Live working mode and safety protection of the hot

2022-07-27
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Live working mode and safety protection of distribution lines (to be continued)

6 ~ 10 kV distribution network is a power infrastructure directly facing users. From the 1960s to the early 1980s, the live line operation of power distribution was popularized in China. However, due to many problems in the operation mode, safety protection tools, operation steps and backup safety protection, this operation was stopped in some areas. At present, in order to improve the reliability and economy of power distribution operation, all power supply units have attached great importance to the live working of power distribution. Many units have set up or reorganized work teams, and the live working of power distribution will face a new development period. In order to ensure the safety of live working personnel and equipment, it is necessary to conduct in-depth analysis and Research on the safe operation mode, human protective equipment and operation requirements of power distribution live working

1 live working mode of distribution lines

live working of distribution lines can be classified according to insulation mode or insulation tools used

1.1 classification by insulation method

1.1.1 indirect operation method

is an operation method with insulation tools as the main insulation and insulation wearers as the auxiliary insulation

this operation method refers to the method that the operator keeps a sufficient safe distance from the live body and works through insulated tools. Moreover, all parts of the human body are kept away from the electrified body and the grounding body through insulating protective appliances (insulating gloves, insulating clothes, insulating boots), and the human body is not at the ground potential. Therefore, this operation method should not be misnamed as the ground potential operation method

1.1.2 direct operation method

refers to the method in which the operator directly approaches the live body with the help of the insulating arm or insulating ladder of the aerial work vehicle, and all parts of the human body wear insulating protective equipment for direct operation. This operation method should not be called equipotential operation method in name, because when working with insulating gloves, human body and electrified body are not equipotential

in live line operation of distribution lines, whether direct operation method or indirect operation method is adopted, if it is divided according to the human potential of operators, it belongs to intermediate potential operation method

1.2 classification according to the insulation tools used

in the live line operation of distribution lines, the cycle is divided into two isothermal processes and two insulation processes according to the main insulation tools used. The frequently used operation methods are as follows:

1.2.1 operation method of insulating tools on poles

operators climb the poles to appropriate positions through pole climbing appliances (foot buttons, etc.), fasten safety belts, and maintain a safe distance corresponding to the system voltage, Then the insulated rod with different tool accessories at the end shall be used for operation. When this operation method is adopted, firstly, the longitudinal insulation protection between the level transfer electrified body and the ground is composed of insulating tools, insulating gloves and insulating boots, in which the insulating tools play the role of main insulation and the insulating boots and insulating gloves play the role of auxiliary insulation; The second is to use insulation shield and insulating clothing to form horizontal insulation protection between electrified bodies and people or between electrified bodies of different phases, so as to avoid phase to phase short circuit or phase to ground short circuit caused by excessive range of human action. The characteristic of this operation method is that it is not limited by traffic and terrain conditions, and can be operated at the pole position that cannot be reached by the high-altitude insulated bucket truck. However, the mobility, convenience and air operation range are not as good as those of insulated bucket trucks. The on-site monitoring and management personnel shall mainly monitor the safe distance between the human body and the electrified body and the minimum effective length of the insulating tools, and strictly check the electrical insulation strength and mechanical strength of the tools before operation

1.2.2 operation method of insulated platform

insulated platform is usually composed of insulated herringbone ladder, one legged ladder, insulated car body, etc. The operators can operate by indirect method through insulating tools or by direct method through insulating gloves. The insulating platform plays the main insulation role between the phase and the ground

either the indirect method or the direct operation method, generally, before the operation on the overhauled phase, insulation shielding and isolation tools shall be used to shield or isolate the electrified body of the adjacent phase. Meanwhile, operators shall wear a full set of insulation protective equipment. When working directly through insulating gloves, protective gloves against abrasion or puncture shall be put on the rubber insulating gloves

1.2.3 operation method of insulated bucket boom truck

the insulated bucket boom truck is used for live line operation, which has the advantages of convenient lifting, strong mobility, large operation range, high mechanical strength and good electrical insulation performance. Since the development of live working insulated bucket trucks in the 1930s in European and American countries, they have been widely used in live working of power transmission and distribution lines by the 1950s. The insulating arm of the insulated bucket truck is made of glass fiber reinforced epoxy resin material and wound into a cylindrical or rectangular cross-section structure. It has the advantages of light weight, high mechanical strength, good insulation performance and strong hydrophobicity. It provides relative insulation protection for the human body during live line operation. Some insulation buckets are single-layer buckets and some are double-layer buckets. The outer bucket is generally made of epoxy FRP, and the inner bucket is made of polytetrafluoroethylene. The insulating bucket shall have high-strength electrical insulation, and form the longitudinal insulation between the phase and the ground together with the insulating arm, so that the leakage current of the whole vehicle is less than 500. At the same time, during operation, if the insulating bucket touches two-phase conductors at the same time, surface flashover shall not occur

the positioning of the operation platform of the insulated boom truck is either directly operated by the operators in the upper platform of the insulated boom, controlled by the personnel on the lower bridge, or hydraulically controlled at the upper and lower parts of the operation truck. The operation platform has the functions of horizontal and vertical rotation, and can move horizontally or vertically parallel to wires or poles. The live line operation with overhead insulated bucket truck for power distribution is a convenient, flexible, widely used and low labor intensity operation method

2 characteristics of live working of power distribution

in live working of EHV transmission lines, it is a safe and convenient operation method for operators to wear shielding clothes to enter high potential and adopt equipotential method for emergency repair and maintenance. However, in live working of distribution lines, due to low voltage of distribution network, small space distance between three-phase conductors and dense distribution facilities, the working range is narrow, and it is easy to touch power facilities with different potentials within the range of human activities. Therefore, the equipotential operation mode in which the operators wear shielding clothes and directly contact the electrified body should not be adopted in the live work of power distribution. Although many units did not have accidents when using this method for operation, strictly speaking, there are hidden dangers. The reason is:

(1) phase to phase short circuit may be caused. When charged body 5 The punishment according to use mainly includes that when the general machine (universal machine) and the special machine are not covered or not covered completely, the operators wearing shielding clothing may contact two-phase electrified bodies at the same time if the action range is large, and the metal of the shielding clothing will cause phase to phase short circuit, and large phase to phase short circuit current will pass through the shielding clothing, not only causing equipment short circuit, Moreover, the short-circuit current will exceed the current capacity of the shielding clothing (5a for type I shielding clothing and 30A for type II shielding clothing), which will directly cause casualties

(2) may cause phase to ground short circuit. When replacing insulators and cross arms on road poles and towers, if operators wear a full set of shielding clothes and adopt equipotential operation, different parts of the body may contact the live body and grounding body at the same time, forming single-phase grounding. Although the neutral point of 6 ~ 10 kV system is not grounded, if the line is long or a certain length of cable is connected, the three-phase capacitive current will also exceed the through current capacity of the shielding clothing, causing casualties

therefore, it is not suitable to wear shielding clothes for equipotential operation in live line operation of distribution lines, but wear a full set of insulation protection tools, and adopt the safe operation mode of combining main and auxiliary insulation and multi-layer backup insulation protection. (to be continued)

(Huyi, wanglinong, huangxiaoming)

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