Overcurrent oc relays are the major protection devices in a distribution system. Time overcurrent relays time overcurrent relays operate with a time delay. Since largescale measurements and tests are typically unfeasible, system calculations have to be used. Pdf nonconventional overcurrent relays coordination. Nec 2017 requirements for generator set overcurrent protection. Pdf online implementation of time augmentation of over. Overcurrent coordination page 3 qualtech engineers, inc. It is equipped with independently adjustable high current and low current circuit closing contacts, and operates similar to a contact closing ac ammeter with inverse time delay. Coordination technique precise overcurrent relay usage asks for the knowledge of the short circuit current that can flow in each section of the power network. A comparison of the time it takes protective devices to operate when certain levels of normal or abnormal current pass through them. Ef relay for over current and earth fault protection. Type co overcurrent relay 41101u 5 energy requirements type co2 relay volt amperes continuous one second power at at 3 times at 10 times at 20 times ampere rating rating factor tap value tap value tap value tap value range tap amperes amperes angle o current current current current 0. It is also necessary to ensure that the fault current at the end of the line being protected is high enough to cause operation of the recloser. The basic element in overcurent protection is the overcurrent relays.
Coordination of over current relays in distribution. This paper presents a study on protection coordination of overcurrent relays ocrs in a 233kv transmission substation by considering its different operating modes using a matlab model. Coordination study pickup current pickup is defined as that minimum current that starts an action. The relay operates as soon as the current gets higher than a preset value. Basics of overcurrent protection linkedin slideshare. The problem of setting and coordination of directional over current relay docr is a highly constrained optimization problem that has been solved as a linear programming problem. Depending on the time of operation the overcurrent relay is categorized into following types. Operation of the timeovercurrent unit thus depends on the closing of an external contact across those terminals. The optimized vale of time of operation of over current relays can be calculated with the help of various optimization techniques. Coordination of distance and overcurrent relays using a. This paper presents a study on protection coordination of over current relays ocrs in a 233kv transmission substation by considering its different operating modes using a matlab model. When the power system is not radial source on one side of the line, an over current relay may not be able to provide adequate protection. Low voltage breaker fuse coordination requires a minimum 0.
A 400v industrial distribution power system is used as a tutorial to simulate and test overcurrent relays performance results, with motor start up inrush. Over current relay and its characteristics electrical concepts. Optimal coordination of over current and distance relays. Where no recommended time margins are available, a minimum margin of 0. On the contrary to other kinds of relays, fuses and reclosers, overcurrent. Features timeovercurrent timeovercurrent units are available in several ranges to meet current pickup settings of from. A multiplestage protection is often required to meet with the sensitivity and operating speed re. For this study, the minimum margin between relay curves. Features time overcurrent time overcurrent units are available in several ranges to meet current pickup settings of from. Jan 08, 2019 instantaneous over current relay is one in which no intentional time delay is provided for the operation. There is only one current operated element in the relay, no voltage coil etc. Transformer overcurrent protection coordination russell w. Relay coordination and grading using time overcurrent.
A relay that operates or picks up when its current exceeds a predetermined value setting value is called over current relay. How coordination is effected by arc current, relay reset times, capacitive current, and snubber installation choosing relay timecurrent characteristics overcurrent versus under. It can be used as main or backup protection relays. Overcurrent relay setting model for effective substation. Fundamental relayoperating principles and characteristics 19 singlequantity relays of the electromagneticattraction type here we shall consider plungertype and attractedarmaturetype ac or dc relays that are actuated from either a single current or voltage source. Relay relay coordination requires 1 that there be a minimum of 0. Overcurrent relays can be used to protect practically any power system. Retired introduction ieee guide for liquid immersed transformer through faultcurrent duration c57.
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. Leave a comment on this post, we will send you the overcurrent fundamental. To implement the timeovercurrent protection coordination on the power system network in the digsilent powerfactory environment using kcgg142 relay model dr s krishnamurthy, deece, cput south africa. The problem of setting and coordination of directional overcurrent relay docr is a highly constrained optimization problem that has been solved as a linear programming problem. Substation protective relay coordination setting plays a vital role in the safe operation of power system. Considering the above arguments and also taking into account, for example the shortcircuit current withstand. Then r4, the relay with the greatest source impedance, would be set with the lowest time dial setting time overcurrent relays fall 2018 u i ece525 example continued lecture 11. Power system protection and control has always been a subject of concern during emergency conditions in a power system like a zero power condition or blackout. The timeovercurrent relay iac, ifc, or sfc has an operating characteristic such that its operating time varies inversely as the current flowing in the relay.
Over current relay working principle types electrical4u. In other words, the minimum value of current for which the relay must operate should be at least 1. Coordination of over current relays in distribution system free download as powerpoint presentation. It owes its application from the fact that in the event of fault the current would increase to a value several times greater than maximum load current. Then the pickup current must be set at or below this current but above maximum load current. Aug 26, 2016 to implement the time overcurrent protection coordination on the power system network in the digsilent powerfactory environment using kcgg142 relay model dr s krishnamurthy, deece, cput south africa. A relay that operates or picks up when its current exceeds a predetermined value setting value is called overcurrent relay. Nov 01, 2017 how coordination is effected by arc current, relay reset times, capacitive current, and snubber installation choosing relay timecurrent characteristics overcurrent versus under. It has a limitation that it can be applied only to simple and non costly equipments.
