In an over current relay or oc relay the actuating quantity is only current. When a shortcircuit occurs, the system voltage falls to a low value and there may be insufficient torque developed in the relay. If the power flow is in the opposite direction, the relay will not operate. There is only one current operated element in the relay, no voltage coil etc. The essentials of directional overcurrent protection in. The induction type nondirectional overcurrent relay has a construction similar to a watthour meter, with slight modification. The relay is designed to operate when the actuating quantity equals, or exceeds, its pickup value. Abstract directional overcurrent relaying 67 refers to relaying that can use the phase relationship of voltage and current to determine direction to a fault. For this reason, directional elements are used to supervise ground overcurrent elements so that they only operate for faults in one direction, either forward or reverse, in order to simplify coordination. This is also a special type of over current relay with a directional features. Directional non directional overcurrent protection.
In power systems relays are used to detect abnormal conditions. The ibc relays consist of two units, an instantaneous powerdirectional unit bottom of the inductioncup type, and a time overcurrent unit. The second unit is an induction disk, ac operated, adjustable timing unit. The type crd relay utilizes the directional unit of the. For example, over current, under voltage, fault conditions etc. Or they can also be set to trip for faults behind the relay in the reverse direction. Directional overcurrent relays when the power system is not radial source on one side of the line, an overcurrent relay may not be able to provide adequate protection. The type krq relay is a highspeed directional overcurrent ground relay in which the directional unit operates on negative sequence current and voltage, and the overcurrent unit operates on residual current. The induction type relays are also called magnitude relays. The directional power relay is unsuitable for use as a directional protective relay under. This is because, besides the sensitivity, induction cup relay have steady non vibrating torque and parasitic torques due to current or voltage alone are small in induction cup directional or power relay, coils of one pair of poles are connected across voltage source, and coils of another pair of poles are. In an over current relay, there would be essentially a current coil. Basics of overcurrent protection linkedin slideshare.
The best and easy way to get familiarised with induction type overcurrent relay. They consist of three units, an instantaneous overcurrent unit top of the induction cup type, a time over current. The negative sequence current and voltage are obtained by means of selfcontained negative current and voltage filters. Constructional details and operation of non directional over current relay wattmeter type a directional over current relay operates when the current exceeds a specified value in a specified direction. The first static relays developed were the high speed differential relays and the distance relays. The name directional overcurrent relay is selfexplanatory. A technicians approach to cable testing directional. Over current relay working principle types electrical4u. The overcurrent relaying is made directional to provide relay coordination between all the relays that can see a given fault. Overcurrent automatic testing of positivenegativezero. These relays work on the principle of the induction motor or an energy meter. Directional overcurrent relay used to provide a sealin around the main protective relay contacts.
Directional overcurrent directional overcurrent ge grid solutions. The directional relays require two inputs that are the operating current and a referenceor polarizing quantity that does not change with fault location. Type krq directional overcurrent negative sequence ground. Directional over current relay linkedin slideshare. Induction cup relay is very suitable for directional or phase comparison units. The relay is built such that the angle of maximum torque occurs for phase current lagging the unity power position by 45 degrees or leading the quadrature voltage by. Overcurrent relays for transmission line protection. Principle of induction type relays electrical concepts.
Calculation of phase fault overcurrent relay settings. Inverse time over current relay inverse time is a natural character of any induction type rotating device. Otherwise, the coordination is often too difficult if not impossible. The paper focuses on how a numeric directional relay uses the phase relationship of sequence components such as positive sequence v1 vs. Bs 142, iac type characteristics, and relay specific curves based on the ieee equation pc37. It contains two relaying units, over current units and the other a directional unit. The paper focuses on how a numeric directional relay uses the. Leave a comment on this post, we will send you the overcurrent fundamental. Scribd is the worlds largest social reading and publishing site. The coils of the electromagnets are energised with the help of alternating currents. The directional power relay is unsuitable for use as a directional protective relay under shortcircuit conditions. The actuating quantity of an overcurrent relay is a current. The cap15b relay is a threephase, highspeed induction cup power relay that is similar to the.
