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1. According to the "Technical Standard for Grounded Short-Circuiting Grounding Cables" (SD332-1989) and the "Preventive Testing Regulations for Power Safety Industrial Devices" of the State Power Corporation (implemented on November 7, 2002), the portable short-circuit grounding in use The periodic test items and cycles of the line shall comply with:
(1) DC resistance test of group grounding wire, five-year test. Measure the DC resistance between each wire nose. According to different sections, the average resistance per meter should be less than the specified value. Through tests, it can be checked whether the contact between the wire nose and clamp and the copper wire is good.
(2) Power frequency withstand voltage test for grounding insulation rods, one test per year. The test voltage is added between the guard ring and the fastening head, and the rated voltage test and the power frequency withstand voltage test are performed respectively.
(3) The test items, cycle, and requirements for the personal protective grounding wire are basically the same as the portable short-circuiting ground wire. Group DC resistance test, a five-year test, DC resistance measured between the nose, and the average resistance value per meter meet the requirements.
2. The use of unqualified portable short-circuit grounding wire (1) Partially short-circuited grounding wiring lug cross section is too small, there is no limit stop limit design, loose joints, it is difficult to ensure a reliable connection;
(2) multiple strands of flexible wire without sheath;
(3) The length of the grounding pole is not enough;
(4) The individual clips are damaged, and many of the products are the ground wires that the former Ministry of Electric Power had reported to the disabled manufacturers in the country;
(5) Clips are mounted with spring clips;
(6) Workers make their own ground wire. Self-made ground wire, most of the rough process does not meet the requirements. For example, there is no limiting groove at the connection between the grounding wire clamp and the braided copper wire ear, and there is no loosening prevention device with a single bolt connection. Loosening occurs after several uses. The ground wire and lug parts are rough, and the middle of the clamp plane is convex, and the connection with the lugs is very poor.
Therefore, it is suggested that the portable short-circuit grounding wire in use should be in accordance with the Technical Standard for Portable Short-Circuit Grounding Wire (SD332-1989) and the Preventive Test Regulations for Power Safety Industrial Devices issued by the State Power Corporation (January 7, 2002). Day implementation) Make a full inspection. The unqualified grounding wire cannot be used. Contact with the manufacturer to prevent loosening of the ear wire, which can be changed to a limited-position grooved structure. Bare copper wire conductors must be insulated. The lug ear contact surface must be flat to ensure good contact. Spring clamps should not be used. It is recommended to use bolted clamps instead. Article 37 of the "Safety Production Act" stipulates that production and business units must provide employees with labor protection articles that conform to national standards or industry standards and supervise and educate employees to wear them in accordance with the rules of use. The portable short-circuit grounding wire should be selected by the Ministry of Economics, the provincial appraisal or the product identified by the accreditation body of the national technical supervision department. The multi-business division of the power company shall also distribute products that have passed the accreditation.
3. Short-time work does not use short-circuit grounding wire to check the task and contents of the team work ticket. Check the corresponding grounding wire use registration book and find that some units did not use the portable short-circuit grounding wire during short-term maintenance work. Some work tickets say that there is a grounding wire to be installed but it is not actually installed. In many cases, the team operators believe that short-term work on power-off equipment will not have electricity. This is a kind of chance, especially when the duration of continuous work is relatively short. This phenomenon is more common. To this end, it is recommended that strict implementation of the "Safety Regulations" stipulates that installing grounding wires will increase a lot of work, but it will play a crucial role in preventing sudden calls and protecting the personal safety of workers. Work on all or part of equipment that is outage, power outage, inspection of electricity, installation of grounding wire are three important technical measures to ensure the safety of operators, and installing grounding wire is the most direct and reliable and last checkpoint to ensure personal safety. . Take the repair of power lines as an example. Although the equipment has been powered off, there are still several types of equipment that may cause the equipment to be charged at any time:
1) Misfeeds to the power line due to misoperation;
2) User-provided power plant misdirects the system to reverse power transmission;
3) The dual power supply user fails to transmit power to the line through the backup power supply due to the failure of the locking device;
4) Temporarily external low-voltage power supply mistakenly transmits power to the high-voltage side through the transformer;
5) Voltage transformer reverse power transmission to power failure equipment;
6) Possible direct contact between crossed crossover and live wire;
7) Inductive power caused by crossover or parallel lines;
8) Lines that have been damaged due to lightning strikes on power outage lines.
