Electrical 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 and Use classification to describe, generally can be divided into three types: leakage protection relay, leakage protection switch and leakage protection socket.
1. 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, because the auxiliary contact and the main circuit switch's separate release are connected in series to form a circuit, the auxiliary contact connects to the separate release and disconnects the air switch, AC contactor, etc. Make it trip and cut 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.
2. Leakage protection switch means not only that it can connect or disconnect the main circuit like other circuit breakers, but also has the function of detecting and judging leakage current. When leakage or insulation damage occurs in the main circuit When 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.
At present, 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) Only with leakage protection The electrical function must be used with protective elements such as fuses, thermal relays, and overcurrent relays.
(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.
3. Leakage protection socket refers to a power socket with leakage current detection and judgment and capable of cutting off the loop. The rated current is generally below 20A, the leakage action current is 6-30mA, and the sensitivity is high. It is often used for the protection of hand-held power tools and mobile electrical equipment, and civil places such as homes and schools.
Since the invention and use of electricity by mankind, electricity has not only brought a lot of convenience to mankind, but also brought disaster to mankind. It may burn out electrical appliances, cause a fire, or cause electric shock. If there is a device that allows people to use electricity safely, many unnecessary losses will be avoided. Therefore, as a variety of electrical appliances came one after another, all kinds of protectors were also born. One of them is specifically designed to protect people, called a leakage protector. Leakage protector, commonly known as leakage switch, is a protective electrical appliance used to prevent personal shock and electrical fire when the circuit or electrical insulation is damaged and a short circuit to the ground occurs. It is generally installed on the socket circuit of each distribution box and the general power distribution of the entire building. The power supply line of the box, the latter is dedicated to prevent electrical fires.
Leakage protectors have experienced a long development process and are now widely used all over the world.
In 1930, a voltage-operated leakage protector was invented in Europe to prevent electrical equipment from electric shock accidents due to insulation damage. In 1960, a current-operated leakage protector appeared. At present, the voltage-operated leakage protector in the world has been eliminated, and the current-operated leakage protector has become the main electrical device for leakage and electric shock protection.
In 1964, Japan began to develop voltage-operated leakage protectors to prevent electric shock accidents at construction sites. In 1966, electromagnetic current-operated leakage protectors were introduced from West Germany, and integrated circuits were produced in 1976. The leakage protector.
The United States has used current-operated leakage protectors since 1967. Due to the electric shock accident in swimming pools, the development of leakage protectors was emphasized, and the leakage protector with a leakage current of 5mA was required from the beginning. .
my country began to develop voltage-operated leakage protectors in 1966, began to develop and produce electromagnetic leakage protectors in 1976, and developed and produced integrated circuit leakage protectors around 1985.
The promotion and application of leakage protectors are inseparable from the formulation of standards and regulations. The 1971 edition of the National Electrical Code (NEC) of the United States stipulates that since January 1, 1973, residential and construction sites must be equipped with leakage protectors. Japan’s "Technical Standards for Electrical Equipment" and the Ministry of Labor’s "Safety and Health Regulations" stipulate that electrical equipment with a working voltage of more than 60V must be equipped with leakage protectors when used in humid places, and all 400V circuits must be equipped with leakage protectors.
In 1981, my country's former State Construction and Industry Administration's "Decision on Strengthening Labor Protection Work" stipulated that electrical equipment on construction sites must be equipped with leakage protection devices. The GB3787-1983 "Safety Technical Regulations for the Management, Use, Inspection and Maintenance of Hand-held Power Tools" formulated in 1983 stipulates that hand-held power tools must use leakage protectors. The "Safety Technical Code" stipulates that electrical construction machinery and hand-held power tools must be equipped with leakage protectors, and require the implementation of secondary leakage protection including the main power leakage protection in the construction site.
First, when the power grid is grounded, the leakage protector operates normally. 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 that the neutral point of the power grid must be grounded, and most of the technical misunderstandings of the leakage protector are related to the neutral point grounding of the power grid. The support is subjected to phase voltage all the year round, so the support is broken down, forming a grid ground point, causing leakage and causing frequent operation of the leakage protector.
Secondly, 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, cause fire, but also increase the frequency of the leakage protector. Move.
Thirdly, because the neutral point is grounded, when a person gets an electric shock, it will immediately produce a large electric shock current, which is very threatening to human life. Even if there is a leakage protector, it will be shocked first and then actuate Protection, if the action is slow or fails, the consequences will be more serious.
Fourth, because the neutral point is grounded, the grid-to-ground distributed capacitance is connected to the loop, which will increase the ground impulse current when the switch is closed and cause malfunction.
