The earth fault can be dispersed by using the restricted earth fault protection scheme. REF protection is fast and can isolate winding faults extremely quickly, thereby limiting damage and consequent repair costs. Earth fault protection must be applied where impedance earthing is employed that limits the earth fault current to less than the pick-up threshold of the overcurrent and/or differential protection for a fault located down to the bottom 5% of the stator winding from the star-point. The current transformers are placed on both sides of the protective zone. Restricted Earth Fault (REF) protection is basically a Differential Protection. In that case, a sensitive ground/earth fault relay is used in addition to the differential protection of alternator. Learn More: What is Dielectric Material In plain language this means that fault protection provides us with protection against receiving an electric shock from conductive parts that are not intended to be live but have become live due to a fault. Residual-current devices (RCDs, RCCBs or GFCIs) are used for this purpose. It is a fast acting circuit breaker to shut down the supply when the earth fault occurs within 1/40th of a second. System at load end in this case is disconnected form source in in case of radial power flow. Earth leakage protection To avoid accidental shock, current sensing circuits are used at the source to isolate the power when leakage current exceed a certain limit. What is the case of i1 current? The Earth Leakage Circuit Breaker detects the leakage current directly and prevents injury to humans and animals due to electrical shock. It also occurs, because of the insulation breakdown. Earth Fault is an inadvertent fault between the live conductor and the earth. Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. The GFCI is designed to protect people from severe or fatal electric shocks. Such settings protect a restricted portion of the winding. Ground faults are frequently the result of insulation breakdown. The Neutral Earth Resistor (NER) allows a clamped resistive earth fault current, which gives protection devices a value on which to act. The stabilising current is connected in series with the relay for avoiding the magnetising inrush current. The fault current is restricted and the fault is dispersed by the Restricted Earth Fault Protection (REFP) scheme. In this video we havr explained how earth fault is detected. Earth fault is an undesirable condition at which current flow from a conductor to earth. Earth fault is the unintended fault between the live conductor and the earth. They are traditionally protected by an Overcurrent + Earth fault relay, normally mounted in the breaker panel. This relay protects the delta or unearthed star winding of the power transformer against the fault current. Sensitive Earth Fault Protection – SEF. The result is to interrupt the circuit if a dangerous voltage is detected. Fault detection is confined to the zone between the two CTs hence the name 'Restricted Earth Fault'. It detects small stray voltages on the metal enclosures of electrical equipment. Stator Earth Fault Protection is one of the major protections providing for generators. The time delay for unloading is not required during the start-up period, therefore the tripping can be made instantaneous when the operating zone of the protection is reached. Restricted Earth fault Protection in Transformers & Generators Transformers and Generators are voltage sources. If there is any difference as little as 5 mA, GFCI restricts the current and trip quickly. The figure below shows the modern method of rotor earth fault protection. Previously, an earth leakage circuit breaker is used. … To protect the equipment and for the safety of people, fault protection devices are used in the installation. If CTs are located on the transformer terminals only the winding is protected. However, if an internal fault F2 occurs inside the protective zone, only I2 flows and I1 is neglected. It also occurs, because of the insulation breakdown. But during internal fault the neutral curren… A DC voltage bias is impressed between the field circuit and earth through a polarized moving iron relay. Some requirements are onerous, including the requirement for Sensitive Earth Fault (SEF) protection on 100% underground cable networks. What type of relaying arrangement will be engaged in stator earth fault protection of alternator depends upon the methods of stator neutral earthing. It is a voltage-sensing device and has recently been replaced by Residual Current Circuit Breaker (RCCB), which is a current sensing device. In this scheme, the CT secondary of each phase of an electrical power transformer are connected together as shown in the figure. Its important to note that damp, wet, and dusty environments require extra diligence in design and maintenance. Save my name, email, and website in this browser for the next time I comment. For domestic premises, earth fault loop impedance testing is the most common method used to verify circuit disconnection. The resultant current I2 passes through the earth fault relay, which senses the fault current and protects the restricted portion of winding. The earth fault principle is the same, as we sum the resistive and capacitive effects at the fault site, and all un-faulted feeders will only see the capacitive effects proportional to their “X’ value. 