Abstract: According to the actual characteristics of our plant, the actual situation, size and characteristics of the geological environment and the operation and maintenance, introduce a ground or zero protection, leakage protection three kinds of leakage protection, the principle of leakage protection, classification, glue stick selection of installation principles and operation of common failures do occur in depth.
Key words: electrical equipment grounding, then the principle of zero leakage protection and run.
First, the need for installation of earth leakage protection. Ground protection, also known as protective ground (safety ground), is the metal casing of electrical equipment connected with the grounding, damage to the insulation of electrical equipment when live shell into the earth fault current directly,glue gun avoiding operator contact with the equipment enclosure and electric shock. Leakage protection is a lethal electric shock to provide indirect contact protection, the leakage current due to or arising out of the neutral point voltage variation of ground motion signals, so do the electric current value setting the action value, the sensitivity high, action is able to effectively cut off the power to protect the personal safety.
Second, the protection of ground and then zero. Construction Site Power ground and then taken to approach zero, and on-site power supply: (a) the neutral point indirectly grounded low-voltage grid, low-voltage electrical installations should be grounded protection. (B) in the neutral ground of the low-voltage power grid directly, then low-voltage electrical installations should be zero protection, and sometimes directly in the neutral point grounded three-phase four-wire TN-C power supply network, do protect the neutral ground PEN repeat enclosure to reduce the leakage to ground voltage; reduce the disruption caused by the neutral line of electric shock hazards; protection of the neutral cross-section of not less than 50% of the phase line section, and as far as possible with the same phase. (C) using a dedicated low-voltage power supply transformer, the electrical installations should be directly grounded neutral three-phase five-wire system (TN-S) protect access to zero system - metal casing of electrical equipment must be zero for the protection of line (PE) and reliable connection; for the protection of the work should be ground zero line, power distribution unit (box-type transformer) of the zero line or first-level supply side leakage protection leads to the zero line. (D) protection of ground and then the principle of zero. 1, the protective grounding principles. In ungrounded low-voltage systems, electrical building needs under normal circumstances, the various electrical devices do not live exposed parts of metal, power supply to the equipment enclosure should be grounded (special exceptions). (1) motors, transformers, portable or mobile electrical equipment of the metal base and shell. (2) transmission of electrical equipment. (3) distribution, control, protection of the screen (cabinet, box iron system distribution box), and welding, welder operating platform of the metal frame and base. (4) gasoline, diesel, engine oil tank shell. (5) 20m above the shaft frame (such as chimney construction of the central mast, electric mention / L-mode device) scaffolding, construction tower crane with the lifting arms folded, curved elevator track. (6) installed in the power line towers on the electrical equipment enclosure and bracket. (7) Crane (electric hoist, gantry crane, DBQ series of tower crane, etc.) 2 points for each track should be set to ground. Between the joints in the track, should make electrical connections; grounding resistance should be less than 4Ω. Connector with ground when the slip, slide connector and the sliding rail or ground wire should be reliable connection. Crane driver's cab and body with a screw connection, the electrical jumper should be, its not less than two cross joints: jumper should adopt the multi-strand copper wire, cross-sectional area of not less than 16mm2, both ends of the crimp terminal should be galvanized screw fixation; when using round or flat steel span, the bar diameter of not less than 12mm, the width and thickness of the flat section of not less than 40mm, 4mm.
2, the principle of protecting access to zero. (1) Under normal circumstances, the construction site of the following electrical equipment is not charged exposed conductive parts should be done to protect access to zero. ① motors, transformers, lighting, appliances, hand-held power tools, metal housing. ② transmission of electrical equipment metal parts. ③ distribution panel and control panel of the metal frame. ④ indoor and outdoor distribution equipment near live parts of the metal frame and metal fences and metal doors. ⑤ power lines of the metal protective tube and wrap wire cable, crane rail sliding metal platform such as a template. ⑥ installed in the power pole line switches, capacitors and other electrical equipment and metal stents. ⑦ bad environment or humid places (such as the boiler room, dining room, basement and bathroom, cable tunnel) of the electrical equipment must be used to protect access to zero.
