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 Your email address will not be published.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