Manufacturing measures for middle head of the hott

2022-08-07
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Manufacturing measures for middle end of high-voltage cable

1 homework task

the high-voltage cable in the cable trench from the main power house of 135MW generator set of Huadian Lu'an Power Plant to the core auxiliary power houses such as chemical water and circulating water needs to be re laid and connected. The primary tasks are: the main power house is separated to 1a1b, and the 2a2b circulating water pump and chemical water are delighted with the hydraulic transformer, plant front area 7 10kV high-voltage cables for municipal power security power supply; It is required to produce 14 10kV heat shrinkable cables

2 according to

2.1 standard for construction and acceptance of cable lines in electrical assembly equipment Engineering (GB)

2.2 task specification for electric power support Enron (dl5009.)

2.3 technical standard for electric power support construction and acceptance sdj

2.4 specification for quality inspection and evaluation of electrical assembly equipment Engineering (dl/t5161.1~5161.17 version 2002)

3.1 preparation and premise of work

3.1.1 before cable laying, check whether the utilization data, tools and instruments are complete and whether the work environment is appropriate

3.1.2 the cable model, voltage and specification shall be designed properly. The cable shall be free of damage and excellent insulation

3.2 homework premise

3.2.1 confirm appropriate heat shrinkable data according to cable mechanism and specification

3.2.2 the construction site shall be kept clean and dry; Protective shed shall be erected for outdoor construction

3.2.3 the construction site has abundant light, and the lighting fixtures must be installed in accordance with the safety regulations

3.2.4 when there are live equipment around, safe isolation measures shall be taken

4 work style and process quality control measures

in order to increase capital and waste, considering the actual environment on site and the opinions of the owner, cut off the defective points at the defective points of the cables on site and make cable bridging

4.1 cable device style and pace

4.1.1 cable laying

 during cable laying, the waterproof layer of cable trench shall not be damaged. The length, model and specification of the power cable used as the head should be the same. The spacing of each fulcrum of the cable shall meet the design requirements

4.1.2 fabrication of middle head of high-voltage power cable:

the cable with perfect function has a certain capacitance between its own conductor, insulation layer and metal sheath or outer fence layer under the influence of voltage. This capacitance is uniformly distributed in all cable lengths and media, so the electric field is also uniformly distributed, and it is only the radial component of the electric field, without axial component, However, the electric field diffusion environment at the cable head has been completely changed. In the production of cable head, it is required to cut off the metal sheath (fence) and insulation layer, change the geometric layout and cross section of the conductor connection, and the dielectric coefficient and thickness of supplementary insulation and additional insulation are inconsistent with the insulation data of the cable body, which will lead to greater changes in the electric field diffusion at the cable head compared with the cable body. The electric field at the cable terminal is no longer a uniform radial electric field, where the electric field has an axial component, and the diffusion of the axial electric field component along the cable length is really uneven. The axial electric field component is the largest, or the axial stress is the most concentrated, at the disconnection of the metal sheath or fence and the connection of the wire core. In addition, because the surface breakdown strength of the insulating tape or insulating film is much lower than the vertical breakdown strength (usually 5% ~ 10% of the vertical breakdown strength), the presence of the axial electric field component will greatly reduce the electrical strength of the cable head. Therefore, when making the cable head, special attention should be paid to the treatment of the above parts

the electric field diffusion at the cable terminal is shown in the figure:

the additional insulation, fence, protective layer, rain cover and branch sleeve in the thermal extension cable accessories are called thermal extension parts. The additional insulation data adopted shall be compatible with the insulation of the cable body in addition to the electrical function meeting the requirements. The physical function targets such as hardness, shrinkage coefficient, tensile strength and elongation at break of the two data should be close. The electric field control of cable terminal is completed by stress control tube or stress control belt. Propane gas blowtorch or high-power industrial hair dryer can be used to heat things. Butane gas, liquefied gas or gasoline blowtorch is also allowed to be used in the environment where the premise does not exist. The high-voltage power cables used in the project are all XLPE cables. The following is 10kV AC, so it can be used as a material that many metal and non-metal materials are not competent. The manufacturing process of polyethylene cable thermal extension Zhongzhi is discussed:

 stripping and cutting cable: peel off the cable outer sheath, steel strip (if any), inner sheath, copper strip, outer semiconducting layer and insulation at the beginning of the core according to the size shown in the figure. Demand statement: ① since the layout and size of the thermal extension cable supplied by each cable accessory manufacturer are not completely the same, and the length of the thermal extension pipe can also be distinguished, the size of the cable stripping length and the fence copper strip stripping length L1 in the drawing shall be determined according to the data supplied by the product manufacturer of the actual device and the device process statement. ② Since it is required to put the insulating tube, semi conducting tube and fence copper wire on each phase core afterwards, then the crimping conductor can be connected in the future. Therefore, it is discussed that l at both ends is not equal, but ll is equal. J is the insulation stripping length at the beginning of the cable, usually 10mm is added to half the length of the conductor connection

 device stress tube: put six stress tubes separately on the six cores of cables at both ends, cover the fence copper strip by 20mm, and heat it to extend and fix it (if the stress tube is a tube through the discussion, it should be fastened after the conductor is connected)

