silicone polymers for high-voltage insulators.

by:Keyuan     2020-06-10
Composite Insulator with umbrella molded with silicone rubber has been used for high
Voltage service in the past 30 years, its popularity is on the rise.
Especially in coastal areas and contaminated areas, silicone compounds are better kept water-repellent than ceramics or glass.
In general, the weight of composite insulators is light, which can significantly reduce the losses caused by damage and damage.
However, due to the lack of industry consensus in polymer performance testing, the development of standard silicone product lines has become complicated, resulting in the selection of customized formula methods by some suppliers.
Most of the power transmission and distribution is carried out through overhead lines, and the insulator provides mechanical support and electrical protection.
High-size and specific design
Depending on the line voltage, the environmental conditions, the materials of the building and the manufacturer, the voltage insulation experience varies.
The two main designs are suspensionand post-type.
The two are characterized by a sloping \"shed\" that maximizes the leakage distance between the line and the tower, guiding the water out of the equipment.
The longer the insulator, the greater the leakage distance.
Electrical, mechanical and environmental factors affect the service life of the insulator.
Air pollution, UV exposure and vandalism are often the biggest physical threats.
Electrical stress is mainly caused by discharge (
When the voltage gradient exceeds the critical value)
, Leakage current of the line and arc or flash discharge from the line to the support structure.
Ceramics and glass have long been the first choice of high-tech materials
Voltage insulator for long
Long-term voltage resistance and outdoor exposure do not deteriorate significantly in most environments.
However, the shortcomings of porcelain and glass design are well known.
First of all, they are usually very heavy and easily damaged.
The estimated range of damage to ceramic insulators is as high as 30% during transport and installation only, excluding damage that occurs during use.
High surface pollution-one of the biggest problems
Voltage applications are air pollution attached to the surface of the insulator.
In some cases, particles in the air are naturally produced, such as in coastal areas exposed to salt spray.
Industrial sources, agricultural sprays and automotive exhaust also help to reduce water resistance and electrical performance.
When the contamination is exposed to moisture, the electrolytic film develops, resulting in discharge, deterioration of the surface, arc of the dry belt, and eventually flash.
Ceramic and glass designs are particularly vulnerable to this build-up, and in coastal areas or contaminated environments they must be maintained by regular cleaning or re-cleaning
Grease with insulation.
During the flashing process, a strong local energy can cause a sudden increase in temperature and a serious arc.
The stress of these conditions may lead to catastrophic fracture of the ceramic or glass insulator.
There is a particular problem with the coastal environment, because the weather can cause the circulation of pollutant deposition, followed by high humidity or fog.
These conditions, for example, have led to more than 170 power outages in one US. S.
Utility for only nine months
Day of 1991 (ref. 1).
The potential benefits of polymer material composite insulators since the first introduction of polymer design in the 1960 s have attracted interest from utility and equipment manufacturers around the world.
They are lighter in weight and less prone to breakage compared to glass or ceramic materials, showing an immediate commitment to reduce shipping costs, simplify installation and reduce maintenance.
Savings may be particularly significant in areas with inconvenient transportation.
The composite material is usually smaller than the ceramic insulator and can also reduce the height of the towerof-
Space requirements.
In particular, it is found that polymer materials can greatly reduce the damage behavior to high
Voltage insulator.
Polymers are usually more resistant to mechanical shocks than ceramics or glass.
The inherent flexibility of these materials helps the insulator absorb impact when hit by a bullet or other projectile, providing a less attractive target for vandalism.
Initial material testing for high voltage insulator applications focuses on some candidate materials including Ethylene Propylene Rubber (such as EPDM)
Epoxy resin, olefin, polyurethane, polyethylene, silicone and PTFE (Teflon).
Whether it is a material or a specific insulator design, water resistance has always been a basic design parameter.
Various types of silicone rubber materials have been used in electrical services for more than 50 years.
In fact, the first application of silicone in World War II was Electrical insulation on aircraft.
