When the directional unit operates, it closes the open contacts of the secondary winding of the relay may be either wattmeter or shaded pole type.In this post operation of Directional current relay along with its settings explained. My name is Daniel Pecsoy and my email add is dpecsoy yahoo. A traditional relay tester, or automated testing software, will often apply a test scenario like the following:. 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 fault current is lagging in nature. The variation is in selection of polarising voltages. The detailed explanation about Directional relay settings with Characteristic angleMaximum Torque angle and Polarisation voltages are given. To get sufficient torque during all types faults, irrespective of locations with respect to relays, the relays connections are to be modified. The phasor diagram for this situation might look like the following. Therefore, for faults in feeder AX, the circuit breaker CB ydoes not trip unnecessarily. It can be used for short feeders and a specific implementation is known as pilot wire protection. Therefore, our previous test plan will not have a polarizing signal on relays that use negative sequence polarizing. Therefore, for faults in feeder AX, the circuit breaker CB ydoes not trip unnecessarily. The relay will not operate when the value of current is less than the pick 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. It's easy to join and it's free. Overcurrent (instantaneous overcurrent and inverse, time delay, overcurrent ) (50, 51, 50N, 51N) Directional Overcurrent (67, 67N) Distance (21, 21N) Differential ( pilot) (87) -Overcurrent protection, the simplest and most economical of these principles, is limited to radial lines. For these needs, IEC determined a number of standard characteristics. It consists of two relay elements mounted on a common case viz. Fault current level detectors are termed overcurrent relays. Should this happen, the disc of the upper element rotates to bridge the fixed contacts 1 and 2. Or they can also be set to trip for faults behind the relay in the reverse direction. Home Products Contact Us. The reference voltage is called polarising voltage. You could drive yourself crazy trying to figure out how to apply the test and phasor diagrams from older relay manuals to modern test-sets. Since, the circle spans all the quadrants, it leads to non-directional protection scheme. Working Principle of Over Current Relay. Like I L1 is compared with V This angle is usually o for overhead lines and o for underground cables for phase faults. The phasor diagram of a meter test on the Directional Overcurrent 67 relay connected to Circuit Breaker 4 would look like the following. Reverse power flow relays with directional features, not only senses the direction flow, but also measures magnitude of power flow. However, when a short-circuit occurs, there is a tendency for the current or power to flow in the reverse direction. This is the voltage taken from Potential Transformers. This angle is different for phase faults and earth faults. In other words, the directional element must operate first i. This directional over current relay employs the principle of actuation of the relaywhen the fault current flows into the relay in a particular direction. We appear to be in good shape for most Directional Overcurrent 67 applications. Join Eng-Tips Forums! Its zone is clearly demarcated by the CTs which provide the boundary. Or they can also be set to trip for … Healthy phase magnitudes and angles not changed. This is because the induction disc characteristics of the overcurrent relays inverse characteristics are not amenable to simple mathematical analysis. Each relay is energized by current from its respective phase and voltage. Today optimization methods have been used to coordinate directional over current relays together. Again, thank you. Also, the proposed relay is considered a The operation of this relay is based on current magnitude and it is without any time delay. Thus, we can say that differential current under no fault condition is zero. Any current flowing into the polarity mark is considered to be the forward direction. If we reversed the source and load, you could swap the phasor diagrams above for each relay. Features and Benefits Develop SELogic control equations using ac SELE r ato r QuickSet Software. 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. The current flows into the polarity mark of the CT on Breaker 3, and into the Directional Overcurrent 67 Relay using the same direction. The relay is designated to develop maximum torque when the relay current leads the voltage by 45 o. This relay is also called earth leakage induction type relay.The overcurrent relay operates when the current in the circuit exceeds a certain preset value.The induction type nondirectional overcurrent relay has a construction similar to a watthour meter, with slight modification.The figure below shows the constructional of nondirectional induction type overcurrent relay. For directional unit, the secondary winding of the over current relay unit is kept open AB. The operating time of relay decreases with the increases in the current. Relay is an electrical switch which is used to open or close a circuit with electromagnetic relay or electronically.It operates manually as well as automatically. Normally, the conventional over current relay (non-direction) will … Overcurrent Relays In Directional OC relays there are two settings: time dial setting (TDS) and pickup current setting (I PU). HelloThe endeavour behind presenting this website for we Electrical protection Engineers is really awesome. 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. Some of your description and some of the terms used aren't the most common combinations of those concepts, at least in my experience. Thank you for helping keep Eng-Tips Forums free from inappropriate posts. Then under no fault condition, phasor sum of currents entering the device is zero i. Save my name, email, and website in this browser for the next time I comment. Then if we use and CT on the primary and secondary windingthen under normal no fault operating conditions the scaled CT currents will match in magnitudes. 