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. Most LV systems fall into this category, for reasons of personnel safety. The Ground Fault Circuit Interrupter is a safety device to prevent an electrical accident when any faulty tool is plugged in. Earth Fault Protection, also known as Protective Earth Ground, also known as the Grounding Conductor, or more simply, just Ground, is a connection ultimately to a system of grounding rods … It should be noted that this protection alone is not adequate. In Victoria, the Victorian Service and Installation Rules (VSIR) describe the state-specific requirements for connecting to the networks of local utilities. The connection of earth fault relay with the star or delta winding of the transformer is shown in the figure below. ?it will goes through earth?? The fault current returns through the earth or any electrical equipment, which damages the equipment. For a large generator, the rotor earth fault protection system is used for the protection of the field winding. Purpose of Metrosil: It is Voltage Limiting Non-Linear Resistor. The secondary terminal of the current transformer is connected in parallel with the relay. The following image shows the Earth Fault Protection with EFR −. Required fields are marked *. Read on to learn more about this device and how it functions. If a second earth fault at “B” occurred on another line in the insulated system, the two earth faults together would be equivalent to a short-circuit fault (via the ship’s hull) and the resulting large current would operate protection devices and cause disconnection of perhaps essential services creating a risk to the safety of the ship. The fault current is restricted and the fault is dispersed by the Restricted Earth Fault Protection (REFP) scheme. for example grid side earth fault). The fault current is approximately 15% more than the rated winding current. When the fault occurs inside the protective zone say F2, then only current I2 exist, and I1 is neglected. The Rotor Earth Fault Protection Device consists of a current injection device which applies an AC voltage to the rotor winding by means of a slip ring fitted on … Methods of fault protection include… Earthing of circuits and equipment The earth fault principle is the same, as we sum the resistive and capacitive effects at the fault site, and all un-faulted feeders will only see the capacitive effects proportional to their “X” value. Since water is c… The earth fault relay is placed in the residual part of the current transformers shown in the figure below. High impedance Restricted Earth Fault protection is the voltage based operating protection. For protection against electric shock, the magnitude of the fault current needs to be sufficient to cause the protective device to automatically disconnect the circuit within the relevant maximum time specified in BS 7671. Safety Measures Related to Gas/Ducts/Fibre material, Safe Electrical Equipment Design Characteristics, Precautions Against Highly Flammable Contents, Safety Measures During Handling Lighting Protection Equipment, Safety Measures During Preventive Maintenance. The connections of Metrosil, Stabilizing Resistor and neural CT are shown in above figure. This fault induces the I1 and I2 current which flows in the secondary of the CTs. We will now understand what Earth Fault Protection is. The term arc-fault protection refers to any device that is designed to guard against faulty connections causing arcing, or sparking. It detects small stray voltages on the metal enclosures of electrical equipment. When earth fault occurs, the electrical system gets short-circuited and the short-circuited current flows through the system. The star connected side is protected by a restricted earth fault protection shown in the figure below. This requires a manual reset process to work again. So that the generator should be taken out of service at leisure. Earth fault protection. The current I2 passes through the earth fault relay. A Standby earth fault relay is nothing but an earth fault protection used to protect the generator, transformer, and motor from the external earth fault (earth fault outside the zone. When the fault current flows from live wire to the earth wire within the installation, the coil of ELCB senses the voltage and switches off the power. The RCCB senses the leakage current and sends a signal to trip the system. When the fault occurs, the short-circuit currents flow through the system, and this current is returned through the earth or any electrical equipment. 