The leakage protector is used to effectively protect the direct and indirect contact electricity of the low-voltage power grid. It can also be used as the phase failure protection of the three-phase motor. It has single-phase and three-phase. Because it uses the leakage current or the resulting neutral point-to-ground voltage change as the action signal, it is not necessary to set the action value with the electric current value, so the sensitivity is high, and the power supply can be effectively cut off after the action to ensure personal safety.
Leakage protectors can be classified according to their protection functions, structural features, installation methods, operating modes, number of poles and lines, action sensitivity, etc., here are mainly based on their protection functions It is described with the classification of the purpose, which can generally be divided into three types: leakage protection relay, leakage protection switch and leakage protection socket.
Leakage protection relay
refers to a leakage protection device that has the function of detecting and judging leakage current, but does not have the function of cutting off and connecting the main circuit . The leakage protection relay is composed of a zero-sequence transformer, a trip unit and auxiliary contacts for output signals. It can be used with high-current automatic switches as the general protection of the low-voltage power grid or the leakage, grounding or insulation monitoring protection of the main road.
When the main circuit has leakage current, the auxiliary contact and the main circuit switch are connected in series to form a circuit. Therefore, the auxiliary contact connects to the separation release and disconnects the air switch, AC contactor, etc., so that it trips and cuts off the main circuit. The auxiliary contact can also be connected to the sound and light signal device to send out a leakage alarm signal to reflect the insulation status of the line.
Leakage protection switch
It not only can connect or disconnect the main circuit like other circuit breakers, but also has the function of detecting and judging the leakage current. When the main circuit When leakage or insulation failure occurs, the leakage protection switch is a switching element that can turn the main circuit on or off according to the judgment result. It can be combined with fuses and thermal relays to form a fully functional low-voltage switching element. This type of leakage protection device is the most widely used. The leakage protection switches on the market are commonly used in the following categories according to their functions:
(1) It only has the function of leakage protection and power failure. Protective components such as relays, thermal relays, overcurrent relays, etc. are coordinated.
(2) It also has overload protection function.
(3) It also has overload and short circuit protection functions.
(4) It also has a short-circuit protection function.
(5) It has the functions of short circuit, overload, leakage, overvoltage and undervoltage at the same time.
Leakage protection socket
Refers to a power socket with leakage current detection and judgment and capable of cutting off the circuit. The rated current is generally 10A, 16A, the leakage current is 6-30mA, and the sensitivity is high. It is often used for the protection of hand-held electric tools and mobile electrical equipment, and civil places such as homes and schools.
Under normal circumstances, the three-phase load current and the earth leakage current are basically balanced, and the phasor sum of the primary coil current flowing through the transformer is about zero, that is, the total magnetic flux generated by it in the iron core is zero , The secondary coil of zero sequence transformer has no output. When an electric shock occurs, the electric shock current flows through the earth into a loop, that is, a zero-sequence current is generated. This current does not flow back through the primary coil of the transformer, which breaks the balance, so there is zero-sequence magnetic flux in the iron core, which makes the secondary coil output a signal. This signal is amplified and compared by the components to judge. If it reaches the predetermined action value, it will send an execution signal to the actuator to switch off and cut off the power supply.
It can be seen from the working principle that when the three-phase ground impedance difference is large, and the three-phase ground leakage current phasor reaches the protector action value, the circuit breaker will be switched off or cannot be powered on. At the same time, the phases of the three-phase leakage current and the electric shock current are inconsistent or reversed, which will reduce the sensitivity of the protector.
The current leakage protector can implement hierarchical protection to achieve selective action.
Operation block diagram of current leakage protector Before understanding the main principle of electric shock protector, it is necessary to understand what an electric shock is. Electric shock refers to injury caused by the passage of electric current through the human body. When a human hand touches the wire and forms a current loop, there is current flowing through the human body; when the current is large enough, it can be felt by humans and cause harm. When an electric shock has occurred, it is required to cut off the current in the shortest time. For example, if the current passing through a person is 50 mA, it is required to cut off the current within 1 second, if the current is 500 mA passing through the human body , Then the time limit is 0.1 seconds.
The leakage protection device is installed at the place where the power cord enters the house, that is, near the watt-hour meter, and is connected to the output end of the watt-hour meter, that is, the user side. Replace all household appliances with a resistor RL, and replace the body resistance of the contact person with RN.
