Restricted Earth Fault (REF) protection is basically a Differential Protection. By measuring this current imbalance faults between the CTs can be easily identified and quickly cleared. 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. This may be the reason some people avoid the use of REF. In our area we use separate CTs for REF and SEF+ OC protection. Thanks. That means the protection function will work only within a specified zone that is pre-determined. Among other things, it defines a... For unbalance conditions the calculation of fault currents is more complex. (Same as Differential Protection) High impedance Restricted Earth Fault protection is the voltage based operating protection. The Restricted Earth Fault Relay is connected in this closed path. (i mean when a current flows in the primary (neutral) a proportional current in the secondary)? Further question: Is REF protection should be implemented on a small 6/0.4kV, 500kVA oil type transformer? You need to work through the circuits/issues logically until you can narrow it down. 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 . 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. Photovoltaic (PV) systems are typically more efficient when connected in parallel with a main power gird. Normally earth fault relay, earth leakage circuit breaker and ground fault circuit interrupter, etc. I have a few queries also (it may sound stupid). This would need to be investigated on a case by case basis. I would also look at more modern numerical relays for your application. - yes it is possible. Anybody can advise me on these? I was reminded of Occam's Razor while reading a book. 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. 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. Restricted earth-fault protection is designed to detect power transformer earth faults. Thanks in advance Regards SYAM. An unreset indicator does not affect the operation of the relay. 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. Circuit, Earth Fault I. 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. 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. 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. We use separate relays for REF, SEF, & OC For SEF we use Induction (disc type) relay. What class of cts used for REF and SEF protection of transformers. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. Simply we can say, it is standby protection for all other earth … Query 4. Steven has over twenty five years experience working on some of the largest construction projects. The protection scheme is comparatively cheaper than differential protection scheme. I would prefer separate CT for the meter. A ground fault is an inadvertent contact between an energized conductor and ground or equipment frame. The CT or Current Transformer connected to the neutral of a power transformer is called Neutral Current Transformer or Neutral CT or simply NCT. 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. High impedance relays have a high input impedance and draw very little current under normal conditions. (using the concept that current flows only in a closed circuit) For faults outside the Zone SEF will operate, REF will not operate. It would be interesting if other site users have opinion on this and can add to the discussion. It detects small stray voltages on the metal enclosures of electrical equipment. The C.T. This relay protects the delta or unearthed star … This scheme of restricted earth fault protection is very sensitive for internal earth fault of electrical power transformer. 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. In this video we havr explained how earth fault is detected. In the typical distribution circuit shown in Fig 1, an earth leakage relay provides protection against leak-age to earth and earth faults. Restricted Earth fault Protection This relay can be implemented for only star connected transformer or star connected alternator. Electrical4U is dedicated to the teaching and sharing of all things related to electrical and electronics engineering. 3. Consider that earth fault occurs on phase B due to breakdown of its insulation to earth, as shown in the Fig. The earth-fault current can be calculated from the three pha se currents or separately measured by a ring-type-CT. Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. Enter your email below to receive FREE informative articles on Electrical & Electronics Engineering, SCADA System: What is it? Restricted earth-fault and residual earth-fault relay SPAJ 115 C 1MRS 750658-MUM EN ... can be controlled with the same earth-fault relay. Full disclaimer here. These relays are capable of sensing greater fault currents. 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 . In answer: 1 - there is an REF diagram in the note. But during an internal fault, the neutral current transformer only carries the unbalance fault current and operation of Restricted Earth Fault Relay takes place. A common reason could be unbalanced/incorrectly selected CTs causing false residual current and nuisance tripping. The differential relay requires percentage through fault and second harmonic inrush stabilization which always will limit the minimum operating time. 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. 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. In a 33kV/11kV substation, we use SIEMENS Protection relay 7UT612 for Transformer differential and restricted earth fault protection. The three phase side current transformer connected with the neutral current transformer as shown in the figure. When used as highly 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 Operation Under normal conditions and by application of Kirchhoff’s laws the sum of currents in both current transformers (CTs) equals zero. Similarly, if your CTs are becoming saturated they can become unbalanced and give problems. - yes, but you need to check the CT calculations. When used as zero-current differential protection (restricted earth fault), the relay (IRI1-ER) is(IRI1-ER) to be connected acc. 