Fifth, since 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 the action and cause the series flow to malfunction.
It can be seen that there are technical errors in the leakage protector, and these technical errors are closely related to the grounding of the central point of the power grid. When using the leakage protector, the central point of the power grid must be grounded. It is impossible to solve the problem of frequent movement and refusal within the technical thinking of the device.
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.
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.
When electrical equipment leaks, it will present an abnormal current or voltage signal. The leakage protector detects and processes this abnormal current or voltage signal to prompt the actuator 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. Protective devices are used more and more widely. The current leakage protector is composed of four parts:
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 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 to be generated on N2, and this signal will be sent to the intermediate link for further processing.
Intermediate links: The intermediate links usually include amplifiers, comparators, and releases. When the intermediate links are electronic, the intermediate links will also need auxiliary power to provide the electronic circuit working place. Power required. 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.
Actuator: This structure is used to receive the instruction signal of the intermediate link, implement actions, and automatically cut off the power supply at the fault.
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.
Basic principle analysis
Before understanding the main principle of electric shock protector, it is necessary to understand what It was an electric shock. 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 figure is a schematic diagram of a simple leakage protection device. It can be seen from the figure that the leakage protection device is installed at the place where the power cord enters the house, that is, near the watt-hour meter, and connected to the output end of the watt-hour meter, that is, the user side. In the figure, all household appliances are replaced with a resistor RL, and RN is used to replace the body resistance of the contact person.
CT in the figure 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 open. The state; otherwise, it will be broken as soon as you let go.
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? It can be seen from the figure that if there is no electric shock, the current in the two wires from the power supply must be the same at all times, but 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 passing through 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 is energized, the hook is sucked off, and the DZ is switched on. Disconnect, 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.
1. It can be seen from the figure that when the circuit is working normally, the current theorem knows that the current flowing in and out of one end of the network is 0, so the sum of the current on the right side of the leakage protector should be 0 , That is, I1+I2+I3+IN=0; therefore, the leakage protector will not work. Note that the actual direction of the current depends on the actual circuit. In this example, the direction of IN is opposite to I1, I2, and I3.
2. When the device shell leaks and someone touches it, a part of the current IK will flow into the ground through the human body, so that the total current on the right side of the leakage protector is not 0, that is to say I1+ I2+I3+IN≠0, when the leakage current reaches the operating current of the leakage protector, the leakage protector will act to turn off the power supply, thus achieving the purpose of leakage protection.
Pay attention to the following two points
1. The neutral line passing through the leakage protector shall not be used as a protection line. From the above figure, it can be seen that when a leakage current is generated, the leakage current IK1 passes through the equipment shell. It flows back to the leakage protector. At this time, the sum of the current on the right side of the leakage protector is still 0, so the leakage protector will not operate, so the purpose of leakage protection is not achieved.
2. The working neutral wire passing through the leakage protector shall not be grounded repeatedly. As can be seen from the above figure, if the grounding is repeated, part of the current will be dissipated by the earth, which will cause the sum of the current on the right side of the leakage protector It is not 0, so that the leakage protector is turned off, and other electrical equipment cannot be used.
3. Description: This example diagram is only to explain the working principle of the leakage protector. How to connect the actual leakage protector should be determined according to the zero protection system used by the system.
Switch schematic diagram
In the figure, L is an electromagnet coil, which can drive the knife switch K1 to open when leakage occurs. Each bridge arm uses two 1N4007 in series to increase the withstand voltage. The resistance values of R3 and R4 are very large, so when K1 is closed, the current flowing through L is very small, which is not enough to cause K1 to disconnect. R3 and R4 are the voltage equalizing resistors of the SCR T1 and T2, which can reduce the voltage resistance requirements of the SCR. K2 is a test button, which simulates leakage. Press the test button K2, K2 is connected, which is equivalent to the leakage of the external live wire to the ground. In this way, the vector sum of the current through the three-phase power line and the neutral line of the magnetic ring is not zero. There is an induced voltage output at both ends of b, and this voltage immediately triggers T2 to turn on. Because C2 has a certain voltage in advance, after T2 is turned on, C2 is discharged through R6, R5, and T2, so that a voltage is generated on R5 to trigger T1 to turn on. After T1 and T2 are turned on, the current flowing through L increases, which causes the electromagnet to act, and the drive switch K1 is turned off. The function of the test button is to check whether the function of the device is intact at any time. The principle of electromagnet action caused by electric equipment leakage is the same. R1 is a varistor, which plays a role of overvoltage protection.
