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Golden Rules For Controlling Eccentricity In CCV Production Lines
May 16, 2018

At present, there are mainly two types of equipment for XLPE extrusion insulation production, namely CCV (Chain Hanging Crosslinking) production line and VCC (Lifting Tower Crosslinking) production line. In the production of 110kv and above voltage grade cables, many domestic companies adopt the VCC production model because there is a general understanding in the industry that when the catenary cross-linked production line produces voltages of 110kv and above, the insulation eccentricity is not easy to control and often exceeds. The scope of the national standard. According to incomplete statistics, the number of towers under construction or already built in China has reached or approached 70, causing serious overcapacity and waste. Theoretically speaking, the cross-linked production line of a vertical tower can squeeze the conductors around the conductor from the top to the bottom, which can better control the extent of insulation eccentricity. However, it should be noted that due to the effect of gravity, it is squeezed around the conductor. There is a tendency for the insulating material to stretch downwards in the molten state, which also affects the eccentricity of the insulation. In fact, the equipment is just one of the important links in the production of cables. This article summarizes the controllability of the eccentricity of the world-class CCV cable with a voltage rating of 110kv and above from the five links “people, machine, object, method, and ring”. Describes the details that need to be focused on in these five areas.


2. People, Machines, Things, Laws, Rings


The so-called "man, machine, object, method, and ring" refers to the operating personnel, equipment units, raw and auxiliary materials, process control and operation specifications, and production environment.


2.1 people


People are the main body of any activity. People here refer to the operators of CCV production lines. As far as the cable industry itself is concerned, the industry is a traditional industry, and training can be performed with a little training. However, as one of the most critical aspects of cable production, operators must undergo rigorous training. CCV production line from the line to the take-off line, there are about five places that require human operation or observation, that is, pay-off line, dial line, main control room display, under the seal, close the line, but the general business only in the dial, the main control The operator is set up in the room and at the take-up line, and an online monitoring camera is configured. The monitoring room can clearly understand the real-time production conditions. In the production process, the general enterprise sets up three shifts. Each shift will record the production conditions at the time of shift, such as the number of meters produced, the temperature of the nose and the fuselage, the extrusion speed, etc. Here, each shift must be in accordance with actual conditions. Record the production situation, be sure to record the traceability, traceability, when the need to replace the cable specifications, generally require a working time of the team to disassemble the head, this process requires on-duty personnel to record the replacement specifications, and handover In case of a complete mold, it is imperative that the replaced mold and head reach the 5S management standard, and that the replaced mold is intact and does not affect production. When the next shift shift, it is necessary to check whether the replaced die is consistent with the previous shift record to ensure the authenticity and completeness of the record.


2.2 Machine


The machine here mainly refers to all the equipment of the CCV production line, mainly including: pay-off line, pulley, storage wheel, upper traction, conductor preheater, conductor shielded extrusion machine, insulation extruder, insulation shield extruder, gravity Blanking system, machine head, monitoring room (operation panel, etc.), online thickness and eccentricity measuring instrument, heating section, cooling section, steering wheel, lower traction and take-up reel, etc., in which the double-rotating track-type traction is an influence The most important factor of cable eccentricity, the thickening theory of cable rotation control insulation eccentricity is: each tiny cell in the XLPE insulation layer is subject to gravity, continuously changing the direction of gravity by itself as a circle, and the cable rotation makes each tiny cell in the insulation The speed of movement is appropriate to maintain the change in its direction of gravity without displacement. In production, it is necessary to monitor the use of equipment in real time, especially the speed of pulling up and down. In the ordinary equipment maintenance, the first-level maintenance and second-level maintenance of the equipment are implemented, and the mechanics are supervised to supervise the operators and effectively promote the employees' awareness of equipment maintenance. The author has observed many times that the quality problems caused by the equipment damage caused by improper human operations account for three to four percent of all quality problems. If you want to pursue your business, you must first sharpen your equipment and do a good job of equipment maintenance. This means increasing the profitability of your company.


2.3 Things


The so-called material refers to the raw and auxiliary materials needed in the production process, such as copper, non-woven fabrics, semi-conductive nylon belts, shielding materials and insulation materials. Oxygen-free copper with a purity of four nines is generally used in high-pressure and ultra-high-pressure production. The copper conductor (circular compacted or split conductor) is required to be bright and unoxidized, and it must be ensured that the surface of the copper conductor cannot be scratched during insulation and insulation. Gravity blanking system is used for shielding materials and all materials must be strictly tested before being put into use. In general, EHV insulation and shielding materials are from Dow Chemical and Borealis. The authors recommend that qualified manufacturers can test the materials of two manufacturers on each CCV production line, do basic research, and obtain cable specifications, CCV. The optimal choice between production lines and materials.


2.4 Act


The law refers to guidance documents such as process documentation and process control in production. The law is in a dominant and dominant position in the five links, and regardless of the content of the process documentation and process guidance, it must ensure that the process documentation and process instructions are developed on the basis of tracking equipment production. In addition to specifying the production cable, the process documentation In addition to the specifications, material quotas, and process parameters, it is also necessary to indicate in which production line the control range of the upper and lower traction, the size of the mold used, the selection of the take-up platter, and so on.

We know that the insulation thickness of high-voltage and ultra-high voltage cross-linked polyethylene power cables is much thicker than that of medium-voltage cables, especially when the conductor diameter is smaller, the higher the field strength of the conductor surface is, the thicker the insulation thickness is. The catenary cross-linking process, due to the insulation extruding, will be subjected to sagging due to gravity before the melted state in the insulation extrusion, causing the insulation eccentricity, the sagging phenomenon and the melt fluidity of the insulating polymer (melt index, temperature ), extrusion pressure, cross-linking tube heating temperature is closely related to the analysis shows that sagging phenomenon is also related to the conductor diameter, insulation thickness. In the author's work, we found that for conductors of the same diameter, the thicker the insulation thickness, the faster the rotation speed is required; for the same insulation thickness, the larger the conductor diameter, the slower the rotation speed is required. In short, the revision or rectification of any process must follow the actual production and carry out effective process revision or rectification with the equipment performance.


2.5 rings


The ring refers to the production environment. In the CCV production line, the most important environmental control point is the storage space for insulation and shielding materials---gravity blanking room (also known as the addition room, which is generally a 1000-class purification room, and each environment is cubic. The number of dust particles floating or suspended in the air of rice is less than or equal to 1000.) Feeders shall wear disinfected work clothes and work caps, and perform body spray treatment each time before entering the feeding room to strictly control the tightness of the material boxes. Ensure that no debris enters the bin when reloading. In this seemingly uncomplicated refueling process, even if you enter a hair, it may lead to breakdown of the cable during use. Mechanism to ensure that operators value the surrounding environment and improve their awareness of dust.


3. Conclusion


Whether it is CCV or VCV, the production of high-quality cables is the hard truth. State Grid and China Southern Power Grid have now allowed qualified cable manufacturers to use CCV to produce high-voltage and ultra-high voltage cables. Far East Cable Co., Ltd. recently used CCV to successfully produce 500kv--1x3000mm2 XLPE insulated power cables with eccentricity control. Within 3%, this conclusion is well verified. The overall cost of the CCV production line is much lower than that of the VCV. If we can properly handle the relationship between the “people, machines, objects, methods, and rings”, we can produce high-quality cables.


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