(2) Note. Zero line in the laying of protection, the protection of the zero line should be a separate installation, not to use it; protection of the zero line switch or fuse shall not be installed. Especially in the construction of electricity lines and the foreign share of electricity supply systems, electrical equipment should be based on the requirements of the local power company or the protection of access used to protect ground zero; in by the same generator, the same transformer or the same bus-powered low-voltage power network , should not also use ground protection and access to zero protection.
Fourth, leakage protection installation and use. Residual current operated protective device referred to as leakage protection, also known as leakage protection switches, mainly used in the device causes a short circuit failure and the risk of fatal electric shock to protect the body. (A) the principle of leakage protection. Leakage protection system is the use of residual current response and action, the normal operation of the system of residual current is almost zero, so it moves tuning setting value can be very small (usually mA level), personal electric shock occurs when the system or equipment enclosure When charged, a larger residual current leakage protection is by detecting and dealing with this residual current is reliably move, cut off the power. (B) the classification of leakage protection. Leakage protection to its protective function, structure, installation, operation mode, the number of poles and lines, action, sensitivity, etc. and this is mainly classified according to their protection and use of the narrative, is generally divided into leakage protection relays, earth leakage protection switching and leakage protection socket three. (C) the selection principle of leakage protection. 1. Buy leakage protection when purchased with the production of qualified product manufacturers and product quality inspection. 2. Should be based on the scope of protection, personal equipment, safety and environmental requirements to determine the power leakage protection voltage, current, leakage current and the number of action time. 3. The power to do with parental leakage protection, should meet, the lower switching selectivity. Level of leakage protection generally rated leakage current of not less than the rated level of leakage protection leakage current, both to protect sensitive personal and equipment safety, but also to avoid the grade trip, check the narrow scope of the accident. 4. Hand-held power tools (except for outside of class III), mobile consumer electronics devices used in daily life (except for outside of class III), other mobile electrical and mechanical equipment, and more dangerous electrical shock electrical equipment must be installed leakage protection. 5. Building construction sites, temporary line of electrical equipment should be installed leakage protection. This is the "construction site temporary electrical safety specifications" (JGJ46-88) clearly required. 6. Offices, schools, businesses, residential buildings in the outlet circuit, hotels, restaurants and guest rooms outlet circuit, leakage protection must also be installed. 7. Installed in water supply lines and equipment, and moisture, heat, metals and other conductive occupy a larger coefficient of good places, such as mechanical processing, metallurgy, textile, electronics, food processing industries in the workplaces and the boiler room, pump room, dining room, bathroom, hospitals and other places, must be used to protect leakage protection. 8. Fixed-line production of electrical equipment and the normal work site should be used with leakage protection of power distribution box. Temporary use of small electrical equipment should be used in leakage protection plug (Block) or with leakage protection socket box. 9. Leakage protection as a direct contact protection when the supplementary protection (not as the only direct contact protection) should be used in high sensitivity, rapid action leakage protector. Select action current general environment does not exceed 30mA, operating time less than 0.1s., These two parameters to ensure that if an electric shock when the body does not produce the electric shock by pathologic effects of biological risk. In the bathroom, swimming pool and other places leakage protection should not exceed the rated operating current 10mA. After the electric shock accident may result in secondary cases, should be used for the rated operating current 6mA of leakage protection. 10. The power of the electrical equipment is not allowed, such as public places, the channel lighting, emergency lighting, fire equipment, power supply, power supply for the anti-theft alarm, the alarm should be used in leakage protection device connected sound, light alarm signal to inform timely processing of management failure.
Jizhong Energy Group Hebei peak peak Security Management Coking Co., Ltd. (Hebei Handan) Huangyan Hai.