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. A line impedance relay would recognize that the fault was not on the transmission line and ignore this fault unless it was programmed to also provide backup protection with a significant time delay. Instantaneously overcurrent relay operates when current exceeds its Pick-up value. The fault current flows into the polarity mark of the CT connected to Circuit Breaker 3, so the Directional Overcurrent 67 relay sees the fault in the forward direction. Are you an Engineering professional? The directional over current relay recognizes the direction in which fault occurs, relative to the location of the relay. Sir kindly share manual of 7sj over current relay manula my email. Our test will work for all common characteristic angles if we modify it to include the phase angle during a fault. In this case, from the magnitude of the current seen by the relay R 2it is not possible to distinguish whether the fault is in the section AB or BC. For Example consider a phase fault occurs at angle of o. The tappings are provided on the upper magnet of overcurrent element and are connected to the bridge. Both fault currents flow into the transmission line, so the directional overcurrent relays connected to Circuit Breakers 3 and 4 will see the current in the forward direction because the current flows into both CT polarity marks. The first protection devices based on microprocessors were employed in 1985. The directional relays identify the zone of operation with the help of polarising voltage and characteristic angle. Overcurrent Ground Protection: Overcurrent ground fault protection can be obtained with only one overcurrent relay by connecting it across a zero phase sequence current filter. shapes of various relays e.g. Promoting, selling, recruiting, coursework and thesis posting is forbidden. By : admin News. The relay operates for the defined direction when the fault current is in the same direction and exceeds the over current setting value. We added the B-C phase-phase voltage to the drawing, which is the polarizing voltage this style of relay uses. The relay has no intentional time delay for operation. The relay will develop maximum torque when its current and voltage are in phase. This scheme is based on the intuition that, faults typically short circuits, lead to currents much above the load current. For an overcurrent relay. This is due to the absence of moving parts, which facilitates the application of automatic reclosing of breakers. Don't know that I've ever seen the notation 50GS. The typical region for a fault in the forward direction occurs in the green shaded area for both relays. The potential coil of this element is connected through a potential transformer P. The current coil of the element is energised through a C. This winding is carried over the upper magnet of the non-directional element. These are also called directional relays. RELAY: A Relay is a protection device that senses the fault in the circuit and gives a trip signal to the Circuit Breaker to isolate the faulty circuit. The most significant advantage of the instantaneous relay is that it has low operating time. The directional phase fault elements, work with a Quadrature connection to prevent loss of polarising quantity for phase faults. When short circuit current can go in both directions through the protection relay location, it may be required to make the response of the protection relay directional by the initiation of a directional control device. DT: Definite Time over current relay The operating time is fixed irrespective of the fault current and the time setting can be controlled manually. Directional Overcurrent Relays Coordination Restoration by Reducing Minimum Fault Current Limiter Impedance 1133 constraints on the relay settings through a set of functional dependencies [5]. You can find out more about Chris here.CSV Jul 14, Jul 14, Pin it. Hence there is no mechanical noise. Definite time overcurrent relays are used for wide variations of systems conditions, as backup relays for differential and distance protection, and differential protection of transformers to avoid mal-operation during magnetization inrush currents. In simple terms, a residually connected ground relay is more appropriate for a solidly, multi grounded wye system. The general kind of a relay makes use of electromagnet so as to perform opening and closing of contacts, whereas in the other types of approaches like in the solid-state type of relays they use semiconductor properties for controlling purposes without depending on the movable components. Conversely, if the relay set in Reverse direction means if a fault occurs in reverse zone then only relay operates. Overcurrent Relays In Directional OC relays there are two settings: time dial setting (TDS) and pickup current setting (I PU). Please send me the PDF on aforementioned documents as announced. Join Eng-Tips Forums! Conventional electromechanical and static relays are hard wired relays.Their wiring is fixed, only their setting can be manually changed. Overcurrent directional relays can be set to trip for faults in the forward direction, which will protect the equipment in front of the relay. The relay is designated to develop maximum torque when the relay current leads the voltage by 45 o. This is expected fault angle, and completely predictable. Possibility of Instantaneous Reset. Benefits or advantages of Solid State Relay. Consider a feeder XY, passing through station A. It is to be noticed that the directional over current operation is different for phase and earth faults. 