Distance relay protections react to the voltage and current, i.e., the impedance, at the relay area. The impedance per mile is genuinely consistent so these relay protections react to the separation between the relay protection area and the deficiency area.
As the power systems become progressively perplexing and the shortcoming current shifts with changes in generation and framework setup, directional overcurrent relay protections become hard to apply and to set for all possibilities, while the Distance relay protection setting is consistent for a wide assortment of changes outside to the secured line.
There are three general Distance relay protection testing types as appeared in Fig. 1. Each is recognized by its application and its working trademark.
Fig-1 Distance Relay protection
The impedance Relay protection testing has a round trademark focused at the starting point of the R-X graph. It is non directional and is utilized principally as an issue indicator.
Induction Relay The induction relay protection is the most regularly utilized separation hand-off. It is the stumbling Relay protection testing in pilot plans and as the reinforcement relay protection in step separation plans. Its trademark goes through the root of the R-X chart and is accordingly directional. In the electromechanical plan it is round, and in the strong state structure, it very well may be formed to compare to the transmission line impedance.
The reactance relay protection testing is a straight-line trademark that reacts just to the reactance of the secured line. It is nondirectional and is utilized to enhance the permission relay protection as a stumbling relay protection to make the general assurance autonomous of opposition. It is especially valuable on short lines where the shortcoming curve obstruction is a similar request of extent as the line length.
Figure 1 shows a three-zone step separation handing-off plan that gives immediate assurance more than 80–90% of the ensured line segment (Zone 1) and time-deferred security over the rest of the line (Zone 2) or more reinforcement insurance over the nearby line area. Zone 3 additionally gives reinforcement insurance to adjoining lines segments.
In a three-phase power system, 10 types of faults are possible:
1. Three single phase to-ground,
2. Three phase to-phase,
3. Three double phase to-ground, and
4. One three-phase issue.
It is fundamental that the relay protections testing given have a similar setting paying little mind to the kind of deficiency. This is conceivable if the relay protections are associated with react to delta voltage and currents. The delta amounts are characterized as the distinction between any two phase amounts, for instance, Ea – Eb is the delta amount between phases a and b. When all is said in done, for a multiphase flaw between phases x and y,
Three-zone step Distance relay to secure 100% of a line and reinforcement the neighboring line.
Three-zone step separation handing-off to secure 100% of a line and reinforcement the neighboring line.
where x and y can be a, b, or c and Z1 is the positive succession impedance between the relay protection area and the issue. For ground Distance relay protections, the faulted phase voltage, and a remunerated faulted phase current must be utilized.
where m is a steady contingent upon the line impedances, and I0 is the zero succession current in the transmission line. A full supplement of relay protections comprises of three phase Distance relay protections testing and three ground Distance relay protections. This is the favored defensive plan for high voltage and additional high voltage systems.