Distance relays are one of the most significant protection components in a transmission line.
Figure:Distance Relay Protection Engineering Classes
Standards and Characteristics of Distance Protection
These relay protection engineering classes may once in a while be set situated in rates of the line impedances, for instance a regular setting for zone 1 is 80% of the impedance of the line so as to not reach at the remote end, the zone 2 can be set at 120% of the impedance of the line so as to reliably exceed the line, Zone 3 sometimes are disabled or set to cover an adjacent line.
Distance relay protection engineering classes attributes might be Mho, Quadrilateral, Offset Mho, and Offset Mho. On account of the quadrilateral trademark or long arriving at mho attributes, extra care might be required to stay secure during overwhelming burden.
On account of parallel lines, the common coupling of these lines can cause distance relays to under reach and over reach. Hence the Relay setting must think about this impact, a few relays have calculations to redress, however it is important to utilize the current of the parallel line which adds intricacy to the establishment.
In certain nations there criteria that a Distance protection cannot reach to fault in other voltage levels, since fault clearing times in sub transmission levels might be more slow than issue clearing times at the transmission level.
The issue of joining quick fault clearance with particular tripping of plant is a key go for the protection of intensity protection.
To meet these prerequisites, rapid protection for transmission and essential dispersion circuits that are reasonable for use with the programmed reclosure of circuit breakers are under consistent advancement and are generally applied.
Distance protection, in its essential structure, is a non-unit arrangement of protection offering impressive financial and specialized favorable circumstances. Not at all like stage and nonpartisan overcurrent protection, is the key bit of advantage of Distance protection that its deficiency inclusion of the ensured circuit is basically free of source impedance varieties.
Figure 1 – Advantages of Distance over overcurrent protection
Distance protection is nearly easy to apply and it tends to be quick in activity for issues situated along the majority of an ensured circuit. It can likewise give both essential and remote back-up capacities in a solitary plan. It can without much of a stretch be adjusted to make a unit insurance conspire when applied with a flagging channel.
In this structure it is prominently appropriate for application with fast auto-reclosing, for the protection of basic transmission lines.
Standards of Distance Relay Protection Engineering Classes
Since the impedance of a transmission line is corresponding to its length, for Distance estimation it is suitable to utilize a Relay equipped for estimating the impedance of a line up to a foreordained point (the reach at point).
Such a Relay is portrayed as a Distance hand-off and is intended to work just for flaws happening between the hand-off area and the chose reach at point, in this manner giving segregation for deficiencies that may happen in various line areas.
The essential standard of Distance insurance includes the division of the voltage at the handing-off point by the deliberate current. The evident impedance so determined is contrasted and the reach at point impedance. In the event that the deliberate impedance is not exactly the reach at point impedance, it is accepted that a shortcoming exists hanging in the balance between the hand-off and the reach a point.
The reach at purpose of a Relay is the point along the line impedance locus that is crossed by the limit normal for the hand-off.
Since this is reliant on the proportion of voltage and current and the stage edge between them, it might be plotted on a R/X graph. The loci of intensity protection impedances as observed by the Relay during deficiencies, control swings and burden varieties might be plotted on a similar chart and as such the exhibition of the hand-off within the sight of protection flaws and aggravations might be considered.
Distance hand-off performance is characterized as far as reach at exactness and working time. Reach at precision is a correlation of the genuine ohmic reach of the Relay under commonsense conditions with the hand-off setting an incentive in ohms.
Arrive at exactness especially relies upon the degree of voltage displayed to the Relay under issue conditions. The impedance estimating procedures utilized specifically Relay structures additionally have an effect. Working times can change with shortcoming current, with deficiency position comparative with the Relay setting, and with the point on the voltage wave at which the fault appears. Contingent upon the estimating strategies utilized in a specific Relay configuration, estimating signal transient mistakes, for example, those delivered by Capacitor Voltage Transformers or soaking CT’s, can likewise unfavorably postpone hand-off activity for issues near the reach a point. It is normal for electromechanical and static Distance relays to guarantee both greatest and least working occasions. Be that as it may, for present day advanced or numerical Distance Relays, the variety between these is little over a wide scope of protection working conditions and shortcoming positions.
Distance Relay Characteristics
Some numerical relays measure the supreme fault impedance and afterward decide if activity is required by impedance limits characterized on the R/X outline.
Customary Distance relays and numerical relays that copy the impedance components of conventional relays don’t quantify total impedance. They contrast the deliberate shortcoming voltage and an imitation voltage got from the issue current and the zone impedance setting to decide if the issue is inside zone or out-of-zone. Distance hand-off impedance comparators or calculations which copy customary comparators are arranged by their polar attributes, the quantity of sign sources of info they have, and the technique by which signal examinations are made.
The basic sorts look at either the relative abundancy or period of two info amounts to acquire working qualities that are either straight lines or circles when plotted on a R/X chart. At each phase of Distance relay protection engineering classes structure advancement, the improvement of impedance working trademark shapes and modernity has been administered by the innovation accessible and the worthy expense.
Since numerous customary relays are still in administration and since some numerical relay scope the strategies of the conventional Relays, a short survey of impedance comparators is supported.
Case of Modern Distance Protection Relay
SIPROTEC 7SA522 insurance Relay – Single line graph (gives full-conspire Distance protection and consolidates all capacities typically required for the protection of an electrical cable)
This particularly hand-off has following ANSI protection capacities:
|21/21N||Distance protection||50HS||Switch-onto-fault protection|
|FL||Fault locator||50BF||Breaker disappointment protection|
|50N/51N; 67N||Directional ground-fault protection||59/27||Overvoltage/under voltage protection|
|50/51/67||Backup overcurrent protection||81O||Over frequency insurance|
|50 STUB||STUB-transport overcurrent stage||81U||Under frequency insurance|
|68/68T||Power swing identification/tripping||25||Synchro-check|
|85/21||Tele protection for Distance protection||79||Auto-Reclosure|
|27WI||Weak-infeed protection||74TC||Trip circuit supervision|
|85/67N||Tele protection for ground-deficiency protection||86||Lockout (CLOSE order – interlocking)|