Sep 08, 2018 overcurrent time protection is a selective type of overload and shortcircuit protection used mainly in radial networks with singleended feed as found in mediumvoltage systems. Here, an aluminum or copper disc is placed between the poles of an. S type lac relay with an ac trip unit rear view burdens. Principle of induction type relays electrical concepts. Induction cup relay work in same principle of induction disc relay.
Standard thermalovercurrent element will time out and trip motor offline motor will never start traditional solution speed switch examples of speed switches proximity probe magnetic type rotating disc laser type if shaft movement is not detected, starting is aborted. Although time inverse characteristic is inherent to electromechanical induction disc relay, the same characteristic can be achieved in microprocessorbased relay also by. Motor protection unit advanced motor protection model for larger, complex motors. The type cdg 24 relay is a cdg 14 with an instantaneous unit. This means that, the time of operation inversely varies with input current. The overcurrent relay inverse definite minimum time idmt characteristics curves based on the simulated fault current data are used as basis and are implemented for single phase circuits. This natural characteristic of electromechanical induction disc relay is very suitable for overcurrent protection. Provides current and temperature protection, data logging, and metering. The above figure shows the wattmeter type induction relay.
Westinghouse induction type overcurrent and directional overcurrent relays i contacts j t1rf. Electromagnetic relay working types of electromagnetic. 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 electromagnetic relay operates on the principle of a splitphase induction motor. Apr 26, 2018 the different types of structure that have been used for an induction type relay are commonly called. The induction type relays are also called magnitude relays. 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 unit d the directional unit minimum pickup is approximately.
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 relay is designed to operate when the actuating quantity equals, or exceeds, its pickup value. The overcurrent relay is the simplest type of protective relay. 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. Electromagneticinduction relays use the principle of the induction motor. This relay in nothing but one version of induction disc relay. Induction cup relay working principle construction and types. The overcurrent relays, even though simplest of all types of electromechanical relays, are the most difficult static relays. A 400v industrial distribution power system is used as a tutorial to simulate and test overcurrent relays performance results, with motor start up inrush. Induction type relay construction detail electrical concepts. Directional over current relay linkedin slideshare.
The fig shows how an induction disc type over current relay with split pole i. These are classified as nondirectional and directional over current relays. Constructional details and operation of non directional over current relay wattmeter type it has a metallic disc free to rotate between the poles of two electromagnets em. Induction type directional over current relay free download as word doc. Jul 14, 2016 the fig shows how an induction disc type over current relay with split pole i. So, high current will operate overcurrent relay faster than lower ones. The coils of the electromagnets are energised with the help of alternating currents. Apr 26, 2018 an induction type relay is a splitphase induction motor with contacts. In induction relay the deflecting torque is produced by the eddy currents in an aluminium or copper disc by the flux of an ac electromagnet. In induction disc type of relays, disc is the moving element on which the moving contact of relay is fixed whereas in the case of induction cup the contact is fixed on the cup. In the relay setting procedure, the user is prompted for relay x or y and then for the application. Scribd is the worlds largest social reading and publishing site. Types cr, crc, crp and crddirectional overcurrent relays.
Type lac time overcurrent relay geh1788 shorting coil main coil ac tripping unit fi g. Inductiontype relays are the most widely used protective. Type lac time overcurrent relay geh1788 shorting coil main coil ac tripping unit fi. Aspects of overcurrent protection for feeders and motors. Determine the time of operation of a relay of rating 5a, 2. This is also a special type of over current relay with a directional features. Here, an aluminum or copper disc is placed between the poles of an ac magnet which produces an alternating flux. Aug 31, 2018 the induction disc type relay is based on the same principle as that of an ammeter or a volt meter, or a wattmeter or a watt hour mater. The first static relays developed were the high speed differential relays and the distance relays. This induction type overcurrent relay works on the induction principle and initiates corrective measures when current in the circuit exceeds the predetermined value. Both relay types are frequently provided in one relay case and are actuated by the. The spindle of this disc carries a moving contact which bridges two fixed contacts when the disc rotates through an angle, which is adjustable between 0 o to 360 o. 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. The actuating source is a current in the circuit supplied to the relay from a current transformer.
According to this standard and its interpretation in 11, the overcurrent relay is described by tripping and reset characteristics with the following equations t trip a ii pu p. There are standard inverse, very inverse and extremely inverse types. 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. Sep 01, 2018 this natural characteristic of electromechanical induction disc relay is very suitable for overcurrent protection. Over current relay working principle types electrical4u. Aunovdec0911 it refers to the current or voltage which is used to activate the relay into operation. The basis construction of this relay is just like four poles or eight pole induction motor. For example, a relay including function 51 would be a timed overcurrent protective relay. These bimetallic strips are heated by a winding around the bimetal strip, which. An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. All the ibcg relays contain a time overcurrent unit of the induction disk type and an instantaneous directional unit of the induction cup type. The shaded pole structure the watthourmeter structure the induction cup and double induction loop structures the single induction loop structure.
Working principle of inductional type overcurrent relaynd15. Overcurrent protection fundamentals r ced engineering. Depending upon the time of operation, overcurrent relays may be categorized as instantaneous over current re. The initial force is developed on the moving element that may be disc or another form of the rotor of the nonmagnetic moving element. The relay can be polarized from a potential source, from a local ground source, or from both simultaneously. The different types of structure that have been used for an induction type relay are commonly called. Inverse time over current relay inverse time is a natural character of any induction type rotating device. Overcurrent time protection is a selective type of overload and shortcircuit protection used mainly in radial networks with singleended feed as found in mediumvoltage systems. The induction type nondirectional overcurrent relay has a construction similar to a watthour meter, with slight modification. The time induction overcurrent unit 51toc protects against motor overloads. Inverse time overcurrent relays idmt relay in this type of relays, operating time is inversely changed with current. First, we need to define the impedance between the relay and the fault location. Directional non directional overcurrent protection.
Attracted armature type relays with time element shows this characteristics. An induction disc type relay adapted to apply to an induction disc a rotational torque proportional to an input so that an operating output is produced at the expiration of a predetermined time dependent on the magnitude of the input after the application of the input. If the power flow is in the opposite direction, the relay will not operate. Electromagnetic relay working types of electromagnetic relays. Depending on the time of operation the overcurrent relay is categorized into following types. Pdf numerical relay for overcurrent protection using. Current sensing relays are always used in conjunction with current transformers cts which are used as low. Induction type overcurrent relay nondirectionalstrictly related to. Type cdg 14 extremely inverse time overcurrent and earth fault relay a high set overcurrent unit type cag can be fitted in the same case to provide instantaneous protection under maximum short circuit conditions see application sheet r5087. An induction type relay is a splitphase induction motor with contacts. The figure below shows the constructional of nondirectional induction type overcurrent relay. Basics of overcurrent protection linkedin slideshare. The time overcurrent unit is similar to the ifc5ia relay except that a voltage restraint umagnet and coil has been added that produces a restraint torque that opposes the operating coil. These relays work on the principle of the induction motor or an energy meter.
The actuating quantity of an overcurrent relay is a current. This induction type overcurrent relay works on the induction principle and initiates corrective measures when current in the circuit exceeds. The second unit is an induction disk, ac operated, adjustable timing unit. If the fault is severe, it will clear the fault faster.
This is because the induction disc characteristics of the overcurrent relays inverse characteristics are not amenable to simple mathematical analysis. The shadedpole structure as shown in figure below is generally actuated by current flowing. Such a scheme is the simplest form of directional overcurrent protection, and at each point the relays provided may be 1 one overcurrent o. Non indirectional induction overcurrent relay construction. Closeup of an inductiontype overcurrent unit, showing the disc rotor and drag.
Overcurrent relay overcurrent relay is a sensing relay, which operates when the current increases beyond the operating value of the relay. The cap15b relay is a threephase, highspeed induction cup power relay that is similar to the. 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. In these relays, a metallic disc is allowed to rotate between the two electromagnets. The type crd relay utilizes the directional unit of the crc relay in conjunction with the directional unit and phase shifting mechanism of the.
Depending on the type of rotor whether a disc or a cup, the relay is known as an induction disc or an induction cup relay. The induction disc type relay is based on the same principle as that of an ammeter or a volt meter, or a wattmeter or a watt hour mater. Application the iac66a, b, and c relays are used to protect a motor against two abnormal conditions. This relay is also called earth leakage induction type relay.
The relay then presents a group of elements to be set. The type ifcv51ad relay is a singlephase, extended range, very inverse time overcurrent relay with voltage restraint. Type cdg 14 extremely inverse time overcurrent and earth. Because of its low pickup, this device is basically a reverse power relay.
The directional unit minimum pickup is 1 volt and 2 ampere s at it s maximum torque angle fo r the 0. The best and easy way to get familiarised with induction type overcurrent relay. Overcurrent, undercurrent, overvoltage, and undervoltage relays are derived directly from the basic singlequantity electromagneticattraction or induction types. It con sists of a steel ball resting between two hemispherical cup jewels, one fixed in the. Wattmetric and shaded pole relays of induction type can be used to obtain this. Modular, compact design overcurrent reduction setting for maintenance dynamic thermal modeling 4line, 80character lcd display communications options for. Many overload relays include bimetallic elements or bimetallic strips, also referred to as heater elements. Thus, it has a time setting adjustment and pick up adjustment. The force is developed by the interaction of electromagnetic fluxes with eddy current, that is induced in the rotor by these. The number of poles in the protective relay depends upon the number of winding to be accommodated. As the name implies, the relay is designed to operate when more than a predetermined amount of current flows into a particular portion of the power system. It protects the equipment of the power system from the fault current.
The type crp relay operates on residual voltage and residual current. Leave a comment on this post, we will send you the overcurrent fundamental. Type crd relay the dual polarized type relay is intended for. Overcurrent protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults, over load etc2. Induction type overcurrent relay construction operation.415 1070 799 586 818 440 855 1349 506 284 474 276 131 686 749 1045 86 385 799 125 816 428 392 710 1443 1142 1136 1031 1244 396 1188 6 231