The circuit breaker has simple principles, few parts, and easy maintenance. When replacing parts, pay attention to the reliability and parameters of the parts to meet the requirements.
In 1992, the national standard GB13955-1992 "Installation and Operation of Earth Leakage Protectors" issued by the State Bureau of Technical Supervision made uniform provisions for the installation of leakage protectors in urban and rural areas across the country .
2.1 Equipment and places where leakage protectors (leakage switches) must be installed
(1) Class I mobile electrical equipment and hand-held power tools (Class I electrical products, That is, the protection against electric shock of the product not only relies on the basic insulation of the equipment, but also includes additional safety precautions, such as the product shell grounding);
(2) Installed in damp, highly corrosive and other harsh places Electrical equipment;
(3) Electrical construction machinery and equipment on construction sites;
(4) Temporary electrical equipment for temporary use of electricity;
(5) ) Socket circuits in guest rooms of hotels, restaurants and guest houses;
(6) Socket circuits in institutions, schools, enterprises, residential buildings and other buildings;
(7) Swimming pools, fountains , Water lighting equipment in baths;
(8) power supply lines and equipment installed in the water;
(9) electrical medical equipment directly in contact with the human body in hospitals;
(10) Other places where a leakage protector needs to be installed.
2.2 Application of alarm-type leakage protector
Once leakage occurs and cut off the power supply, electrical installations or places that will cause accidents or major economic losses should be installed with alarm-type leakage protectors , Such as:
(1) Channel lighting and emergency lighting in public places;
(2) Fire-fighting elevators and equipment to ensure safety in public places;
(3) Power supply for fire-fighting equipment, such as fire alarm devices, fire-fighting water pumps, fire-fighting passage lighting, etc.;
(4) Power supply for anti-theft alarm;
(5) Other special equipment and places where power failure is not allowed.
The leakage protector is installed at the outlet of the branch circuit, and the leakage protection socket is installed at each end of the electrical appliance, which is a terminal installation. Installation and maintenance are more convenient.
2, the difference when leakage occurs
When the line leakage, because it is installed at the exit of the branch line, the terminal failure will cause the entire branch to be powered off and there is no electricity in the house, and leakage Protect the socket. When there is electricity leakage in the branch or line, only the single branch line is not energized, and the electrical appliance cannot work.
3. The difference of wiring protection
The leakage protector has only live line protection, while the leakage protection socket has live line and neutral line protection.
4. The difference between leakage current and leakage trip time:
Leakage protector: I△n=30mA, action time 0.1S, leakage protection socket: I△n=6mA, The action time is 0.025S. Leakage protection socket, the rated residual leakage current is smaller, safer, less harmful to the human body, and quick tripping. Protect human life and property safety.
Its applicable scope is AC 50HZ rated voltage 380V, rated current to 250A.
The installation of a leakage protector in the low-voltage power distribution system is one of the effective measures to prevent personal electric shock accidents, and it is also a technical measure to prevent electrical fires and electrical equipment damage accidents caused by electrical leakage. However, the installation of a leakage protector does not mean absolute safety. During operation, prevention should be given priority, and other technical measures to prevent electric shock and damage to electrical equipment should be taken at the same time.
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 "Leakage A series of standards and regulations such as the installation and operation of protectors (GB13955-92).
According to these standards and regulations, we should follow the following main principles when choosing a leakage protector:
1. Qualified manufacturer's products, and the product quality inspection is 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 Code for Safety of Temporary Use of Electricity at Construction Sites" (JGJ46-88).
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 operations in machinery processing, metallurgy, textiles, 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.
The main operating performance parameters are: rated leakage operating current, rated leakage operating time, and rated leakage non-operating current. Other parameters include: power frequency, rated voltage, rated current, etc.
①Rated leakage operating current
Under the specified conditions, the current value that causes the leakage protector to operate. For example, a 30mA protector, when the current value reaches 30mA, the protector will act to disconnect the power supply.
②Rated leakage action time
refers to the time from when the rated leakage action current is suddenly applied to the time the protection circuit is cut off. For example, for a 30mA×0.1s protector, the time from the current value reaching 30mA to the separation of the main contact does not exceed 0.1s.
③Rated non-operating leakage current
Under the specified conditions, the current value of the non-operating leakage protector should generally be one-half of the leakage operating current value. For example, a leakage protector with a leakage action current of 30mA, when the current value reaches 15mA or less, the protector should not operate. Otherwise, it may malfunction due to too high sensitivity and affect the normal operation of electrical equipment.
