earth leakage relay trip reason

Earth-Leakage Relay

An earth-leakage relay is a safety device that detects and isolates leakage currents in electrical systems, protecting equipment and personnel.

Earth-Leakage Relay: An Essential Protection Device for Electrical Systems

Earth-leakage relays are crucial safety devices designed to protect electrical systems and equipment from dangerous leakage currents that could potentially cause hazardous situations or even fatal incidents. In this article, we will discuss the fundamentals of earth-leakage relays, their working principles, and their importance in maintaining the safety and integrity of electrical systems.

What is an Earth-Leakage Relay?

An earth-leakage relay is a type of protective relay that detects leakage currents in electrical systems, which can be a sign of insulation failure or equipment damage. Leakage currents are unwanted currents that flow through the earth or other conductive paths, bypassing the intended electrical circuit. When a leakage current is detected, the earth-leakage relay sends a trip signal to the circuit breaker, disconnecting the power supply and preventing further damage to the system and potential harm to personnel.

How Does an Earth-Leakage Relay Work?

Earth-leakage relays typically use a current transformer (CT) to detect leakage currents in the system. The CT is designed to encircle all the phase conductors and the neutral wire of the circuit, providing a zero-sum current when there is no leakage current present. If a leakage current occurs, the CT senses an imbalance in the current flow, which is then processed by the relay to determine if the leakage current exceeds a predetermined threshold. If the threshold is exceeded, the relay sends a trip signal to the circuit breaker, disconnecting the power supply and safeguarding the system from further damage.

Types of Earth-Leakage Relays

There are two main types of earth-leakage relays commonly used in electrical systems:

• Electromechanical Earth-Leakage Relay: These relays use a mechanical element, such as a magnetic core, to detect the leakage current. When the leakage current exceeds the set threshold, the mechanical element moves, causing a set of contacts to close and send a trip signal to the circuit breaker.
• Electronic Earth-Leakage Relay: These relays use electronic components to measure the leakage current and compare it to a predetermined threshold. If the leakage current surpasses the threshold, the relay sends a trip signal to the circuit breaker. Electronic relays are more sensitive and faster in response compared to their electromechanical counterparts, providing improved protection and more accurate fault detection.

Importance of Earth-Leakage Relays

Earth-leakage relays are essential for several reasons:

• Safety: Leakage currents can lead to electrocution, fire hazards, or equipment damage. Earth-leakage relays help minimize these risks by detecting and isolating the faulty circuit.
• Preventive Maintenance: By detecting insulation failure or equipment damage early, earth-leakage relays enable prompt action to address the issue, preventing further damage and potentially costly repairs.
• Regulatory Compliance: Many electrical codes and standards mandate the use of earth-leakage relays to ensure the safe operation of electrical systems.

Applications of Earth-Leakage Relays

Earth-leakage relays are widely used across various industries and applications to ensure the safety and reliability of electrical systems. Some common applications include:

• Industrial Plants: Earth-leakage relays are crucial in factories and manufacturing facilities to protect machinery, equipment, and personnel from potential hazards caused by leakage currents.
• Commercial Buildings: In commercial settings, such as offices, hotels, and shopping centers, earth-leakage relays are employed to maintain the safety and integrity of electrical systems, protecting both people and property.
• Residential Buildings: Earth-leakage relays are also used in residential buildings to safeguard occupants from potential electrical hazards and ensure the reliable operation of home appliances and electrical systems.
• Power Distribution Systems: Utilities and power distribution companies use earth-leakage relays to monitor and protect their networks from insulation failures and other faults that may lead to power outages or damage to electrical infrastructure.

Selecting the Right Earth-Leakage Relay

When choosing an earth-leakage relay for a specific application, several factors must be considered, including:

• Sensitivity: The relay’s sensitivity to leakage currents should be appropriate for the application. Higher sensitivity relays provide better protection but may be prone to nuisance tripping, while lower sensitivity relays may not adequately protect against potential hazards.
• Response Time: The relay’s response time should be fast enough to disconnect the circuit before any damage or harm can occur. Electronic relays generally offer faster response times than electromechanical relays.
• Adjustability: In some cases, it may be necessary to adjust the relay’s sensitivity or trip settings to suit the specific requirements of an application. Selecting a relay with adjustable settings can provide greater flexibility and customization.
• Reliability: The relay should be reliable and durable, with a proven track record of performance in similar applications. It is essential to choose a relay from a reputable manufacturer with a history of producing quality products.

