Sensitive Earth Fault Protection – SEF. This fault induces the I1 and I2 current which flows in the secondary of the CTs. The earth fault relay must be very sensitive for sensing the fault. 2. However, if an internal fault F2 occurs inside the protective zone, only I2 flows and I1 is neglected. They are traditionally protected by an Overcurrent + Earth fault relay, normally mounted in the breaker panel. Earth fault protection. The star connected side is protected by a restricted earth fault protection shown in the figure below. 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. The resultant current of the I1 and I2 becomes zero. Fault detection is confined to the zone between the two CTs hence the name 'Restricted Earth Fault'. It is a safety device used in electrical installations with high earth impedance. 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. For a large generator, the rotor earth fault protection system is used for the protection of the field winding. A ground fault is an inadvertent contact between an energized conductor and ground or equipment frame. 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. 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. 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. To avoid the magnetizing inrush current, the stabilizing current must be in series with the relay. In Victoria, the Victorian Service and Installation Rules (VSIR) describe the state-specific requirements for connecting to the networks of local utilities. 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. Since water is c… The fault current is restricted and the fault is dispersed by the Restricted Earth Fault Protection (REFP) scheme. 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 RCCB senses the leakage current and sends a signal to trip the system. When earth fault occurs, the electrical system gets short-circuited and the short-circuited current flows through the system. 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. When the fault occurs, the short-circuit currents flow through the system, and this current is returned through the earth or any electrical equipment. It is a voltage-sensing device and has recently been replaced by Residual Current Circuit Breaker (RCCB), which is a current sensing device. Required fields are marked *. 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 current I2 passes through the earth fault relay. The devices give the tripping command to break the circuit when earth fault occurs. It also occurs, because of the insulation breakdown. The fault current returns through the earth or any electrical equipment, which damages the equipment. The current transformers are placed on both sides of the protective zone. 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 secondary terminal of the current transformer is connected in parallel with the relay. Restricted Earth Fault (REF) protection is basically a Differential Protection. Continue reading below Our Video of the Day Earth Fault is an inadvertent fault between the live conductor and the earth. So this protection will not be actuated for external earth fault. It also interrupts the continuity of the supply and may shock the user. Such settings protect a restricted portion of the winding. System at load end in this case is disconnected form source in in case of radial power flow. 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. This fault current damaged the equipment of the power system and also interrupted the continuity of the supply. The GFCI is designed to protect people from severe or fatal electric shocks. 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 … The Neutral Earth Resistor (NER) allows a clamped resistive earth fault current, which gives protection devices a value on which to act. The resultant of I1 and I2 will be zero. The term arc-fault protection refers to any device that is designed to guard against faulty connections causing arcing, or sparking. In this scheme, the CT secondary of each phase of an electrical power transformer are connected together as shown in the figure. … Earth Fault Protection Devices The devices give the tripping command to break the circuit when earth fault occurs. 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. Some requirements are onerous, including the requirement for Sensitive Earth Fault (SEF) protection on 100% underground cable networks. Earth fault is the unintended fault between the live conductor and the earth. are used to restrict the fault current. Restricted Earth fault Protection in Transformers & Generators Transformers and Generators are voltage sources. The earth fault relay operates only for the internal fault of the protective zone. The EFR is protected against tripping from transients and prevents shock. Your email address will not be published. For domestic premises, earth fault loop impedance testing is the most common method used to verify circuit disconnection. Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. High impedance Restricted Earth Fault protection is the voltage based operating protection. Save my name, email, and website in this browser for the next time I comment. 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 is a fast acting circuit breaker to shut down the supply when the earth fault occurs within 1/40th of a second. The Neutral Earth Resistor (NER) allows a clamped resistive earth fault current, which gives protection devices a value on which to act. Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. This requires a manual reset process to work again. When an external fault F1 occurs in the network, I1 and I2 flow through the secondary side of the CTs. 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. Solidly-Earthed System. But during internal fault the neutral curren… hi guys, whats the difference between basic and fault protection. GFCI does not help much with line contact hazards but protects from fire, overheating and destruction of wire insulation. Your email address will not be published. The Ground Fault Circuit Interrupter is a safety device to prevent an electrical accident when any faulty tool is plugged in. It detects small stray voltages on the metal enclosures of electrical equipment. 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. It also occurs, because of the insulation breakdown. The fault current is approximately 15% more than the rated winding current. Sensitive Earth fault Protection scheme is used for the detection of earth fault. If there is any difference as little as 5 mA, GFCI restricts the current and trip quickly. 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. In this video we havr explained how earth fault is detected. Even if the fault occurs nearby neutral the relay will protect the winding unlike differential protection. What type of relaying arrangement will be engaged in stator earth fault protection of alternator depends upon the methods of stator neutral earthing. Most LV systems fall into this category, for reasons of personnel safety. The connection of earth fault relay with the star or delta winding of the transformer is shown in the figure below. The output of the current transformer is equal to the zero sequence current flows in the line. It is a special type of latching relay that is connected to the main power supply. 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. Residual-current devices (RCDs, RCCBs or GFCIs) are used for this purpose. In this video the philosophy behind the restricted Earth Fault Protection has been elaborated. It detects small stray voltages on the metal enclosures of electrical equipment. The stabilising current is connected in series with the relay for avoiding the magnetising inrush current. It should be noted that this protection alone is not adequate. The Earth Leakage Circuit Breaker detects the leakage current directly and prevents injury to humans and animals due to electrical shock. Restricted Earth Fault Protection Earth fault is the unintended fault between the live conductor and the earth. 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. 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. 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. In that case, a sensitive ground/earth fault relay is used in addition to the differential protection of alternator. When the fault occurs inside the protective zone say F2, then only current I2 exist, and I1 is neglected. Ground faults are frequently the result of insulation breakdown. 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. Hence the name restricted earth fault protection. What is the case of i1 current? The result is to interrupt the circuit if a dangerous voltage is detected. It compares the incoming and outgoing current from the equipment along the circuit conductor. If CTs are located on the transformer terminals only the winding is protected. So that the generator should be taken out of service at leisure. Previously, an earth leakage circuit breaker is used. When the fault occurs, the short-circuit currents flow through the system, and this current is returned through the earth or any electrical equipment. REF protection is fast and can isolate winding faults extremely quickly, thereby limiting damage and consequent repair costs. Purpose of Metrosil: It is Voltage Limiting Non-Linear Resistor. Let F1 be the external fault occurs in the network. The connections of Metrosil, Stabilizing Resistor and neural CT are shown in above figure. The fault current is restricted and the fault is dispersed by the Restricted Earth Fault Protection (REFP) scheme. The return path of the fault current is through the grounding system and any personnel or equipment that becomes part of that system. 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. Its important to note that damp, wet, and dusty environments require extra diligence in design and maintenance. For reasons of personnel safety faulty tool is plugged in GFCIs ) are used electrical... 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