④Other parameters such as: power frequency, rated voltage, rated current, etc., when selecting a leakage protector, it should be compatible with the circuit and electrical equipment used. The working voltage of the leakage protector should adapt to the rated voltage of the normal fluctuation range of the power grid. If the fluctuation is too large, it will affect the normal operation of the protector, especially for electronic products. When the power supply voltage is lower than the rated working voltage of the protector, it will refuse to operate. The rated working current of the leakage protector should also be consistent with the actual current in the loop. If the actual working current is greater than the rated current of the protector, it will cause overload and cause the protector to malfunction.
It is very important to select the rated leakage current of the leakage protector correctly and reasonably: on the one hand, when an electric shock occurs or the leakage current exceeds the allowable value, the leakage protector can be selected Ground action; on the other hand, the leakage protector should not operate under the action of normal leakage current to prevent the interruption of power supply and cause unnecessary economic losses.
The rated leakage operating current of the leakage protector should meet the following three conditions:
(1) In order to ensure personal safety, the rated leakage operating current should not be greater than the human safety current value. It is recognized that no higher than 30 mA is a safe current value for the human body;
(2) In order to ensure the reliable operation of the power grid, the rated leakage action current should avoid the normal leakage current of the low-voltage power grid;
(3) In order to ensure the selectivity of multi-level protection, the rated leakage current of the next level should be less than the rated leakage current of the previous level, and the rated leakage current of each level should have a level difference of 112 to 215 times.
The first-level leakage protector is installed at the outlet of the low-voltage side of the distribution transformer.
The line of this level of protection is long and the leakage current is large. The rated leakage action current shall not exceed 100mA without perfect multi-level protection; when it has perfect multi-level protection, the leakage current is small. For power grids, 75mA in non-rainy seasons and 200mA in rainy seasons. For grids with larger leakage currents, it is 100 mA in non-rainy seasons and 300mA in rainy seasons.
The second-level leakage protector is installed at the exit of the branch circuit. The protected circuit is short, the power consumption is not large, and the leakage current is small. The rated leakage current of the leakage protector should be between the rated leakage current of the upper and lower level protectors, generally 30～75 mA.
The third-level leakage protector is used to protect single or multiple electrical equipment. It is a protective equipment to directly prevent personal electric shock. The power consumption of the protected circuit and equipment is small, and the leakage current is small, generally not exceeding 10mA. A leakage protector with a rated operating current of 30 mA and an operating time of less than 0.1 s should be selected.
TN system means that the low-voltage neutral point of the distribution network is directly grounded, and the exposed conductive part of the electrical equipment is connected to the grounding point through the protective wire.
TN system can be divided into:
TN-S system The neutral line and the protection line of the whole system are separated.
TN-C system The neutral line and the protection line of the entire system are integrated.
The first part of the protection line and the neutral line of the TN-C-S system trunk line are shared, and the latter part is separate.
Phase line (English LIVE) L is generally red or brown (IEC system) or black (UL system)
Neutral line (English NEUTRAL) N (neutral line) general Blue (IEC system) or white (UL system)
Earth wire (English EARTH) E Generally yellow or yellow-green
Operation and maintenance
Except In addition to the conventional electrical equipment installation regulations, the following points should be noted:
1. The 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.
Instructions for use
(1) The leakage protector is suitable for low-voltage power distribution systems where the neutral point of the power supply is directly grounded or grounded through resistance and reactance. For systems where the neutral point of the power supply is not grounded, leakage protectors should not be used. Because the latter cannot constitute a leakage electrical circuit, even if a ground fault occurs and a rated operating current greater than or equal to the leakage protector is generated, the protector cannot act in time to cut off the power circuit; or rely on the human body to connect to the fault point to form a leakage electrical circuit. The circuit prompts the action of the leakage protector and cuts off the power circuit. However, this is still not safe for the human body.显而易见，必须具备接地装置的条件，电气设备发生漏电时，且漏电电流达到动作电流时，就能在0.1 秒内立即跳闸，切断了电源主回路。
(2) 漏电保护器保护线路的工作中性线N 要通过零序电流互感器。否则，在接通后，就会有一个不平衡电流使漏电保护器产生误动作。
(3) 接零保护线(PE) 不准通过零序电流互感器。因为保护线路(PE) 通过零序电流互感器时，漏电电流经PE 保护线又回穿过零序电流互感器，导致电流抵消，而互感器上检测不出漏电电流值。在出现故障时，造成漏电保护器不动作，起不到保护作用。
(5) 漏电保护器后面的工作中性线N 与保护线(PE) 不能合并为一体。如果二者合并为一体时，当出现漏电故障或人体触电时，漏电电流经由电流互感器回流，结果又雷同于情况(3) ，造成漏电保护器拒绝动作。