It is backup protection for restricted earth fault (REF) relay. The earth fault can be dispersed by using the restricted earth fault protection scheme. 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. (i mean when a current flows in the primary (neutral) a proportional current in the secondary)? 1. But during an internal fault, the neutral current transformer only carries the unbalance fault current and operation of Restricted Earth Fault Relay takes place. Ever wondered what kind of power an aircraft uses when parked at the airport stand. I am bit confused between the operation of REF and Standby earth fault relay. Photovoltaic (PV) systems are typically more efficient when connected in parallel with a main power gird. It detects small stray voltages on the metal enclosures of electrical equipment. Query 2. Normally earth fault relay, earth leakage circuit breaker and ground fault circuit interrupter, etc. 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 neutral transformer is called as NCT. In a 33kV/11kV substation, we use SIEMENS Protection relay 7UT612 for Transformer differential and restricted earth fault protection. 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. Restricted earth-fault protection is designed to detect power transformer earth faults. In this scheme the CT secondary of each phase of electrical power transformer are connected together. The stabilized earth fault current relay IRI1-ER serves as a supplement for the transformer differen-tial protection. I would prefer separate CT for the meter. 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. 3. I have a few queries also (it may sound stupid). Further question: Is REF protection should be implemented on a small 6/0.4kV, 500kVA oil type transformer? In the diagram 87N is the ANSI Device Number for restricted earth fault. When used as highly In this scheme, the CT secondary of each phase of an electrical power transformer are connected together as shown in the figure. My query is that is it possible to use only one type of (PS Class) CT for all the protections..? 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 . One method of dealing with this is symmetrical components. In this video the philosophy behind the restricted Earth Fault Protection has been elaborated. The fault current I f will flow through the core, frame of machine to earth and complete the path through the earthing resistance. The only difference in between the Differential Protection and REF Protection is that, latter protection is more sensitive as compared to the former protection scheme. are used to restrict the fault current. 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. Restricted earth fault is to detect earth faults in the zone from secondary winding to Secondary CTs. Among other things, it defines a... For unbalance conditions the calculation of fault currents is more complex. Similarly, if your CTs are becoming saturated they can become unbalanced and give problems. 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. 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. 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). In case of phase to ground faults, high currents flow to the grounded neutral of the transformer. Sensitive Earth fault Protection scheme is used for the detection of earth fault. The P&B MREF high impedance differential relay can be used over a wide range of applications. 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. The connection of a restricted earth fault relay is shown in Figure 3. REF protection is fast and can isolate winding faults extremely quickly, thereby limiting damage and consequent repair costs. The operation principle is primarily based on the biased differential protection scheme with threefol d tripping characteristic. Another method of connecting an earth-fault relay is illustrated in Fig 5. I think 64 is strictly more relevant to detecting earth/ground faults due to breakdown of insulation. 4. 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..? 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. The differential relay requires percentage through fault and second harmonic inrush stabilization which always will limit the minimum operating time. This scheme of restricted earth fault protection is very sensitive for internal earth fault of electrical power transformer. The earth fault relay is placed in the residual part of the current transformers shown in the figure below. The inner section of the relay is shown in … An unreset indicator does not affect the operation of the relay. You should also make sure that the CT ratios, phase shift, logic, etc. Such protection can be provided at various voltage levels by connecting earth-fault relay in the neutral-to-earth … I think the intent is that both mean the same thing. 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. 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 yellow LEDs (∆I The windings of many medium and small sized transformers are protected by restricted earth fault (REF) systems. 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. 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 earlier posts we have already discussed Differential Protection of Transformer and various characteristics of Differential Protection. These relays are capable of sensing greater fault currents. 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. Without REF, faults in the transformer star secondary winding need to be detected on the primary of the transformer by the reflected current. Any information regarding testing procedure for Transformers restricted earth fault will be higly appreciated. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. A differential system can be arranged to cover the complete transformer . 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? Simply we can say, it is standby protection for all other earth … This would need to be investigated on a case by case basis. secondary current I s flows through the operating coil and the restricted earth fault relay coil of the differential protection. Can you please clarify? There is a lot of debate on which to use and some theory. 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. I was reminded of Occam's Razor while reading a book. 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. Then common terminals are connected to the secondary of a Neutral Current Transformer or NCT. Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. Some modern relays are able to compensate for differences in CT performance. Consider that earth fault occurs on phase B due to breakdown of its insulation to earth, as shown in the Fig. 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. 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 same principle of operation applies for faults on the MV side because the HV and MV earths are separated. 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. You have explained it in simple terms. When used as zero-current differential protection (restricted earth fault), the re-lay (IRI1-ER) is to be connected acc. At 500 kVA, I would tend to think the cost may not be justified (unless the transformer were particularly important). I would also look at more modern numerical relays for your application. Fault detection is confined to the zone between the two CTs hence the name 'Restricted Earth Fault'. We use separate relays for REF, SEF, & OC For SEF we use Induction (disc type) relay. Hence the relay will not respond even there is an unbalancing in-phase current of the power transformer. That means the protection function will work only within a specified zone that is pre-determined. 