On the research and development status of fluoroplastic insulated power cables

1.
Preface

Fluoroplastic is an excellent organic high-temperature resistant material, with mechanical properties, chemical resistance, weather resistance, electrical properties, low dielectric constant, low flammability, low moisture absorption, fouling resistance and other excellent electromechanical and chemical properties
.
Fluoroplastics have always been favored by the cable industry for their excellent and safe electromechanical properties
.
Fluoroplastics commonly used in the wire and cable industry are: polyperfluoroethylene propylene (FEP, F46), polytrifluoroethylene (PCTFE), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE, F40), polyvinylidene fluoride (PVDF), etc.
, the above materials have been safely used for cable insulation sheath for many years
.
The main types of fluoroplastic insulated cables are: high temperature compensation wires, high temperature signal lines, Ethernet cables, industrial high temperature power and control cables, rail transit locomotives high temperature power and control cables, high temperature heating cables, etc
.
Fluoroplastic insulated frequency conversion power cable is mainly used in iron and steel, metallurgy, petrochemical, power station and other high temperature working environment harsh places with power transmission connection line, the general temperature resistance range is -
65---+260 °C.
With the rapid development of China's economy, the demand for high-temperature cables in special industries is becoming increasingly strong, according to incomplete statistics, heat-resistant and high-temperature cables grow
at a rate of greater than 15% per year.
However, although fluoroplastics have thousands of benefits, but have not issued their national standards, at present only apply the industry standards issued by research institutions in China, the following will focus on domestic and foreign fluoroplastic insulated cable national standards and industry standards
.

2.
R&D status of fluoroplastic insulated power cable at home and abroad

The research of fluoroplastics in China originated from the Shanghai Fluoroplastic Molding Process Research Institute in 1963, and it has been applied to the cable industry for
only a few decades.
In the 60s of the last century, China's earliest batch of cable factories - the former Xiangtan Cable Factory, is China's earliest production of fluoroplastic cable enterprises, belongs to the military special cable production plant, its fluoroplastic control cable, fluoroplastic power cable production more
。 With the reform and opening up brought about China's economic take-off, with fluoroplastic cable production capacity of more and more enterprises, due to the cable industry heavy material light industry unique attributes, many domestic cable factories have introduced physical foaming, irradiation cross-linking and other production lines, at present, computers, buildings, industry and other fluoroplastic cables have been basically self-sufficient, no need to import, most enterprises can produce 0.
6/1kV and below fluoroplastic fireproof cable, fluoroplastic high-temperature silver plating wire and other cables and control cables, Fluoroplastics can only be used for cables
with voltage levels of 1kV and below.
There are many types of fluoroplastics, and the most widely used are polyperfluoroethylene propylene, polytetrafluoroethylene and polyvinylidene fluoride
.
At present, China can produce nearly 500 manufacturers of fluoroplastics for wires and cables, basically low-end products, the world's largest material manufacturer DuPont of the United States launched fluoroplastics for cables with high temperature resistance up to 300 °C in October 2012, improving the temperature resistance level
of general fluoroplastic insulated cables.

Although the wire and cable industry is a traditional industry, but there is currently no national standard for fluoroplastic insulated cable in China, only cable or machinery and other related industry research institutions and authoritative scientific research have some standards, they are: the National Wire and Cable Quality Supervision and Inspection Center compiled "rated voltage 0.
6/1kV fluoroplastic insulated fluoroplastic sheathed power cable" and "rated voltage 0.
6/1kV and below fluoroplastic insulated fluoroplastic sheathed control cable" two technical specifications; GJB 773A-2000 "Fluoropolymer Insulated Wires and Cables for Aerospace", HG/T 2904-1997 "Polyperfluoroethylene propylene resins for molding and extrusion" (equivalent to ASTM D2116-02 "Fluorinated ethylene propylene (FEP) - Fluorocarbon moldings and extrusions"), EN 50306:2002 "Railway applications - Railway vehicle cables with special fire performance - Thin walls" and other standards
.
The basic models of fluoroplastic insulated cables in China are shown in Table 1
.

Foreign cable industry started early, to the French cable giant Nexans cable group as an example, the company from the 19th century 30s began to develop aerospace high temperature fluoroplastic insulated wire and cable, after nearly a century of development, the company has become the largest cable manufacturer in the aerospace industry, products have basically covered all fields
of aerospace cables.
Today, many foreign cable companies firmly occupy the market
of high-end cables with excellent fluoroplastic insulation materials and mature process control.

3.
Control of key processes in the production of fluoroplastic insulated power cables

Taking polyperfluoroethylene propylene insulated power cable as an example, the price of polyperfluoroethylene propylene is more expensive, and it is required to be thin during the production of insulation or sheath process, and the production quality of the conductor will directly affect the appearance and performance
of the finished cable.