From this, it can be seen that despite the short duration of short-term work, once you make a call, there is no guarantee of personal safety. You should fundamentally solve ideological and cognitive problems. Do not take life safety as a bet for fear of trouble.
4. The storage and storage of the portable short-circuit grounding cable is not standardized The portable short-circuiting grounding cable of some units has not been implemented in the storage and storage of the counter-seat type, but a large bundle is stored on the tool cabinet. Some units are stacked on the corner of the high-pressure indoor wall, and the sheath is worn away near the wire ear, and the copper strand is damaged. Some were hung on the damp walls of the high-voltage room and factory power room, and they were numbered on the wall, but the grounding line itself was not numbered. The low-voltage grounding line is duplicated with the 10kV, 110kV, 220kV grounding lines. Both are the same number and are easily confused. To this end, it is recommended that the portable short-circuit ground wire should be placed in a specially designed safety equipment room. Experience has shown that the registration and storage of the counter seat is not just a form, but a good way to start preparations and finish the work, and more importantly, it is convenient to check the condition of the grounding line and prevent the unsuitable grounding line from being used. Or the grounding wire is removed after the work is completed. Therefore, it is worthwhile to promote the registration of seated seats. Insulation tools should be moved from a humid place to a dry, ventilated, moisture-proof device. No two sets of ground wires with the same number should appear in the same plant.
Many units also posted a list of the ground wires of their own unit or department at the place where the ground wire was stored. The numbers, voltage levels, lengths, cross-sections, test dates, and management departments were marked on them.
5. There is no option to calculate the cross-sectional area of ​​the short-circuit grounding cross-sectional area of ​​the short-circuit grounding cable. Many units are convenient for the purchase and the convenience of the staff. The 25mm2 cross-section grounding wire is not used according to the system specific conditions. This practice does not meet industry standards. Through the investigation of on-site operations personnel, it is generally believed that as long as the grounding wire is installed and the three-phase short-circuit grounding is secure, personal safety can be guaranteed. This is an incorrect understanding. A grounding line with a small cross-sectional area cannot pass a fault current. Using a ground wire with a uniform cross-section specification indicates that the fault current value and the current value that the grounding device can withstand cannot be correctly understood. Therefore, it is suggested that the cross-sectional area of ​​the portable short-circuit grounding wire should be selected according to the short-circuit current that is subject to the "Technical Standard for Portable Short-circuit Grounding Wires" (SD332-1989), that is, the temporary grounding wire for local wire-suspended points should be cut. The area is calculated and approved so that the temporary grounding line can not be blown in the case of a sudden incoming call to ensure the safety of the operator. Near the ground point of the power supply end, due to the large short-circuit current, the cross-section of the combined portable short-circuiting grounding wire used is too large. When the grounding operation is inconvenient, separate grounding wires can be used for grounding, and each phase of the iron tower is individually grounded. When the area of ​​each phase-to-ground grounding cable is too large, the difficulty of operation is increased. Two or more parallel bundles of soft copper and multiple strands can also be used, but the cross-sectional area should be able to meet the protective grounding after the verification calculation. Line section requirements.
The selection of the portable short-circuit ground wire cross-section can be calculated by the following simplified formula:
S ≥ Ik / C in the S - portable grounding line selection cross section; Ik - flow through the ground wire of the three-phase short-circuit current stability value; C - ground wire selection of material stability factor, copper take 264; t - corresponding The relay protection operation time (s) taken by Ik. We recommend using the main protection action time.
Portable short-circuit ground wire comprehensive knowledge
There is no periodical test of the portable short-circuit grounding wire used on the field. The grounding wire used in the short-circuited field has not been tested regularly. Some units have used the grounding wire for ten years and eight years. The terminals have loosened each other. The grounding insulated operating rod is never subjected to a withstand voltage test. For some suggestions: