I agree to receive commercial messages from GlobalSpec including product announcements and event invitations, So, high current will operate overcurrent relay faster than lower ones. Include me in professional surveys and promotional announcements from GlobalSpec. Thus, the relay with the lower setting operates first and disconnects load at the point nearest to the fault. Figure 5.2a illustrates the effect of the source impedance on the short-circuit level at a substation, and for a fault at point B down the line. – used for alternating current or direct current. There is only one current operated element in the relay, no voltage coil etc. Practically all the relaying device is based on either one or more of … UNLIMITED Electromagnetic Relay Working. Setting Overcurrent Relays Using Software Techniques, 5.10: An overcurrent relay can be either of two types: instantaneous or time-delay type. Co-ordination Across Dy Transformers, 5.7: All the Relays react to voltage or current with the end goal that they open or close the contacts or circuits. For this purpose, definite time overcurrent relay is used. An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. The protective relays are either single actuating quantity relays such as overcurrent, under-voltage, earth fault relay or double actuating quantity relays such as distance relays, differential relays. For feeder protection, there would be more than one over-current relay to protect different sections of the feeder. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. Overcurrent protections are applied only where the direction of FREE transmission lines, transformers, generators, or motors. The pickup values may be adjusted … They usually require changes to their settings as the system configuration changes. There Over current relays are to protect an electrical system or equipment from over current faults like thermal current or short circuit current. Overcurrent relays are the most commonly-used protective relay type. Unlike instantaneous overcurrent relays, IDMT relays operate for a wide range of short-circuit currents above pickup and unlike definite time relays, IDMT relays operate in a wide range of time depending on the magnitude of short-circuit current. Instantaneous Overc1r11e1nt Relay; Inverse Time Overcurrent Relay (IDMT Relay) Directional overcurrent relay; 1Mixed IDMT and high set instantaneous; Instantaneously overcurrent relay operates when current exceeds its Pick-up value. In this over current relay there is one current operated element is present. The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time. In an over current relay or o/c relay the actuating quantity is only current. On the other hand, overcurrent relays must be able to effectively detect both pole-to-pole and pole-to-ground faults, whereas there is a significant difference between the current magnitudes of these two types of fault. Based on the relay operating characteristics, overcurrent relays can be classified into three groups: definite current or instantaneous, definite time, and inverse time. Protection Schemes and Substation Design Diagrams, Chapter 14: Depending on the time of operation the overcurrent relay is categorized into following types. Three types of overcurrent relays are used: Inverse time delay overcurrent (TDOC) relays, Instantaneous overcurrent relays, Directional overcurrent relays. This type of protection has the drawback of having little selectivity at high values of short-circuit current. Magnetic circuit breakers, fuses and overcurrent relays are commonly used to provide overcurrent protection. Overcurrent relay are deployed extensively in the electric power system. The operation of this relay is based on current magnitude and it is without any time delay. You may withdraw your consent at any time. Directional Overcurrent Relays, Chapter 10: An instantaneous overcurrent relay is one in which no intentional time delay is provided for operation. Another disadvantage is the difficulty of distinguishing between the fault current at one point or another when the impedance between these points is small in comparison to the impedance back to the source, leading to the possibility of poor discrimination. The shut of the whole system and its restart is a costly process so we need a relay which could sense the fault in a more intelligent way as compared to the over-current relay. Overcurrent Relays with Voltage Control, 5.9: TO THE So the protection against the over current or exceeds current in the line is the essential protection for the device. Traditionally, such a relay has only the pick-up setting and it does not have any TMS. Instantaneous overcurrent relays have no inherent time delay and are used for fast short-circuit protection. If the overcurrent only exists for say 190 ms, the relay will not operate. Short circuit is a type of overcurrent. In general, overcurrent relays are difficult to implement where coordination, selectivity, and speed are important. current flow is immaterial or where the current can flow in one Depending upon time of operation, there are various types of Over Current relays, such as, Instantaneous over current relay. Introduction To Relay & Different Types Of Relays | Its Terminals, Working & Applications Relays are the essential component for protection & switching of a number of the control circuits & other electrical components. One main security characteristic of this relay is that stops the motor from instantly restarting. The setting is chosen so that, at the substation furthest away from the source, the relay will operate for a low current value and the relay operating currents are progressively increased at each substation, moving towards the source. Despite a number of limitations, it is used frequently as the complete Depending on the operating principle and structural features relays are of different types such as electromagnetic relays, thermal relays, power varied relays, multi-dimensional relays, and so on, with varied ratings, sizes, and applications. protection on radial feeders and as a backup protection on such Classification or the types of relays depend on the function for which they are used. The characteristic curves of these three types are shown in Figure 5.1, which also illustrates the combination of an instantaneous relay with one having an inverse time characteristic. are required to construct this protective relay.. The over current relay can be used as overload (thermal) protection when protects the resistive loads, etc., however, for motor loads, the over current relay cannot serve as overload protection Overload relays usually have a longer time setting than the over current relays. BEST IDEAS. MIXED IDMT AND HIGH SET INSTANTANEOUS OVERCURRENT PROTECTION RELAYS A high-set instantaneous device can be utilized where the source impedance is small in comparison with the protected circuit impedance. This allows a decrease in the … Companies affiliated with GlobalSpec can contact me when I express interest in their product or service. They provide protection to important power system equipment including power transformers, generators, transmission lines, loads, motors, busbars etc. Working Principle of Over Current Relay . 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