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. 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. Some relays have an operating characteristic like the following picture:. Advantages of directional overcurrent relay, advantages of directional overcurrent relay, i spilled hydrogen peroxide on my clothes. It consists of two relay elements mounted on a common case viz. The primary coil is connected to the secondary of CT through tapping in it. It protects the equipment of the power system from the fault current. 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. 4. Each relay is energized by current from its respective phase and voltage. 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. One important thing to be noted here is that the connection of the star points of both the C.T. Directional relays needed reference voltage to identify the direction of currents. The relay will not operate when the value of current is less than the pick value. The Char Angle setting must be specified while configuring Directional over current relay. June 23, Your email address will not be published. It has very high life time. 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. Save my name, email, and website in this browser for the next time I comment. Overcurrent Relays/Elements; Directional Overcurrent Relays; Over/under Voltage Relays; Distance Relays; Day 3 Out-of-Step Relaying. Any current flowing into the polarity mark is considered to be the forward direction. We appear to be in good shape for most Directional Overcurrent 67 applications. The trip contacts 1 and 2 of the directional element are connected in series with the secondary circuit of the overcurrent element. The first protection devices based on microprocessors were employed in 1985. Some relays use the negative sequence voltage as the polarizing signal. We will start with a simple transmission line with the source on the left and a load on the right. 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. 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 directional relays identify the zone of operation with the help of polarising voltage and characteristic angle. The current flows into the polarity mark of the CT on Breaker 3, and into the Directional Overcurrent 67 Relay using the same direction. 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. The detailed explanation about Directional relay settings with Characteristic angleMaximum Torque angle and Polarisation voltages are given. We added the B-C phase-phase voltage to the drawing, which is the polarizing voltage this style of relay uses. The relay is used for the protection of the distribution lines. If the fault current is larger than the overcurrent setting, the relay will trip. Inverse Definite Minimum Time Relay. Overcurrent relays are also employed in conjunction with distance relays to provide backup protection. Join your peers on the Internet's largest technical engineering professional community. 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. 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. 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. secondary’s and relay windings by a neutral conductor should be made. Consider a simple radial system, which is fed from a single source. The tappings are provided on the upper magnet of overcurrent element and are connected to the bridge. Fault current Lags the voltage by 30 o. Overcurrent directional relays can be set to trip for faults in the forward direction, which will protect the equipment in front of the relay. Differential protection can be used for tapped lines multiterminal lines where boundary conditions are defined as follows:. This difficulty is overcome in the Induction Type Directional Overcurrent Relay which is designed to be almost independent of system voltage and power factor. Thank you. Home Products Contact Us. I used to occasionally run into problems when testing Directional Overcurrent 67 elements using traditional testing techniques.CSV Jul 14, Jul 14, Pin it. Permits high line loading. It contains two relaying units, over current units and the other a directional unit. In other words, the directional element must operate first i. By : admin News. It's easy to join and it's free. 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. 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 performance of CT under short-circuit condition is also improved. If we reversed the source and load, you could swap the phasor diagrams above for each relay. Instantaneous overcurrent relays are also useful in other protective relay systems. Very often, the relays do not need to be directional, and then no a-c voltage source is required. advantages of directional overcurrent relay. The contacts of the relay are closed instantly when the current inside the relay rises beyond the operational value. Or they can also be set to trip for faults behind the relay in the reverse direction. The negative sequence, or unbalance voltage, is zero in a balanced system. In conventional electromagnetic relays, n may vary between 2 and 8. For these needs, IEC determined a number of standard characteristics. There are no physical moving parts involved in the design of solid state relay. The phasor diagram for this situation might look like the following. The Eng-Tips staff will check this out and take appropriate action. Sir kindly share manual of 7sj over current relay manula my email. The relay operates only when the magnitude of their operating current is inversely proportional to the magnitude of the energize quantities. If the source impedance stays constant, it is then feasible to accomplish high-speed relay protection over a large part of the protected circuit. It can be used for short feeders and a specific implementation is known as pilot wire protection. Mistake to make to measuring unit is kept open AB and characteristic angle is also called directional angle it. Direction only are physically located near each other low and the moving contact attached to it closes the trip.... 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