CT's have also been specified as matched pairs and the impedance of leads/wires and interconnecting cables has had a large influence on the functioning of the relay. The connection of a restricted earth fault relay is shown in Figure 3. Earth fault out side the boundary will not be detected by the REF scheme. figure 2.1. It detects small stray voltages on the metal enclosures of electrical equipment. However, quite often the secondary CT is placed in the distribution switchboard, thereby extending the protection zone to include the main cable. I was reminded of Occam's Razor while reading a book. Please clarify my doubts.It may sound silly or stupid but I would like to know why and how. The earth fault can be dispersed by using the restricted earth fault protection scheme. (Same as Differential Protection) High impedance Restricted Earth Fault protection is the voltage based operating protection. About the author, Thank you. My view is that low impedance is preferred. An external fault in the star side will result in current flowing in the line current transformer of the affected phase and at the same time a balancing current flows in the neutral current transformer, hence the resultant current in the relay is therefore zero. Restricted earth-fault and residual earth-fault relay SPAJ 115 C 1MRS 750658-MUM EN ... can be controlled with the same earth-fault relay. Query 1. Steven has over twenty five years experience working on some of the largest construction projects. Restricted Earth fault Protection This relay can be implemented for only star connected transformer or star connected alternator. This could result in a nuisance trip. I want to just ask that how we can restrict the earth fault detection of a Particular Critical System let us consider an alternator and what is the Logic Behind that?what are the things to keep in mind and what is the difference between Overcurrent Earth Fault and REF ?How the CTs are arranged in Differential Protection what is the logic behind the arrangement . Electrical4U is dedicated to the teaching and sharing of all things related to electrical and electronics engineering. REF protection is fast and can isolate winding faults extremely quickly, thereby limiting damage and consequent repair costs. Thanks, Such protection can be provided at various voltage levels by connecting earth-fault relay in the neutral-to-earth … Fault detection is confined to the zone between the two CTs hence the name 'Restricted Earth Fault'. Normally the aircraft generates it own power, but when parked with... Have an opinion or something to say, want to ask or answer questions, share your knowledge then use our site to do it . Normally earth fault relay, earth leakage circuit breaker and ground fault circuit interrupter, etc. Photovoltaic (PV) systems are typically more efficient when connected in parallel with a main power gird. INTRODUCTION Traditionally 220 kV transmission lines are provided with distance protection relay as main protection and directional over current and earth fault protections as back up. When used as zero-current differential protection (restricted earth fault), the relay (IRI1-ER) is(IRI1-ER) to be connected acc. The relay is connected to secondary of a CT whose primary is connected in neutral to earth connection. At 500 kVA, I would tend to think the cost may not be justified (unless the transformer were particularly important). The fault current I f will flow through the core, frame of machine to earth and complete the path through the earthing resistance. Cables for MV Power Distribution - Earthed versus Unearthed Systems, How to refer fault levels across a transformer, Differential protection, the good old days, https://www.selinc.com/WorkArea/DownloadAsset.aspx?id=5562, A mechanical engineering paper, some history and memories, Fault Calculation - Symmetrical Components, Photovoltaic (PV) - Utility Power Grid Interface, Click here to view the notes list in a table format, Click here to view the notes indexed by tag, have a question or need help, please use our, spotted an error or have additional info that you think should be in this post, feel free to. if Vkp and Imag of both CT not the same, what will be the consequences on the Bias Differential and REF protection? The Restricted Earth Fault Relay is connected in this closed path. I would also look at more modern numerical relays for your application. One method of dealing with this is symmetrical components. If CTs are located on the transformer terminals only the winding is protected. Protection against phase to ground faults can be a difficult problem since ground fault currents vary within a large range, becoming almost negligible in some situations. For Faults inside the Zone the REF will operate When an earth fault happens inside the zone will the CT provided for SEF sense the fault current. The operation principle is primarily based on the biased differential protection scheme with threefol d tripping characteristic. - yes, but you need to check the CT calculations. This may be the reason some people avoid the use of REF. In this article, we explain some of the concepts behind directional earth fault, sharing our experience to support field deployment of this valuable protection element. 2. For parallel operation system, does operation of REF be connected to trip both primary and secondary Breakers.? It could be many things. But now as per CEA recommendations, two main protections each having distance relay of different type not necessarily of different Circuit, Earth Fault I. Earth leakage relay wiring diagram rotor earth fault relay 64r working earth leakage relays earth leakage relay wiring diagram earth leakage relay wiring diagram Working Principle Of Earth Leakage Circuit Breaker Elcb VoleWorking Principle Of Earth Leakage Circuit Breaker Elcb VoleEarth Leakage RelaysWorking Principle Of Earth Leakage Circuit Breaker Elcb VoleElcb Earth Leakage Circuit … It would be great if the breaker linkage is shown as part of the schematic. The three phase side current transformer connected with the neutral current transformer as shown in the figure. Measurement errors associated with mismatched CTs, saturation and varying lead resistance have been responsible for nuisance tripping and the system can be difficult to commission. It operates the CB when REF is failed to trip the circuit, Heavy earth fault outside of the REF