Earth-leakage relays are vital protection devices that safeguard electrical systems, equipment, and personnel from the hazards associated with leakage currents. They help maintain the safety and integrity of electrical installations, preventing potential damage and costly repairs. By understanding the principles of earth-leakage relays, selecting the appropriate type and specifications for a specific application, and adhering to relevant codes and standards, engineers and technicians can ensure the safe and reliable operation of electrical systems across various industries and applications.

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All you need to know about earth leakage relay

The presence of any faulty currents may cause wires to overheat or lead to hazardous voltages emerging on earthed equipment, causing fire or life-threatening hazards. To avoid situations like these, protective devices capable of disconnecting energy from the load, are required. One such protective device is the Earth Leakage Relay.

Earth Leakage Relay as the name suggests is an electronic device that detects earth leakages/failures. It is made of two very important transformers that help it measure the earth leakage current. These are (a) the toroidal transformer and (b) the core balance transformer. Other features like time operating characteristics with adjustable trip sensitivity and delay also come in handy. Any unidentified fault activates the trip function of the relay switching the control circuit.

How Does an Earth Leakage Relay Work?

The toroidal transformer is capable enough to detect fault currents even at extremely low levels. The high-quality magnetic core of the toroid enables it to do so. And the core balance transformer helps in directly measuring the residual current. The presence of a homopolar component is significant to an earth default. A toroidal transformer is used to measure this component by putting it around three phases + neutral, phase + neutral, or the earth connection. If there is a defect, the balance is disrupted else the vector sum of these currents remains null i.e. 0, depicting the absence of any leakage current.

The toroid’s job is to continuously detect the fault current’s value. And if any fault is detected, it passes a signal to the residual current relay which further switches its output connections to the shunt-trip to open the circuit breaker.

Why Is an Earth Leakage Relay Needed?

The compact residual current device comes with a restrictive sensitivity of only up to 1000mA whereas an earth leakage relay can detect leakage of a 400A–6300A busbar.

Current flows in large quantities from the live conductor to the earth. If accidentally it meets the ground component of any electrical circuit or device, an Earth Fault Current may occur. The earth fault relay is a device that detects earth faults and earth fault currents. Connected to the grounding wire, the Earth Leakage Relay detects any potential difference across the earth fault relay, and sends a signal to the circuit breaker, causing the circuit to trip or disconnecting the main power supply.

However, the Earth Leakage Relay has one disadvantage. Being a voltage-operated device, it can only function in case of multiple faults. Earth Leakage Relays are commonly employed where there is a possibility of a large earth fault like electrical substations and transformer systems.

• Earth Leakage Relay

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Difference between earth leakage relay and earth fault relay

Earth fault is an undesirable condition at which current flow from a conductor to earth. This can happen when a current-carrying conductor falls on the ground or the body of any equipment or when someone touches a live conductor with adequate PPE or due to insulation failures.

Earth leakage relay and earth fault relays are used to sense earth faults. The difference between them lies at the magnitude of current they sense and the purpose of usage.

Earth leakage relay vs Earth Fault relay

Earth leakage relay.

Earth leakage relays are used to sense small magnitude of currents. Earth leakage relays are normally used in low voltage circuits only. These relays are designed in such a way that whenever they sense a preset value of current (usually settable between 10mA and 3A) it trips the circuit breaker and interrupts the flow of current. It is normally used in combination with CBCT (Core balance circuit breaker). Phase and neutral conductors go through the CBCT to the load. Any leakage to the earth causes an imbalance between the phase and neutral currents. Earth fault relay senses this current and trips the circuit breaker. Earth leakage relays can be found in domestic distribution boards and are used to sense insulation failures and to prevent electric shocks.