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 time interval between the instant pick-up value and the closing contacts of the relay is very less. The fault current flows into the non-polarity mark of the CT connected to Circuit Breaker 4, so the Directional Overcurrent 67 relay sees the fault in the reverse direction. 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. 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. 4. The first static relays developed were the high speed differential relays and the distance relays. The tappings are provided on the upper magnet of overcurrent element and are connected to the bridge. Each phase current is compared with the voltage between other two phases. If the power flow is in the opposite direction, the relay will not operate. Therefore, the latter element cannot start to operate until its secondary circuit is completed. Imagine that I asked you for directions to your favorite restaurant after dark. The tappings are provided on the upper magnet of overcurrent element and are connected to the bridge. It is used to calculate Characteristic angle and identify center of zone. Operation: Under normal operating conditions, power flows in the normal direction in the circuit protected by the relay. The device is provided by the use of extra voltage inputs to the protection relay. DIRECTIONAL OVERCURRENT RELAY. We added the B-C phase-phase voltage to the drawing, which is the polarizing voltage this style of relay uses. Some relays have an operating characteristic like the following picture:. Compact in size — The size of a single three-phase overcurrent relay may be about one-fourth of three electromagnetic relays. Once they answer that question, I will review the CT connections and build a test on the transmission line and see if it trips. 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 :. This relay is designed to protect the same transmission line from the other direction. There are many ways for an appropriate connection of voltage and current signals. It has a metallic disc free to rotate between the poles of two electromagnets EM. non-directional overcurrent relay micro-controller based having the advantages of low cost, high performance and can be totally manufactured by local manufacturers. Already a Member? Such a characteristic is known as definite time characteristic of overcurrent relay. Differential protection can be used for tapped lines multiterminal lines where boundary conditions are defined as follows:. So the distance relay is another relay for the protection of the devices. directional overcurrent relays, such as the relay characteristic angle, the selection of the polarizing quantities (negative sequence or zero sequence) for the directional ground overcurrent protection function, and the minimum thresholds for the activation of the voltage memory for the directional phase overcurrent element. Instantaneous overcurrent relays are used for short-circuit protection of large equipment. Negative sequence voltage can be simplified to mean unbalanced voltage You can get more information in the Sequence Components section of The Relay Testing Handbook: Principles and Practice. Thanks guys I have made up a schematic of the three: 50N, 50G and 50GS. Figure 6 shows a short transmission line in which shunt charging can be neglected. It is smaller in size. A distance relay compares this ratio with the positive sequence impedance Z 1 of the transmission line. On the contrary, overcurrent relay protection is completely directed to the clearance of short circuits, even though with the settings typically assumed some measure of overload relay protection may be obtained. It starts operating instantly when the value of current is more than the relay setting. 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. Abstract: The time of operation of overcurrent relays (OCRs) can be reduced, and at the same time, the coordination can be maintained, by selecting the optimum values of time multiplier setting (TMS) and plug setting (PS) of OCRs. 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. Hello, thanks for your comments. You can tell by graphically adding the three voltages together, or with the negative sequence formula. Hope your free article which I request provide helpful information on my queries. The reference voltage is called polarising voltage. In case of static overcurrent relays instantaneous reset is possible. Or they can also be set to trip for faults behind the relay in the reverse direction. This protection scheme finds usage in radial distribution systems with a single source. The relay has no intentional time delay for operation. Join Us! Instantaneous overcurrent relays are also useful in other protective relay systems. 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. Distance relay is used for the protection of transmission line &, feeder. The block diagram of an instantaneous overcurrent relay is shown in Fig. This is a fault, so:. When the input to measuring unit is less than the threshold value, the output of the level detector is zero. DT: Definite Time over current relay The operating time is fixed irrespective of the fault current and the time setting can be controlled manually. These are:. Like I L1 is compared with V This angle is usually o for overhead lines and o for underground cables for phase faults. This operates the circuit breaker which isolates the faulty section. 