3.
1 Conductor stranding

In the conductor stranding process, it is necessary to ensure that the diameter of the monofilament in the conductor is consistent, and the conductor should be stranded on the plate as much as possible to ensure the neatness and uniform tension of the cable, if the conductor tension is uneven or the wire is out of order, then when the insulation is extruded, it will cause the monofilament in the conductor to jump or scratch the insulation, thus affecting the next process
.
At the same time, due to the thin insulation of fluoroplastics, when the conductor is stranded, it is necessary to carefully check whether there are abnormal phenomena
such as burrs, protrusions, oxidation and greening on the surface of the conductor.

3.
2 Insulating extrusion

The most difficult point in the production of polyperfluoroethylene propylene insulated cable is the insulation extrusion process, the selection and design of insulation extrusion mold is very important, according to the empirical formula 3-1 and 3-2 to calculate the appropriate mold size, as follows:

(D large 2-D small 2)/(d _large 2-d _small ²) = K (3-1)

(D large 2 * d small 2)/(D _small 2* d _large 2) = P (^3-2)

D_.
Large inner diameter of the mold sleeve ----

D _small ---- outer diameter of the mold core

_dLarge ---- outer diameter of the cable

d _Small ---- outer diameter of the conductor

K------- tensile ratio (35-65)

P------- modulus coefficient (1.
01-1.
05)

Insulation extrusion temperature control is also one of the main factors affecting the quality of finished cables, taking six temperature control zones as an example:

High temperature fluoroplastic insulated cable can not be cooled with ordinary PVC insulated cable water, because cooling with ordinary water will crack the fluoroplastic insulating surface, so install a constant temperature cooling device in the water cooling tank to control the water temperature, in the cooling process, the internal stress of the inner surface and outer surface of the fluoroplastic insulation (caused by uneven heat dissipation) is effectively improved
.
At the same time, due to the high cost of fluoroplastics and the thin insulation thickness, it is extremely necessary
to train employees before production.

4.
Fluoroplastic cable prospect and a foreign fluoroplastic cable introduction

At present, there are only a few fluoroplastic insulated cables that can be used for physical foaming in China, and the quality of the products is uneven, among which there are equipment reasons, and there are also reasons for the research and development of fluoroplastic materials for cables, but there is a reason that cannot be ignored is that there is no unified national standard for fluoroplastic cables currently used in China, most enterprises are independent, even if the National Wire and Cable Supervision and Inspection Center has issued corresponding technical specifications, most enterprises produce fluoroplastic cable structure size, use materials, voltage level, temperature application range, The use of places is not uniform, these problems make the domestic fluoroplastic cable market show a "hundred flowers" bad situation, to the user's choice, use, maintenance are confusing and safety hazards
.
If the relevant functional departments of the state take the existing fluoroplastic cable standards (TICW2, TICW3, etc.
) as the benchmark, combined with international standards such as UL, VDE, EN and the actual situation of domestic fluoroplastic cables, and formulate unified national standards, it is believed that it will effectively improve the current situation
of domestic fluoroplastic cable products with good and bad and "Zhang three and Li four".

As shown in Figure 1, it is a fluoroplastic insulated cable with UL as the standard, and its technical parameters are as follows:

FEP insulated single-core cable, reference standard: UL1330, temperature resistance range: -100°C-+200°C

Nominal voltage 600V, minimum bending radius: mobile installation 10 times cable outer diameter, fixed installation 4 times cable outer diameter, conductor temperature range: copper conductor 130 °C, tinned copper conductor 180 °C, silver plated copper conductor 200 °C
.

Performance: High insulation resistance, low dielectric loss, environmental resistance, self-extinguishing function, flame retardant in accordance with IEC 60332-1

Cable structure: stranded pure copper wire, tinned, silver-plated, etc.
, FEP insulated
.

It is worth noting that the cable has a self-extinguishing function
.
It is understood that one of the world's cable giants, an Italian nationality cable Co.
, Ltd.
has disclosed a power cable with self-healing function, the cable insulation and sheath are filled with a fluid, when the sheath is broken, the fluid between the broken insulation and the sheath will quickly fill the broken sheath, quickly heal the sheath damage, and achieve self-healing function
.

The number of cable enterprises in China is the largest country in the world, the products basically cover all types of wires and cables, but most of the products of our enterprises are concentrated in the field of medium and low voltage power cables, wires, power lines and other ordinary products, in recent years, wire and cable industry enterprises, scientific research, administrative institutions and other departments are actively advocating the development of high-end products, China's fluoroplastic insulated cables should fully develop better performance insulating materials, develop national standards, unified operating specifications, promote the efficient improvement of product quality in the industry
。

(Far East Cable Co.
, Ltd.
Electrical Equipment Cable R&D Department Wang Yilei)

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