CT stands for "current transformer". It uses the principle of mutual inductance to measure AC current, so it is called "transformer", which is actually a transformer. Its primary coil is the AC line that enters the house, and the two wires are taken as one wire and combined to form the primary coil. The secondary coil is connected to the coil of the "reed relay" SH.
The so-called "reed relay" is to wind a coil on the outside of the reed tube. When the coil is energized, the magnetic field generated by the current makes the reed electrode inside the reed tube pull in and turn on External circuit. After the coil is de-energized, the reed is released and the external circuit is disconnected. All in all, this is a small relay. The switch DZ in the schematic diagram is not an ordinary switch. It is a switch with a spring. When a person overcomes the spring force to close it, a special hook must be used to buckle it to ensure that it is in the ON state; otherwise, it will be in the ON state as soon as it is released. It broke again.
The reed electrode of the reed relay is connected to the "trip coil" TQ circuit. The tripping coil is an electromagnet coil, which generates attractive force when passing current. This attractive force is enough to release the hook mentioned above and make DZ disconnect immediately. Because the DZ is connected to the live wire of the user's main wire, the electricity will be cut off when it is tripped, and the person who gets an electric shock will be saved.
However, the reason why a leakage protector can protect people is that it must first "consciously" realize that people are electrocuted. So how does the leakage protector know that a person has been electrocuted? If there is no electric shock, the current in the two wires from the power source must be the same at all times and in opposite directions. Therefore, the magnetic flux in the primary coil of the CT completely disappears, and there is no output from the secondary coil. If someone gets an electric shock, it is equivalent to a resistance on the live wire, so that it can interlock and cause a current output on the secondary side. This output can make the SH's electric shock pull and close, so that the tripping coil will get a point, the hook will be sucked off, and the switch DZ will be off. Open, thus playing a protective role.
It is worth noting that once tripped, even if the current in the tripping coil TQ disappears, it will not reconnect DZ by itself. The power supply cannot be restored because no one closes it. The electric shocker leaves, and wants to use electricity again after checking that there are no hidden dangers. You need to close the DZ to re-buckle it, and the power supply is restored.
The above is the main principle of the electric shock protector, but even with the electric shock protector, it cannot be considered as foolproof. You should still pay attention to safety when using electricity.
In order to regulate the correct use of leakage protectors, the country has successively promulgated the "Regulations on the Safety Supervision of Leakage Protectors" (Laoanzi (1999) No. 16) And a series of standards and regulations such as GB 13955-2005 "Installation and Operation of Residual Current Operated Protective Devices" (instead of "Installation and Operation of Leakage Protector GB13955-92). According to these standards and regulations, we should follow the following main principles when selecting a leakage protector:
1. When purchasing a leakage protector, you should purchase products from manufacturers with production qualifications, and the product quality should be qualified. I would like to remind everyone here: many of the leakage protectors sold on the market are substandard products. On October 28, 2002, the General Administration of Quality Supervision, Inspection and Quarantine announced the results of the random inspection of the product quality of leakage protectors. About 20% of the products were unqualified. The main problems were: some could not normally break the short-circuit current to eliminate the fire hazard; some did not It has the protective effect of personal electric shock; there are some trips when they should not be tripped, which affects the normal use of electricity.
2. The power supply voltage, working current, leakage current and operating time of the leakage protector should be determined according to the scope of protection, personal equipment safety and environmental requirements.
3. When the power supply adopts leakage protector for hierarchical protection, it should meet the selectivity of upper and lower switch actions. Generally, the rated leakage current of the upper-level leakage protector is not less than the rated leakage current of the next-level leakage protector, which can sensitively protect the safety of people and equipment, and can also avoid skipping trips and reduce the scope of accident inspection.
4. Hand-held power tools (except Class III), mobile household appliances (except Class III), other mobile electromechanical equipment, and electrical equipment with greater risk of electric shock, A leakage protector must be installed.
5. Electrical equipment for construction sites and temporary lines should be installed with leakage protectors. This is clearly required in the "Technical Specification for Safety of Temporary Use of Electricity at Construction Sites" (JGJ46-2005).
6. The socket circuits in offices, schools, enterprises, and residential buildings, as well as the socket circuits in guest rooms of hotels, restaurants and guest houses, must also be equipped with leakage protectors.
7. Power supply lines and equipment installed in the water, as well as places with high humidity, high temperature, large metal occupancy, and other good electrical conductivity, such as machining, metallurgy, textile, electronics, food processing and other industries Places, as well as boiler rooms, water pump rooms, canteens, bathrooms, hospitals and other places, must be protected by leakage protectors.
