANCE RELAY Since this type of relay involves impedance-type units, let us first become acquainted with them. Without careful setting of digital relays in such applica-tions, power transformer inrush can cause distance relay meas-urement errors and unwanted operations. Distance relaying should be considered when overcurrent relaying is too slow or is not selective.Distance relays are generally used for phase-fault primary and back-up protection on subtransmission lines, and on transmission lines where high-speed automatic reclosing is not necessary to maintain stability and where the short time delay for end-zone … Hope you enjoyed the post. Distance relay types- Application: 1. In normal operation, the distance protection device ‘D’ at point A sees an impedance equal to the sum of the impedance of power lines Z V1, Z V2, and the load impedance, Z Load.Since Z Load >> Z V1 and Z V2, the impedance measured by the distance protection will be very high. For Ground fault relaying: Introduction to distance protection. The impedan ce of a transm ission line is generally Quadrilateral characteristics Distance relay schemes The Zone 1 of the distance relays are generally set 70 to 80 % of the line to be protected. generally used at transmission-level voltages (138 kV and up) to provide secondary voltage signals to relays. ... generally the setting of Zone-4 protection is set at 10 percent of the line impedance or 10 percent of the shortest line connected whichever is minimum. Again, it should not be encroached by load. R 1PG-G = R 2PG-G = R 3PG-G = 80% of 28.8 = 23.032 Ω. Generally, this reach is set 80% of minimum load impedance. The phase to ground resistive reach is defined by the maximum phase to ground fault arc resistance and tower footing resistance for which relay should operate. Quadrilateral characteristics require even more. 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