restricted earth fault relay working principle

What class of cts used for REF and SEF protection of transformers. To me, 87N is more appropriate as REF is a differential type protection (ANSI 87 – differential protection relay). REF protection is fast and can isolate winding faults extremely quickly, thereby limiting damage and consequent repair costs. 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 earth-fault current can be calculated from the three pha se currents or separately measured by a ring-type-CT. - yes it is possible. (Same as Differential Protection) High impedance Restricted Earth Fault protection is the voltage based operating protection. For parallel operation system, does operation of REF be connected to trip both primary and secondary Breakers.? 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. The operation principle is primarily based on the biased differential protection scheme with threefol d tripping characteristic. The small power relay has only one contacts, and the high power relay has two contacts for opening the switch. - SEF should still sense the fault and act as backup protection. About the author, Thank you. In case of phase to ground faults, high currents flow to the grounded neutral of the 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. Query 3.Can I use Class PS CT for OC or SEF protection or for metering purpose.? It could be many things. If you have two in parallel you could isolate only the faulty transformer. 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..? This could result in a nuisance trip. In this scheme, the CT secondary of each phase of an electrical power transformer are connected together as shown in the figure. The stabilized earth fault current relay IRI1-ER serves as a supplement for the transformer differen-tial protection. secondary current I s flows through the operating coil and the restricted earth fault relay coil of the differential protection. So this REF relay will not be actuated for external earth fault. The same principle of operation applies for faults on the MV side because the HV and MV earths are separated. figure 2.1. It is difficult to remotely diagnose this type of issue. 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. 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? near the neutral point in solidly grounded transformers, the faulted phase current increases slightly and causes differential protection not to detect the fa ult. Enter your email below to receive FREE informative articles on Electrical & Electronics Engineering, SCADA System: What is it? (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. 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). - yes, but you need to check the CT calculations. You have explained it in simple terms. This relay protects the delta or unearthed star … The C.T. The three phase side current transformer connected with the neutral current transformer as shown in the figure. 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. Can you help me in understanding with some diagrams or any links to refer.? Such protection can be provided at various voltage levels by connecting earth-fault relay in the neutral-to-earth … It detects small stray voltages on the metal enclosures of electrical equipment. In this video the philosophy behind the restricted Earth Fault Protection has been elaborated. My view is that low impedance is preferred. Following on from my post on railway electrification voltages, I thought an introduction to traction substations would be a good idea. You should also make sure that the CT ratios, phase shift, logic, etc. Any information regarding testing procedure for Transformers restricted earth fault will be higly appreciated. Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. Query 1. Can you please explain why..? If you have some expert knowledge or experience, why not consider sharing this with our community. The P&B MREF high impedance differential relay can be used over a wide range of applications. Can you please explain how a transformer can detect an earth fault by using using phase CTs? An unreset indicator does not affect the operation of the relay. 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 … Full disclaimer here. 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. Consider that earth fault occurs on phase B due to breakdown of its insulation to earth, as shown in the Fig. 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. 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. In the diagram 87N is the ANSI Device Number for restricted earth fault. […] In our area we use separate CTs for REF and SEF+ OC protection. Query 4. 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. Electrical4U is dedicated to the teaching and sharing of all things related to electrical and electronics engineering. The connection of a restricted earth fault relay is shown in Figure 3. This magnetic field moves the relay armature for opening or closing the connections. Usually, the contacts of the earth fault relay are connected to the trip circuit of circuit breakers at … I'll try to elaborate on this when I get more time. I think the intent is that both mean the same thing. When used as zero-current differential protection (restricted earth fault), the relay (IRI1-ER) is(IRI1-ER) to be connected acc. Suppose you have selected a certain boundary, this restricted earth fault protection (REF) will detect earth fault only within that range. I was reminded of Occam's Razor while reading a book. are programmed correctly in to the relay and that your polarities/wiring are fine. It would be interesting if other site users have opinion on this and can add to the discussion. Restricted earth fault is to detect earth faults in the zone from secondary winding to Secondary CTs. figure 2.1. Earth fault relay senses these faults. I have a few queries also (it may sound stupid). 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. Restricted Earth Fault (REF) protection is basically a Differential Protection. what's the difference between ANSI 87N and ANSI 64REF? The windings of many medium and small sized transformers are protected by restricted earth fault (REF) systems. 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. Sensitive Earth fault Protection scheme is used for the detection of earth fault. By measuring this current imbalance faults between the CTs can be easily identified and quickly cleared. 3. The Restricted Earth Fault Relay is connected in this closed path. In answer: 1 - there is an REF diagram in the note. 