In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. ⊗=open bus-section circuit breaker. For Later, Many developing countries confront widespread theft of, In India electricity theft leads to annual losses estimated at, #onest consumers, poor people, and those without, connections, who bear the burden of high tariffs, system, inefficiencies, and inadeuate and unreliable power. In a small generator, the neutral end of the three phase windings is connected internally to a … 4.4.2). Earth fault: Earth fault is an Open Circuit fault; where the power carrying cable or conductor breaks and gets into contact with earth or a conductor capability material in contact with earth. Low voltage restricted earth fault (LVREF) protection is applied to the LV 11 kV transformer star winding and neutral connections as shown in Fig. Consider the case of two auxiliary transformers, A and B, used to derive the substation auxiliary LVAC supply. Copyright © 2021 Elsevier B.V. or its licensors or contributors. Figure 10.13b. Earth-fault Relay connected in Neutral to Earth Circuit (Fig. For an earth fault, IF=IFA+IFB, on the left-hand side LV switchgear busbar fed by transformer A a proportion of the fault current, IFB, may return to the neutral of transformer A via the earthing path of transformer B. Earth faults, in other words, the accidental contact between an active (phase) and an earthed conductive part can lead to dangerous situations … Under worst case conditions for an internal fault with three CTs receiving magnetizing current from the CT in the faulted phase, then CT output required to operate the relay=11+(3×32)=107 mA. Plain overcurrent relays operating on bus-section switches cannot, of course, remove the faulted section from the supply, unless it is being fed via another section. DrC.R. Directional earth fault relays sense the direction in which earth fault occurs with respect to the relay location and it operates for fault in a particular direction. Earth Leakage Protection Relays (ELR series) Earth Leakage relays (ELR’s) or also known as ground fault relays are residual current monitors (RCM’s) that are used to detect potentially dangerous ground fault currents before they cause any hazard. A single earth fault in the rotor circuit will complete the circuit comprising the voltage source (ac or dc), sensitive overvoltage relay and earth fault and thus earth fault will be sensed by the relay. The earth systems associated with high-voltage substations must satisfy the following conditions: The resistance of the system to earth must be low enough to ensure that earth fault protection equipment operates correctly. A reverse-phase sequence and undervoltage relay can be used to detect this condition. Figure 4.6b shows such a system with a key-interlocked normally open LV busbar-section circuit breaker and the same ‘classic’ SBEF CT location. In the event of an earth fault the difference in potential between any point which may be touched and the ground (touch potential) should not reach dangerous levels. Bayliss CEng FIET, B.J. The relay is designed for sensing the fault current which is 15% more than that of the rated winding current. Read about company. Thermal relays are employed for overloading, also a separate stalling relay is employed for motor stalling conditions. In this video the philosophy behind the restricted Earth Fault Protection has been elaborated. Lead and CT resistances to common LVREF relay connection point=0.4 ohm neutral to relay cable resistance per core. Under fault free or external fault conditions the CT currents will sum to zero and the relay will not operate. Simple directional overcurrent busbar protection scheme. 4.6a–c. Claire Soares, in Gas Turbines (Second Edition), 2015. Bayliss CEng FIET, B.J. At the same time maloperation of transformer B protection is avoided and transformer B continues to supply the healthy busbar and associated substation LVAC loads. A current transformer (CT) associated with secondary unrestricted earth fault protection is located on the earth side of the neutral to earth link. Triple harmonics are of particular importancesince these harmonics are additive and cophasal in a three phase system and thus appearin the system neutral or in an earth fault relay aszero sequence (or earth fault) current. The NewElec GA Earth Leakage relay provides earth leakage protection also known as ground fault protection designed to protect personnel and equipment by rapid disconnection of main supply to faulted equipment a unique feature is the integrated distinguishing between Earth leakage and Earth fault routing trips to incoming circuit breaker rather than the fault level limited main circuit contactor. A single earth fault results in a rise in the voltage between system neutral and earth, which may be detected by a relay measuring the residual voltage of the system (normally zero for a perfectly balanced, healthy system). In addition it should be noted that the IFB proportion of the fault current will bypass, and not be summated by the neutral CT associated with the transformer supplying the fault. The most occurred and severe earth fault happens when insulation of winding get damaged, and it touches the core of the machine. Omar Salah Elsayed Atwa, in Practical Power System and Protective Relays Commissioning, 2019. The disadvantage of this connection arrangement is that the SBEF CTs will now register 3rd harmonic or out of balance load currents. Relays with harmonic restraint filters can be employed in cases where the harmonic component of the load (such as with discharge lighting) is high. magnetising inrush giving secondary currents in one set of CTs only. Hardy CEng FIET, in, Transmission and Distribution Electrical Engineering (Fourth Edition), I G Crow