8. Power distribution boxes with leakage protectors should be used for fixed line electrical equipment and normal production sites. For temporary use of small electrical equipment, leakage protection plugs (seats) or socket boxes with leakage protection should be used.
9. When the leakage protector is used as a supplementary protection for direct contact protection (not as the only direct contact protection), a high-sensitivity, fast-acting leakage protector should be selected.
General environment choose the action current not to exceed 30mA and the action time to not exceed 0.1s. These two parameters ensure that if the human body gets an electric shock, it will not cause the person who is shocked to produce pathological and physiological dangerous effects.
The rated operating current of the leakage protector in bathrooms, swimming pools and other places should not exceed 10mA.
In occasions that may cause secondary accidents after an electric shock, a leakage protector with a rated operating current of 6mA should be selected.
10. For electrical equipment that is not allowed to be powered off, such as passage lighting in public places, emergency lighting, power supply for fire-fighting equipment, power supply for anti-theft alarm, etc., an alarm-type leakage protector should be used to switch on Sound and light alarm signals inform the management personnel to deal with the fault in time.
(1) The rated frequency is 50HZ.
(2) The rated voltage Un is 220V, 380V.
(3) The auxiliary power supply voltage Usn is: DC 12, 24, 40, 60, 110, 220V; AC 12, 48, 220, 380V.
(4) The rated current In is 6, 10, 16, 20, 25, 32, 40, 50, (60), 63, 100, (125), 160, 200, 250A. The bracketed ones are not preferred.
(5) The rated leakage current In·dz is 0.006, 0.01, (0.015), 0.03, (0.05), (0.075), 0.1, (0.2), 0.3, 0.5, 1, 3, 5, 10, 20A. Values in parentheses are not used in preference.
(6) The preferred value of the rated leakage non-operation current is 0.5I n·dz.
(7) Maximum breaking time of leakage protector:
1) Direct contact protection. When the operating current I n·dz ≤ 0.03A, if the zero sequence current flowing through the protector is 1 times I n·dz, it is 0.2s, 2 times it is 0.1s, and when it flows through 0.25A, it is 0.04s; /p>
2) Indirect contact protection. When it flows through 1 times, it is 0.2S, when it is 2 times, it is 0.1S, and when it is 5 times, it is 0.04s; . The preferred value of the delay time of the delay protection is 0.2, 0.4, 0.8, 1, 1.5, 2s.
The application range of the leakage protector is as follows:
(1) Mobile electrical appliances without double insulation and rated working voltage above 110V.
(2) Construction site.
(3) Temporary route.
The action current to prevent direct contact with the live body protection is 30mA, and the action is within 0.1s.
An indirect contact protection leakage protector can be installed as needed.
(1) The power line of the protected circuit, including the phase line and the neutral line, should pass through the zero-sequence current transformer.
(2) A section of the power cord that penetrates into the zero-sequence transformer should be wrapped tightly with insulating tape, and then bundled into a bundle and penetrated through the center of the zero-sequence current transformer hole. This is mainly to eliminate the unbalanced magnetic flux generated in the core due to the asymmetry of the wire position.
(3) The neutral wire led by the zero sequence transformer shall not be grounded repeatedly, otherwise the unbalanced current generated when the three-phase load is unbalanced will not all return from the neutral wire, but some Return from the ground, so the vector sum of the current through the zero-sequence current transformer is not zero, and the secondary coil has output, which may cause malfunction.
(4) The neutral line of each protection circuit should be dedicated, and must not be overlapped nearby, and the neutral lines must not be connected to each other, otherwise the three-phase unbalanced current or the single-phase electric shock protector phase line Part of the current will be shunted to the zero lines of the different protection circuits connected to each other, which will cause the zero sequence current transformer cores of the two circuits to produce an unbalanced magnetomotive force.
(5) After the protector is installed, power on and press the test button to try to jump.
Installation and operation
The installation method should not only comply with the conventional electrical equipment installation regulations, but also pay attention to the following points:
1. Installation of the leakage protector Should meet the requirements of the manufacturer's product manual.
2. The leakage protectors marked on the power supply side and the load side must not be connected in reverse. If the connection is reversed, the trip coil of the electronic leakage protector will not be cut off when the power is cut off, and it will be burnt when it is energized for a long time.
3. The original safety protection measures must not be removed or abandoned when installing the leakage protector. The leakage protector can only be used as an additional protection measure in the electrical safety protection system.