2. The detailed explanation about Directional relay settings with Characteristic angleMaximum Torque angle and Polarisation voltages are given. This protection scheme finds usage in radial distribution systems with a single source. Directional relays allow for continuous time dial setting and discrete pickup current setting. The phasor diagram of a meter test on the Directional Overcurrent 67 relay connected to Circuit Breaker 4 would look like the following. Required fields are marked *. Figure 6 shows a short transmission line in which shunt charging can be neglected. Instantaneous overcurrent relays are also useful in other protective relay systems. Save my name, email, and website in this browser for the next time I comment. The variation is in selection of polarising voltages. Such a characteristic is known as definite time characteristic of overcurrent relay. 4. Applications and Advantages of Distance Relays. Consequently, fault is fed from both the ends of the feeder. Characteristic Angle is also called Directional angle as it decides the direction of operation of the relay. Therefore, for faults in feeder AX, the circuit breaker CB ydoes not trip unnecessarily. Optimize Overcurrent Protection, Integration, and Automation SEL-351 Directional Overcurrent and Reclosing Relay Apply the SEL-351 Relay to enhance service quality of lines and equipment. The disc of this element rotates and the moving contact attached to it closes the trip circuit. Directional overcurrent protection schemes were replaced with line impedance relays 21 to prevent a situation like this from occurring. The Advantages of Electromechanical relays are- They are quick acting and can be reset fast. Whenever, fault occurs on transmission line or busbars the voltage reduces proportional to the severity of fault and current increases larger than the normal currents. A directional over current relay operates when the current exceeds a specified value in a specified direction. 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. This difficulty is overcome in the Induction Type Directional Overcurrent Relay which is designed to be almost independent of system voltage and power factor. The two relay elements are so arranged that final tripping of the current controlled by them is not made till the following conditions are satisfied :. The most significant advantage of the instantaneous relay is that it has low operating time. Inverse Definite Minimum Time Relay. The current flows into the polarity mark of the CT on Breaker 3, and into the Directional Overcurrent 67 Relay using the same direction. Very often, the relays do not need to be directional, and then no a-c voltage source is required. Your email address will not be published. Click Here to join Eng-Tips and talk with other members! This type of relay is also called reverse power relaySo far as the direction of fault current power flow is concerned. Digital over current relays have advantages over electromechanical relays. When the input to measuring unit is less than the threshold value, the output of the level detector is zero. Both fault currents flow into the transmission line, so the directional overcurrent relays connected to Circuit Breakers 3 and 4 will see the current in the forward direction because the current flows into both CT polarity marks. If the directional relay set in Forward direction means if a fault occurs in forward zone then only relay operates. The Selection of Polarising voltage is different for these two types of earth faults. Overcurrent relays are the most common protective relay in an electrical system. Less effect of fault levels and fault current magnitudes. The relay operates only when the magnitude of their operating current is inversely proportional to the magnitude of the energize quantities. The reference voltage is called polarising voltage. Forward and reverse are typically determined by the normal flow of current into the relay, so be sure to confirm the CT connections before you make any assumptions. This difficulty is overcome in the Induction Type Directional Overcurrent Relay which is designed to be almost independent of system voltage and power factor. Their fast, compact and reliable operation results in minimum outage of power system in case of fault. Related Projects. Directional overcurrent protection schemes were replaced with line impedance relays 21 to prevent a situation like this from occurring. By adjusting this angle, the travel of moving contact can be adjusted so that the relay can be given any desired time setting which is indicated by a pointer, The dial is calibrated from The relay time from name plate curve is to be multiplied by time multiplier setting. Some overcurrent relays can operate in one direction only. This is the voltage taken from Potential Transformers. That is, each of the current elements is directionalised by a voltage derived from the other two phases. Introduction Application of the zero- and negative-sequence currents and voltages to fast ground overcurrent protection brings several advantages (section 2): • The zero- and negative-sequence currents practically do not contain any load comp o-nents. Where, I is the relay current, t is the time of operation and n is the characteristic index of relay and K is constant. Operation: Under normal operating conditions, power flows in the normal direction in the circuit protected by the relay. One of the methods of such connections is 30 o connection and other is 90 o connection. Incorrectly determining forward and reverse is an easy mistake to make. This relay operates only when the impedance between the source and the relay is less than that provided in the section. Already a member? Gives faster operation. This operates the circuit breaker which isolates the faulty section. The different connections depend on the phase angle, at unity system power factor, by which the current and voltage