It's simpler, there is more flexibility in the CTs and inputs and coupled with all the functions of a modern numerical relay it eliminates a lot of problems that exist in high impedance systems. 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 … 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. Without REF, faults in the transformer star secondary winding need to be detected on the primary of the transformer by the reflected current. This may be the reason some people avoid the use of REF. Please clarify my doubts.It may sound silly or stupid but I would like to know why and how. 5. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. Earth fault relay senses these faults. This would need to be investigated on a case by case basis. What is a Ground 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 . The earth fault relay is placed in the residual part of the current transformers shown in the figure below. 2. 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. Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. However, the principle may be extended over a much wider range to encompass machine / busbar differential protection. The C.T. 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. This magnetic field moves the relay armature for opening or closing the connections. (Same as Differential Protection) High impedance Restricted Earth Fault protection is the voltage based operating protection. If CTs are located on the transformer terminals only the winding is protected. 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. It detects small stray voltages on the metal enclosures of electrical equipment. It would be great if the breaker linkage is shown as part of the schematic. 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. i.e 4 or 5 nos PS class CTs (3 in Phases 2 in Neutral) along with 4 no 5P10 class CT ( 3 in Phases 1 in Neutral for SEF+OC. There is a lot of debate on which to use and some theory. For parallel operation system, does operation of REF be connected to trip both primary and secondary Breakers.? Which is the correct or better to use may be open to interpretation. I would prefer separate CT for the meter. You need to work through the circuits/issues logically until you can narrow it down. 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 . The REF is unit protection and restricted to one transformer. When used as highly I think 64 is strictly more relevant to detecting earth/ground faults due to breakdown of insulation. Can you please explain why..? are used to restrict the fault current. Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. In case of phase to ground faults, high currents flow to the grounded neutral of the transformer. That means the protection function will work only within a specified zone that is pre-determined. The Restricted Earth Fault Relay is connected in this closed path. Working Principle: The CT secondaries ( phase and neutral CTs) are wired to cancel each other’s currents during external faults and to drive all secondary current to the relay when the fault is inside the protected zone. 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. 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. The earth-fault current can be calculated from the three pha se currents or separately measured by a ring-type-CT. For REF protection, PS class CT are used for high accurecy and for SEF 5P10 type CTs are used. Suppose you have selected a certain boundary, this restricted earth fault protection (REF) will detect earth fault only within that range. I was digging in my bookshelf and came across the 80th Anniversary Association of Mine Resident Engineers, Papers and Discussions Commemorative Edition... IEC 60228 is the International Electrotechnical Commission's international standard on conductors of insulated cables. 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. If these both currents are equal in amplitude there will not be any resultant current circulates through the said closed path. When looking at the design of a lighting scheme it is useful to have an understanding on the nature of light itself and some of the basic theory associated... Request to look at induction motor starting time have come up a few times on the site. 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. To me, 87N is more appropriate as REF is a differential type protection (ANSI 87 – differential protection relay). Query 1. 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. This scheme of restricted earth fault protection is very sensitive for internal earth fault of electrical power transformer. REF protection is fast and can isolate winding faults extremely quickly, thereby limiting damage and consequent repair costs. Low impedance relays are the opposite. Usually, the contacts of the earth fault relay are connected to the trip circuit of circuit breakers at … Ever wondered what kind of power an aircraft uses when parked at the airport stand. secondary current I s flows through the operating coil and the restricted earth fault relay coil of the differential protection. In this video the philosophy behind the restricted Earth Fault Protection has been elaborated. 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..? Query 3.Can I use Class PS CT for OC or SEF protection or for metering purpose.? The earth fault can be dispersed by using the restricted earth fault protection scheme. If you have some expert knowledge or experience, why not consider sharing this with our community. Following on from my post on railway electrification voltages, I thought an introduction to traction substations would be a good idea. Normally earth fault relay, earth leakage circuit breaker and ground fault circuit interrupter, etc. You have explained it in simple terms. REF is a fault in the winding and you need to isolate the transformer - trip the MV/HV side. Query 2. Restricted Earth Fault (REF) protection is basically a Differential Protection. When the circuit of the relay senses the fault current, it energises the electromagnetic field which produces the temporary magnetic field. Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. You should also make sure that the CT ratios, phase shift, logic, etc. At 500 kVA, I would tend to think the cost may not be justified (unless the transformer were particularly important). (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 protection is provided in electrical power transformer for sensing internal earth fault of the transformer. Electrical4U is dedicated to the teaching and sharing of all things related to electrical and electronics engineering. 2. Hence the relay will not respond even there is an unbalancing in-phase current of the power transformer. The P&B MREF high impedance differential relay can be used over a wide range of applications. - yes, but you need to check the CT calculations. If you have two in parallel you could isolate only the faulty transformer. Query 4. Restricted earth-fault protection is designed to detect power transformer earth faults. My query is that is it possible to use only one type of (PS Class) CT for all the protections..? 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? Earth fault out side the boundary will not be detected by the REF scheme. Hi Steven, "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)". We use separate relays for REF, SEF, & OC For SEF we use Induction (disc type) relay. Consider that earth fault occurs on phase B due to breakdown of its insulation to earth, as shown in the Fig. 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. A common reason could be unbalanced/incorrectly selected CTs causing false residual current and nuisance tripping. Can you please explain how a transformer can detect an earth fault by using using phase CTs? A ground fault is an inadvertent contact between an energized conductor and ground or equipment frame. (i mean when a current flows in the primary (neutral) a proportional current in the secondary)? 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. Similarly, if your CTs are becoming saturated they can become unbalanced and give problems. It should be remembered that the protection as illustrated covers only the secondary of the transformer. To get started and understand our policy, you can read our How to Write an Electrical Note. In this video we havr explained how earth fault is detected. Whenever there is an unbalancing in between three phases of the power transformer, a resultant unbalance current flow through the closed path connected to the common terminals of the CT secondaries. In a 33kV/11kV substation, we use SIEMENS Protection relay 7UT612 for Transformer differential and restricted earth fault protection. It would be interesting if other site users have opinion on this and can add to the discussion. Can you help me in understanding with some diagrams or any links to refer.? I was reminded of Occam's Razor while reading a book. The connection of a restricted earth fault relay is shown in Figure 3. 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. 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. 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). The stabilized earth fault current relay IRI1-ER serves as a supplement for the transformer differen-tial protection. 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. 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. Steven has over twenty five years experience working on some of the largest construction projects. The earth fault protection scheme consists the earth fault relay, which gives the tripping command to the circuit breaker and hence restricted the fault current. On a through fault (if the CTs saturate) the currents will be different and the relay will see a zone fault where one does not exist. Thanks, Restricted earth-fault and residual earth-fault relay SPAJ 115 C 1MRS 750658-MUM EN ... can be controlled with the same earth-fault relay. Restricted Earth fault Protection This relay can be implemented for only star connected transformer or star connected alternator. In the typical distribution circuit shown in Fig 1, an earth leakage relay provides protection against leak-age to earth and earth faults. Thanks in advance Regards SYAM. - SEF should still sense the fault and act as backup protection. The neutral transformer is called as NCT. Circuit, Earth Fault I. what's the difference between ANSI 87N and ANSI 64REF? A differential system can be arranged to cover the complete transformer . This relay protects the delta or unearthed star … In the diagram 87N is the ANSI Device Number for restricted earth fault. High impedance relays have a high input impedance and draw very little current under normal conditions. 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