Overcurrent directional relays can be set to trip for faults in the forward direction, which will protect the equipment in front of the relay. Induction cup relay is very suitable for directional or phase comparison units. 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 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. Digital directional and nondirectional overcurrent. Directional over current relay linkedin slideshare. Idmt relay electrical engineering protection relays. There is only one current operated element in the relay, no voltage coil etc.
Induction type directional overcurrent relay construction working. The first static relays developed were the high speed differential relays and the distance relays. Leave a comment on this post, we will send you the overcurrent fundamental. What is the difference between induction type directional. This induction type overcurrent relay works on the induction principle and initiates corrective measures when current in the circuit exceeds the predetermined value. The directional unit contacts control the operation of the overcurrent unit directional control, application phase faultmc the type ibc relays are frequently applied for. 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. 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. Mohammed tawfeeq overcurrent protective relays overcurrent relays overcurrent relaying is the simplest and cheapest type of protection used for protection of. Directional non directional overcurrent protection. Abstract directional overcurrent relaying 67 refers to relaying that can use the phase relationship of voltage and current to determine direction to a fault. A technicians approach to cable testing directional. Overcurrent protection fundamentals r ced engineering.
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. When normal current flows through this coil, the magnetic effect generated by the. Well be looking at directional overcurrent relays from a testing perspective in this post. Each directional stage has instantaneous start forwardreverse outputs available.
Consider a typical electromechanical phase directional relay. The essentials of directional overcurrent protection in. 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. Type irv directional overcurrent relayfor phase protection. The type crd relay utilizes the directional unit of the. The best and easy way to get familiarised with induction type overcurrent relay. The paper focuses on how a numeric directional relay uses the phase relationship of sequence components such as positive sequence v1 vs. In an over current relay, there would be essentially a current coil. When a shortcircuit occurs, the system voltage falls to a low value and there may be insufficient torque developed in the relay. An induction type relay is a splitphase induction motor with contacts. The coils of the electromagnets are energised with the help of alternating currents. Scribd is the worlds largest social reading and publishing site.
When there is fault in power system, power flows through fault. 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 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. Forward and reverse are typically determined by the normal flow of current into the relay, so be sure to confirm the. Medium voltage products technical guide protection. It con sists of a steel ball resting between two hemispherical cup jewels, one fixed in the. The negative sequence current and voltage are obtained by means of. The relay can be polarized from a potential source, from a local ground source, or from both simultaneously. Fundamentals and improvements for directional relays.
Calculation of phase fault overcurrent relay settings. For example, over current, under voltage, fault conditions etc. The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time. The type crp relay operates on residual voltage and residual current. 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. The type ibcg relays are ground directional overcurrent relays used primarily for the protection of feeders and transmission lines. The directional element is quadrature polarized, meaning the aphase relay uses aphase current and vbc voltage. Overcurrent is used for automatic testing of directional and non directional overcurrent relays with autoassessment of the trip time characteristic, the directional boundaries of the current stages, and the pickupdropoff ratio. Directional overcurrent directional overcurrent ge grid solutions. The ibc relays consist of two units, an instantaneous powerdirectional unit bottom of the inductioncup type, and a time overcurrent unit. 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. 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. Otherwise, the coordination is often too difficult if not impossible.
In power systems relays are used to detect abnormal conditions. Type crd relay the dual polarized type relay is intended for. Depending on the time of operation the overcurrent relay is categorized into following types. The type kh2 instantaneous directional overcurrent relay is used whenever a directional unit with an adjustable pickup is desired. 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. Because of its low pickup, this device is basically a reverse power relay. Over current relay working principle types electrical4u. Testing directional overcurrent relays from valence. Digital directional and non directional overcurrent relays modeling and performance analysis. These relays work on the principle of the induction motor or an energy meter. Induction type overcurrent relay construction operation.
In an over current relay or oc relay the actuating quantity is only current. Bs 142, iac type characteristics, and relay specific curves based on the ieee equation pc37. Aunovdec0911 it refers to the current or voltage which is used to activate the relay into operation. 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. Considerations in choosing directional polarizing methods. Mechanical and solid state relays determine direction by connection. This type of relay operates in on direction of current flow and blocks in the opposite direction. It contains two relaying units, over current units and the other a directional unit. The overcurrent relay operates when the current in the circuit exceeds a certain preset value.
There are a variety of concepts by which this task is done. 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. This is because the induction disc characteristics of the overcurrent relays inverse characteristics are not amenable to simple mathematical analysis. The cap15b relay is a threephase, highspeed induction cup power relay that is similar to the. 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. Finding the direction in directional overcurrent relays.
The currenttime tripping characteristics of idmt protection relays may need to be changed according to the functioning time needed and the characteristics of other relay protection elements used in the electrical network. Directional overcurrent protection devices can achieve this requirement, albeit at extra cost. Type kh2 instantaneous directional overcurrent relay. In these relays, a metallic disc is allowed to rotate between the two electromagnets. The name directional overcurrent relay is selfexplanatory. Or they can also be set to trip for faults behind the relay in the reverse direction.
Types cr, crc, crp and crddirectional overcurrent relays. They consist of three units, an instantaneous overcurrent unit top of the induction cup type, a time over current. Directional overcurrent relaying 67 concepts my protection guide. This type of directional relay is made by combining overcurrent protection equipment with an equipment to measure the phase displacement between the current. The figure below shows the constructional of nondirectional induction type overcurrent relay. Westinghouse induction type overcurrent and directional overcurrent relays i contacts j t1rf. Induction type directional over current relay free download as word doc. Overcurrent relays for transmission line protection. It protects the equipment of the power system from the fault current. The directional power relay is unsuitable for use as a directional protective relay under shortcircuit conditions.
Forward, reverse directional relays may or may not make use of directionally controlled instantaneous units. If the power flow is in the opposite direction, the relay will not operate. Type krq directional overcurrent negative sequence ground. The paper focuses on how a numeric directional relay uses the. The induction type nondirectional overcurrent relay has a construction similar to a watthour meter, with slight modification. The actuating quantity of an overcurrent relay is a current. Most ground directional overcurrent relays can be thought of as having two components, a directional component and an overcurrent component. Basics of overcurrent protection linkedin slideshare. 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 directional relays require two inputs that are the operating current and a referenceor polarizing quantity that does not change with fault location. The overcurrent relaying is made directional to provide relay coordination between all the relays that can see a given fault.
Both relay types are frequently provided in one relay case and are actuated by the. This relay is also called earth leakage induction type relay. Medium voltage products technical guide protection criteria for medium voltage networks. Overcurrent automatic testing of positivenegativezero. The relay is designed to operate when the actuating quantity equals, or exceeds, its pickup value. Directional overcurrent relay used to provide a sealin around the main protective relay contacts. The negative sequence current and voltage are obtained by means of selfcontained negative current and voltage filters.
536 791 556 757 439 1363 958 732 1391 241 1030 1 1184 1149 1236 764 1264 1342 1185 750 578 661 416 1102 8 1029 1251 746 373 1232 275 903 552