Device selection
There are many factors to consider when selecting a leakage protection device. Among them, the first is to correctly select the leakage action current of the leakage protection device.
In bathrooms, swimming pools, tunnels and other places with high risk of electric shock, a high-sensitivity, fast-type leakage protection device should be selected (the operating current should not exceed 10mA). If there is an electric shock accident in the installation site, other people can help to disconnect from the power source in time, the action current of the leakage protection device can be greater than the escape current; if it is a fast protection device, the action current can be selected according to the ventricular fibrillation current. If it is the pre-protection, that is, the total protection in front of the sub-protection, the action current can exceed the ventricular fibrillation current.
If the workplace cannot get the help of others to disconnect from the power source in time, the operating current of the leakage protection device should not exceed the release current. In occasions that may lead to a serious secondary accident after an electric shock, a fast leakage protection device with an operating current of 6 mA should be selected. In order to protect children or patients, a fast leakage protection device with an operating current of less than 10mA should also be used. For Class I hand-held electric tools, a fast-type leakage protection device with an operating current of 10 to 30 mA should be installed according to the degree of risk in the workplace. When selecting the operating current, the possibility of malfunction should also be considered. The protector should be able to avoid the unbalanced leakage current of the line without action; it should also be able to not malfunction under the electromagnetic interference that may occur at the installation position. The actual conditions of the protector manufacturing should also be considered when selecting the operating current.
The leakage alarm device used to prevent leakage fire should adopt the medium sensitivity leakage protection device. The operating current can be selected from 25 to 1000mA.
Electrical equipment connected to outdoor overhead lines should be equipped with impulse voltage non-operating leakage protection devices.
For the motor, the protector should be able to avoid the starting leakage current of the motor (100kW motor can reach 15mA) without action. The protector should have good balance characteristics to avoid malfunctioning under the impact of a locked-rotor current several times the rated current. For motors that are not allowed to stop, the leakage alarm method should be used instead of the leakage cut-off method.
For lighting circuits, it is advisable to adopt a hierarchical protection method according to the size and distribution of the leakage current. Use high-sensitivity protectors for branch lines and medium-sensitivity protectors for trunk lines.
In construction sites, metal structures and other occasions with high risk of electric shock, Class I portable equipment or mobile equipment should be equipped with high-sensitivity leakage protection devices.
The insulation resistance of electric heating equipment fluctuates in a wide range with temperature changes. For example, the insulation resistance of polyethylene insulating material at 60 ℃ is only one-tenth of that at 20 ℃. Therefore, the operating current of the protector should be selected according to the thermal leakage condition.
For the welding machine, it should be considered that the normal operation of the protector is not affected by the short-term impulse current of the electric welding, the rapid change of the current, and the fluctuation of the power supply voltage. For high-frequency welding machines, the protector should also have good anti-electromagnetic interference performance.
For equipment with non-linear parts that generate high-order harmonics and for equipment with rectifying parts, a protector with a filter capacitor connected to the secondary side of a zero-sequence current transformer should be used, and the transformer core should be selected Made of soft magnetic material with low remanence.
The number of poles of the leakage protection device should be selected according to the characteristics of the circuit. Two-pole protectors are used for single-phase lines, three-pole protectors can be used for only three-phase lines or three-phase equipment with three-phase loads, and four-pole protectors must be used for three-phase four-wire lines and three-phase lighting lines that are used for power and lighting. .
The performance indicators such as the rated voltage, rated current, and breaking capacity of the leakage switch should be adapted to the line conditions. The type of leakage protection device is compatible with the power supply line, power supply mode, system grounding type and characteristics of electrical equipment.
Device installation
The protection type and installation method of the leakage protection device should be compatible with the environmental conditions and use conditions. Class I mobile electrical equipment and hand-held power tools with metal shells, electrical equipment installed in harsh places such as damp or strong corrosion, electrical construction machinery and equipment at construction sites, temporary electrical equipment, sockets in guest rooms of hotels, Sockets in civil buildings with greater risk of electric shock, underwater lighting equipment in swimming pools or baths, power supply lines and electrical equipment installed in the water, and electrical medical equipment in hospitals that directly contact the human body (except for thoracic surgery rooms), etc. All leakage protection devices should be installed.