In the 1970 s, the Dow developed a room-
Temperature curing elastic material, specially designed for application of spraying on porcelain insulator, to reduce maintenance of insulator and anti-flash network, especially in salt spray environment.
The product is still in use today, allowing utilities to improve the electrical performance of porcelain lightning arresters without replacing them.
Insulator molded from silicone rubber as an effective alternative to traditional ceramic and glass design is also increasingly recognized (refs. 2-4).
In fact, almost all the major manufacturers of high
Voltage-electric insulator has now introduced silicone products into its products.
The main advantages of silicone insulator include light weight (
1/10 of porcelain electrical equivalent)
Anti-impact, good performance in polluting the environment.
Unlike ethylene-propylene rubber and other organic materials for high pressure applications, silicone rubber is resistant to UV exposure, salt spray (figure 1)
And extreme temperatures.
For high-
The application of voltage insulator is usually high
Consistency rubber (HCR)compounds.
Two types of fillers are usually used: silica is a filler to enhance the physical strength of the polymer, while three-water alumina (ATH)
Increased arc resistance.
A small amount of filler treatment, pigment and curing agent may also be part of the formula. The polymer-
Packing combination is important in silicon insulator.
Processing, physical properties and electrical properties are all affected by the molecular weight and structure of the polymer and the type, size, shape, surface treatment and residual catalyst or contaminants of the filler.
In determining the best formula for a specific application, equipment manufacturers and silicone suppliers must determine the best balance of performance, processing properties, and economic considerations.
Compared to most organic polymers, silicone exhibits better drainage performance and lower surface area.
The surface properties of the silica gel are unique because it restores the drain between contamination and/or Crown attacks, while other materials gradually deteriorate.
Crown exposure does temporarily increase the wetting properties of silicone rubber, a phenomenon associated with an increase in oxygen content on the surface, but water-
After a period of rest, insect repellent will recover.
The material\'s ability to restore its water-repellent properties is considered to be at least partly due to the diffusion of low molecular weight silicone rubber (polydimethyl-siloxane)
Fluid on the surface (refs. 6 and 7).
Another force that affects the drain recovery shown by the silicone insulator is the surface reorient.
The extreme flexibility of the silicone chain and the low molecular weight between the methyl group produce a low glass transition temperature and a high free volume silicone rubber.
These conditions easily allow the surface reorientation of silicone rubber, the most liquid surface of all common polymers in high pressure applications.
When applied to composite materials, the existing test standards for testing ceramic insulators do not show good correlation with actual use experience.
In particular, it has proved difficult to develop test conditions for accurate replication of material degradation occurring over a long period of timeterm service.
Improvements to test equipment and procedures specifically for polymer materials remain a focus area for some utilities, universities and research organizations.
Electric Power Research Institute (EPRI)
High voltage transmission research center in the United StatesS.
A fog chamber has been developed to allow testing at different levels of contamination.
A particular insulator design can withstand many stresses that closely simulate the environment in which it is used.
The results of the center\'s aging study show that, compared to the B-C rubber design, the performance of silicone rubber insulators is less affected by aging conditions regardless of the manufacturer.
In addition, it is found that silicone rubber insulator can resist pollution better. A nine-
The annual study conducted by Chalmers University of Technology in Sweden compared the effectiveness of molded composite insulators with porcelain and glass, and found that \". . .
In severe weather conditions, the silicone rubber insulator has a very low current pulse in the range of 6 mA, while all ethylene-propylene rubber insulators exhibit very high discharge activity \"(ref. 4).
Utility companies have been
For many years, the overall satisfaction of ceramic insulators has been very high (ref. 8).
Some of these insulators have been in use for 20 years.
For example, Florida Electric Power and Lighting Company\'s experience with silicone is so positive that after extensive damage caused by Hurricane Andrew, the company replaced many porcelain insulators with a silicone device.
These alternatives are not subject to any service disruption that plagues the salt contamination of the ceramic unit, nor do they show any UV deterioration found in other polymers (ref. 9).
Despite the progress made in testing, much of the industry still relies on porcelain insulator programs developed decades ago.
