It has a metallic disc free to rotate between the poles of two electromagnets EM. With higher value of n, the characteristic becomes more and more inverse. 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. You can find out more about Chris here.CSV Jul 14, Jul 14, Pin it. This relay is designed to protect the same transmission line from the other direction. Required fields are marked *. Thank you. Therefore, the latter element cannot start to operate until its secondary circuit is completed. This is a fault, so:. This test plan has a good chance of being successful because we have an operating signal and a polarizing signal. 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. Instantaneous Overcurrent Relay. I hope this helps clear up the definitions of forward and reverse for Directional Overcurrent 67 relays. This is also a special type of over current relay with a directional features. A directional over current relay operates when the current exceeds a specified value in a specified direction. Fast Ground Directional Overcurrent Protection – Limitations and Solutions Page 2 of 22 1. Applications and Advantages of Distance Relays. Conventional electromechanical and static relays are hard wired relays.Their wiring is fixed, only their setting can be manually changed. Directional relays needed reference voltage to identify the direction of currents. 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. 5. 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. Grading with the protection relay directly behind the protection relay, which has the instantaneous devices enabled, is accomplished at the current setting of the instantaneous devices and not at the maximum short circuit level. The detailed explanation about Directional relay settings with Characteristic angleMaximum Torque angle and Polarisation voltages are given. It is to be noticed that the directional over current operation is different for phase and earth faults. This directional over current relay employs the principle of actuation of the relaywhen the fault current flows into the relay in a particular direction. From this basic method, the graded overcurrent relay protection system, a discriminative short circuit protection, has been formulated. June 23, Your email address will not be published. This angle is different for phase faults and earth faults. If the fault current is larger than the overcurrent setting, the relay will trip. Instantaneously overcurrent relay operates when current exceeds its Pick-up value. 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. You could also perform a test in either direction first and see what direction the relay is set to trip. Always ask the engineer what they intended if there is any doubt. Conversely, if the relay set in Reverse direction means if a fault occurs in reverse zone then only relay operates. This difficulty is overcome in the Induction Type Directional Overcurrent Relay which is designed to be almost independent of system voltage and power factor. Each phase current is compared with the voltage between other two phases. 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 operation of this relay is based on current magnitude and it is without any time delay. 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. 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. 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. The relay whose operating time is approximately proportional to the fault current is known as the IDMT relay. The various advantages of the distance relays are: 1. If we reversed the source and load, you could swap the phasor diagrams above for each relay. There are no physical moving parts involved in the design of solid state relay. Therefore, Induction Type Directional Overcurrent Relay upper element does not operate, thereby keeping the overcurrent element lower element unenergised. This is usually refered to as a 50G device. A directional over current relay operates when the current exceeds a specified value in a specified direction. Incorrectly determining forward and reverse is an easy mistake to make. For directional unit, the secondary winding of the over current relay unit is kept open AB. These are:. Overcurrent relaying is well suited to distribution-system protection for several reasons. Overcurrent Relays In Directional OC relays there are two settings: time dial setting (TDS) and pickup current setting (I PU). This relay operates only when the impedance between the source and the relay is less than that provided in the section. If the power flow is in the opposite direction, the relay will not operate. However, when a short-circuit occurs, there is a tendency for the current or power to flow in the reverse direction. Again, thank you. DT: Definite Time over current relay The operating time is fixed irrespective of the fault current and the time setting can be controlled manually. 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. 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. It protects the equipment of the power system from the fault current. Or they can also be set to trip for … 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. Register now while it's still free! Operation: Under normal operating conditions, power flows in the normal direction in the circuit protected by the relay. Directional relays need a reference to work correctly, and that reference is called the polarizing signal. DIRECTIONAL OVERCURRENT RELAY 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. For an overcurrent relay. 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. You can choose a good fault angle using one of these methods:. The operation of the relay depends on the magnitude of the current. Close this window and log in. Hello, thanks for your comments. 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. This directional over current relay employs the principle of actuation of the relaywhen the fault current flows into the relay in a particular direction. A distance relay compares this ratio with the positive sequence impedance Z 1 of the transmission line. 4. 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. Maximum torque angle is the angle made by fault current with respect to its phase voltage. At this line relay current is in phase with the reference or polarising voltage. It may not seem like much, but it helps us keep creating more free content for you.Relay protection against high current was the earliest relay protection mechanism to develop. This ratio also indicates the distance of the fault from the relay. The phasor diagram of a meter test on the Directional Overcurrent 67 relay connected to Circuit Breaker 4 would look like the following. At this line relay current is in phase with the reference or polarising voltage. The static instantaneous overcurrent relays can have operating time of as small as 10 or 20 ms while in case of conventional electromagnetic relays it is of the order of 0. My notes from class show a window type as one relay over all phases the 50N? The time interval between the instant pick-up value and the closing contacts of the relay is very less. Less effect of fault levels and fault current magnitudes. The primary coil is connected to the secondary of CT through tapping in it. If the directional relay set in Forward direction means if a fault occurs in forward zone then only relay operates. 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. Also, the proposed relay is considered a Any current flowing into the polarity mark is considered to be the forward direction. It'll be easier to answer the questions if I or others have a better understanding of the question. A traditional relay tester, or automated testing software, will often apply a test scenario like the following:. The relay is designated to develop maximum torque when the relay current leads the voltage by 45 o. The trip contacts 1 and 2 of the directional element are connected in series with the secondary circuit of the overcurrent element. 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 upper magnet has two windings. Related Projects. 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. In simple terms, a residually connected ground relay is more appropriate for a solidly, multi grounded wye system. Its zone is clearly demarcated by the CTs which provide the boundary. The tappings are provided on the upper magnet of overcurrent element and are connected to the bridge. 3. In conventional electromagnetic relays, n may vary between 2 and 8. Neither did I Davidbeach However it shows that the 50GS having a dedicated ground relay feeding the relay as shown in the figure on page The 50N does not refer to figure on page 20 of the manual. Overcurrent relays are also employed in conjunction with distance relays to provide backup protection. The inverse time relay is of three types. The directional earth fault elements, to sense Earth faults Zero phase sequence polarising technique is used. The contacts of the relay are closed instantly when the current inside the relay rises beyond the operational value. 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. Join Eng-Tips Forums! It consists of two relay elements mounted on a common case viz. The directional relays identify the zone of operation with the help of polarising voltage and characteristic angle. 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. 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. 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. Since, the circle spans all the quadrants, it leads to non-directional protection scheme. 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. The trip law for mho relay is given by if:. This angle is different for phase faults and earth faults. 2. If the power flow is in the opposite direction, the relay will not operate. Directional over current relays operate in either forward or reverse directions with over current protection. The Selection of Polarising voltage is different for these two types of earth faults. If the source impedance stays constant, it is then feasible to accomplish high-speed relay protection over a large part of the protected circuit. They are more complicated in static form as compared to their electromagnetic counterparts. The directional phase fault elements, work with a Quadrature connection to prevent loss of polarising quantity for phase faults. 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. Hence there is no mechanical noise. 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