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. Not only is overcurrent relaying basically simple and inexpensive but also these advantages are realized in the greatest degree in many distribution circuits. To get sufficient torque during all types faults, irrespective of locations with respect to relays, the relays connections are to be modified. Sir kindly share manual of 7sj over current relay manula my email. Distance relay is used for the protection of transmission line &, feeder. The various advantages of the distance relays are: 1. Whenever a near or close-up fault occurs, the voltage becomes low and the directional relay may not develop sufficient torque for its operation. 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. When the measured polarising voltage falls below this setting level, no directional output is given and hence direction protection will be inhibited. They are simple in construction. The impedance relay trips if the magnitude of the impedance is within the circular region. In other words, the directional element must operate first i. These are:. When a short-circuit occurs, the system voltage falls to a low value and there may be insufficient torque developed in the relay to cause its operation. Please send me the PDFs officeaninda gmail. 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. 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 voltage of faulty phase drops and other phases remain healthy.I used electro-mechanical directional relays as an example, which may have been a mistake. Register now while it's still free! If we reversed the source and load, you could swap the phasor diagrams above for each relay. This is the voltage taken from Potential Transformers. To illustrate the principle let us consider that current rating of primary winding is A and secondary winding is A. This is a fault, so:. If the fault current is larger than the overcurrent setting, the relay will trip. In other words, the directional element must operate first i. The fault current is fed from only one end of the feeder. The disc of this element rotates and the moving contact attached to it closes the trip circuit. The time interval between the instant pick-up value and the closing contacts of the relay is very less. These are also called directional relays. 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. Simpler to co-ordinate. Some relays use the negative sequence voltage as the polarizing signal. The directional relays identify the zone of operation with the help of polarising voltage and characteristic angle. Uses and Benefits; Hands on Testing of Relays. It consists of two relay elements mounted on a common case viz. The detailed explanation about Directional relay settings with Characteristic angleMaximum Torque angle and Polarisation voltages are given. In simple terms, a residually connected ground relay is more appropriate for a solidly, multi grounded wye system. 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. This operates the circuit breaker which isolates the faulty section. Whenever a near or close-up fault occurs, the voltage becomes low and the directional relay may not develop sufficient torque for its operation. There are no physical moving parts involved in the design of solid state relay. The first static relays developed were the high speed differential relays and the distance relays. What is out-of-step condition; How does a relay detect out-of-step condition; Hands-on Relays Testing Introduction. The characteristic curve for the relay is shown in the figure below. Overcurrent directional relays can be set to trip for faults in the forward direction, which will protect the equipment in front of the relay. Again, thank you. We will start with a simple transmission line with the source on the left and a load on the right. The tappings are provided on the upper magnet of overcurrent element and are connected to the bridge. 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. Therefore, our previous test plan will not have a polarizing signal on relays that use negative sequence polarizing. Their fast, compact and reliable operation results in minimum outage of power system in case of fault. After operation of the measuring unit, the output is amplified by the amplifier. This is due to the absence of moving parts, which facilitates the application of automatic reclosing of breakers. If the directional relay set in Forward direction means if a fault occurs in forward zone then only relay operates. Directional element: It is essentially a directional power relay which operates when power flows in a specific direction. The most important feature of the relay is their speed of operation. A high-set instantaneous device can be utilized where the source impedance is small in comparison with the protected circuit impedance. 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. Instantaneously overcurrent relay operates when current exceeds its Pick-up value. Promoting, selling, recruiting, coursework and thesis posting is forbidden. The quick short circuit clearance time helps to decrease damage at the short circuit location. The principle of directional protection is as under:. Extremely inverse overcurrent relays are used for the fuse coordination and thermal protection of transformers and induction motors. The relay is designated to develop maximum torque when the relay current leads the voltage by 45 o. In the case of transmission lines supplied from both ends, it is employed with directional relays. We start with the raw currents and voltages, then calculate the negative sequence voltage, and then plot the operating current and polarizing signal V2. It contains two relaying units, over current units and the other a directional unit. 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. We appear to be in good shape for most Directional Overcurrent 67 applications. However, there will be times when this test plan will not work. The directional over current relay recognizes the direction in which fault occurs, relative to the location of the relay. This is also a special type of over current relay with a directional features. shapes of various relays e.g. Inverse-time relays are used where the source impedance is much smaller than the line impedance. If the source impedance stays constant, it is then feasible to accomplish high-speed relay protection over a large part of the protected circuit. The device is provided … Figure 2 shows such a case for a radial system with source at both ends. For directional unit, the secondary winding of the over current relay unit is kept open AB. The directional relays identify the zone of operation with the help of polarising voltage and characteristic angle. Where, I is the relay current, t is the time of operation and n is the characteristic index of relay and K is constant. Directional over current relays operate in either forward or reverse directions with over current protection. In case of transmission line, implementation of differential protection requires a communication channel to transmit current values to the other end. From this basic method, the graded overcurrent relay protection system, a discriminative short circuit protection, has been formulated. Directional relays allow for continuous time dial setting and discrete pickup current setting. The contacts of the relay are closed instantly when the current inside the relay rises beyond the operational value. Theses tapings are connected to plug setting bridge. 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 :. To get sufficient torque during all types faults, irrespective of locations with respect to relays, the relays connections are to be modified. : 4 The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current, overvoltage, reverse power flow, over-frequency, and under-frequency. Overcurrent Relays/Elements; Directional Overcurrent Relays; Over/under Voltage Relays; Distance Relays; Day 3 Out-of-Step Relaying. Over current relays generally have 50% to 200% setting while earth leakages over current relays have either 10% to 40% or 20% to 80% current settings. The relay operates for the defined direction when the fault current is in the same direction and exceeds the over current setting value. The phasor diagram of a meter test on the Directional Overcurrent 67 relay connected to Circuit Breaker 4 would look like the following. This angle is different for phase faults and earth faults. Once they answer that question, I will review the CT connections and build a test on the transmission line and see if it trips. 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. This difficulty is overcome in the Induction Type Directional Overcurrent Relay which is designed to be almost independent of system voltage and power factor. Always ask the engineer what they intended if there is any doubt. This test plan has a good chance of being successful because we have an operating signal and a polarizing signal. Benefits or advantages of Solid State Relay. The principle of directional protection is as under:. 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. In conventional electromagnetic relays, n may vary between 2 and 8. 5. 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. 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. Your email address will not be published. It is to be noticed that the directional over current operation is different for phase and earth faults. Directional element: It is essentially a directional power relay which operates when power flows in a specific direction. Please share me the document in rajendraneee gmail. 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