Distance Relay

Distance or distance relays are used as a safety relay main (main protection) in a transmission system, whether or SUTET SUTT, and as a backup or a backup for the front section. Distance relay works by measuring the amount of impedance (Z), and transmission is divided into several areas of security coverage of Zone-1, Zone-2, and Zone-3, and equipped also with teleproteksi (TP) in a bid for protection work is always fast and selective inside the security area. etc..

Working Principle Distance Relay Relay distance relays measure voltage and current at the point of visible disruption of the relay, by dividing the amount of voltage and current, the impedance to the point of interference can be determined. The calculation of the impedance can be calculated using the following formula:
Zf = Vf / If
Where: Zf = Impedance (ohm) Vt = Voltage (Volts) If = Flow disturbance
Distance relays will work by comparing the measured impedance interference with impedance settings, with the following provisions: a. When the price of disorder impedance is smaller than the impedance setting of the relay then the relay will trip. b. If the price is greater than the impedance disorder impedance relay setting the relays will not trip. 

Impedance Measurement Disturbance By Distance Relay
According to the types of disturbances in electric power system, consisting of three-phase short circuit fault, two phase, two phase to ground and single phase to ground. Distance relay as the main security should be able to detect all kinds of disorders and then separate the disturbed system with a system that is not disturbed.
1. Three Phase Short circuit interruption
In the event of disruption of symmetrical three-phase, then the amplitude of phase voltage VR, VS, VT decreased, but differences remain phase electricity in 1200. Distance relay impedance measured during a three-phase short circuit fault are as follows:
Vrelai = VR
Irelai = IR
ZR = VR / IR
Where, ZR = relay impedance is readable by VR = Voltage phase to neutral IR = Current phase
2. Short circuit interruption Phase Two
To measure the impedance during a two-phase short circuit fault, the voltage coming into the comparator phase voltage relays are affected, while the flow are the difference (a vector) currents are disrupted. Suppose the short circuit occurred between phases S and T, then the impedance measurement for short circuit between phases S and T are as follows:
V relay = VS - VT
I relay = IS - IT
Thus,
ZR = Vrelai / Irelai = (VS - VT) / (IS - IT)
3. Short circuit interruption Single Phase To Land
To measure the impedance at the time of single phase short circuit to ground, the voltage that is inserted into a voltage relay is disrupted, while the phase currents disturbed plus residual current compensation factor multiplied. For example, an interruption of short circuit single phase R to the ground, the impedance measurements performed in the following way:
Voltage at the relay: Vrelai = VR
Flows on the relay: Irelai = IR + K0.In
Neutral currents: In = IR + IS + IT
Zero sequence compensation: K0 = 1 / 3 (Z0-Z1/Z1)
Z1 = VR / (IR + K0.In)
for single phase short circuit fault to ground, zero sequence impedance will result in soil disturbance. K0 existence is to compensate the zero sequence impedance of these. Thus, the measured impedance to be true.
Characteristics of Distance Relay
Characteristics of the distance relay is a direct application of basic principles of distance relay. These characteristics usually described in the RX diagram. Various kinds of distance relay characteristics are as follows:
1. Characteristic impedance Its characteristics: a. Is a circle with its center point in the middle, so have the nature of non-directional. To be applied as a safety relay should be added SUTT relay directional or direction. b. Having anticipated the limitations of high ground fault resistance. c. Impedance characteristics sensitive to a change in burden, especially for long SUTT thus reach the circle close to the load impedance.
2. Mho characteristic Characteristics: a. The epicenter has shifted so that the directional properties. b. Have limitations for the anticipated high ground fault resistance. c. For a long SUTT selected Zone-3 with a sliding lens mho characteristics.

3. Reactance Characteristics Characteristics: a. Reactance characteristics have a non-directional nature. For applications in SUTT need plus relays relay directional or direction. b. By setting the resistive reach large enough to anticipate the reactance relay ground fault with high resistance.

4. Quadrilateral Characteristics Characteristics: a. Quadrilateral characteristic is a combination of 3 kinds of components are: reactance, trending and resistive. b. By setting a large enough range of resistive, then the quadrilateral relay characteristic can anticipate the disturbance of land with high resistance. c. Generally slower than the speed relay mho type.