For aisle lighting power supply and emergency lighting power supply in public places, fire-fighting elevators and electrical equipment to ensure safety in public places, power supplies for fire-fighting equipment (such as fire alarm devices, fire-fighting water pumps, fire-fighting passage lighting, etc.) ), the power supply used for anti-theft alarm, and the power supply of other places or electrical devices that do not allow sudden power outages. If the power supply is cut off immediately when the power leaks, it will cause accidents or major economic losses. In these cases, a leakage alarm device that does not cut off the power supply should be installed.
From the perspective of preventing electric shock, electrical equipment using safe voltage power supply, electrical equipment with double insulation or reinforced insulation structure used under general environmental conditions, electrical equipment using isolation transformer power supply, Electrical equipment used in places with grounded local equipotential bonding measures, and other electrical equipment that does not have a risk of leakage or electric shock, may not be equipped with leakage protection devices.
The installation of the leakage protection device should meet the requirements of the manufacturer's product manual.
The leakage current of electrical circuits and equipment equipped with leakage protection devices must be controlled within the allowable range. The rated non-operating current of the selected leakage protection device should not be less than 2 times the maximum value of the normal leakage current of the electrical circuit and equipment. When the leakage current of the electrical circuit or equipment is greater than the allowable value, the electrical circuit or equipment with good insulation must be replaced. When the electrical equipment is equipped with a highly sensitive leakage protection device, the grounding resistance of the separate grounding device of the electrical equipment can be appropriately relaxed, but the expected contact voltage should be restricted within the allowable range. The insulation resistance of motors and other electrical equipment installed with leakage protection devices during normal operation shall not be less than 0.5M Ω.
Before installing the leakage protection device, carefully check whether the enclosure, nameplate, wiring terminal, test button, certificate, etc. are intact.
The leakage protection device used to prevent electric shock accidents can only be used as additional protection. The original safety protection measures shall not be cancelled or abandoned while the leakage protection device is installed.
When installing a leakage switch with short-circuit protection, you must ensure that there is enough arcing distance in the arc spray direction. The leakage protection device should not be installed in a location with high mechanical vibration or strong alternating magnetic field. The installation of leakage protection devices should take into account the hazards of water, dust and other factors, and take necessary protective measures.
After installing the leakage protection device, in principle, the basic anti-shock measures for low-voltage power supply lines and electrical equipment cannot be removed, but only appropriate adjustments within a certain range are allowed.
Operation 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 truly plays a protective role. The management work mainly includes the following aspects:
1. After the leakage protection switch is put into operation, it should consciously establish operation records and improve the corresponding management system;
2, the leakage protection switch After being put into operation, when the power is on, the test button must be pressed once or twice a month to check whether the leakage protection switch is normal and reliable, especially in the thunderstorm season, the number of tests should be increased;
3. Regular analysis The operating conditions of the leakage protection switch, timely replacement of the faulty leakage protection switch;
4. The maintenance of the leakage protection switch should be carried out by professionals. If there is an abnormal phenomenon during operation, an electrician should be dealt with to avoid enlarged accidents. Scope;
5. After the leakage protection switch is activated by thunderstorm or other unknown reasons, it should be checked and analyzed;
6. After the leakage protection switch is activated, the cause of the accident is not found after inspection , It is allowed to try to close once, if it is operated again, the cause should be found out, the fault should be found, and the action characteristic test should be carried out if necessary, and the power should not be continuously forcibly supplied. Unless it is confirmed that the leakage protection switch itself is faulty, it is strictly prohibited. Remove the leakage protection switch and force the power supply;
7. Before using the leakage protection switch that has been out of operation, perform the action characteristic test according to the items specified by the relevant department;
8. Leakage protection The operating characteristics of the switch are set by the manufacturer and used according to the product manual. It should not be changed at will during use; 9. After an accidental electric shock accident occurs within the protection range of the leakage protection switch, the leakage protection switch should be checked. The operation situation, analyze the reasons for failure to protect, and protect the site before investigating, and do not disassemble the leakage protection switch;
10. To check the operation characteristics of the leakage protection switch in operation and Its changes should be tested regularly for operating characteristics. Characteristic test items include: test leakage current value, test leakage non-operation current value, test breaking time;
11. When performing the operation characteristic test of the leakage protection switch, the special test qualified by the relevant national departments should be used. For testing equipment, it is strictly forbidden to use the test method of the phase line to directly touch the grounding device;
12. The leakage protection switch used should be tested according to the leakage protection characteristics, and the circuit breaker should be in accordance with the relevant requirements of low-voltage electrical appliances. Regular inspection and maintenance.