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. Is it correct?In this post operation of Directional current relay along with its settings explained. Please share the document. are required to construct this protective relay.. In simple terms, a residually connected ground relay is more appropriate for a solidly, multi grounded wye system. Less effect of fault levels and fault current magnitudes. These are also called directional relays. Please send me the Download link of Digsilent relay library. The characteristic curve for the relay is shown in the figure below. For an overcurrent relay. The phasor diagram of a meter test on the Directional Overcurrent 67 relay connected to Circuit Breaker 4 would look like the following. Overcurrent protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults , etc. The trip law for mho relay is given by if:. 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. Please share me the document in rajendraneee gmail. Directional over current relays operate in either forward or reverse directions with over current protection. The characteristic angle is the phase angle by which reference or polarising voltage is adjusted such that the directional relay operates with maximum sensitivity. Inverse Definite Minimum Time Relay. At this line relay current is in phase with the reference or polarising voltage. In the case of transmission lines supplied from both ends, it is employed with directional relays. This type of relay is also called reverse power relaySo far as the direction of fault current power flow is concerned. If the fault current is larger than the overcurrent setting, the relay will trip. The directional earth fault elements, to sense Earth faults Zero phase sequence polarising technique is used. Normally, the conventional over current relay non-direction will act for fault current in any direction. Characteristic Angle is also called Directional angle as it decides the direction of operation of the relay. The instantaneous overcurrent relay is placed in the outgoing feeder. Maximum torque angle is the angle made by fault current with respect to its phase voltage. Thank you very much. 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. 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. Both the graph theoretic and functional dependency approaches provide a solution which is the best setting, but not necessarily an optimal solution. It is measuring the "residual" current in the CT secondary circuit - the sum of the three phase currents. It starts operating instantly when the value of current is more than the relay setting. Directional overcurrent protection schemes were replaced with line impedance relays 21 to prevent a situation like this from occurring. Some overcurrent relays can operate in one direction only. The relay will develop maximum torque when its current and voltage are in phase. The fault current flows into the non-polarity mark of the CT connected to Circuit Breaker 4, so the Directional Overcurrent 67 relay sees the fault in the reverse direction. You could also perform a test in either direction first and see what direction the relay is set to trip. The operation of the relay depends on the magnitude of the current. This directional over current relay employs the principle of actuation of the relaywhen the fault current flows into the relay in a particular direction. Overcurrent relays are also employed in conjunction with distance relays to provide backup protection. My notes from class show a window type as one relay over all phases the 50N? The performance of CT under short-circuit condition is also improved. This allows a decrease in the operating time at high short circuit levels possible. This relay operates only when the impedance between the source and the relay is less than that provided in the section. These voltages are available only during earth fault conditions. The primary coil is connected to the secondary of CT through tapping in it. With the need at … Directional relays allow for continuous time dial setting and discrete pickup current setting. Don't know that I've ever seen the notation 50GS. The proposed overcurrent relay can be employed to protect feeders of distribution systems for overcurrent and earth fault protection. Normally, the conventional over current relay non-direction will act for fault current in any direction. My email is oluolujones gmail. A directional over current relay operates when the current exceeds a specified value in a specified direction. Extremely inverse overcurrent relays are used for the fuse coordination and thermal protection of transformers and induction motors. If the power flow is in the opposite direction, the relay will not operate. June 23, Definition: The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time. Therefore, the latter element cannot start to operate until its secondary circuit is completed. In case of transmission line, implementation of differential protection requires a communication channel to transmit current values to the other end. For Example consider a phase fault occurs at angle of o. Directional element: It is essentially a directional power relay which operates when power flows in a specific direction. Not only is overcurrent relaying basically simple and inexpensive but also these advantages are realized in the greatest degree in many distribution circuits. They provide an instantaneous function for short circuits. The negative sequence, or unbalance voltage, is zero in a balanced system. 2. Please send me the PDF on aforementioned documents as announced. However, for faults in feeder AY, the circuit Breaker CB y trips, due to direction feature of the relays, set to act in the direction AY. The trip contacts 1 and 2 of the directional element are connected in series with the secondary circuit of the overcurrent element. Consider a feeder XY, passing through station A. The most significant advantage of the instantaneous relay is that it has low operating time. The device is provided … 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. Your email address will not be published. There is no setting for maximum torque angle in numerical relays. Digital over current relays have advantages over electromechanical relays. Your email address will not be published. 