Accurate Selection, Operation and Maintenance of Leakage Protection Switch for High and Low Temperature Humidity Test Chamber

Abstract: Leakage protection switching devices are people's more commonly used protection switches, which play a protective role in the safety of people and equipment. Therefore, the correct choice of leakage switch is very important. This article briefly describes the proper selection, daily maintenance and operation management of the leakage protection switch, and initially summarizes the operation and maintenance management measures for the leakage protection switch.

Keywords: leakage protection selection maintenance management

Leakage protection device is a kind of grounding protection device used to prevent accidents caused by human electric shock and leakage. When the leakage current of circuit or electricity equipment is greater than the setting value of the device or the risk of electric shock to people or animals, it can quickly act and cut off the accident. Power supply to prevent accidents from expanding to ensure the safety of people and equipment. Therefore, the correct selection, maintenance and management of the leakage protection switch are the main technologies and management measures for the safe use of electricity in rural areas.

First, the correct selection of leakage protection device

The selection of leakage protection device shall be determined according to the protection method of the system, the purpose of use, the installation site, the voltage level, the leakage current of the controlled circuit and the value of the grounding resistance of the electrical equipment.

1. According to the purpose of use, a leakage protection device for preventing personal electric shock accidents is generally selected according to two different requirements of direct contact protection and indirect contact protection, and there should be a difference in selecting the operating characteristics.
(1) Direct contact protection is to prevent electric shock accidents caused by direct contact with the human body and live conductors of electrical equipment. When the human body and live conductors are in direct contact, before the operation of the leakage protection device cuts off the power supply, the human body's electric shock current and current leakage protection The selection of the operating current of the device is irrelevant. It is entirely determined by the voltage and body resistance of the human body. The leakage protection device cannot limit the electric 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 have the inverse time characteristics specified by the IEC leakage protection device standards.

(2) Indirect contact protection is to prevent dangerous electrical contact voltages on exposed metal parts such as metal enclosures when electrical insulation is damaged. The selection of the operating current IΔn of the leakage protection switch shall be considered in conjunction with the grounding resistance R of the electrical equipment and the permissible contact voltage U. The contact voltage U on the electrical equipment shall be less than the specified value. Leakage protector operating current IΔn selection: IΔn ≤ U / R where: U - allow contact voltage R - contact resistance of the equipment is generally for fixed voltage rated 220V or 380V fixed electrical equipment, such as pumps Other electrical devices that are easily in contact with the human body, such as mills, can be used with a leakage protection device that can operate within 30s to 50 mA when the electrical equipment has a metal housing with a grounding resistance of 500 ohms or less; When the grounding resistance is less than 100Ω, a 200-500mA leakage protection device can be selected. For the more important electrical equipment, a time-delayed protection device with an operating current of 0.2s can be used to reduce the momentary power failure. Electrical equipment for household use often has plugs that are frequently plugged in and out, and at the same time, some residential houses do not consider grounding protection facilities. When electrical equipment is used to cause insulation faults such as leakage or shell leakage, the equipment enclosure may present a dangerous voltage that is the same as the operating voltage, and is prone to electrical shock and death. Therefore, the electrical equipment installation regulations stipulate that the electrical energy meter must be on the household entrance line. Later, install a high-sensitivity leakage protection switch with an operating current of 30mA and 0.1S.

2, according to the use of places to choose generally in the low-voltage 380/220V line, if the metal casing and other metal parts of electricity equipment is easily touched by people, at the same time these electrical equipment can not be in accordance with China's electricity regulations require its grounding resistance When it is less than 4Ω or 10Ω, it is advisable 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, it is also necessary to reasonably select the leakage switch of different operating current according to different use places. For example, in a wet work place, because the human body is more likely to sweat or wet, the skin's insulation performance is reduced, and the human body resistance is significantly reduced. When an electric shock accident occurs, the current through the human body is necessarily greater than that of a dry place. High, therefore, suitable for installation of 15 ~ 30mA, and can operate within the 0.1S leakage protection device.

3, according to the normal leakage current of the circuit and electrical equipment to choose

(1) The lower the operating current of the leakage protection device, the higher the sensitivity of the switch. However, with any power supply circuit and electrical equipment, the insulation resistance cannot be infinite, and there will always be some leakage current. Therefore, in terms of ensuring the stable operation of the circuit and providing uninterrupted power supply, the selection of the operating current of the leakage protection device is restricted by the normal leakage current of the circuit.
(2) Due to the measurement of current leakage currents, more complex test methods or special test equipment must be used for measurement. For ease of use, the following empirical formulas can be consulted: Single-phase circuits for lighting circuits and residential life: n≥IH/2000 For three-phase three-wire or three-phase four-wire power lines and power and lighting hybrid lines: I △ n ≥ IH/1000 where: I △ n - leakage protection switching device operating current IH - circuit The actual maximum supply current is generally for home power supply circuits. If users of 3A energy meters are used, the leakage current of each household is approximately 1mA under normal conditions. In principle, the leakage current in the home single-phase circuit exceeds 1/1 of the maximum supply current of the circuit. At 3000, the circuit should be overhauled.
(3) China's rural low-voltage power grids have low insulation levels and large leakage currents. According to the actual measurement results, the leakage current value is not significantly related to the size of the distribution transformer capacity, but it has a clear relationship with the number of households in the low-voltage power grid, that is, regardless of the transformer capacity, which supplies domestic electricity. 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-level protection, the action current of the next level of leakage protection should be less than the leakage current of the previous level, and the leakage current at all levels should have a level difference of 1.2 to 2.5 times. The first-stage leakage protection device shall be installed at the outgoing end of the main line of the low-voltage side of the distribution transformer. The line protected by this stage is long and the superposed leakage current is relatively large. The leakage current of the leakage current must not exceed 100mA in the case of unsatisfactory multistage protection. When perfecting multistage protection, the maximum leakage current of the leakage current must not exceed 300mA. The secondary leakage protection device shall be installed at the outlet end of each branch line. Since the protected line is short, the leakage current is relatively small, and the leakage action current should be between the leakage action currents of the upper and lower protection, generally taking 30 ~75mA. The third level leakage protection device (also known as the last stage protection) is used to protect the electrical equipment and personal safety, the protected circuit is short, the leakage current is small, generally not exceeding 10mA, the leakage current should be removed from the current value by human body's electric shock (10~ 20mA) selection, should not be greater than 30mA, generally take 15 ~ 30mA.

Second, the leakage protection switch into operation after the management

After the leakage protection switch is put into operation, effective management must be carried out to ensure that the leakage protection maintains a good operating state and really plays a protective role. Management work mainly includes the following aspects:

1. After the leakage protection switch is put into operation, it shall consciously establish an operation record and improve the corresponding management system;
2. After the leakage protection switch is put into operation, under the power-on state, the test button shall be pressed once or twice a month to check whether the leakage protection switch is normal and reliable, especially in the thunderstorm season;
3. Regularly analyze the operation of the leakage protection switch and replace the faulty leakage protection switch in time;
4. The maintenance of the leakage protection switch should be carried out by a professional.

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