In the feeder with small impedance, distinguishing between the fault currents at both ends is difficult and leads to poor discrimination and little selectivity at high levels of short-circuit currents. Over-current protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults, etc. Required fields are marked *. SKC series. The relay setting is adjusted based on its location in the network. The ANSI device number is 50 for an instantaneous overcurrent (IOC) or a Definite Time overcurrent (DTOC) and 51 for the Inverse Definite Minimum Time. I’m working on Overcurrent relay setting of Primary Transformer Protection (2000KVA with 6% impedance) with 200/5 CT ratio. The operating time of relay decreases with the increases in the current. From the book, Protective Relaying by J. Blackburn and T. Domin, protective relaying is defined as Protective relaying is, therefore, the craft of configuring protection relays to identify an intolerable system condition, initiate an alarm, and/or circuit isolation at the right instant. The adjustment of definite-time and inverse-time relays can be carried out by determining two settings: time dial setting and pickup setting. Overcurrent protection devices Overcurrent protection is critical to personal safety and protection from a number of hazardous conditions that can result from materials igniting due to improper overload protection or short-circuit protection. The relay whose operating time is approximately proportional to the fault current is known as the IDMT relay. These devices typically consist of a manual circuit breaker or contactor and a current sensing relay which interlocks with it. So, high current will operate overcurrent relay faster than lower ones. A relay that operates or picks up when its current exceeds a predetermined value (setting value) is called Over-current Relay. The disadvantage of this type of protection is that it’s difficult to coordinate and requires changes with the addition of load and that the short-circuit fault close to the source may be cleared in a relatively long time in spite of its highest current value. And the normally closed contact is connected to the branch where the contactor coil is to shut off contractor coil. Over current relay protection is usually provided by either instantaneous or time delay over current relays. The characteristic curve for the relay is shown in the figure below. Overcurrent protection is protection against excessive currents or current beyond the acceptable current rating of equipment. This is relay coordination basics! The settings of this kind of relay at different locations in the network can be adjusted in such a way that the breaker closest to the fault is tripped in the shortest time and then the other breakers in the direction toward the upstream network are tripped successively with longer time delay. The instantaneous overcurrent relay is placed in the outgoing feeder. Can you guide me on how to calculate min & max fault current. The relay operates only when the magnitude of their operating current is inversely proportional to the magnitude of the energize quantities. It starts operating instantly when the value of current is more than the relay setting. The relay has no intentional time delay for operation. They are available with standard inverse, very inverse and extremely inverse characteristics. Overcurrent relays are the typical protection for conventional distribution systems. The current is measured by using /5 or /1 current transformers. This relay is referred as definite (instantaneous) overcurrent relay. Inverse-Time Overcurrent Relay 3. From this basic method, the graded overcurrent relay protection system, discriminative short circuit protection, has been formulated. The time interval between the instant pick-up value and the closing contacts of the relay is very less. Depending on the time of operation the overcurrent relay is categorized into following types. Connecting coil of over current relay to circuit under protection, when current reaches to the setting value, over current relay operates. Fuses, circuit breakers, overcurrent relays, current limiters, temperature sensors and solid state power switches are used against overcurrent protection devices. Directional overcurrent protection schemes were replaced with line impedance relays (21) to prevent a situation like this from occurring. The relay is used for the protection of the distribution line. Overcurrent protection SIPROTEC 7SJ80 The SIPROTEC 7SJ80 relays can be used for feeder protection of high and medium-voltage networks with grounded, low-resistance grounded, isolated or a compensated neutral point. transmission lines, transformers, generators, or motors. Overcurrent Protection Relay Relay protection against the high current was the earliest relay protection mechanism to develop. 51P1T Phase Time-Overcurrent Element Curve Timing and Reset Timing 51P1P 51P1C 51P1TD 51P1RS 51P1CT 51P1MR Settings Relay Word Bits 51P1P 51P1T 51P1R Controls the Torque Control Switch Instantaneous Over current Protection (50): This is typically applied on the final supply load or on any protection relay with sufficient circuit impedance between itself and the next downstream protection relay. Short circuit is a type of overcurrent. The ANSI/IEEE number code designation for a directional current-sensing protection is 67. Example, when the overcurrent relay is connected to the end of distribution feeder, Inverse Time relays are also referred to as, Get access to premium HV/MV/LV technical articles, advanced electrical engineering guides, papers, and much more! There is only one current operated element in the relay, no voltage coil etc. One such application is generator protection, where an overcurrent relay monitors the amount of current at the point where an electrical power generator connects to a larger network of generators. This relay is used for protecting the cable, transformer, etc. Very Inverse Relay 6. There are two feeders connected in parallel from source to load. There is no intentional time delay set. Contact. The relay is used in the places where there the magnitude of the short-circuit current fall rapidly because of the large distance from the source. The operating time of the relay is maintained by adjusting the time delay setting. over-current protection relay. 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