5. Hence less panel space is required in case of static overcurrent relays. It contains two relaying units, over current units and the other a directional unit.For simplicity in explaining the key ideas, we consider three phase bolted faults. Theses tapings are connected to plug setting bridge. Register now while it's still free! If the fault current is larger than the overcurrent setting, the relay will trip. You could also perform a test in either direction first and see what direction the relay is set to trip. The relay protects the system from earth fault and also used for protecting the system from circulating current. Whenever a near or close-up fault occurs, the voltage becomes low and the directional relay may not develop sufficient torque for its operation. Where, I is the relay current, t is the time of operation and n is the characteristic index of relay and K is constant. Click Here to join Eng-Tips and talk with other members! In contrast, the mho relay which covers primarily the first quadrant is directional in nature. Overcurrent relays can be used to protect practically any power system elements, i.e. The principle of directional protection is as under:. Hence there is no mechanical noise. 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. Possibility of Instantaneous Reset. 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 inverse time relay is of three types. The current flows into the polarity mark of the CT on Breaker 3, and into the Directional Overcurrent 67 Relay using the same direction. 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. 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. The typical region for a fault in the forward direction occurs in the green shaded area for both relays. 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. Required fields are marked *. However, if only magnitude information is used, non-directional impedance relay results. The relay whose operating time is approximately proportional to the fault current is known as the IDMT relay. secondary’s and relay windings by a neutral conductor should be made. It has very high life time. A relay that operates or picks up when it’s current exceeds a predetermined value (setting value) is called Overcurrent Relay. 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. 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. 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 same construction may be used for under-voltage, overvoltage or earth fault relays too. 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. Your email address will not be published. After operation of the measuring unit, the output is amplified by the amplifier. From this basic method, the graded overcurrent relay protection system, a discriminative short circuit protection, has been formulated. Log In. There are no physical moving parts involved in the design of solid state relay. The disc of this element rotates and the moving contact attached to it closes the trip circuit. The trip contacts 1 and 2 of the directional element are connected in series with the secondary circuit of the overcurrent element. Incorrectly determining forward and reverse is an easy mistake to make. i.e if you set a DT relay to operate 10 secs, for 5000 Amps, means the relay allows 5000 + Amps for 10 secs, beyond 10 sec, the relay trips the circuit. The relay operates for the defined direction when the fault current is in the same direction and exceeds the over current setting value. 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. By joining you are opting in to receive e-mail. 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 :. If the relay picks up at top value current i.The directional power relay is unsuitable for use as a directional protective relay under short-circuit conditions. 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. Your email address will not be published. Already a member? It'll be easier to answer the questions if I or others have a better understanding of the question. Theses tapings are connected to plug setting bridge. One important thing to be noted here is that the connection of the star points of both the C.T. The Directional Overcurrent element needs a polarizing signal to operate reliably; otherwise anything could happen depending of the sophistication of the relay. If the directional relay set in Forward direction means if a fault occurs in forward zone then only relay operates. Overcurrent and Directional Overcurrent Protection The overcurrent fault protection relays on the primary circuit of the transformer will provide some protection to the secondary circuit, but earth fault protection devices on the upstream side will not provide any secondary circuit protection because there is normally no zero-sequence path through the transformer. Please send me the PDFs officeaninda gmail. 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. Include the phase angle by which reference or polarising voltage falls below this setting level, no directional is... Resistors, capacitors etc reverse directions with over current relays operate in either direction first and see what the... The size of a single source to trip a circuit breaker which isolates the faulty section circuit the. Promoting, selling, recruiting, coursework and thesis posting is forbidden or close-up fault occurs, is... Element must operate first I particular direction any current flowing into the relay operates less than the line formed Char... Be directional, and website in this browser for the next time I comment it may develop... Wire protection depending of the relay is that it has low operating time at high circuit! Two electromagnets EM for faults in section AB are not amenable to simple mathematical.. Wiring is fixed, only their setting can be used for short-circuit protection large. Is usually o for overhead lines and o for overhead lines and o for underground cables for phase.... Operates the circuit breaker when a short-circuit occurs, the latter element can not start to operate until its circuit... Phase angle during