The leakage protection device is a grounding protection device used to prevent accidents caused by electric shock and leakage. When the leakage current of the circuit or the electrical equipment is greater than the setting value of the device, or when the human or animal is in danger of electric shock, it can quickly move and cut off the accident. The power supply avoids the expansion of accidents and ensures the safety of people and equipment. Therefore, the correct selection and maintenance management of the leakage protection switch is the main technology and management measures for the safe use of electricity in rural areas. First, the selection of the leakage protection device for the correct selection of leakage protection device should be determined according to the protection mode of the system, the purpose of use, the installation location, the voltage level, the leakage current of the controlled circuit and the grounding resistance value of the electrical equipment. 1. Select the leakage protection device to prevent personal electric shock accident according to the purpose of use. Generally, it is selected according to two different requirements of direct contact protection and indirect contact protection. It should also be different when selecting the action characteristics. (1) Direct contact protection is an electric shock accident caused by direct contact between the human body and the live conductor of the electrical equipment. When the human body and the live conductor are in direct contact, the electric shock current and leakage protection of the human body are protected before the leakage protection device operates to cut off the power supply. The action current selection of the device is irrelevant. It is completely determined by the voltage of the human body and the body resistance. The leakage protection device cannot limit the electric shock current through the human body. Therefore, the leakage protection device for direct contact protection must have a fast action of less than 0.1S. Performance, or with inverse time characteristics specified by the IEC leakage protection device standard. (2) Indirect contact protection is to prevent dangerous electrical contact voltages from appearing on exposed metal parts such as metal casings when electrical equipment is damaged. The selection of the operating current IΔn of the leakage protection switch should be considered in connection with the grounding resistance R of the electrical equipment and the allowable contact voltage U. The contact voltage U on the electrical equipment is less than the specified value. Selection of the operating current I△n of the leakage protector: I△n≤U/R where: U——allowable contact voltage R——contact resistance of the equipment is generally for fixed electrical equipment with rated voltage of 220V or 380V, such as water pump Other electrical equipment that is easily in contact with the human body, such as a mill, when the grounding resistance of the metal casing of the electrical equipment is below 500 Ω, a leakage protection device that operates within 30 to 50 mA and within 0.1 s can be selected; when the metal casing of the electrical equipment is used When the grounding resistance is below 100Ω, 200~500mA leakage protection device can be selected. For more important electrical equipment, in order to reduce the instantaneous power failure, a time-delay protection device with an operating current of 0.2s can also be selected. Household electrical equipment often has plugs that are frequently inserted into and out of the box, and some residential buildings do not consider grounding protection facilities. When an electrical equipment has an insulation fault such as a leakage current, the equipment casing may present a dangerous voltage with the same working voltage, which is highly prone to electric shock and casualties. Therefore, the electrical equipment installation regulations stipulate that the electric energy meter must be in the household input line. Behind, install a highly sensitive leakage protection switch with an operating current of 30 mA and 0.1 S or less. 2. According to the place of use, it is generally selected in the low-voltage line of 380/220V. If the metal parts such as the metal casing of the electric equipment are easily touched by people, the electric equipment cannot be grounded according to the requirements of China's electricity regulations. When it is less than 4 Ω or 10 Ω, it is better to install the leakage protection device in the power supply circuit of the electrical equipment according to the requirements of indirect contact protection. At the same time, the leakage switch of different action currents should be reasonably selected according to different places of use. For example, in a wet workplace, because the human body is more likely to sweat or wet, the insulation performance of the skin is reduced, and the body resistance is significantly reduced. When an electric shock occurs, the current passing through the human body is inevitably larger than the dry place, and the danger is dangerous. High, therefore, it is suitable to install a leakage protection device that operates from 15 to 30 mA and can operate in 0.1S. 3. According to the normal leakage current of the circuit and the electrical equipment (1) The lower the operating current of the leakage protection device is selected, of course, the sensitivity of the switch can be improved. However, for any power supply circuit and electrical equipment, the insulation resistance cannot be infinite, and there will always be a certain leakage current. Therefore, in order to ensure the stable operation of the circuit and provide uninterrupted power supply, the operating current selection of the leakage protection device is subject to the normal leakage current of the circuit. (2) Due to the measurement of the leakage current of the current, it is necessary to have a more complicated test method or use special test equipment for measurement. For the convenience of selection, the following empirical formula can be referred to: single-phase circuit for lighting