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I don't know how you got this posted in the Dodge forum but I will explain.

The directional overcurrent relay is a relay that will provide overcurrent protection in a directional manner. I know this sounds simplistic but let me give you a scenario.

A large industrial company has its own electrical generation provided by a few generators. One might think that the company would have no outside connection to a public utility because they generate their own electricity.

However this is not the case as having a tie to the utility affords a few advantages. Some advantages are that synchronization of the industrial companies generators can easily be maintained at 60Hz. Additional inrush current can be easily provided by the utility, whereas should the industrial company only rely on their generators a larger voltage swing might occur when a large motor is started. The industrial customer can also be provided with backup power levels in case of some failure with their own generation.

So you do want to provide a tie to the utility. You must protect the tie against overcurrents. However, if something were to happen to cause the utility power to fail you certainly do NOT want to try to power all the utilities other customers.

Thats where the directional overcurrent relay comes into play. It will allow power to flow and protect a circuit as long as power is coming into a plant by a tie line. However should power try to flow out of the utility tie the directional overcurrent relay will trip.

A mechanical directional overcurrent relay is actually a combination of a directional relay and an overcurrent relay. The directional portion is closely resembles a watt-hour meter. A potential transformer is required to provide a reference and if current is flowing one direction then a positive torque is placed on a mechanical disk. If current is flowing in the other direction then a negative torque is placed on the disk.

Should the CT and PT connections be made such that positive torque is placed on the disk when current is flowing out of the industrial customer and to the utility then the disk will rotate and cause a contact to close. The closing contact will operate a breaker trip coil. However if current is flowing from the utility to the industrial customer then negative torque will be placed on the disk and it will be stopped by mechanical stops and the breaker will continue to remain closed.

Of course you can use normally open or closed contacts to make the relays operate when and how you want.

Other applications are as a reverse power relay for a generator and for line protection in a grid type system.

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What is difference between reverse power relay and directional relay in electrical protection?

A reverse power relay is a directional overcurrent relay. Directional relays are relays that sense power flow in one direction, and include (directional) overcurrent relays, reverse power, and impedance based relays. So a reverse power relay is a directional relay, but a directional relay is not necessarily a reverse power relay.


Can you define the term OCR in electrical terminology?

OverCurrent Recloser, or OverCurrent Relay.


What is pick up of a relay?

The "pick up" of a relay is a setting at which the relay will begin to operate. Such as an overcurrent relay - if the pickup is set to 5A, when 5A is flowing through the relay, the relay will operate.


Earth fault relay and an overcurrent relay Methods to energise an earth fault relay?

Earth fault relay and an over current relay Methods to energies an earth fault relay with simulation diagram?


What is the difference between voltage restrained overcurrent protection and voltage controlled overcurrent protection?

Voltage restrained overcurrent protection uses a fixed voltage threshold to trip the protection device when an overcurrent condition is detected. In contrast, voltage controlled overcurrent protection adjusts the trip threshold based on the system voltage level, allowing for more precise coordination with other protective devices and better protection of the equipment. The key distinction lies in the method of setting the trip threshold: fixed voltage for voltage restrained, and voltage-dependent for voltage controlled overcurrent protection.

Related Questions

What is difference between reverse power relay and directional relay in electrical protection?

A reverse power relay is a directional overcurrent relay. Directional relays are relays that sense power flow in one direction, and include (directional) overcurrent relays, reverse power, and impedance based relays. So a reverse power relay is a directional relay, but a directional relay is not necessarily a reverse power relay.


What are the directional characteristics of an over current relay?

Directional relay opeartes +/- 90degree of MTA (maxumum torque angle). Relay is set either forward or reverse depending on the direction of current flow. 180 degree to MTA is always restraint region. Some relay has chareteristic of +/- 85 degree to MTA.


Can you define the term OCR in electrical terminology?

OverCurrent Recloser, or OverCurrent Relay.


What is the theory behind a definite time overcurrent relay?

A definite time overcurrent relay operates like an instantaneous overcurrent relay coupled with a timer. once current reaches the pickup value, the relay overcurrent relay will trip, which initiates the timing circuit. as long as current stays above this pickup value, the timer will continue to time. Once the definite time setting is reached, the timer will close the relay tripping contacts.


What is the main concern regarding overcurrents?

On directional element stability, directional overcurrent applications, and have exploded and pose safety concerns, which are discussed later.


What do relay and circuit breakers use?

No. A relay is an electric switch and a circuit breaker is an overcurrent device.


What is pick up of a relay?

The "pick up" of a relay is a setting at which the relay will begin to operate. Such as an overcurrent relay - if the pickup is set to 5A, when 5A is flowing through the relay, the relay will operate.


Why use over current relay?

To protect things from getting damaged by overcurrent.


Earth fault relay and an overcurrent relay Methods to energise an earth fault relay?

Earth fault relay and an over current relay Methods to energies an earth fault relay with simulation diagram?


What is relay coordination system?

Coordination between upstream relays for a overcurrent fualt on down stream.


What is meant by residual overcurren?

Residual overcurrent protection is often provided in modern microprocessor based relays that have three phase inputs, and no neutral input. Sometimes this is provided even if a neutral input is present. It is similar to neutral overcurrent, where the neutral current is directly measured through the neutral input of the relay. for residual overcurrent, the three phase currents are vectorially summed together to form the residual overcurrent. This relay measured 3I0 current, or ground current.


How is the relay effecting the bimetallic strip of circuit breaker?

The relay controls the flow of current through the circuit breaker by responding to an overcurrent situation. When the relay detects an overcurrent, it triggers the circuit breaker to open, which releases the tension on the bimetallic strip inside. This causes the bimetallic strip to bend and disconnect the circuit, effectively breaking the flow of electricity to prevent damage or hazards.