used to the protection relay are displaced. The output of this summation CT is fed to an auxiliary CT, whose output is rectified, smoothened and supplied to the measuring unit level detector. Operation: Under normal operating conditions, power flows in the normal direction in the circuit protected by the relay. Following are the benefits or advantages of Solid State Relay: It offers very fast response usually about 1µs ON and 0.5 µs OFF. There is no setting for maximum torque angle in numerical relays. The fault current is lagging in nature. Now our Directional Overcurrent 67 test plan looks like the following drawing where we start with the raw currents and voltages, calculate the non-faulted phase-to-phase voltage, and plot the operating current and polarizing signal, which in this case is VBC. Theses tapings are connected to plug setting bridge. They provide an instantaneous function for short circuits. Any current flowing into the polarity mark is considered to be the forward direction. Its zone is clearly demarcated by the CTs which provide the boundary. The Directional Overcurrent element needs a polarizing signal to operate reliably; otherwise anything could happen depending of the sophistication of the relay. In case of static overcurrent relays instantaneous reset is possible. I used electro-mechanical directional relays as an example, which may have been a mistake. Therefore, the latter element cannot start to operate until its secondary circuit is completed. The coordination problem is linear if pickup current is considered to be fixed. The time interval between the instant pick-up value and the closing contacts of the relay is very less. Each relay is energized by current from its respective phase and voltage. For directional unit, the secondary winding of the over current relay unit is kept open AB. To get sufficient torque during all types faults, irrespective of locations with respect to relays, the relays connections are to be modified. The fault current is lagging in nature. Conventionally denotes that forward direction refers to power flow away from the busbar towards the protected zonewhile reverse direction refers to power flowing towards the busbar. Overcurrent Relays/Elements; Directional Overcurrent Relays; Over/under Voltage Relays; Distance Relays; Day 3 Out-of-Step Relaying. Since faults in section AB are not in its jurisdiction, it should not trip. The directional earth fault elements, to sense Earth faults Zero phase sequence polarising technique is used. Overcurrent relays can be used to protect practically any power system elements, i.e. If the fault current is larger than the overcurrent setting, the relay will trip. This is also a special type of over current relay with a directional features. The phasor diagram for this situation might look like the following. Whenever a near or close-up fault occurs, the voltage becomes low and the directional relay may not develop sufficient torque for its operation. Log In. Differential protection tends to be extremely accurate. Therefore, for faults in feeder AX, the circuit breaker CB ydoes not trip unnecessarily. If the system is resistance grounded in the range of 25 to amps, then a zero sequence window CT feeding a ground relay is more appropriate. This ratio also indicates the distance of the fault from the relay. Features and Benefits Develop SELogic control equations using ac SELE r ato r QuickSet Software. It may be noted that plug-setting bridge is also provided in the relay for current setting but has been omitted in the figure for clarity and simplicity. This test plan has a good chance of being successful because we have an operating signal and a polarizing signal. The proposed overcurrent relay can be employed to protect feeders of distribution systems for overcurrent and earth fault protection. However, there will be times when this test plan will not work. By adjusting this angle, the travel of moving contact can be adjusted so that the relay can be given any desired time setting which is indicated by a pointer, The dial is calibrated from The relay time from name plate curve is to be multiplied by time multiplier setting. The fault current flows into the polarity mark of the CT connected to Circuit Breaker 3, so the Directional Overcurrent 67 relay sees the fault in the forward direction. This relay is designed to protect the same transmission line from the other direction. Maximum torque angle is the angle made by fault current with respect to its phase voltage. Should this happen, the disc of the upper element rotates to bridge the fixed contacts 1 and 2. One important thing to be noted here is that the connection of the star points of both the C.T. Most electro-mechanical relays, and GE relays like the one from The Relay Testing Handbook example, use the phase-phase voltage from the two un-faulted phases as a polarizing signal. Please send me the PDFs officeaninda gmail. If the fault current is larger than the overcurrent setting, the relay will trip. I'm curious when you would favor using a residual short circuit relay for gnd fault detection relay 50N versus a ground fault relay 50GS and vice versa. This is expected fault angle, and completely predictable. This angle is different for phase faults and earth faults. Overcurrent directional relays can be set to trip for faults in the forward direction, which will protect the equipment in front of the relay. The negative sequence, or unbalance voltage, is zero in a balanced system. The principle of directional protection is as under:. The principle of directional protection is as under:. In conventional electromagnetic relays, n may vary between 2 and 8. If the power flow is in the opposite direction, the relay will not operate. In this scenario, you