TIME OVERCURRENT RELAYS TYPES IFC51I\ and 51B IFC43A and 53B IFC77A and 7713 DESCRIPTION The type IFC relays covered by these instructions are extended range, single phase, time overcurrent relays. These over-current relays need to coordinate with each other such that the relay nearest fault operates first. Overcurrent relays are also employed in conjunction with distance relays to provide backup protection. The voltage-controlled (51/27C) feature allows the relays to be set below rated current, and operation is blocked … 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. 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. An overcurrent relay can be either of two types: instantaneous or time-delay type. There is only one current operated element in the relay, no voltage coil etc. By submitting your registration, you agree to our Privacy Policy. – used for either alternating current or direct current to Salient features are described below: Instantaneous Relay (no intentional time delay) : The operating time of an instantaneous relay is of the order of a few milliseconds. Time-overcurrent relays are available with various timing characteristics to coordinate with other protective devices and to protect specific equipment. 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. 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. Classification or the types of relays depend on the function for which they are used. Use of Digital Logic in Numerical Relaying, 5.11: So the protection against the over current or exceeds current in the line is the essential protection for the device. 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. All the Relays react to voltage or current with the end goal that they open or close the contacts or circuits. I agree to receive commercial messages from GlobalSpec including product announcements and event invitations, In general, overcurrent relays are difficult to implement where coordination, selectivity, and speed are important. So, high current will operate overcurrent relay faster than lower ones. Over current relays are to protect an electrical system or equipment from over current faults like thermal current or short circuit current. ACCESS 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. Despite a number of limitations, it is used frequently as the complete are required to construct this protective relay.. Industrial Plant Load Shedding, Chapter 12: Protection of Industrial Systems, Chapter 11: Calculation of Short-Circuit Currents, Chapter 3: Overcurrent protections are applied only where the direction of There are standard inverse, very inverse and extremely inverse types. Include me in professional surveys and promotional announcements from GlobalSpec. Based on the relay operating characteristics, overcurrent relays can be classified into three groups: definite current or instantaneous, definite time, and inverse time. Overload protection is a protection against a running overcurrent that would cause overheating of the protected equipment. The actuating quantity of an overcurrent relay is a current. The design and size of the overcurrent protection system are outlined by national codes. The operation of this relay is based on current magnitude and it is without any time delay. This reference guide uses detailed examples and exercises to explain the co-ordination and inception of protection schemes. Classification and Function of Relays, Chapter 4: Protection of Electricity Distribution Networks, 2nd Edition, Copyright The Institution of Electrical Engineers 2004 under license agreement with Books24x7, Microprocessor Arc-flash Protection Relay, Optimize your food and beverage operations, Compact 3-Phase Monitors w/Enhanced Noise Immunity, MPR20 Monostable IP6K9K/IP67 Power Relays, Watchdog Monitoring Relay Protects 24/7 Processes, 3-Phase Monitoring Relay w/NFC Configuration, NEC 240.67 Arc Energy Reduction Technical Paper. One current operated element in the electric power system Privacy Policy overload relay can used! Outlined by national codes inverse time delay is provided for operation may do at any.... For feeder protection, there are various types of relays, operating time inversely... 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