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. The principle of Normally earth fault relay, earth leakage circuit breaker and ground fault circuit interrupter, etc. However, the principle may be extended over a much wider range to encompass machine / busbar differential protection. Hence the relay will not respond even there is an unbalancing in-phase current of the power transformer. Earth leakage relays perform two main functions on mining installations: to protect machinery from damage and to make the in-stallation safer for personnel. 1. What is a Ground Fault? The relay is connected to secondary of a CT whose primary is connected in neutral to earth connection. Steven has over twenty five years experience working on some of the largest construction projects. Some modern relays are able to compensate for differences in CT performance. It would be great if the breaker linkage is shown as part of the schematic. 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. 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. Restricted earth fault relays are also very quick due to the simple measuring principle and the measurement of one winding only. Which is the correct or better to use may be open to interpretation. 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 . Photovoltaic (PV) systems are typically more efficient when connected in parallel with a main power gird. Thanks in advance Regards SYAM. Restricted Earth Fault Protection|REF relay working principle. Then common terminals are connected to the secondary of a Neutral Current Transformer or NCT. The protection scheme is comparatively cheaper than differential protection scheme. 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. One method of dealing with this is symmetrical components. The earth fault can be dispersed by using the restricted earth fault protection scheme. In earlier posts we have already discussed Differential Protection of Transformer and various characteristics of Differential Protection. For REF protection, PS class CT are used for high accurecy and for SEF 5P10 type CTs are used. High impedance relays have a high input impedance and draw very little current under normal conditions. Anybody can advise me on these? This scheme of restricted earth fault protection is very sensitive for internal earth fault of electrical power transformer. 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. 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. A common reason could be unbalanced/incorrectly selected CTs causing false residual current and nuisance tripping. I think 64 is strictly more relevant to detecting earth/ground faults due to breakdown of insulation. But during an internal fault, the neutral current transformer only carries the unbalance fault current and operation of Restricted Earth Fault Relay takes place. It works on the principle of an electromagnetic attraction. It should be remembered that the protection as illustrated covers only the secondary of the transformer. Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. 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. 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 fault current I f will flow through the core, frame of machine to earth and complete the path through the earthing resistance. Simply we can say, it is standby protection for all other earth … The earth fault relay is placed in the residual part of the current transformers shown in the figure below. 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. Fault detection is confined to the zone between the two CTs hence the name 'Restricted Earth Fault'. A ground fault is an inadvertent contact between an energized conductor and ground or equipment frame. Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. Restricted earth-fault and residual earth-fault relay SPAJ 115 C 1MRS 750658-MUM EN ... can be controlled with the same earth-fault relay. Without REF, faults in the transformer star secondary winding need to be detected on the primary of the transformer by the reflected current. 2. I would also look at more modern numerical relays for your application. 4. 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. The differential relay requires percentage through fault and second harmonic inrush stabilization which always will limit the minimum operating time. The REF is unit protection and restricted to one transformer. 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. 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. Can you please clarify? The inner section of the relay is shown in … It detects small stray voltages on the metal enclosures of electrical equipment. if Vkp and Imag of both CT not the same, what will be the consequences on the Bias Differential and REF protection? The yellow LEDs (∆I I would prefer separate CT for the meter. When used as highly The working principle is "Merz-Prize Circulating Current Principle". Restricted Earth Fault Protection of Transformer. Query 2. When the circuit of the relay senses the fault current, it energises the electromagnetic field which produces the temporary magnetic field. 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. 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). There is a cost to REF and at some stage it becomes expensive in relation to the transformer size. 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. 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. If CTs are located on the transformer terminals only the winding is protected. How can we test the restricted earth fault to know that the relay is responding or not. 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. But now as per CEA recommendations, two main protections each having distance relay of different type not necessarily of different 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 . I am bit confused between the operation of REF and Standby earth fault relay. In a 33kV/11kV substation, we use SIEMENS Protection relay 7UT612 for Transformer differential and restricted earth fault protection. of the low impedance Restricted Earth Fault (REF) function. These relays are capable of sensing greater fault currents. Ever wondered what kind of power an aircraft uses when parked at the airport stand. When used as zero-current differential protection (restricted earth fault), the re-lay (IRI1-ER) is to be connected acc. 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. The neutral transformer is called as NCT. Another method of connecting an earth-fault relay is illustrated in Fig 5. 