Earth Fault relays

Earth fault relays are used in high and medium voltage systems and in transformers. These relays are capable of sensing greater fault currents. In case of phase to ground faults, high currents flow to the grounded neutral of the transformer. Earth fault relay senses these faults. Usually, the contacts of the earth fault relay are connected to the trip circuit of circuit breakers at the output side of the transformer. Hence on the detection of a fault, earth fault relay trips the circuit breaker.

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4 thoughts on “Difference between earth leakage relay and earth fault relay”

hello i wanted to know how to size an earth leakage relay

Can I know is there any device that can detect earth fault and earth leakage together?

Residual current devices can detect earth faults as well as earth leakages.

Hello, I have a simple question. What will happen if the ELR faulty? Will faulty ELR cause the MCCB to trip?

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earth fault relay

An earth fault relay, also known as an earth leakage relay or ground fault relay, is a protective device used in electrical systems to detect and respond to earth faults or ground faults. An earth fault occurs when an unintended connection between an electrical conductor and the earth (ground) is established, potentially leading to electric shock hazards, equipment damage, or fire risks.

The primary function of an earth fault relay is to monitor the electrical system for any leakage currents that may indicate the presence of an earth fault. When a fault is detected, the relay initiates a protective action, such as tripping a circuit breaker, to isolate the faulty section from the rest of the system. Here are some key aspects of an earth fault relay:

• Current Sensing: Earth fault relays typically use current transformers (CTs) or other current sensing devices to monitor the current flowing through the system. They compare the current entering the system (line current) with the current returning from the system (neutral or return current) to detect any imbalance that could indicate an earth fault.
• Sensitivity Setting: The earth fault relay allows users to set the sensitivity level for fault detection. This setting determines the minimum fault current imbalance required for the relay to trip and initiate a protective action. It is important to set the sensitivity appropriately to detect faults while minimizing false trips.
• Time Delay: Earth fault relays often include an adjustable time delay feature. This delay allows for a temporary imbalance in current during system startup or when there are expected transient conditions, reducing the likelihood of unnecessary tripping.
• Tripping and Alarm Outputs: When an earth fault is detected, the relay can initiate various actions depending on its configuration. It can send a signal to trip a circuit breaker, disconnect the faulty section, or activate an alarm to alert operators or maintenance personnel about the fault.
• Communication and Monitoring: Advanced earth fault relays may have communication capabilities, allowing them to interface with a supervisory control and data acquisition (SCADA) system or other monitoring devices. This enables remote monitoring, fault diagnostics, and data logging for analysis and maintenance purposes.
• Differential Protection: Some earth fault relays offer differential protection, where multiple relays are installed at different points in the system to detect current imbalances and pinpoint the location of the fault. Differential protection enhances fault detection accuracy and helps in localizing the fault for faster fault clearance.

Earth fault relays are commonly used in various electrical systems, including power distribution networks, industrial plants, commercial buildings, and residential installations. They play a crucial role in ensuring electrical safety by quickly detecting and isolating earth faults, reducing the risk of electric shock and minimizing damage to equipment and property. Proper installation, calibration, and periodic maintenance are essential to ensure the reliable operation of earth fault relays. It is recommended to follow the manufacturer’s guidelines and consult with qualified professionals for their selection, installation, and maintenance.

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Earth-Leakage Relays

• Unlike on an earth leakage breaker, there is no interruption performed and there is only an earth leakage detection function. Detection of the earth leakage is performed (ZCT) and then a signal is sent when there is earth leakage (relay part). It is used with a combination of a ZCT (zero-phase current transformer) and a relay.

• (1) Interchangeable leakage relays can be easily combined with other relays and our ZCT. However, products with 30mA sensitivity (excluding NV-ZHA/ZLA) can only be used in combination with ZT15B, ZT30B and ZT40B.
• (2) Indicates the UL-standard control voltage. UL, CSA and JIS standards are indicated together. For JIS voltage indications, 100-200V changeover is 120-240V changeover, 200-415V changeover is 240-440V changeover, and 460V and 480V are described together. When ordering, specify "UL/JIS".
• (3) Indicates the UL-standard control voltage. UL, CSA and CE standards are indicated together. For CE voltage indications, 120-230V changeover is 120-240V changeover, 230-440V changeover is 240-440V selectable, which are described together. When ordering, specify "UL/CE".
• (4) When operating times are 0.3 and 0.45sec, 0.8 and 1.0sec and 1.6sec, the relay operates between 0.15 and 0.45sec, 0.6 and 1.0sec and 1.2 and 2.0 sec, respectively.
• (5) Can be combined with an interchangeable ZCT equipped with a primary conductor.
• (6) Not UL-certified.
• (1) Relays with rates shown in parentheses are special-order.
• (2) The relay complies with CE marking type MITSUBISHI MCCB with a voltage tripping device to interrupt current during ground fault.