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? In this video we havr explained how earth fault is detected. In our area we use separate CTs for REF and SEF+ OC protection. The working principle is "Merz-Prize Circulating Current Principle". Electrical4U is dedicated to the teaching and sharing of all things related to electrical and electronics engineering. - yes it is possible. 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. The three phase side current transformer connected with the neutral current transformer as shown in the figure. This relay protects the delta or unearthed star … It is difficult to remotely diagnose this type of issue. Steven has over twenty five years experience working on some of the largest construction projects. Earth leakage relays perform two main functions on mining installations: to protect machinery from damage and to make the in-stallation safer for personnel. It should be remembered that the protection as illustrated covers only the secondary of the transformer. (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. By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community. For REF protection, PS class CT are used for high accurecy and for SEF 5P10 type CTs are used. 7 with the RESET push-button. 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. By measuring this current imbalance faults between the CTs can be easily identified and quickly cleared. 2. If you are also able to get a recording of the voltages and currents during an incident this will help you a lot. The REF is unit protection and restricted to one transformer. REF is a fault in the winding and you need to isolate the transformer - trip the MV/HV side. near the neutral point in solidly grounded transformers, the faulted phase current increases slightly and causes differential protection not to detect the fa ult. The result is to interrupt the circuit if a dangerous voltage is detected. Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. 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. 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)". Is the polarity of connection samefor both protection schemes? About the author, Thank you. 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. Following on from my post on railway electrification voltages, I thought an introduction to traction substations would be a good idea. It would be interesting if other site users have opinion on this and can add to the discussion. But now as per CEA recommendations, two main protections each having distance relay of different type not necessarily of different Earth fault out side the boundary will not be detected by the REF scheme. The principle of Thanks in advance Regards SYAM. 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. What is a Ground Fault? Enter your email below to receive FREE informative articles on Electrical & Electronics Engineering, SCADA System: What is it? 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. are programmed correctly in to the relay and that your polarities/wiring are fine. There is a cost to REF and at some stage it becomes expensive in relation to the transformer size. - SEF should still sense the fault and act as backup protection. For parallel operation system, does operation of REF be connected to trip both primary and secondary Breakers.? This magnetic field moves the relay armature for opening or closing the connections. It would be great if the breaker linkage is shown as part of the schematic. This could result in a nuisance trip. Usually, the contacts of the earth fault relay are connected to the trip circuit of circuit breakers at … How can we test the restricted earth fault to know that the relay is responding or not. When used as zero-current differential protection (restricted earth fault), the relay (IRI1-ER) is(IRI1-ER) to be connected acc. If CTs are located on the transformer terminals only the winding is protected. figure 2.1. It detects small stray voltages on the metal enclosures of electrical equipment. To get started and understand our policy, you can read our How to Write an Electrical Note. Suppose you have selected a certain boundary, this restricted earth fault protection (REF) will detect earth fault only within that range. 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. It could be many things. 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 … (Same as Differential Protection) High impedance Restricted Earth Fault protection is the voltage based operating protection. 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. Restricted Earth fault Protection This relay can be implemented for only star connected transformer or star connected alternator. The illustration shows the principal of REF protection. 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. - yes, but you need to check the CT calculations. Please clarify my doubts.It may sound silly or stupid but I would like to know why and how. Restricted earth fault relays are also very quick due to the simple measuring principle and the measurement of one winding only. A ground fault is an inadvertent contact between an energized conductor and ground or equipment frame. So this REF relay will not be actuated for external earth fault. Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. The Restricted Earth Fault Relay is connected in this closed path. 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). of the low impedance Restricted Earth Fault (REF) function. 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. If these both currents are equal in amplitude there will not be any resultant current circulates through the said closed path. (using the concept that current flows only in a closed circuit) For faults outside the Zone SEF will operate, REF will not operate. Earth fault relay senses these faults. 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. 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 . A common reason could be unbalanced/incorrectly selected CTs causing false residual current and nuisance tripping. 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. 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. The CT or Current Transformer connected to the neutral of a power transformer is called Neutral Current Transformer or Neutral CT or simply NCT. figure 2.1. The most common application of the MREF is in the protection of transformer restricted earth fault and is detailed in this note. Thanks. 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. 2. It works on the principle of an electromagnetic attraction. Is it possible to use a single relay(if the relay is capable of) to incorporate all the protections.? Restricted Earth Fault (REF) protection is basically a Differential Protection. if Vkp and Imag of both CT not the same, what will be the consequences on the Bias Differential and REF protection? Query 1. Thanks. To me, 87N is more appropriate as REF is a differential type protection (ANSI 87 – differential protection relay). What class of cts used for REF and SEF protection of transformers. In Restricted Earth Fault scheme the common terminals of phase CTs are connected to the secondary of Neutral CT in such a manner that secondary unbalance current of phase CTs, and the secondary current of Neutral CT will oppose each other. Be investigated on a small 6/0.4kV, 500kVA oil type transformer same earth-fault relay is connected neutral. Same as differential protection scheme protected by restricted earth fault I to detecting earth/ground faults due to breakdown its... 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