While many manufacturers have adopted specific techniques to evaluate polymer compounds, the products of different companies are different.
The wide range of process conditions between manufacturers also complicate the development of standard compounds that form high-pressure insulators.
As a result, some silicone suppliers have chosen a custom recipe method.
The current test data show that,
The filled rubber provides the best electrical protection, and silicone suppliers usually maintain a high level of filling as much as possible and maintain good processing properties.
However, if a utility or insulator manufacturer insists on passing a traditional tracking wheel test or other standard that does not allow recovery time between stress events, it forces the composite to reduce the content of the three-water alumina filler.
The growing market for alternative materials for material development
The demand to reduce the overall cost greatly stimulates the voltage components.
With a standard product line, material suppliers will be forced to provide a range of materials that demonstrate optimal dielectric properties, physical properties, and processing properties in general moldingused equipment.
Unfortunately, no two manufacturing processes are exactly the same, which makes it difficult to reach the highest level of performance in both areas.
By customizing composite silicone materials for specific standards, a product can be developed that can not only pass the required physical and electrical tests, but also help the mold optimize the processing technology of specific equipment.
How the latest generation of Silicon insulators has evolved over the past 25 years.
Current research focuses primarily on surface chemistry to better understand the effects of long periods of time
Term aging and discharge.
As researchers perform chemical analysis using electron microscopy, electron spectroscopy, the analytical tools become more complex (ESCA)
Scanning spiral probe (SAM)
And other techniques for accurate measurement at different depths and angles.
Insulator manufacturers and material suppliers are combining the knowledge they have learned from test results and field experience to have a more comprehensive understanding of silicone compounds to effectively resist high pressureVoltage service.
Customizing the composite method helps progress, which integrates the ability to quickly adjust the material formulation through design.
Suppliers have no resistance to changes that standard product lines may experience, and insulator manufacturers are able to reach levels of performance and processing efficiency that are difficult to repeat with off-the-shelf products.
In addition, fewer process adjustments are required to customize the composite, as it is made according to a specific process.
With the latest advances in polymer technology and insulator design, manufacturers now find that other applications traditionally provided by ceramic materials can take advantage of the unique properties of silica gel.
Engineers are testing a variety of lightning arresters, terminals, joints, sleeves and other heights
Voltage element. References [1. ]Burnham, J. T, D. W. Busch and J. D.
Renowden, \"Christmas 1991 transmission interruption for FPL\", paper published at the IEEE/PES Winter Conference, 1993. [2. ]Hall, J. F.
The paper \"History and Bibliography of outdoor application of polymer insulators\" published at the IEEE/PES Winter Conference on 1992 \". [3. ]Burnham, J.
T, \"silicone rubber insulator improves transmission line performance\", pp, August 1992. 20-25. [4. ]Vlastos, A. E. and E.
Sherif, \"experience of RTV silicone rubber shed and shed coated insulator\", paper published at the IEEE/PES Winter Conference, 1989. [5. ]Kim, S. H. , E. A. Cherney, and R.
Hackam, \"al properties of RTV silicone rubber coating as a function of the filling layer\", IEEE Trans. Electr. Insul. , 27 (6):1065 (1992). [6. ]Smith, P. J. , M. J. Owen, P. H. Holm and G. A.
Toskey, \"the surface study of the corona --
High treated silicone rubber
Voltage insulation, \"IEEE Conference on Electrical insulation and Dielectric Phenomena, Annual Report of 1992, Paper No. 10-21, p. 843. [7. ]
Kindersberger, J. and M.
Kuhl: the 6 th International Symposium on High insulation performance paper \"The influence of drainage on insulation performance\"
Voltage Engineering, August 28, 1989. [8. ]Schneider, H. M. , J. F. Hall, G. Karady and J.
Renowden, \"non-ceramic insulator for transmission lines\", paper published at the IEEE/PES Winter Conference, 1989. [9. ]
\"The application of silicone rubber insulators in transmission lines is becoming more and more popular,\" material News, June 1993, p. 6.
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