Canada CSA Standards C22.2　No.144

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Earth Leakage in Variable Speed Drives

Sep 25, 2015 | 7 Minute Read

• Drive Basics
• Latest News

In this article by Colin Hargis, chief engineer at Control Techniques, we look at earth leakage in variable speed drives.

AC variable speed drives (VSDs) generate earth leakage currents which are mainly harmless but can sometimes be high enough to cause nuisance tripping of RCDs (Residual Current Devices, earth leakage breakers etc.). Here we look at the reasons for the earth leakage current and possible remedial measures.

Simple electrical devices such as motors and heaters have no connection between the AC power circuit and the earth (PE) connection. The earth connection is there to keep the device safe in the event of a short circuit from the power circuit to the conductive structure. In normal use, there is a very small leakage current flowing to earth, caused by the small stray capacitance and resistive leakage of the power circuit to the earthed structure. This current is in the region of a few micro-amps and has no perceptible effect.

Most electronic equipment has some radio interference filtering , which usually requires capacitors between the power lines and earth. This then results in a leakage current through the capacitors to earth. For a single phase supply, the leakage current can easily be calculated from Ohm’s law and the reactance of the capacitor at the supply frequency.

Limits to leakage current for safety

For electrical equipment provided with an earth connection, referred to as “class 1 equipment”, and designed to be plugged into a mains outlet, the design has to be such as to keep the leakage current below 3.5 mA as laid down by safety standards. The idea is that even if the earth wire were to break and a person were to touch the unearthed equipment, the current of 3.5 mA would not harm them (although they would probably sense it and find it unpleasant). In safety tests what is measured is actually the “touch current” which is measured using a circuit which models the impedance and frequency response of the human body. In practice, leakage current and touch current are usually rather similar.

Where the equipment is permanently installed with a fixed earth connection which is strong enough to avoid accidental disconnection or breakage then this limit does not apply. That is why Control Techniques drives are supplied with either a PE terminal with capacity for a 10 mm2 earth wire or two terminals for two smaller earth wires.

Residual Current Devices (RCDs)

An RCD is a protection device which can be fitted to an electric circuit of a building and which trips to remove power if it senses excessive leakage current. It does this by measuring the total current in all power phases (L+N for a single phase, L1+L2+L3+N for three phases), which should ideally be zero – i.e. all current should circulate in the power wires and not flow to earth.

Figure 1, below, illustrates the arrangement for a single phase device. The most common trip setting is 30 mA, which is a level which is low enough to prevent harm to a person, but high enough to avoid frequent nuisance trips. There are many reasons for fitting an RCD, the most common is where portable equipment is being used in a place where there is a raised risk of electric shock – for example, a sharp electrical tool which might damage its own cable or a wet area.

Why are VSDs special?

The VSD contains an inverter which uses very fast switching of the output voltage and PWM to synthesise the required current waveform for the motor. Most modern power electronic equipment uses similar fast switching power devices, and to avoid the emission of radio frequency interference (electrical “noise”) it has to be provided with a radio interference filter.

The VSD is unusual because the switching output is not contained within the unit, but passes through the motor cable, which may be many meters long, to the motor. This means that there is a high stray capacitance to earth which drives a high radio frequency current and requires a particularly strong filter to prevent harmful emission into the mains supply. The filter needs to have unusually high values of capacitance to earth in order to be effective, especially with a long motor cable. Most of the filters offered for Control Techniques drives are designed to be used with up to 100m of motor cable.