General of seri es devices from the load to the source ar e. Blinding of protection and falsesympathetic tripping. Protection and overcurrent coordination part 2 youtube. The information needed for a relay protection setting analysis is. There are five different types of time overcurrent relays. Figure 4 shows the application of time overcurrent re.
Patterson patterson power engineers elmo price consultant, abb inc. Optimal coordination of overcurrent relay protection using evolutionary programming noor shah rizal bin abdul manap research report submitted in partial fulfilment of the requirements for the degree of master of engineering power systems faculty of electrical engineering institute of graduate studies university of malaya kuala lumpur 2018. Thus over current protection is one of the major concerns in power system protection. In the project a new optimal method for the coordination of over current and distance relay based on genetic algorithm has been developed. Medium voltage products technical guide protection. By appropriate relay coordination we can achieve proper fault identification and fault clearance sequence. Overcurrent protection fundamentals r ced engineering. Cod current sensing relay the cod current sensing relay is used to initiate switching or control functions upon a change in line current. He is presently associate with one of the leading business group as a deputy manager at ahmedabad,india. The objective of protective relay coordination in an interconnected power system is to achieve selectivity without sacrificing sensitivity and fast fault clearance time. If the type 67 relay element is to provide backup protection, they use definite time delay for downstream coordination the 67 element requires more attention to detail for coordination than do type 51 relays the advantage that the stepped time has over the 51 is that the time steps are independently set.
Equipment damage, personal injury, and even death can result from the improper application of a devices voltage rating, current rating, or. Thus overcurrent protection is one of the major concerns in power system protection. Retired introduction ieee guide for liquid immersed transformer through fault current duration c57. Relay coordination and grading using time overcurrent relay. The timecurrent coordination curves, drawn for this study, are located at the. In an over current relay or oc relay the actuating quantity is only current. A convert the fault current into the relay coil current by using the current transformer ratio. Instantaneous over current relay is employed where the impedance between the source and the relay is small as compared with the impedance of the section to be provided. The minimum current at which the relay operates pick up current is also adjustable. The modeling of overcurrent relay and other protection relays is. Therefore in order to prevent such conditions, protection system needs to be strong and.
This is the simplest of the ways to protect a line and therefore widely used. Time grading with fuses is also easier to obtain with inverse time relays. Coordination of overcurrent relay in distributed system for. Pdf modeling and simulation of inverse time overcurrent. The time of operation of such relay is approximately 100 ms. English pdf manual type co relay coordination and impulse margin time instruction leaflet il 41101.
B express the relay current as a multiple of current setting, i. Overcurrent relay is an important relay used to protect transmission and distribution feeders, transformer, bus coupler etc. In this paper a typical wind farm is taken as the case study and found that coordination in the over current relay is affected by the variationin the penetration of. Relay coordination settings the relay current setting is given by plug setting. Coordination of distance and overcurrent relays using a mathematical optimization technique a dissertation submitted to the electrical engineering graduate program at the state university of londrina in ful. The overcurrent relay can be supervised by some external device, such as a directional relay. Over current oc relays are the major protection devices in a distribution system. For an effective substation protection scheme, a time delay should be. Operation of the time overcurrent unit thus depends on the closing of an external contact across those terminals. C from the timepsm curve of the relay, with the calculated psm the corresponding time of operation can be obtained. There is always an inherent time delay of the order of a few milliseconds. Under normal operating conditions and three phase fault conditions the current in the 3phase are equal and symmetrically displaced by 120. Nowadays coordination of overcurrent relays is a very important subject in different networks. Overcurrent protection devices are meant to protect against the potentially dangerous effects of overcurrents, such as an overload current or a shortcircuit current, which creates a fault current.
The flowchart for the relay coordination procedure is shown in figure 2 below. A coordination study provides data useful for selection of instrument. Overcurrent relay coordination for phase and earth faults using etap proceedings of 7 th irf international conference, 27 april2014, pune, india, isbn. Coordination of definite current relays is based on the fact that the fault current varies with the position of the fault because of the difference in the impedance between the fault and the source the relay located furthest from the source operate for a low current value. Overcurrent protection relay electrical engineering. The main application of long time over current relays is as backup earth fault protection. The relay setting is adjusted based on its location in the network. An organized timecurrent study of protective devices from the utility to a device. Different optimization techniques for optimum coordination of ocrs have been proposed in literature. From this basic method, the graded overcurrent relay protection system, a discriminative short circuit protection, has been formulated. For phase to phase faults the relays in only the affected phases operate.
Overcurrent protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults, etc. Nec 2017 requirements for generator set overcurrent. The relay located furthest from the source, operates for a low current value. It protects the equipment of the power system from the fault current. The optimized vale of time of operation of overcurrent relays can be calculated with the help of various optimization techniques. Over current protection protects electrical power systems against excessive currents which are caused by. Overcurrent protection an overview sciencedirect topics. Overcurrent relays co, cod, com, coq, cov co relays, a complete coordinated line, assure accurate and reliable primary or backup protection against phase or ground faults. If relay r2 is expected to provide backup protection for. A 400v industrial distribution power system is used as a tutorial to simulate and test overcurrent relays performance results, with motor start up inrush current consideration and backup relay coordination for safe and reliable operation. Coordination of overcurrent relay in distributed system.
Calculate idmt over current relay setting 5051 october 11. All the studies as mentioned above, related to the coordination problem of the over current relay are performed by connecting the dg at node 864 and introducing fault at node 842 and 810. Also the overcurrent relay coordination curve for the generator must lie below the decrement curve and the overload curve. The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time.