 set various pipes and fence copper: the heat shrinkable outer protective sleeve and metal protective sleeve (if any) will be discussed to be set on one end of the cable while the electrical continuity increases the efficiency, and then the fence copper and three groups of pipes (including insulating tubes and semi conducting tubes) will be separately set on three wire cores at the stripped long end

 crimping the conductor connection: after the conductor connection is crimped, remove the flash and burr, break the metal chips, wrap the semi conductive rubber self-adhesive tape to fill the compression resistance, and then wrap the connection and the depressions at both ends with the filling tape. Make it smooth and round

 device insulating pipe: use filling tape or insulating rubber self-adhesive tape to wrap the steps between the end of the stress pipe and the insulation of the wire core. Be careful during operation to make it a uniform transition cone. Then pull out the inner insulating tube and heat it for extension after it is placed in the middle of the discussion. Finally, pull out the outer insulating tube and put it in the middle of the discussion for assembly and heating for extension. The heating shall be slowly pushed from the middle to both ends along the circumferential target to prevent bubbles from being left outside

 device semiconducting tube: wrap and fill both ends of the insulating tube with filling tape or insulating rubber self-adhesive tape to form a uniform transition cone, then move the semiconducting tube to the middle of the discussion, heat and extend evenly from the middle to both ends, and wrap and fill the overlap between both ends and the cable semiconducting layer with semiconducting tape to form a uniform transition cone. If two semi conducting tubes are used to overlap each other, air gap shall be prevented at the overlap

 device fence copper wire: move the fence copper wire to the middle of the discussion, stretch it evenly to both sides to make it carefully cover the semi conducting tube, and bind both ends to the cable fence copper strip with bare copper wire and weld it firmly. The fence copper wire can also be wrapped outside the semi conducting layer by means of encircling and entanglement

 welding bridge crossing line: bind and weld the two ends of tinned copper braided wire with specified cross-section separately with bare copper wire on the fence copper of three wire cores, then close the three-phase wire cores, apply filler between the cores, and tie them tightly with white gauze tape or PVC tape

 inner protective sleeve of the device: wrap sealing tape around the inner sheath of the cable at both ends of the discussion, move the inner protective sleeve to the discussion, lap both ends on the inner sheath of the cable and heat it for extension

 welding Jumper: use 10mm2 tinned copper braided wire or multiple stranded copper wires, bind and weld the two ends separately on the steel strip of the cables on both sides

 device outer protective sleeve: move the metal protective sleeve to the discussion position, tie both ends with copper wires on the outer protective layer of the cable, then move the heat shrinkable protective sleeve to the metal protective sleeve, heat and extend, and both ends shall be covered on the outer protective layer of the cable. When the metal protective sleeve is not eliminated, the heat shrinkable outer protective sleeve shall be moved to the discussion position to cover the inner protective sleeve for heating and extension

 it is not allowed to move the cable without complete cooling. Because the thermal extension data is only elastic above the extension temperature, and there is no elasticity and compression force at room temperature, the thermal shrinkage terminal head of the device should not be twisted and pulled in the future, otherwise it will form interlayer separation, form an air gap, and cause external discharge when applying voltage. If the terminal head device must be pulled or twisted when it is fixed to the equipment, it shall be heated and extended again in the future to eliminate the interlayer gap caused by pulling or twisting

demand statement: ① if it is not required to separate the cable fence copper strip and steel strip for grounding, the internal protective sleeve and steel strip jumper are not required. The bridge crossing line shall be bound and welded on the cable fence copper strip and steel strip, and then the heat shrinkable external protective sleeve or metal protective sleeve shall be installed. ② For 35kV extruded insulated cables, it is not appropriate to use multi-layer heat shrinkable insulating tube group to decompose and strengthen the insulation, because it is difficult to prevent the air gap between layers. Therefore, the composite tube layout with effective outer semiconducting layer (heat shrinkable tube) and insulating layer (elastic material) as a whole is used

4.2 right and task measures

4.2.1 if it is true that the high-voltage cable head is made under the despicable premise due to the production demand, the demand measures should be properly done, such as building a rainproof shed, adding isolation measures, and doing a good job of moisture and dust prevention

4.3.2 after the completion of the task, the power shall be removed and cleared in time, and the task measures shall be taken

4.3 process quality control measures

4.3.1 heat shrinkable cable accessories have huge manufacturing process, convenient installation, excellent stability and reliability. Therefore, agile implementation and widespread use have been achieved. The production quality of heat shrinkable cable head is particularly important. However, because the cable head manufacturer is not familiar with the technology and process of heat shrinkable materials, the production process is not standard, and some primary links are not properly grasped, the most critical process is easy to produce defects in the production process. Thus, the normal use of heat shrinkable data is affected, and even electrical problems are caused. In the final analysis, the quarrel over the manufacturing quality of cable head depends on whether the operator strictly follows the manufacturing process and stops the operation. The production quality of heat shrinkable cable accessories can be ensured as long as they can be operated properly according to the process requirements. During cable termination and discussion, the manufacturing process specification shall be strictly followed

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