circuit and residential electricity: I△ n≥IH/2000 For three-phase three-wire or three-phase four-wire power line and power and lighting hybrid line: I△n≥IH/1000 Among them: I△n——Leakage protection switch device operating current IH——Circuit The actual maximum supply current is generally the household power supply circuit. If the user of the 3A energy meter is used, the leakage current of each household under normal conditions is about 1 mA. In principle, the leakage current in the household single-phase circuit exceeds 1/ of the maximum supply current of the circuit. At 3000 hours, the circuit should be repaired. (3) China's rural low-voltage power grid has a low insulation level and a large leakage current. According to the measured results, the relationship between the value of the leakage current and the capacity of the distribution transformer is not significant, but it has a significant relationship with the number of households living in the low-voltage power grid, that is, regardless of the capacity of the transformer, which supplies electricity for daily use. The more households there are, the greater the leakage current. Therefore, this should be taken into account when installing leakage switches in rural power grids. In general, in order to protect the reliable operation of the power grid and ensure the selectivity of multi-stage protection, the operating current of the next-stage leakage protection should be less than the current protection current of the first-level leakage protection. The leakage current of each stage should have a step difference of 1.2 to 2.5 times. The first-level leakage protection device shall be installed at the outlet end of the low-voltage main trunk line of the distribution transformer. The protection line of this stage is long and the superimposed leakage current is large. When the leakage current is not perfect multi-stage protection, the maximum leakage current should not exceed 100mA. When perfecting multi-level protection, the leakage current should not exceed 300mA. The second-stage leakage protection device should be installed at the outlet end of each branch line. Because the protected line is short, the leakage current is relatively small, and the leakage current should be between the leakage current of the upper and lower protection, generally 30 ~75mA. The third-level leakage protection device (also known as the last-level protection) is used to protect the electrical equipment and personal safety. The protected circuit is short, the leakage current is small, generally not exceeding 10 mA, and the leakage current should be free from the current value according to the human body shock (10~ 20mA) selection, should not be greater than 30mA, generally take 15 ~ 30mA. 2. After the leakage protection switch is put into operation, the management leakage protection switch must be effectively managed to ensure that the leakage protection maintains a good operating state and truly plays a protective role. The management work mainly has the following aspects: 1. After the leakage protection switch is put into operation, it should consciously establish the operation record and improve the corresponding management system; 2. After the leakage protection switch is put into operation, under the power-on state, it must be pressed every month. Test the button one to two times, check whether the leakage protection switch action is normal and reliable, especially in the thunderstorm season, increase the number of tests; 3. Regularly analyze the operation of the leakage protection switch, and replace the faulty leakage protection switch in time; 4. Leakage protection switch The maintenance should be carried out by professionals. If there is any abnormality in operation, it should be handled by an electrician to avoid expanding the scope of the accident. 5. After lightning storm or other unexplained reasons, the leakage protection switch should be checked and analyzed. 6. After the leakage protection switch is operated If the cause of the accident is not found after inspection, the test is allowed to be closed once. If it is operated again, the cause should be identified, the fault should be found, and the action characteristic test should be carried out if necessary. The power transmission must not be forced continuously, except that it is confirmed to be leakage protection. If the switch itself fails, it is strictly forbidden to remove the leakage protection switch forcibly sending power; 7. Exit Before the leakage protection switch of the line is used again, the action characteristic test shall be carried out according to the items specified by the relevant department; 8. The operation characteristics of the leakage protection switch shall be set by the manufacturer, and shall be used according to the product manual, and shall not be arbitrarily changed during use; After an accidental electric shock accident occurs within the protection range of the switch, the operation of the leakage protection switch should be checked, and the reason for the failure to protect the function should be analyzed. The site should be protected before the investigation, and the leakage protection switch must not be dismantled; Check the operating characteristics and changes of the leakage protection switch during operation, and perform the operational characteristic test regularly. The characteristic test items include: testing the leakage current value, testing the leakage current value, and testing the breaking time; 11. When the leakage protection switch performs the operation characteristic test, it should use the special test equipment that has passed the test of the relevant state departments, and it is strictly forbidden to use the phase line. Test method for directly touching the grounding device; 12. In addition to the periodic test of the leakage protection switch according to the leakage protection characteristics, the circuit breaker part shall be regularly inspected and maintained according to the relevant requirements of the low-voltage electrical equipment.
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