BEng, PhD, CEng, FIMechE, FIMarE, MemASME, R Robinson BSc, CEng, FIEE, in, Plant Engineer's Reference Book (Second Edition), Transformer Faults and Protection Devices, Differential protection is rarely used on transformers offshore. This arrangement could be used for the connection of a third generator, with all outgoing feeders (except third generator auxiliaries) fed from the end sections (see Fig. Supplied with TecQuipment’s Protection and Relay Test Set (PSL50), the relay enables investigations into protection and monitoring of transformers, transmission lines and distribution schemes. In Electrical Systems and Equipment (Third Edition), 1992. Hardy CEng FIET, in Transmission and Distribution Electrical Engineering (Fourth Edition), 2012. Discover everything Scribd has to offer, including books and audiobooks from major publishers. Figure 4.6. OVERCURRENT AND EARTH FAULT RELAY An entry-level three-phase and earth fault overcurrent relay presented in an educational format. Consider an earth fault on motor terminal, ASB. 10.13c. At the same time unbalanced or harmonic currents involving the neutral (3rd harmonics and multiples) will not be ‘seen’ by the CT in this position. Unbalanced or negative-phase sequence protection should be used as rotor heating due to unbalanced currents being a function of the negative-sequence component of line currents. Kerala Switchgear Sales Corporation - Offering Earth Fault Relay, पृथ्वी फॉल्ट रिले, Earth Relay in Kadavanthra, Kochi, Kerala. 5). It is also a high resistance earth fault. Maximum 11 kV fault current If=1,347×33/11=4,042 A (see Section 10.5.3.1). It is provided with flag. Normally, during earth-fault conditions, very high earth-fault currents will flow in a solidly-earthed transformer. Hence the name restricted earth fault protection. and earth-fault relay REJ 525 and presents detailed instructions on how to use the Human-Machine Interface (HMI) of the relay, also known as the Man-Machine Interface (MMI). The most important part in SEF or Sensitive Earth Fault Protection is to make proper setting of the Relay. Field failure relay should be provided for synchronous machines larger than about 500 HP which are not provided with loss of synchronism protection, preventing overheating of the rotor after continuous operation as an induction motor. LVREF protection CT arrangement and lead-CT resistances. Failure of a bearing can cause motor stalling. The bias slope is chosen so that the relay is insensitive to unbalanced external lead burdens which normally give a lower ratio of differential current to through current than an internal fault. All the protection systems mentioned above, depending on circuit conditions, trip their own unit, the banked generator-motor unit, the 400 kV circuit-breakers and send a trip signal to the starting busbar system to trip the generator-motor, if they are in a starting sequence. The directional earth fault relay (single phase unit) has two coils. Figure 10.13c. 4.4.1). An earth fault relay is activated by the fault current flowing from line to earth, while an over-current relay is activated if the line current exceeds a certain value. To prevent voltages being transferred through interwinding capacitance coupling, an earthed screen is provided between windings. 1.2. These are normally fitted in machines of 1000 HP and above. The substation and its environment should not be connected to metal objects such that the voltages arising within the substation under fault conditions can be transferred to a point remote from the substation. Another method of connecting an earth-fault relay is illustrated in Fig 5. BEF protection CT arrangement. IFB=component of earth fault current returning via transformer ‘B’ neutral to earth link. This kind of earth fault protection is also known as unrestricted earth fault protection. 1.7 Case Study 1.7.1 Coordination of earth fault by fuse Consider the system shown in Figure 1-1 for earth fault coordination. This is the ‘classic’ standby earth fault (SBEF) protection CT location and transformer connection to the LVAC switchboard for a single transformer source of supply. Assume worst case earth fault with solid earthing equals 3 phase fault level with one transformer feeding maximum CT current. IF=busbar earth fault current. However, it does have the advantage over restricted, The overcurrent fault protection relays on the primary circuit of the transformer will provide some protection to the secondary circuit, but, . That actually means a standby-scheme should have a long time delay to ensure positive operation for downstream schemes. The relay will only operate for faults appearing in the protection zone between the sets of sensing CTs at the primary and secondary terminals. This relay can detect the earth’s fault, so we can say that RCCB does the same function. If these currents become unequal because of a fault current being sensed in the transformer windings, the resulting current energises the operating coil. The purpose of a standby relay is to trip if all other earth-protection schemes fail to remove the fault. =0.1 ohm phase-to-relay cable resistances per core. Traditionally, such a relay has only the pick-up setting and it does not have any TMS. Where the overloads period is short a loss of synchronism relay can be arranged to disconnect the field supply only, so that the machine runs as an induction motor during overload then the relay resynchronizes the machine automatically after overload periods. Lvac Distribution switchboard earth and neutral busbars via links as shown in 1-1... Because it can go out of step with supply after an interruption setting of the 18 kV winding included... Electrical Systems and Equipment ( Third Edition ), 2015 system at load in... 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