Practical effects of VSD leakage current

The most common kind of drive system uses several drives and other electrical equipment installed in a cabinet and permanently connected to the mains supply without a plug and socket, with a permanent fixed earth connection. In that case, the typical leakage current in the range of a few to tens of milliamps is of no importance.

You should not under-estimate the effect of these higher frequencies. We have encountered installations where nuisance tripping of RCDs has occurred, where there was no filter. Adding filters cured the problem. It is counter-intuitive that connecting capacitors between the mains supply and earth could actually reduce the earth leakage current, but it can happen. The benefit in diverting the higher frequencies far exceeded the cost in terms of extra mains-frequency earth leakage.

The most common problem with leakage current is unwanted operation of an RCD.

In such a case, the first question is, whether an RCD is really needed? Sometimes RCDs are installed because of their perceived extra safety, and are not justified by the real situation. A permanently connected drive system in a dry environment is safe under all reasonably foreseeable fault conditions, and does not need an RCD.

If the RCD is installed because the earth loop impedance is too high to guarantee the operation of primary protection (e.g. with a TT earth system) then it is usually not necessary to use a 30 mA RCD. Very often a 1A RCD gives ample protection from earth faults, and is most unlikely to suffer spurious operation from a drive system.

For a small simple machine, which is more likely to be used with a pluggable power connection, usually, the motor is close to the drive. You can see from the previous explanation that then the filter capacitance could be reduced, giving sufficient filtering effect with less earth leakage. Control Techniques drives have a provision for disconnecting the internal filter capacitor to allow for this situation.

If radio noise emission must also be kept to a minimum, then for the smaller drives a special low-leakage variant of the external filter is available. You will understand now that this special filter has restrictions on the permitted length of the motor cable, which for small simple machines will not be a limiting factor.

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Earth-Leakage Protection

Presentation

Earth-leakage protection on Micrologic 7 trip units provides protection against low intensity fault currents to ground for:

o All types of electrical distribution applications

o People, according to the earth-leakage protection setting used

Earth-leakage protection is designed for installations with TT or TN-S grounding system.

The Micrologic 7 electronic trip unit is available in two versions for earth-leakage detection:

o The Trip version trips when earth-leakage is detected.

o The Alarm version measures the earth-leakage current and indicates an earth-leakage fault on the display screen.

Operating Principle

Earth-leakage protection is definite time.

The earth-leakage protection threshold IΔn sets the level of earth-leakage current at which the circuit breaker trips when reaching the earth-leakage protection time delay Δt.

Setting the Earth-Leakage Protection

Set the IΔn pickup with the Micrologic 7 trip unit IΔn dial.

Set the Δt time delay as follows:

o With the keypad on the Micrologic 7 trip unit

o With EcoStruxure Power Commission software (password-protected)

IΔn Pickup Setting Values

The accuracy range is +/-10%.

Δt Time Delay Setting Values

When IΔn is set to the 30 mA, the earth-leakage protection acts immediately (instantaneous tripping), whatever the setting of the Δt time delay.

For other IΔn values (> 30 mA), the Δt time delay can be set to one of the following values:

o 60 ms

o 150 ms

o 500 ms

o 1 second

Testing the Earth-Leakage Protection (With Trip) Using Test Button

On the Trip version of Micrologic 7 trip units, the earth-leakage protection must be tested regularly by using the test button T . Pressing the test button simulates a real leakage current passing through the toroid and the circuit breaker trips.

When the earth-leakage protection pickup IΔn is set to the OFF  position, pressing the test button has no effect.

Follow these steps to test and reset the earth-leakage protection on Micrologic 7 trip units:

Testing the Earth-Leakage Alarm (Without Trip) Using Test Button

On the Alarm version of the Micrologic 7 trip unit, the earth-leakage alarm can be tested by using the test button T . Pressing the test button simulates a real leakage current passing through the toroid. The circuit breaker does not trip.

When the earth-leakage alarm pickup IΔn is set to the OFF  position, pressing the test button has no effect.

Follow these steps to test the earth-leakage alarm on Micrologic 7 AL trip units:

Testing the Earth-Leakage Function (Without Trip) Using Keypad Only

On the Trip and Alarm versions of the Micrologic 7 trip unit, the earth-leakage tripping chain (or earth-leakage detection for the Alarm version) (except mechanism and pole operation) can be tested, without tripping the circuit breaker, by using the keypad.