might get frustrated and start disabling the directional function, or start looking for the non-directional relay definitions so you can map them to a test output. Static overcurrent relay is made in the form of a single unit in which diodes, transistors, resistors, capacitors etc. Compact in size — The size of a single three-phase overcurrent relay may be about one-fourth of three electromagnetic relays. This means that it is a coin toss whether the relay will operate or not. advantages of directional overcurrent relay. The tappings are provided on the upper magnet of overcurrent element and are connected to the bridge. Once they answer that question, I will review the CT connections and build a test on the transmission line and see if it trips. This angle is different for phase faults and earth faults. The measuring unit determines whether the quantity has attained the threshold value set value or not. Overcurrent directional relays can be set to trip for faults in the forward direction, which will protect the equipment in front of the relay. Each phase current is compared with the voltage between other two phases. Characteristic Angle is also called Directional angle as it decides the direction of operation of the relay. The detailed explanation about Directional relay settings with Characteristic angleMaximum Torque angle and Polarisation voltages are given. The performance of CT under short-circuit condition is also improved. Please send me the Download link of Digsilent relay library. The secondary is connected to the lower electro magnet; the torque exerted on the disc is due to the interaction of eddy currents produced therein by the flux from the upper EM and the lower EM. I have seen instances where the 50G and 50N designations have been used interchangeably, though. To understand simply it is like a brain in our human body, when the brain gives the sense the body parts are operate to do any work. To illustrate the principle let us consider that current rating of primary winding is A and secondary winding is A. The relay will develop maximum torque when its current and voltage are in phase. Over current relaying and fuse protection uses the principle that when the current exceeds a predetermined value, it indicates presence of a fault short circuit. Always ask the engineer what they intended if there is any doubt. The basic principle of distance relay is that the apparent impedance seen by the relay, which is defined as the ratio of phase voltage to line current of a transmission line Z appreduces drastically in the presence of a line fault. This is a fault, so:. Today optimization methods have been used to coordinate directional over current relays together. Thus by comparing the two currents either in magnitude or in phase or both we can determine a fault and issue a trip decision if the difference exceeds a predetermined set value. It consists of two relay elements mounted on a common case viz. By joining you are opting in to receive e-mail. This operates the circuit breaker which isolates the faulty section. In this type of 30 o connections, the current coil of the current coil of the relay of phase A is energized by phasor current I A and the line voltage V AC. Working Principle of Over Current Relay. They are more complicated in static form as compared to their electromagnetic counterparts. The secondaries of the line CTs are connected to a summation circuit not shown in the figure. There are no physical moving parts involved in the design of solid state relay. 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 o. With the need at … It can be used for short feeders and a specific implementation is known as pilot wire protection. Directional element: It is essentially a directional power relay which operates when power flows in a specific direction. The same construction may be used for under-voltage, overvoltage or earth fault relays too. The inverse time relay is of three types. Conventionally denotes that forward direction refers to power flow away from the busbar towards the protected zonewhile reverse direction refers to power flowing towards the busbar. Extremely inverse overcurrent relays are used for the fuse coordination and thermal protection of transformers and induction motors. I came up with these are just a guess : 1 50N requires only one CT on all conductors thus can detect phase faults as well. The variation is in selection of polarising voltages. It'll be easier to answer the questions if I or others have a better understanding of the question. transmission lines, transformers, generators, or … The circuit breaker in feeder AY is provided with a directional relay R, which will trip the breaker CB yif the fault power flow is in the direction AY alone. The most important feature of the relay is their speed of operation. The relay protects the system from earth fault and also used for protecting the system from circulating current. The widespread acceptance of numerical technology by the customer and the experiences of the user helped in developing the second generation numerical relays in 1990. In other words, the directional element must operate first i. Some relays have an operating characteristic like the following picture:. The characteristic angle is the phase angle by which reference or polarising voltage is adjusted such that the directional relay operates with maximum sensitivity. We will start with a simple transmission line with the source on the left and a load on the right. Fault current Lags the voltage by 30 o. The secondary is connected to the lower electro magnet; the torque exerted on the disc is due to the interaction of eddy currents produced therein by the flux from the upper EM and the lower EM. We will start with a simple