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. A ground fault is an inadvertent contact between an energized conductor and ground or equipment frame. So this protection will not be actuated for external earth fault. Earth fault is an Open Circuit fault; where the power carrying cable or conductor breaks and gets into contact with earth or a conductor capability material in contact with earth. In this video the philosophy behind the restricted Earth Fault Protection has been elaborated. Sensitive Earth fault Protection scheme is used for the detection of earth fault. Your email address will not be published. The relay is designed for sensing the fault current which is 15% more than that of the rated winding current. Continue reading below Our Video of the Day Even if the fault occurs nearby neutral the relay will protect the winding unlike differential protection. To avoid the magnetizing inrush current, the stabilizing current must be in series with the relay. Normally earth fault relay, earth leakage circuit breaker and ground fault circuit interrupter, etc. A detection device senses the electrical arc and breaks the circuit to … The zero sequence current is absent for the external fault and for the internal fault it becomes twice the value of fault current. 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. This fault current damaged the equipment of the power system and also interrupted the continuity of the supply. Your email address will not be published. The resultant current of the I1 and I2 becomes zero. Let us consider a star winding transformer, which is protected by a Restricted Earth Fault Protection with EFR protecting device as shown in the figure below. 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. 2. The Neutral Earth Resistor (NER) allows a clamped resistive earth fault current, which gives protection devices a value on which to act. It is a special type of latching relay that is connected to the main power supply. Solidly-Earthed System. It also interrupts the continuity of the supply and may shock the user. Stator ground or earth faults protection depends of stator grounding. Restricted Earth Fault Protection Earth fault is the unintended fault between the live conductor and the earth. The output of the current transformer is equal to the zero sequence current flows in the line. Hence the name restricted earth fault protection. Earth Fault Protection Devices The devices give the tripping command to break the circuit when earth fault occurs. The resultant of I1 and I2 will be zero. Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. Restricted earth fault protection (ANSI/IEEE/IEC code 64G/64REF) is used as a complement or to replace differential protection for windings faults to earth. Because a GFCI detects ground faults, it can also prevent some electrical fires and reduce the severity of others by interrupting the flow of electric current. Difference Between Active & Passive Transducer, Two Wattmeter Method of Power Measurement, Difference Between Conduction and Convection, Difference Between Circuit Switching and Packet Switching, Difference Between Static and Kinetic Friction, Difference Between Ductility and Malleability, Difference Between Physical and Chemical Change, Difference Between Alpha, Beta and Gamma Particles, Difference Between Electrolytes and Nonelectrolytes, Difference Between Electromagnetic Wave and Matter Wave. It compares the incoming and outgoing current from the equipment along the circuit conductor. When an external fault F1 occurs in the network, I1 and I2 flow through the secondary side of the CTs. The following figure shows the Earth Fault Relay −. am i right in guessing fault protection is the means of earth were as basic protection is means of instulation of wires, ect When the one earth fault occurs in the rotor then it is not necessary that the system is completely trip, only the relay indicates that the fault has occurred. The earth fault relay is an advanced device, RCCB is used to prevent electric shock and thus it can provide human protection but the EFR is not used for human protection it is used to protect the equipment. For resistance grounding system an overcurrent relay connected to a “ring type” CT within the neutral connection or a voltage relay at resistance terminals may be used. are used to restrict the fault current. The result is to interrupt the circuit if a dangerous voltage is detected. When the fault occurs, the short-circuit currents flow through the system, and this current is returned through the earth or any electrical equipment. The earth fault relay must be very sensitive for sensing the fault. The magnitude of earth fault currents falls with frequency as the earth fault loop is predominantly resistive and the ratio of voltage to frequency is kept constant. GFCI does not help much with line contact hazards but protects from fire, overheating and destruction of wire insulation. The return path of the fault current is through the grounding system and any personnel or equipment that becomes part of that system. In earlier posts we have already discussed Differential Protection of Transformer and various characteristics of Differential Protection. The devices give the tripping command to break the circuit when earth fault occurs. 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