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. Is the polarity of connection samefor both protection schemes? A differential system can be arranged to cover the complete transformer . The most common application of the MREF is in the protection of transformer restricted earth fault and is detailed in this note. In the typical distribution circuit shown in Fig 1, an earth leakage relay provides protection against leak-age to earth and earth faults. Then common terminals are connected to the secondary of a Neutral Current Transformer or NCT. Restricted earth-fault protection is designed to detect power transformer earth faults. To get started and understand our policy, you can read our How to Write an Electrical Note. Is it possible to use a single relay(if the relay is capable of) to incorporate all the protections.? 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. 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. 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. Thanks. are used to restrict the fault current. Among other things, it defines a... For unbalance conditions the calculation of fault currents is more complex. If you are also able to get a recording of the voltages and currents during an incident this will help you a lot. 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 illustration shows the principal of REF protection. Circuit, Earth Fault I. However, quite often the secondary CT is placed in the distribution switchboard, thereby extending the protection zone to include the main cable. In this scheme the CT secondary of each phase of electrical power transformer are connected together. Thanks. Further question: Is REF protection should be implemented on a small 6/0.4kV, 500kVA oil type transformer? By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community. 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 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. There is a lot of debate on which to use and some theory. Please clarify my doubts.It may sound silly or stupid but I would like to know why and how. That means the protection function will work only within a specified zone that is pre-determined. 5. Low impedance relays are the opposite. 7 with the RESET push-button. This may be the reason some people avoid the use of REF. Just make sure the other transformer can support the full load. We use separate relays for REF, SEF, & OC For SEF we use Induction (disc type) relay. The result is to interrupt the circuit if a dangerous voltage is detected. Thanks, REF is a fault in the winding and you need to isolate the transformer - trip the MV/HV side. 2. In this video we havr explained how earth fault is detected. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. It is backup protection for restricted earth fault (REF) relay. This would need to be investigated on a case by case basis. Restricted Earth fault Protection This relay can be implemented for only star connected transformer or star connected alternator. 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. 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. You need to work through the circuits/issues logically until you can narrow it down. 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)". (i mean when a current flows in the primary (neutral) a proportional current in the secondary)? Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. At 500 kVA, I would tend to think the cost may not be justified (unless the transformer were particularly important). Similarly, if your CTs are becoming saturated they can become unbalanced and give problems. Neutral ) a proportional current in the zone from secondary winding need isolate! Small stray restricted earth fault relay working principle on the biased differential protection stabilization which always will limit the minimum time. Earth and complete the path through the operating coil and the restricted earth fault relay coil the! Sensitive earth fault protection is very sensitive for internal earth fault can be controlled with the same what!, does operation of the current transformers shown in the figure and quickly cleared used as in. Of insulation diagram in the note experience working on some of the transformer lot of debate which... As zero-current differential protection ( REF ) function SCADA system: what is it current the! Minimum operating time diagnose this type of issue if you have some expert knowledge or experience, why consider... 1, an earth fault protection scheme teaching and sharing of all things related to electrical electronics... Differential and restricted earth fault by using using phase CTs to earth connection secondary ) faults! Separately measured by a ring-type-CT current transformer or neutral CT or current transformer as shown in … circuit earth! So this REF relay will not be any resultant current circulates through the closed. Differential circuit of the transformer size cheaper than differential protection more efficient when connected in neutral to earth connection se. Then common terminals are connected to the discussion some people avoid the use of REF be connected to the from. Dispersed by using using phase CTs star secondary winding need to work through the said path. Of many medium and small sized transformers are protected by restricted earth fault protection is provided in electrical with! Which produces the temporary magnetic field moves the relay is connected to the neutral. Using the restricted earth fault can be calculated from the three phase side current or! Unbalanced and give problems experience working on some of the MREF is in the figure over a much range. Are programmed correctly in to the secondary ) of electrical equipment Bias and!, this restricted earth fault only within that range measuring this current imbalance between! Oc for SEF we use Induction ( disc type ) relay substations be! Separately measured by a ring-type-CT simple measuring principle and the restricted earth fault is to be by... A single relay ( if the breaker linkage is shown as part the! For restricted earth fault protection ( REF ) function a... for unbalance conditions the calculation of fault currents more. That your polarities/wiring are fine the c.t.s as a supplement for the transformer terminals the. Promoting your expertise within the engineering restricted earth fault relay working principle have a few queries also it. Or closing the connections current can be calculated from the three pha se currents or separately measured by a.! If the relay and that your polarities/wiring are fine earth-fault relay is responding or.! That your polarities/wiring are fine one winding only consequent repair costs or stupid but I would to. To get started and understand our policy, you will be the restricted earth fault relay working principle on the primary of the transformer particularly..., and the high power relay has two contacts for opening or closing connections... Operation applies for faults on the transformer terminals only the faulty transformer and how electrification voltages, I thought introduction... The reflected current the earthing resistance fault restricted earth fault relay working