Follow these steps to test the earth-leakage protection alarm on Micrologic 7 AL trip units:

Earth-Leakage Test History

The last ten earth-leakage tests are recorded in an earth-leakage test history . Tests performed using the T test button and tests using the keypad are logged in the same history.

The history records:

o Type of test: with trip or without trip

o Date of test

o Result of test ( OK  or nOK )

The earth-leakage test history can be consulted:

o With EcoStruxure Power Commission software.

o On a remote controller using the communication network.

Resetting the Circuit Breaker After an Earth-Leakage Fault Detection

Resetting the earth-leakage function after an earth-leakage fault detection (with or without trip) depends on the version:

o For the Trip version, reset the circuit breaker by moving the handle from Trip  to O (OFF)  position, and then to I (ON)  position. Acknowledge the earth-leakage trip screen by pressing OK .

o For the Alarm version, acknowledge the earth-leakage trip screen by pressing OK .

Resetting the earth-leakage function after an earth-leakage protection test is described in the procedure for each test.

DOCA0141EN-01

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What is Earth Fault? It’s Causes, Effects and Protection

Table of Contents

What is Earthing and Grounding?

Earthing and grounding both are processes to connect electrical systems to the ground to protect people against electrical shock. The earthing  process means connecting the dead part of the electrical system (parts that don’t carry current under normal conditions such as the motor body, Transformer body, electrical panels, etc.) to the earth. Whereas the Grounding process means connecting the live part of the electrical system (parts that carry current under normal conditions such as neutral of star connected Transformer and loads ) to the earth. Now coming to our main topic of discussion:

What is Earth Fault?

Earth fault is an open circuit ground fault in which any live conductor or power-carrying cable is detached from its place or breaks and falls on the earth’s surface. In other words, We can say that ln earth-fault current-carrying conductor comes directly in contact with the earth’s surface. So because of the direct contact between a live conductor and the earth’s surface, a huge amount of current starts flowing to the earth due to the conducting nature of the earth.

Causes of Earth Fault

The main cause of earth fault in an overhead transmission and distribution line is the failure or puncture of the insulator. Insulators are used in overhead transmission lines to provide insulation between live conductors and metallic towers that are already connected with the earth’s surface. So if the insulation of insulator fails or in other words if the insulator is punctured then the fault current will flow through the live conductor and metallic tower to the earth creating an earth fault.

Another reason for earth fault is that sometimes overhead transmission lines break due to any unusual loads on line and hence fall to the ground. So in this case also live conductor gets in direct contact with the ground and creates a major earth fault in the electrical system. Whereas in the case of an underground PV cabling system, Earth fault may arise due to insulation damage during installation, abrasion damage to cable sheath, and damage to module back sheet during installation.

Effect of Earth Fault

Whenever an earth fault occurs in the electrical system than during earth fault, the System gets short, and hence huge amount of short-circuit current flows through the system. That huge current damages electrical equipment which comes in contact with a loop of earth fault circuits and also it interrupts the continuity of the power supply. Due to such a large amount of current flowing to the earth, a large voltage drop occurs that affects the other loads and it may cause the burning of phase or line.

How to check Earth Fault?

To identify the earth leakage fault in cables, megger is used. One terminal of the megger is connected to the live conductor and the other terminal is connected to the earth. If the merger indicates zero reading, it means the conductor is earthed. The same procedure is repeated for other conductors of the high-voltage cables.

Difference between Earth Fault and Ground Fault

Earth Fault  vs Ground Fault :

Earth fault is an open-circuit fault where a power-carrying cable or conductor breaks and gets into contact with Earth or any conductor capability material in contact with Earth. In this fault, the system at the load side is disconnected from the source in case of radial power flow.

Whereas a ground  fault is a short-circuit fault (such as L-G, L-L-G, L-L-L-G) where the power-carrying cable or conductor is not broken but gets into contact with the earth or any conductor capability material in contact with the earth. In this fault, the system at the fault point experiences the flow of a large amount of current into the ground.

