The non-unit schemes, while also intended to protect specific areas, have no fixed boundaries. Electrical Engineering, Devices, Relays, Overcurrent Relays, Classification of Overcurrent Relays. Figure 4 shows the connection of a distance relay for line protection. Used where there is a reduction in fault current, as the distance from source increases. He is member of Institution of Engineers (MIE), India. Used when Fault current is dependent on fault location. Eg., upto 1.0 In, you may select a curev like NI-3.0, for secoond stage-I>> you can again select curve or give defenite tme tripping. With so fast an operation it is likely that the relay may operate on transients beyond the normal range of setting. Expensive cables, etc. Other Relay Classifications. Single phase fault currents are NOT always lower than Phase fault currents. Therefore, relay connected for earth fault protection is different from those for phase to phase fault protection. The relay is used for the purpose of protection of the equipment connected with it. Application: This type is applied to the outgoing feeders. 10. There are four typical types of current transformers: window, bushing, bar, and wound.The primary winding can consist merely of the primary current conductor passing once through an aperture in the current transformer core (window- or bar-type), or it may consist of two or more turns wound on the core together with the secondary winding (wound type). Directional overcurrent relays are constructed using a normal overcurrent unit plus a unit that can determine the direction of the power flow in the associated distribution system element. Protective relay SlideShare. •A comparison of the time it takes protective ... •Protective relay characteristics and settings •Fuse ratings •LV circuit breaker ratings, characteristics, and settings. On some sub transmission lines where the cost of distance relaying cannot be justified. At values of current less than pick-up value, the relay never operates: At higher values, the operating time of the relay decreases steadily with the increase of current. IDMT Relay High Current setting : Plug setting of Relay is 2.5 Amp and Time Delay (TMS) is 0.100 Sec, Relay Curve is selected as Normal Inverse Type In our co-gen Plant , we are facing the problem of frequent tripping of grid breaker on stand by earth fault protection due to 110 KV line earth fault or even due to small disturbance at 110 KV line or at 110 KV substation where we are exporting the power. TABLE V. COMPARISON RELAY SETTING ON 20 KV - "Setting Analysis of Over Current Relay and Ground Fault Relay on Transformer Protection System of High Voltage Substation System" Separate earth fault relay provided makes earth fault protection faster and more sensitive. Current Differential Relay. In these schemes, the effects of any disturbance or operating condition outside the area of interest are totally ignored and the protection must be designed to be stable above the maximum possible fault current that could flow through the protected area. Thus when over heat occurs the bi-metallic strip connected to the motor heats up and in turn releases a spring to operate the contacts of the relay. This is in place to show greater stability in the classifications which are based on compliance over five years instead of the standard ... Current classification lists. Classification is based on the mechanical capacity activated by the speed of gas or liquid outflow, pressure. The IEEE defines protective relays as: “relays whose function is to detect defective lines or apparatus or other power system conditions of an abnormal or dangerous nature and to initiate appropriate control circuit action ”. 5.2.1 Definite-Current Relays. Hi to all engineers in here may I ask for a LINE PROTECTION CALCULATION and Over Current protection calculations? Study specialized technical articles and papers. The curve IV in Fig. Types and Applications Of Overcurrent Relay (1), Cost of protection / against cost of potential hazards. Please let me know that this 7SJ614 can be used in the Switchgear Panels (33kV and 13.8kV) for ARC FLASH Protection by sensing light, Pressure and heat . (ii) Under-Voltage, Under-Current and Under-Power Relay: The relay operates when the voltage, current or power falls below a specified value. For Operation of Definite Time Overcurrent Relay operating time is constant. why psm calculation is important if we are using plug setting ?iam so much confussed about this topic? When the power system is not radial (source on one side of the line), an overcurrent relay may not be able to provide adequate protection. In the event of switching arc jumps across the contacts which results to melting of the contact surface over a small section. It has more inverse characteristics than that of IDMT and very inverse overcurrent relay. Differential Protective Relay is a protective relay that functions on a percentage or phase angle or other quantitative difference of two currents. You can use combinations of curve types to achieve the design requirements. Inverse-Time Overcurrent Relay 3. A relay is a simple electromechanical switch made up of an electromagnet and a set of contacts. Overcurrent induction disc relays used offshore usually have a current/time operating characteristic in accordance with BS EN 60255-151 for an inverse definite minimum time relay. Over current Relay • Definite time over current relay • Instantaneous over current relay • Inverse time over current relay • Inverse definite minimum time (IDMT) over current relay • Very inverse –time over current relay • Extremely inverse time over current relay Inverse time overcurrent relays: Slow to trip at low currents. I commonly use inverse-time, definite-time, and instantaneous elements, all on the same relay. Relays are used to protect the electrical system and to minimize the damage to the equipment connected in the system due to over currents/voltages. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts, or combinations thereof.. IDMT Relay Low Current setting: Over Load Current setting is 125%, Plug setting of Relay is 0.8 Amp and Time Delay (TMS) is 0.125 Sec, Relay Curve is selected as Normal Inverse Type. Instantaneous Overcurrent Relay 2. 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