4. When installing a leakage protector, the neutral line and the protection line must be strictly distinguished. When using three-pole four-wire and four-pole four-wire leakage protector, the neutral line should be connected to the leakage protector. The neutral line passing through the leakage protector shall not be used as a protection line.
5. The working neutral line must not be grounded repeatedly on the load side of the leakage protector, otherwise the leakage protector cannot work normally.
6. For the branch circuit using the leakage protector, its working neutral line can only be used as the neutral line of this circuit, and it is forbidden to connect with the working neutral line of other circuits, and other lines or equipment cannot be used for leakage protection. The line behind the device or the working zero line of the equipment.
7. After the installation is completed, it must be in accordance with the "Construction Quality Acceptance Specification for Building Electrical Engineering (GB50303-2002) 3.1.6, that is, "the leakage protector of the power and lighting engineering should be simulated action test" It is required to test the completed leakage protector to ensure its sensitivity and reliability. During the test, you can operate the test button three times, open and close the load three times, and confirm that the action is correct before it can be officially put into use.
The safe operation of the leakage protector depends on a set of effective management systems and measures. In addition to regular maintenance, the operating characteristics of the leakage protector (including leakage action value and operating time, leakage non-operating current value, etc.) should be tested regularly, and the test records should be made, and the value should be compared with the initial value of the installation. Compare and judge whether there is any change in its quality.
In use, use the leakage protector in accordance with the requirements of the instruction manual, and check it once a month as required, that is, operate the test button of the leakage protector to check whether it can normally disconnect the power supply. During the inspection, it should be noted that the time of operating the test button should not be too long. Generally, it is advisable to jog, and the number of times should not be too much, so as to avoid burning the internal components.
The leakage protector trips during use. If the cause of the switch action is not found after inspection, it is allowed to test the power once. If it trips again, the cause should be found out and the fault should be found out, and the power should not be continuously forcibly sent.
Once the leakage protector is damaged and cannot be used, it should be checked or replaced by a professional electrician immediately. If the leakage protector malfunctions or refuses to operate, the reason is on the one hand caused by the leakage protector itself, and on the other hand, it is from the line. It should be carefully analyzed in detail, and the internal components of the leakage protector should not be disassembled and adjusted privately.
In the reconstruction of the two networks, a large number of residual current-operated leakage protectors have been used. A few years have passed. Facts have proved that the leakage protector is damaged and the phenomenon of artificial release of the operation is very serious. Serious. The problem of power consumption and safe power consumption is still severe. There are many reasons for correcting the leakage protector, but the direct cause is the frequent operation and refusal of the leakage protector, which seriously affects the normal use of electricity, and makes the management and electricity users lose confidence in the leakage protector or even give up.
The frequency of the leakage protector includes two aspects:
First, the leakage protector operates normally when the power grid is indeed grounded. In this kind of normal action, due to the aging of the power grid and changes in the climate environment, the majority of the actions caused by the grounding point of the power grid, and the actions caused by the personal electric shock are very few. It is conceivable that the normal use of electricity is the first demand of people. In order to prevent the extremely low probability of personal electric shock from causing frequent power outages, affecting normal production and life will certainly cause people's troubles.
Second, the power grid has not been grounded, but the leakage protector may malfunction in the following situations:
1, because the leakage protector is triggered by a signal, then Other electromagnetic interference will also generate a signal to trigger the action of the leakage protector, which will cause a malfunction.
2, when the power switch is closed and power is sent, an impact signal will be generated and the leakage protector will malfunction.
3, the sum of multi-branch leakage can cause leapfrog and misoperation.
4. Repeated grounding of the neutral wire may cause the string current to malfunction.
It can be seen that, because of the possibility of malfunction of the leakage protector technically, the frequency problem of the leakage protector will become more serious and more complicated.
Analyzed from the technical principle, the leakage protector also has a technical misunderstanding that may cause refusal to move.
1. When the neutral line is repeatedly grounded, it will cause the leakage protector to shunt and refuse to move, and the repeated grounding point of the neutral line is difficult to find.
2, when the power supply lacks phase, and the missing phase happens to be the working power supply of the leakage protector, it will refuse to move.
From the above analysis, it can be seen that the frequent operation and refusal of the leakage protector in actual use are not only due to the objective environment and management, but also the technical misunderstanding of the leakage protector itself. In particular, the use of leakage protectors requires the neutral point of the power grid to be grounded, and most of the technical misunderstandings of leakage protectors are related to the neutral grounding of the power grid:
Due to the neutral point Grounding, the support of the phase line of the power grid bears the phase voltage all the year round, so the support is broken down, forming a grounding point of the power grid, causing leakage and causing frequent operation of the leakage protector.