transmission line with the source on the left and a load on the right. Whenever a near or close-up fault occurs, the voltage becomes low and the directional relay may not develop sufficient torque for its operation. Figure 2 shows such a case for a radial system with source at both ends. In the case of transmission lines supplied from both ends, it is employed with directional relays. There is no setting for maximum torque angle in numerical relays.The overcurrent relays, even though simplest of all types of electromechanical relays, are the most difficult static relays. If we reversed the source and load, you could swap the phasor diagrams above for each relay. Despite modern distance relays, directional over current (DOC) relays are the best choice for local backup of distance relays from the economical and technical point of view, But it is too complicate to coordinate these relays together. The device is provided … Both the graph theoretic and functional dependency approaches provide a solution which is the best setting, but not necessarily an optimal solution. Time Delay between Relay.In the previous post about Directional Overcurrent relay 67 testing Finding the Direction in Directional Overcurrent Relayswe reviewed Directional Overcurrent protection from a system perspective to enhance the descriptions in The Relay Testing Handbook: Principles and Practice. This directional over current relay employs the principle of actuation of the relaywhen the fault current flows into the relay in a particular direction. It is measuring the "residual" current in the CT secondary circuit - the sum of the three phase currents. June 23, Your email address will not be published. This is because the induction disc characteristics of the overcurrent relays inverse characteristics are not amenable to simple mathematical analysis. It is quite simple to implement. It is smaller in size. Differential protection for detecting faults is an attractive option when both ends of the apparatus are physically located near each other. Not only is overcurrent relaying basically simple and inexpensive but also these advantages are realized in the greatest degree in many distribution circuits. If the power flow is in the opposite direction, the relay will not operate. Should this happen, the disc of the upper element rotates to bridge the fixed contacts 1 and 2. Directional relays needed reference voltage to identify the direction of currents. 3. It may be noted that plug-setting bridge is also provided in the relay for current setting but has been omitted in the figure for clarity and simplicity. The upper magnet has two windings. Fault current level detectors are termed overcurrent relays. Advantages of directional overcurrent relay, advantages of directional overcurrent relay, i spilled hydrogen peroxide on my clothes. Directional over current relays operate in either forward or reverse directions with over current protection. The circuit breaker in feeder AY is provided with a directional relay R, which will trip the breaker CB yif the fault power flow is in the direction AY alone. The operating time of relay decreases with the increases in the current. They provide a time delay function for overloads. Forward and reverse are typically determined by the normal flow of current into the relay, so be sure to confirm the CT connections before you make any assumptions. However, static overcurrent relays offer several advantages over the electromagnetic form:. Home Products Contact Us. At this line relay current is in phase with the reference or polarising voltage. This is the voltage taken from Potential Transformers. Thus, we can say that differential current under no fault condition is zero. A distance relay compares this ratio with the positive sequence impedance Z 1 of the transmission line. non-directional overcurrent relay micro-controller based having the advantages of low cost, high performance and can be totally manufactured by local manufacturers. The relay is used for the protection of the distribution lines. The directional relays identify the zone of operation with the help of polarising voltage and characteristic angle. The device is provided by the use of extra voltage inputs to the protection relay. Simpler to co-ordinate. Now if an internal fault occurs within the device like interturn short etc.The directional power relay is unsuitable for use as a directional protective relay under short-circuit conditions. Or they can also be set to trip for … It is used to calculate Characteristic angle and identify center of zone. Reverse power flow relays with directional features, not only senses the direction flow, but also measures magnitude of power flow. A traditional relay tester, or automated testing software, will often apply a test scenario like the following:. Or they can also be set to trip for … When short circuit current can go in both directions through the protection relay location, it may be required to make the response of the protection relay directional by the initiation of a directional control device. The answer is never. So the distance relay is another relay for the protection of the devices. Differential protection is based on the fact that any fault within an electrical equipment would cause the current entering it, to be different, from the current leaving it. The article is organized as follows: Section 2 has a brief description of the coordination of directional overcurrent relay; In Section 3, we discuss the optimal coordination of DOCR; Section 4 contains the proposal for an adaptive protection system; In Sections 5 and 6, the methodology used, and results obtained are discussed; Finally, Section 7 contains the conclusions. Are the voltages unbalanced in the previous test plan?