Threephase directional overcurrent 67 each one of the threephase overcurrent stages of the p127 can be independently configured as directional protection with specific relay characteristic angle rca settings and boundaries. It responds to excessive current flow in a particular direction in the power system. Overcurrent relay protection is given at b, c, d and e, that is, at the infeed position of each part of the electrical power system. The ibc relays consist of two units, an instantaneous power directional unit bottom of the induction cup type, and a time overcurrent unit top of the induction. When normal current flows through this coil, the magnetic effect generated by the. Because of its low pickup, this device is basically a reverse power relay. In these relays, a metallic disc is allowed to rotate between the two electromagnets. The directional element is quadrature polarized, meaning the aphase relay uses aphase current and vbc voltage.
Digital directional and non directional overcurrent relays modeling and performance analysis. Most ground directional overcurrent relays can be thought of as having two components, a directional component and an overcurrent component. Type kh2 instantaneous directional overcurrent relay. The relay can be polarized from a potential source, from a local ground source, or from both simultaneously. This directional over current relay employs the principle of actuation of the relay, when the fault current flows into the relay in a particular direction. Directional over current and ef relays 01092015 when fault currents can flow in more than one direction it is desirable to determine which direction the fault current is flowing and trip the. Westinghouse induction type overcurrent and directional overcurrent relays i contacts j t1rf.
Idmt relay electrical engineering protection relays. Directional overcurrent relaying 67 concepts my protection guide. Both relay types are frequently provided in one relay case and are actuated by the. Digital directional and nondirectional overcurrent. Considerations in choosing directional polarizing methods. Each relay protection device comprises a definitetime delay overcurrent protection relay in which the trip of the current sensitive element starts the time delay device. This type of relay operates in on direction of current flow and blocks in the opposite direction. There are a variety of concepts by which this task is done. Aunovdec0911 it refers to the current or voltage which is used to activate the relay into operation. This type of directional relay is made by combining overcurrent protection equipment with an equipment to measure the phase displacement between the current. Overcurrent protection fundamentals r ced engineering. Mohammed tawfeeq overcurrent protective relays overcurrent relays overcurrent relaying is the simplest and cheapest type of protection used for protection of. Finding the direction in directional overcurrent relays. Type crd relay the dual polarized type relay is intended for.
When there is fault in power system, power flows through fault. Mechanical and solid state relays determine direction by connection. Depending on the time of operation the overcurrent relay is categorized into following types. What is the difference between induction type directional. Medium voltage products technical guide protection criteria for medium voltage networks. The type ibcg relays are ground directional overcurrent relays used primarily for the protection of feeders and transmission lines. The actuating source is a current in the circuit supplied to the relay from a current transformer. The overcurrent relays, even though simplest of all types of electromechanical relays, are the most difficult static relays. The ibc directional overcurrent relays are employed primarily for the protection of feeders and transmission lines in applications where singlephase relays are desired or required. The type kh2 instantaneous directional overcurrent relay is used whenever a directional unit with an adjustable pickup is desired. This is because the induction disc characteristics of the overcurrent relays inverse characteristics are not amenable to simple mathematical analysis. The figure below shows the constructional of nondirectional induction type overcurrent relay. Testing directional overcurrent relays from valence. Directional overcurrent protection devices can achieve this requirement, albeit at extra cost.
Actuating force is developed in a movable element that may be a disc or other form of rotor of nonmagnetic currentconducting material by the interaction of electromagnetic fluxes with eddy currents that are induced in the rotor by these fluxes. Induction type directional over current relay free download as word doc. Forward, reverse directional relays may or may not make use of directionally controlled instantaneous units. The directional unit contacts control the operation of the overcurrent unit directional control, application phase faultmc the type ibc relays are frequently applied for. Induction type overcurrent relay construction operation. Medium voltage products technical guide protection. The type crp relay operates on residual voltage and residual current. The negative sequence current and voltage are obtained by means of. Directional ieds determine the direction of the fault current by measuring the voltage with a voltage transformer as well as the current with a current transformer, and establishing the phase difference this technical article does not go into details of exactly how this is achieved, but it can be. The overcurrent relay operates when the current in the circuit exceeds a certain preset value. The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time.
Consider a typical electromechanical phase directional relay. It protects the equipment of the power system from the fault current. The directional unit minimum pickup is 1 volt and 2 ampere s at it s maximum torque angle fo r the 0. Induction cup relay working principle construction and types. This relay is also called earth leakage induction type relay.
Overcurrent directional relays can be set to trip for faults in the forward direction, which will protect the equipment in front of the relay. Well be looking at directional overcurrent relays from a testing perspective in this post. An induction type relay is a splitphase induction motor with contacts. Each directional stage has instantaneous start forwardreverse outputs available.