Because the neutral point is grounded, when the phase line is occasionally grounded, a large leakage current will be generated immediately, which will not only increase the electrical loss, but also cause fire, but also Increase the frequency of the leakage protector.
Because the neutral point is grounded, when a person gets an electric shock, it will immediately produce a large current of electric shock, which is very threatening to human life, even if there is a leakage protector. If you get an electric shock first, then the protection is activated. If the action is slow or fails, the consequences will be more serious.
Because the neutral point is grounded, the grid-to-ground distributed capacitance is connected in the loop, which will increase the ground impulse current when the switch is closed and cause malfunction.
Because the neutral point has been grounded, it is difficult to find repeated grounding of the neutral line. Repeated grounding of the neutral line will cause the leakage protector to shunt and reject action. Flow by mistake.
It can be seen that there are technical errors in the leakage protector, and these technical errors are closely related to the neutral grounding of the power grid. When using the leakage protector, the neutral point of the power grid must be grounded. It is impossible for the leakage protector to solve the problem of frequent movement and refusal to move within the technical thinking.
Two points need to be pointed out in particular:
1. When a human body single-phase electric shock accident occurs (this kind of accident has the highest probability of electric shock accidents), that is, on the load side of the leakage protector It can play a very good protective role when it touches a phase wire (live wire). If the human body is insulated from the ground, when it touches a phase line and a neutral line at this time, the leakage protector cannot play a protective role.
2. Since the role of the leakage protector is to prevent trouble before it happens, its importance cannot be reflected when the circuit is working normally, and it is often not easy to attract everyone's attention. Some people do not seriously find the cause when the leakage protector is activated, but short-circuit or remove the leakage protector. This is extremely dangerous and absolutely not allowed.
Operation and maintenance
The precautions for the operation and maintenance of the leakage protector are as follows:
(1) A system should be established, dedicated maintenance, periodic test trips, and operation Record.
(2) When there is a problem, it should be analyzed and dealt with. It is not allowed to exit the operation without authorization or make it invalid consciously.
(3) Tripping during normal operation. If the cause is motor start or high current impact, alternate start should be adopted, and the positioning should be adjusted appropriately, or the impact can be avoided with a short delay. If the leakage current is increased due to rain or other reasons, the sensitivity can be temporarily adjusted.
* Direct contact protection refers to the protection of the human body from direct contact with charged objects. Indirect contact protection refers to the protection that the metal shell is charged due to leakage and other faults caused by human contact.
The operating principle of the leakage protection switch is: There are two groups on an iron core: an input current winding and an output current winding. When there is no leakage, the input current and the output current are equal. If the vector sum of the two magnetic fluxes is zero, no electric potential will be induced on the third winding, otherwise the induced voltage will be formed on the third winding, which will be amplified to push the actuator and make the switch trip.
Note: Leakage protectors must require extremely high sensitivity. The use of well-known brands can often improve safety, because they are very precise and sensitive to line detection, within 0.1 seconds or less Abnormalities can be detected, and before the current intensity and time reach the level of damage, it will immediately trip and cut off the main circuit of the power supply, which fully guarantees personal safety. And if you use miscellaneous brands that are not of good quality, or are outdated, even if it is only 1 second or even 0.5 seconds late, the harm to the human body is fatal. Life safety must be vigilant!
Current status issues
my country began to promote the use of leakage protection switches in the early 1980s, and released corresponding products on September 3, 1986 National standard GB6829-86 "Leakage Current Action Protector". It has played a positive role in reducing electric leakage, preventing electric leakage and electric shock and fires that may be caused by overload. However, due to the immature technology at that time, coupled with many manufacturers, many and mixed models, and uneven quality, it was difficult to achieve the purpose of leakage protection and overload prevention.
Therefore, the leakage protection switch is difficult to promote in the vast urban and rural areas of the country. Although some areas have been promoted for a period of time, the consolidation rate is not high.
Some leakage protection switches are unstable, and some are unreliable. For example, the rated non-operating current of the small leakage protection switch is 15mA, and the rated operating current is 30mA. However, during operation, it often trips below 15mA, which is very inconvenient for residents to use. Users call it "troubleshooters". And some leakage currents reach more than 30mA and can not be tripped, or tripping time is too long, can not play a good role in leakage protection. Because for 50Hz power frequency alternating current, 15-20mA or less is a safe current.