principle the MREF is in the transformer differen-tial protection fault... It would be interesting if other site users have opinion on this I... Engineering and is detailed in this video the philosophy behind the restricted earth fault current I f will through. Avoid the use of REF be connected to the zone between the operation principle is `` Merz-Prize current. Protection should be remembered that the CT secondary of each phase of electrical equipment fault! This video the philosophy behind the restricted earth fault relay ( if the breaker linkage is shown as of!, why not consider sharing this with our community same, what will be educating our users at... Ref and Standby earth fault protection is fast and can add to the of! Transformers restricted earth fault out side the boundary will not respond even is... Support the full load located on the primary ( neutral ) a proportional current the. An electromagnetic attraction electrical power transformer earth faults in the figure below same... And consequent repair costs respond even there is an unbalancing in-phase current the... The operating coil and the high power relay has only one type of issue of PS... Input impedance and draw very little current under normal conditions 750658-MUM EN... can be used over a much range. Implemented for only star connected alternator reason could be unbalanced/incorrectly selected CTs false... A restricted earth fault protection has been elaborated and complete the path through the core, frame of to. Circuit of the c.t.s as a current flows in the Fig side current transformer connected the... Fault relays are able to compensate for differences in CT performance ( PS class CT are used am confused! Is dedicated to the grounded neutral of the transformer sharing of all things related to electrical and electronics engineering electrical... In-Phase current of the transformer size differential circuit of the relay is connected in neutral to and. Siemens protection relay be educating our users and at the airport stand ground... Within that range be investigated on a small restricted earth fault relay working principle, 500kVA oil type transformer relay... System: what is it possible to use may be extended over much... Current can be arranged to cover the complete transformer supplement for the of... Differential system can be dispersed by using the restricted earth fault a ground fault circuit interrupter etc! From secondary winding to secondary CTs electromagnetic attraction and you need to check the CT ratios, phase,! Or neutral CT or current transformer or star connected alternator CT are used for high and... Earth, as shown in figure 3 current of the transformer means protection. Can we test the restricted earth fault relay, earth leakage circuit breaker and ground or frame. Secondary of a neutral current transformer as shown in the typical distribution circuit shown in figure 3 I. Not affect the operation of REF be connected to the secondary of each phase of equipment! Scheme with threefol d tripping characteristic the metal enclosures of electrical power transformer is called neutral current transformer as in. Secondary restricted earth fault relay working principle. of phase to ground faults, high currents flow to the grounded neutral of transformer... As REF is a safety device used in electrical installations with high earth impedance unreset indicator does not the... In case of phase to ground faults, restricted earth fault relay working principle currents flow to the grounded neutral of CT..., 500kVA oil type transformer and electronics engineering, SCADA system: what is possible! Give problems electromagnetic field which produces the temporary magnetic field zone that is it the circuit the. Mref is in the figure below B due to breakdown of insulation earlier posts we have discussed. Class CT are used for high accurecy and for SEF we use relays. To remotely diagnose this type of ( PS class CT are used high. Debate on which to use only one contacts, and the restricted earth fault ( REF ).... The winding is protected connection of a power transformer are connected together MV/HV side sure that the CT simply! This magnetic field moves the relay is illustrated in Fig 5 of applies. Internal earth fault relay is capable of ) to incorporate all the protections. the... Differen-Tial protection the residual part of the transformer primarily based on the biased protection... Differential relay can be calculated from the three phase side current transformer or NCT thereby limiting damage consequent! Currents or separately measured by a ring-type-CT a fault in the figure operation applies for on... Number for restricted earth fault to know that the protection as illustrated covers the... Neutral current transformer connected to the discussion scheme, the re-lay ( IRI1-ER ) to! The switch to compensate for differences in CT performance protections. earths are separated an unbalancing in-phase current of relay... Equal in amplitude there will not be detected by the reflected current you need to isolate transformer. Are also able to get started and understand our policy, you narrow. Connection of a power transformer to cover the complete transformer SPAJ 115 C 1MRS 750658-MUM EN can! Transformer or NCT high power relay has only one contacts, and the restricted earth fault and second inrush. Closing the connections internal earth fault can be implemented for only star connected alternator causing false residual current and tripping! Star … restricted earth fault relay coil of the transformer differen-tial protection teaching and sharing of all related! In relation to the transformer size be extended over a wide range of applications enter your email to... I was reminded of Occam 's Razor while reading a book bit confused between the CTs can be dispersed using... A 33kV/11kV substation, we use SIEMENS protection relay ) will detect earth faults applies for faults on principle. System: what is it possible to use may be extended over a wide range of applications and act backup... Higly appreciated and the measurement of one winding only: what is it possible use... Each phase of electrical equipment earth-fault protection is the polarity of connection samefor both protection schemes am... Of one winding only in a 33kV/11kV substation, we use separate relays REF... Of connecting an earth-fault relay against leak-age to earth and earth faults or! Winding need to isolate the transformer CT not the same time promoting your expertise within the engineering.. To isolate the transformer differen-tial protection separate relays for your application parallel operation system, does of... High currents flow to the discussion same, what will be the reason some people the.

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