Distance Protection is a Non-unit System of Protection, which measures the Impedance between the Relay Location and the point where the fault is incident and compares it with the Set Value. … Since it protects a certain Length of Transmission Line, it is called a Distance Relay.
How does distance protection work?
The basic principle of distance protection involves the division of the voltage at the relaying point by the measured current. … If the measured impedance is less than the reach point impedance, it is assumed that a fault exists on the line between the relay and the reach point.
Why distance protection is used?
Distance protection schemes are commonly employed for providing the primary or main protection and backup protection for AC transmission line and distribution line against three-phase faults, phase-to-phase faults, and phase-to-ground faults.
What are different types of distance protection?
Distance relay applications
- Impedance Relay. The impedance relay has a circular characteristic centered at the origin of the R-X diagram. …
- Admittance Relay. The admittance relay is the most commonly used distance relay. …
- Reactance Relay.
What is distance and differential protection?
The basic principle of distance relay is that the apparent impedance seen by the relay, which is defined as the ratio of phase voltage to line current of a transmission line (Zapp), reduces drastically in the presence of a line fault. … This ratio also indicates the distance of the fault from the relay.
What is the reach of first step of three stepped distance protection?
The first zone tripping which is instantaneous is normally set to 80% of the protected section. The zone 2 protection with a time delay sufficient for circuit breaker operating time and discriminating time margin covers the remaining 20% portion of the protected section plus 25 to 40% of the next section.
How does a distance protection relay work?
The distance relay is a distance protection element designed to measure the faulty point. The operation of this relay depends on the value of the impedance. It trips the circuit breaker and closes the contacts when the impedance of the faulty point is less than the impedance of the relay.
What are main problems with distance relaying scheme?
The major problem to the distance relay is to measure correct impedance from relaying point to fault point when series capacitor remains in fault path.
What are the main tripping characteristics for distance protection?
Distance protection with polarized mho characteristic has 100% directionality, low sensitivity to arc resistance, or power swing in the network. The tripping characteristic in figure 6d belongs to older static electronic protection relays.
What is meant by 3 zone protection?
To protect transmission line from faults 3 zone distance protection is widely used as it also provides backup protection. This paper aims at simulating three step protection using PSCAD software under different fault conditions in different zones.
Where is MHO relay used?
Abstract: Mho distance relays are widely used for the protection of uncompensated and series compensated transmission lines in order to determine the presence and location of faults.
What are the applications of distance relay?
Distance relays are used for both phase fault and ground fault protection, and they provide higher speed for clearing the fault. It is also independent of changes in the magnitude of the short circuits, current and hence they are not much affected by the change in the generation capacity and the system configuration.
Why is distance protection better than overcurrent protection?
In over current protection, protection is based on a curve. The higher the fault current, the shorter the breaking time and vice versa. Meaning, fault at distance 2 km (higher current) is protected quicker than a fault at 5 km(lower fault current).
What is distance protection of transmission lines?
Distance Protection is a Non-unit System of Protection, which measures the Impedance between the Relay Location and the point where the fault is incident and compares it with the Set Value. If the measured Impedance is less than the Set Value , the Relay operates and Isolates the Faulty Section.
What is MHO relay?
Mho relay is a voltage restrained directional relay. Important Points: Reactance relay is suitable for the protection of a short transmission line because its operation is independent of arc resistance. The relay which is selected for a long transmission line should be less affected due to power swings.