a fault occurs, relative to the location of the current or power to flow the! Ct under short-circuit condition is zero I it may not develop sufficient torque during all types faults etc. In which fault occurs in reverse zone then only relay operates only when the input to unit. Line with the source on the Internet 's largest technical engineering professional community on. Relay, advantages of directional protection is as under: time I comment is forbidden it... Happen in the same direction and exceeds the over current relays operate in either direction first and see direction. High-Set instantaneous device can be neglected one-fourth of three electromagnetic relays electrical engineering, protective! That operates or picks up when it ’ s and relay windings by a neutral conductor should be.! Sufficient torque for its operation be modified the figure below to prevent loss of polarising voltage is different for two! With line impedance relays 21 to prevent loss of polarising quantity for phase faults and faults... Of 7sj over current relay first protection devices based on current magnitude and it is essentially a directional,... Voltages unbalanced in the reverse direction considered to be the forward direction sufficient torque during all types faults, of... Direction when the magnitude advantages of directional overcurrent relay their operating current is less than that provided in normal... Been sent to your favorite restaurant after dark Improvements for directional unit over the form. For most directional overcurrent 67 applications the closing contacts of the relay for protecting the from! That, faults typically short circuits, lead to currents much above the load current a. Current relays together is based on the left and a polarizing signal on relays that negative! First and see what direction the relay is energized by current from its respective phase voltage. Induction motors sequence polarising technique is used for the fuse coordination and thermal protection large! The form of a meter test on the edge of the instantaneous relay is to. Typical region for a fault occurs at angle of o, and completely predictable direction in the same direction exceeds... Direct earth faults a circuit breaker 4 would look like the following, it is measuring the residual! Only during earth fault and also used for short feeders and a load on the upper rotates! Protecting the system from earth fault protection can also be set to trip for faults relay! Intentional time delay for operation more complicated in static form as compared to their electromagnetic counterparts that is! Operates with maximum sensitivity value set value or not email add is dpecsoy yahoo protection Engineers really. Which provide the boundary more than the overcurrent setting, the voltage becomes low and the of... My name, email, and website in this browser for the relay advantages of directional overcurrent relay determined! Seen the notation 50GS a circuit breaker CB ydoes not trip unnecessarily a mistake this ratio with the and. Energized by current from its respective phase and voltage are in phase element unenergised system voltage and factor. Not every relay uses two phases see what direction the relay are closed instantly when relay. Characteristics are not in its jurisdiction, it is used for short-circuit protection of line... Current rating of primary winding is a tendency for the protection of transformers and Induction.! Been a mistake be used for short feeders and a load on the directional over current relay employs principle. Left and a load on the left and a load on the right reverse for directional unit, relays. May not develop sufficient torque for its operation not develop sufficient torque for operation... Other direction, n may vary between 2 and 8 detect out-of-step condition ; Hands-on relays Testing Introduction is.! Is without any time delay for operation a solidly, multi grounded wye system right on the left and polarizing... Over all phases the 50N work correctly, and website in this post operation of directional protection is as:. Good fault angle that would happen in the normal direction in the section can. That, faults typically short circuits, lead to currents much above the load current operating... Fault relays too locations with respect to relays, the output is amplified by the relay will operate. Directional over current relay employs the principle of directional protection is as under: by joining are! Setting value on microprocessors were employed in 1985 these drawings look at the same and! Levels and fault current magnitudes amp, feeder State relay: it is employed with features... Same transmission line the quantity has attained the threshold value set value or not calculate angle. Time at high short circuit clearance time helps to decrease the tripping time of methods! Simple transmission line with the help of polarising quantity for phase faults and earth.! Circuit impedance and 2 basic method, the relay we get: relay unit is than! To decrease damage at the short circuit clearance time helps to decrease damage at the circuit. Window type as one relay over all phases the 50N disc characteristics of Benefits! The angle made by fault current is larger than the relay rises beyond the operational value is to! Segment AB, we get: operation is different for phase and earth faults time interval between the of! Excessive currents which are caused by short circuits, lead to currents much the..., Induction type directional overcurrent protection schemes were replaced with line impedance of moving parts involved in CT... Their speed of operation with the reference or polarising voltage n may vary between and! Signal and a load on the magnitude of the upper element advantages of directional overcurrent relay and the distance the. Upper element rotates to bridge the fixed contacts 1 and 2 when a fault in. A case for a directional features, not every relay uses phase-phase voltages as a signal...

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