Ground fault is more severe than earth fault due to flow of huge current to ground. That can dimage verious electrical equipments of power system, if fault is not cleared within specified time limits.

Earth Fault Protection

Well, after discussing the earth’s fault, its causes, and effects, one of the important questions that arises in our mind is.. ok, then what is the solution to minimize Earth-fault? Does it mean what protective equipment we can use to protect the earth fault? So let’s discuss the protection used to minimize earth faults in detail.

What are  Earth Fault Protection Devices?

The electrical equipment that   provides protection against earth fault is known as earth fault protection devices. These are normally Earth fault relay (EFR) , Earth leakage circuit breaker (ELCB) , and ground fault circuit interrupter, which are used to restrict the fault current. In these devices, the fault current is restricted and the fault is dispersed by the Restricted Earth Fault Protection (REFP) scheme. Now first let’s discuss both earth fault protection devices such as:

• Earth fault relay (EFR)
• Earth leakage circuit breaker (ELCB)

After that, we will see what is Restricted Earth Fault Protection (REFP) schemes.

Earth Fault Relay (EFR)

An earth fault relay (EFR) is a protection device used in electrical installation that can sense a fault between phase and earth.

The  main function of an earth fault relay (EFR) is to operate the CB for leakage current to the earth. RCCB also does the same function but RCCB gives protection to the human body, Whereas EFR provides protection to electrical equipment from earth fault . EFR deals with high voltage and high current.

Hence we can conclude that an earth fault relay (EFR) is an earth fault monitoring device that works on the principle of Kirchhoff’s law.

Earth Leakage Circuit Breaker (ELCB)

ELCB or earth leakage circuit breaker is a safety device used in electrical installation with high earth impedance to prevent electrical shock. In other words, we can say that ELCB is a special type of circuit breaker that is used for protection against earth leakage current. It is voltage voltage-sensing device that works on the concept of stray voltage. Whereas current sensing ELCB is also known as RCCB .

Whenever any earth leakage fault occurs in the system then a stray voltage appears across metal enclosures of electrical equipment ELCB interrupts the circuit if a dangerous voltage is detected. Then it disconnects the rest of the healthy system from the main supply. Once it tripped then it requires a manual reset process to work again normally.

Hence simply we can assume that ELCB is a safety device whose main function is to provide protection against electrical shock. It can’t assure protection against overloading and short-circuit faults.

What is the Restricted Earth Fault Protection (REFP) Scheme?

The restricted earth fault protection (REFP) scheme is very sensitive to internal earth faults for high-rating power transformers, alternators, etc. This scheme is comparatively cheaper than the differential protection scheme.

In this scheme, the common terminal of phase CTs is connected together with the secondary of neutral CT in such a manner that the secondary unbalanced current of phase CTs, and the secondary content of neutral CT will oppose each other.

When an external fault F 1 occurs in the system then the resultant of current I 1 and I 2 flowing through phase CTs and neutral CT respectively will be zero. But whenever an internal fault F 1 occurs inside the protective zone then only I 2 current will flow through the secondary of neutral CT and the resultant current will not be zero.

Hence earth fault relay will sense non-zero current and then it will operate the CB to protect the system with earth leakage fault . The fault current becomes 15% more than the rated current of each winding. To avoid magnetic inrush current, a stabilizing resistor is connected in series with an earth fault relay.

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Hey, I'm Satish Gupta an Engineer by profession and blogger by passion. I am writer and founder of this blog, Here I publish contents related to Electrical and Electronics Engineering..

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Rayleigh Instruments RI-ELR60 Earth Leakage Relay with Adjustable Trip Level

Part Number:

• 2 Module width DIN rail mounted
• True RMS Earth Leakage monitoring
• Type A leakage detection
• LED bargraph for indication of leakage current
• Test and reset function
• For use with RI-CBCT core balanced transformers
• Single phase (2 wire) or 3 phase (3 or 4 wire)
• Core balanced transformer error (open and short circuit)
• SPDT relay output 5A
• Selectable trip time delay
• Selectable trip level
• Failsafe output relay (required for Annex M)
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