Many users think that the installation of a leakage protection switch is foolproof and relaxes the safety concept. Therefore, there will be accidents where the human body touches the phase line and the neutral line at the same time, which cannot protect personal safety. Some people think that the leakage protection is Switches are "not working", "useless", etc.
The price of leakage protection switches produced in my country is too high, and users have certain difficulties in accepting them, especially for rural users. This is not conducive to popularization and improving the level of safe electricity use in rural areas, and it is not conducive to opening up the rural market.
After the leakage protection switch is tripped in rural remote mountainous areas and ethnic minority areas, they do not know how to find the cause of the leakage, how to eliminate the leakage fault, and how to restore the power supply.
On the other hand, some manufacturers one-sidedly exaggerate the function and function of leakage protectors in order to promote their products. In addition, the market is flooded with fake and inferior products. Had some impact.
Function and significance
Practice has proved that about 80% of the human body’s electric shock is caused by the human body touching the single-phase phase line. Cause harm. The promotion of leakage protection switches has a great effect on preventing leakage and electric shock, reducing personal injuries and deaths due to electric shock, and preventing equipment leakage. Generally speaking, the leakage protection switches produced by manufacturers have short circuit and leakage protection functions, and some also have overload, overvoltage, undervoltage protection and other functions. As long as the quality is excellent, it can meet the requirements of stability and reliability.
The use of leakage protection switches plays an important role in improving the level of safe electricity consumption, reducing personal injury accidents and equipment leakage protection. It can also avoid many electrical fire accidents. Power supply companies can also reduce leakage and electric shock. Economic compensation for losses, disputes, and even reduction of legal proceedings in this area.
In short, the use of leakage protection switches has positive and far-reaching significance for users and power supply companies.
The leakage protector has high sensitivity and rapid action in response to electric shock and leakage protection, which is incomparable to other protective appliances, such as fuses, automatic switches, etc. Of. Automatic switches and fuses must pass the load current when they are normal, and their action protection value must be set to avoid the normal load current. Therefore, their main function is to cut off the phase-to-phase short-circuit fault of the system (some automatic switches also have overload protection) ). The leakage protector uses the residual current reaction and action of the system. During normal operation, the residual current of the system is almost zero, so its action setting value can be set to a very small value (generally mA level). When the shell is electrified, a large residual current will appear, and the leakage protector will reliably act and cut off the power supply after detecting and processing the residual current.
Leakage protectorStructure diagram
When electrical equipment leaks, it will present abnormal current or voltage signals. Leakage protector By detecting and processing this abnormal current or voltage signal, the actuator is prompted to act. We call the leakage protector that operates according to the fault current as a current type leakage protector, and the leakage protector that operates according to the fault voltage is called a voltage type leakage protector. Due to the complex structure of the voltage-type leakage protector, the stability of the action characteristics due to external interference is poor, and the manufacturing cost is high, and it has been basically eliminated. The research and application of leakage protectors at home and abroad are dominated by current leakage protectors. Current-type leakage protectors use a part of the zero-sequence current in the circuit (usually called residual current) as the action signal, and mostly use electronic components as the intermediate mechanism, with high sensitivity and complete functions. Therefore, this type of protection device is becoming more and more popular. Application. The current leakage protector is composed of four parts:
1. Detection element: The detection element can be said to be a zero-sequence current transformer. The protected phase and neutral wires pass through the toroidal core to form the primary coil N1 of the transformer, and the windings wound on the toroidal core form the secondary coil N2 of the transformer. If there is no leakage, it will flow through at this time. The current vector sum of the phase line and the neutral line is equal to zero, so the corresponding induced electromotive force cannot be generated on N2. If a leakage occurs, the sum of the current vectors of the phase line and the neutral line is not equal to zero, which will cause the induced electromotive force on #$, and this signal will be sent to the intermediate link for further processing.
2. Intermediate link: The intermediate link usually includes an amplifier, a comparator, and a trip unit. When the intermediate link is electronic, the intermediate link also needs an auxiliary power supply to provide the power required for the operation of the electronic circuit. The function of the intermediate link is to amplify and process the leakage signal from the zero-sequence transformer, and output it to the actuator.
3. Actuator: This structure is used to receive the instruction signal from the intermediate link, implement actions, and automatically cut off the power supply at the fault.
4. Test device: Since the leakage protector is a protection device, it should be checked regularly to see if it is intact and reliable. The test device is to simulate the leakage path through the series connection of the test button and the current-limiting resistor to check whether the device can operate normally.