Directional relay

What is a directional relay?
Why do we use directional relay?
What is directional and non directional relays?
What are directional relays used to protect?
What are the three types of relays?
What does directional relay respond to?
What is the difference between reverse power relay and directional relay?
What are the problems of directional relays?
Do relays need AC or DC?
What is the difference between a directional and a non directional test?
What are the two classifications of relays?
What are the advantages of directional overcurrent relay?
What is L1 and L2 in a relay?
What is the most commonly used relay?
How do relays work?
What does directional relay respond to?
What is the difference between reverse power relay and directional relay?
Which distance relay is directional relay?
What is directional earth fault relay?
What are the disadvantages of directional relays?
What are the problems of directional relays?
What are the two classifications of relays?
What happens if you install a relay backwards?
Is distance relay directional or non directional?
Why zone 1 is 80?
Why is it called distance relay?

What is a directional relay?

Definition: A protection relay in which the tripping decision is dependent in part upon the direction in which the measured quantity is flowing.

Why do we use directional relay?

The directional relays permit tripping only for a certain direction of current flow, and the other relays determine (1) if it is a short circuit that is causing the current to flow, and (2) if the short circuit is near enough so that the relays should trip their circuit breaker.

What is directional and non directional relays?

In the protection of parallel feeders, non-directional overcurrent relays are used on the source side, and directional overcurrent relay used on the load side.

What are directional relays used to protect?

In a complex distribution or sub-transmission network, these relays may be used to improve the coordination of the system. Hence, we can use a directional overcurrent relay for the protection of the ring main distribution lines.

What are the three types of relays?

The three main types of relays are electromechanical, solid-state, and reed.

What does directional relay respond to?

Directional relays can respond to positive sequence, negative sequence, or zero sequence inputs. This should be a consideration when applying directional relays at locations where zero-sequence voltage is minimal.

What is the difference between reverse power relay and directional relay?

P RINCIPLE OF R EVERSE POWER R ELAY A reverse power relay is a directional relay that is used to monitor the power flow from generator (running in parallel with another generator or the utility) and in case of abnormal condition take appropriate action.

What are the problems of directional relays?

Directional relays use voltage as the polarizing quantity. When three-phase faults occur close to the relay bus, the available voltage becomes nearly zero and this creates a problem in estimation of the fault direction. The capacitor coupling voltage transformer subsidence transients add to this problem.

Do relays need AC or DC?

The operating voltage of a relay is generally in DC. Small signal relays and low voltage power relays are usually in DC, but mains control relays and contactors quite frequently have AC coils. The rest of the terminals of a relay are used to connect either a AC(generally 50/60Hz) or DC circuit.

What is the difference between a directional and a non directional test?

Directional tests are known as "one-tailed" tests because all of the error is is one "tail" of the distribution (less than). Non-directional tests are called "two-tailed" tests because we must include the possibility that the alternative population could be less than m or greater than m.

What are the two classifications of relays?

Classification of relay can be mainly into two types: mechanical relays and solid state relays.

What are the advantages of directional overcurrent relay?

Due to its ability to detect the direction of a short-circuit current, directional overcurrent protection helps to protect an installation against short-circuit currents that could circulate in both directions through the circuit breaker.

What is L1 and L2 in a relay?

1. The two vertical lines that connect all devices on the relay logic diagram are labeled L1 and L2. The space between L1 and L2 represents the voltage of the control circuit. 2. Output devices are always connected to L2.

What is the most commonly used relay?

Electromechanical Relays. Electromechanical relays are perhaps the most widely used relays in ATE applications today. They are made of a coil, an armature mechanism, and electrical contacts. When the coil is energized, the induced magnetic field moves the armature that opens or closes the contacts.

How do relays work?

The relay permits a small amount of electrical current to control high current loads. When voltage is supplied to the coil, small current passes through the coil, resulting in a larger amount of current passing through the contacts to control the electrical load.

What does directional relay respond to?

What is the difference between reverse power relay and directional relay?

Which distance relay is directional relay?

The relay is called Mho relay because its characteristic is a straight line, when plotted on an admittance diagram. It is inherently a directional relay as it detects the fault only in the forward direction.

What is directional earth fault relay?

The directional earth-fault relay SPAS 120 C is used for selective feeder earth-fault protection in isolated neutral and impedance earthed networks. The relay is especially useful in networks, where the operation characteristic of the earth-fault relay must be remotely controllable.

What are the disadvantages of directional relays?

Disadvantages or demerits:

The directional feature is absent in electromagnetic relays. Requires periodic maintenance and testing unlike static relays. Relay operation can be affected due to ageing of the components and dust, pollution resulting in spurious trips.

What are the problems of directional relays?

What are the two classifications of relays?

Classification of relay can be mainly into two types: mechanical relays and solid state relays.

What happens if you install a relay backwards?

Many relays, if installed for the wrong application, could and will cause a short (Internal Relay Circuit) and most likely cause functionality issues or even damage to the vehicle computer systems.

Is distance relay directional or non directional?

It is nondirectional and is used to supplement the admittance relay as a tripping relay to make the overall protection independent of resistance. It is particularly useful on short lines where the fault arc resistance is the same order of magnitude as the line length.

Why zone 1 is 80?

As we discussed in the previous video, Zone 1 is set at 80% of the line to compensate for any CT accuracy and calculation errors, and Zone 2 will protect the other 20% of the line with a 20-cycle time delay.

Why is it called distance relay?

Time Distance Relays

That means its operation depends on the distance between the fault and the relay point. It works more efficiently and earlier when the fault is nearer to the relay point. These come under impedance, reactance, or mho type relays.