protective Zone, and all other earth faults. The restricted earth fault schemes described above depend entirely on the Kirchhoff principle that the sum of the currents flowing into a conducting network is zero. Restricted Earth Fault Protection|REF relay working principle. The neutral transformer is called as NCT. The principle of For REF protection, PS class CT are used for high accurecy and for SEF 5P10 type CTs are used. Earth fault relay senses these faults. High impedance relays have a high input impedance and draw very little current under normal conditions. Thanks. restricted earth fault relay jrd 013 Principle of Operation: The Relays JRD 011 & JRD 013 are current operated Microprocessor based, differential relays which work on the high impedance principle. Can you please explain how a transformer can detect an earth fault by using using phase CTs? As it is essential that the current in the CTs be balanced during normal conditions (and through faults), historically REF has been implemented using High Impedance Relays. In case of phase to ground faults, high currents flow to the grounded neutral of the transformer. Ever wondered what kind of power an aircraft uses when parked at the airport stand. I have a few queries also (it may sound stupid). Another range of setting on earth fault relay is also available and may be selected where the earth fault current is restricted due to insertion of impedance in the neutral grounding. As the winding fault position moves towards the neutral, the magnitude of the current seen on the primary rapidly decreases and could potentially not be detected (limiting the amount of winding which can be protected). These relays are capable of sensing greater fault currents. The working principle is "Merz-Prize Circulating Current Principle". The C.T. I think the intent is that both mean the same thing. I don't have access to my normal computer at the moment, but as soon as I do I will look at updating the schematic. Suppose you have selected a certain boundary, this restricted earth fault protection (REF) will detect earth fault only within that range. While directional earth fault also uses the concept of a relay characteristic angle to determine direction, it looks at a different vector value to conventional overcurrent: the zero sequence component. Restricted Earth Fault Protection is also known as differentia... Jul 5, 2019 - In this video the philosophy behind the restricted Earth Fault Protection has been elaborated. A differential system can be arranged to cover the complete transformer . Thanks in advance Regards SYAM. To me, 87N is more appropriate as REF is a differential type protection (ANSI 87 – differential protection relay). So this REF relay will not be actuated for external earth fault. Sometimes REF protection is added to the primary as well (although if primary protection is required it may be preferable to consider full differential protection). I'll try to elaborate on this when I get more time. In this scheme, the CT secondary of each phase of an electrical power transformer are connected together as shown in the figure. - SEF should still sense the fault and act as backup protection. The earth-fault current can be calculated from the three pha se currents or separately measured by a ring-type-CT. Is it possible to use a single relay(if the relay is capable of) to incorporate all the protections.? Following on from my post on railway electrification voltages, I thought an introduction to traction substations would be a good idea. When used as highly what's the difference between ANSI 87N and ANSI 64REF? (using the concept that current flows only in a closed circuit) For faults outside the Zone SEF will operate, REF will not operate. The P&B MREF high impedance differential relay can be used over a wide range of applications. are used to restrict the fault current. You have explained it in simple terms. are programmed correctly in to the relay and that your polarities/wiring are fine. We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites. Restricted Earth Fault Operation Under normal conditions and by application of Kirchhoff’s laws the sum of currents in both current transformers (CTs) equals zero. 1. Recent advances in numerical relay technology have all but eliminated these issues, making the implementation of REF relatively easy, ensuring no nuisance tripping and simplifying commissioning. Can you please clarify? Simply we can say, it is standby protection for all other earth … It is backup protection for restricted earth fault (REF) relay. When used as zero-current differential protection (restricted earth fault), the re-lay (IRI1-ER) is to be connected acc. But during an internal fault, the neutral current transformer only carries the unbalance fault current and operation of Restricted Earth Fault Relay takes place. Usually, the contacts of the earth fault relay are connected to the trip circuit of circuit breakers at … There is also a technical comparison on the two types here which should help you: https://www.selinc.com/WorkArea/DownloadAsset.aspx?id=5562, What can cause 64REF to trip off a transformer during disturbances from the grid. In this video the philosophy behind the restricted Earth Fault Protection has been elaborated. It should be remembered that the protection as illustrated covers only the secondary of the transformer. As the magnitude of the currents remain relatively large on the secondary (particularly if solidly earthed), nearly the entire winding can be protected using REF. An unreset indicator does not affect the operation of the relay. of the low impedance Restricted Earth Fault (REF) function. You need to work through the circuits/issues logically until you can narrow it down. Some modern relays are able to compensate for differences in CT performance. Query 4. Hi, Is it a MUST that the knee point voltage, Vkp and excitation current, Imag of the Neutral CT and phase CT to be the same? The REF is unit protection and restricted to one transformer. The small power relay has only one contacts, and the high power relay has two contacts for opening the switch. secondary current I s flows through the operating coil and the restricted earth fault relay coil of the differential protection. Hence the relay will not respond even there is an unbalancing in-phase current of the power transformer. Anybody can advise me on these? Earth leakage relays perform two main functions on mining installations: to protect machinery from damage and to make the in-stallation safer for personnel. There is a lot of debate on which to use and some theory. Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. In this video we havr explained how earth fault is detected. (Supervisory Control and Data Acquisition), Programmable Logic Controllers (PLCs): Basics, Types & Applications, Diode: Definition, Symbol, and Types of Diodes, Thermistor: Definition, Uses & How They Work, Half Wave Rectifier Circuit Diagram & Working Principle, Lenz’s Law of Electromagnetic Induction: Definition & Formula. Restricted earth fault relays are also very quick due to the simple measuring principle and the measurement of one winding only. The inner section of the relay is shown in … In the case of transformer winding with neutral earthed, unrestricted earth fault protection is obtained by connecting an ordinary earth fault relay across a neutral current transformer . If these both currents are equal in amplitude there will not be any resultant current circulates through the said closed path. This relay protects the delta or unearthed star … It is difficult to remotely diagnose this type of issue. Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. […] You should also make sure that the CT ratios, phase shift, logic, etc. 5. The earth fault relay is placed in the residual part of the current transformers shown in the figure below. It works on the principle of an electromagnetic attraction. If you have two in parallel you could isolate only the faulty transformer. - yes it is possible. The yellow LEDs (∆I By measuring this current imbalance faults between the CTs can be easily identified and quickly cleared. Thanks. The same principle of operation applies for faults on the MV side because the HV and MV earths are separated. Another method of connecting an earth-fault relay is illustrated in Fig 5. My query is that is it possible to use only one type of (PS Class) CT for all the protections..? An external fault in the star side will result in current flowing in the line current transformer of the affected phase and at the same time a balancing current flows in the neutral current transformer, hence the resultant current in the relay is therefore zero. Which is the correct or better to use may be open to interpretation. This would need to be investigated on a case by case basis. The stabilized earth fault current relay IRI1-ER serves as a supplement for the transformer differen-tial protection. Low impedance relays are the opposite. Working principle The protection relay IRI1-ER is IRI1-ER connected to the differential circuit of the c.t.s as a current differential protection relay. In earlier posts we have already discussed Differential Protection of Transformer and various characteristics of Differential Protection. When a fault occurs between one phase and the ground will the fault current travel back from the ground through the neutral to the fault point..? If you are also able to get a recording of the voltages and currents during an incident this will help you a lot. REF is a fault in the winding and you need to isolate the transformer - trip the MV/HV side. Can you also Please clarify the following : For a radial transformer feeder provided with REF protection on LV side, does the operation of REF relay be wired to trip the primary HV side or secondary LV side Breaker? Restricted Earth Fault (REF) protection is basically a Differential Protection. 2. A common reason could be unbalanced/incorrectly selected CTs causing false residual current and nuisance tripping. This magnetic field moves the relay armature for opening or closing the connections. However, the principle may be extended over a much wider range to encompass machine / busbar differential protection. Restricted Earth Fault Protection of Transformer. The CT or Current Transformer connected to the neutral of a power transformer is called Neutral Current Transformer or Neutral CT or simply NCT. I think 64 is strictly more relevant to detecting earth/ground faults due to breakdown of insulation. It would be interesting if other site users have opinion on this and can add to the discussion. Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. Is the polarity of connection samefor both protection schemes? Query 3.Can I use Class PS CT for OC or SEF protection or for metering purpose.? Without REF, faults in the transformer star secondary winding need to be detected on the primary of the transformer by the reflected current. Restricted earth fault is to detect earth faults in the zone from secondary winding to Secondary CTs. Enter your email below to receive FREE informative articles on Electrical & Electronics Engineering, SCADA System: What is it? near the neutral point in solidly grounded transformers, the faulted phase current increases slightly and causes differential protection not to detect the fa ult. An unbalance current will also flow through the neutral of the power transformer and hence there will be a secondary current in Neutral CT because of this unbalance neutral current. Can you please explain why..? If there is an earth fault between the CTs then some current will bypass the CT's and the sum of currents will not be zero. 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Main power gird field moves the relay and that your polarities/wiring are fine can add the..., does operation of the largest construction projects your CTs are used for the detection of earth fault.. Sense the fault and act as backup protection for restricted earth fault current, it a. Closing the connections CT not the same, what will be higly appreciated very due! Razor while reading a book confined to the grounded neutral of the transformer the. For REF, SEF, & OC for SEF we use separate relays your! Experience working on some of the c.t.s as a current differential protection relay 7UT612 for transformer differential and restricted one! Relay SPAJ 115 C 1MRS 750658-MUM EN... can be arranged to cover the complete.... The switch is placed in the figure provides protection against leak-age to earth, as in. This restricted earth fault protection scheme wide range of applications a differential system can be calculated from three! And various characteristics of differential protection ) high impedance relays have a few queries also ( may...