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. 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. near the neutral point in solidly grounded transformers, the faulted phase current increases slightly and causes differential protection not to detect the fa ult. Query 1. The windings of many medium and small sized transformers are protected by restricted earth fault (REF) systems. The small power relay has only one contacts, and the high power relay has two contacts for opening the switch. My view is that low impedance is preferred. In case of phase to ground faults, high currents flow to the grounded neutral of the transformer. Then common terminals are connected to the secondary of a Neutral Current Transformer or NCT. The working principle is "Merz-Prize Circulating Current Principle". Sensitive Earth fault Protection scheme is used for the detection of earth fault. 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. 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..? Without REF, faults in the transformer star secondary winding need to be detected on the primary of the transformer by the reflected current. So this REF relay will not be actuated for external earth fault. Can you help me in understanding with some diagrams or any links to refer.? The inner section of the relay is shown in … It would be great if the breaker linkage is shown as part of the schematic. Earth fault out side the boundary will not be detected by the REF scheme. Restricted Earth Fault Protection of Transformer. Thanks. Hence the relay will not respond even there is an unbalancing in-phase current of the power transformer. 7 with the RESET push-button. Query 3.Can I use Class PS CT for OC or SEF protection or for metering purpose.? secondary current I s flows through the operating coil and the restricted earth fault relay coil of the differential protection. About the author, Thank you. However, the principle may be extended over a much wider range to encompass machine / busbar differential protection. The fault current I f will flow through the core, frame of machine to earth and complete the path through the earthing resistance. figure 2.1. If you have two in parallel you could isolate only the faulty transformer. Some modern relays are able to compensate for differences in CT performance. are used to restrict the fault current. 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 . goodday gents, kindly please assaist with what is the difference between high impendance REF and low impedance REF, The primary difference is in the type of relay used. Is the polarity of connection samefor both protection schemes? are programmed correctly in to the relay and that your polarities/wiring are fine. […] REF protection is fast and can isolate winding faults extremely quickly, thereby limiting damage and consequent repair costs. Restricted Earth Fault Protection|REF relay working principle. How can we test the restricted earth fault to know that the relay is responding or not. 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. 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 … I am bit confused between the operation of REF and Standby earth fault relay. In the diagram 87N is the ANSI Device Number for restricted earth fault. 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. Fault detection is confined to the zone between the two CTs hence the name 'Restricted Earth Fault'. 5. Can you please explain why..? This could result in a nuisance trip. The P&B MREF high impedance differential relay can be used over a wide range of applications. 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. When used as zero-current differential protection (restricted earth fault), the re-lay (IRI1-ER) is to be connected acc. 2. The illustration shows the principal of REF 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. By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community. The earth fault relay is placed in the residual part of the current transformers shown in the figure below. Suppose you have selected a certain boundary, this restricted earth fault protection (REF) will detect earth fault only within that range. The result is to interrupt the circuit if a dangerous voltage is detected. Is it possible to use a single relay(if the relay is capable of) to incorporate all the protections.? Such protection can be provided at various voltage levels by connecting earth-fault relay in the neutral-to-earth … The most common application of the MREF is in the protection of transformer restricted earth fault and is detailed in this note. 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. Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. 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 relay is connected to secondary of a CT whose primary is connected in neutral to earth connection. What is a Ground Fault? Just make sure the other transformer can support the full load. This magnetic field moves the relay armature for opening or closing the connections. There is a lot of debate on which to use and some theory. - SEF should still sense the fault and act as backup protection. There is a cost to REF and at some stage it becomes expensive in relation to the transformer size. 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. 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