The applications of polymers and rubber materials to electrical power apparatus and cables are reviewed. Polymers and rubber materials have been widely used as insulation and structure materials because of their excellent electrical/mechanical properties and easy manufacturing. They have played an important role to the development of high-performance apparatus in this half century. OF (Oil-Filled) cables are replaced with cross-linked polyethylene cables except UHV (Ultra High Voltage) AC and DC cables. Polymer insulators become popular in the field of outdoor insulators. Polymeric materials are also very important in transformers, rotating machines, GIS (Gas Insulated Switchgear) and so on.
On the other hand, polymers and rubber materials are rather weak at heat-resistance and ageing (degradation). Recent compact and high-performance power apparatus have strongly required the improved heat-resistance and long-term stability of polymers and rubber materials.

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Advantages of polymer insulators over traditional ceramics insulators are light weight, high mechanical strength to weight ratio and high vandal damage resistance. Easy handling, easy installation and the thereby reduced cost are expected to contribute to more effective and labor-saving power delivery systems. The induced aging can reduce the electrical performances as well as the durability of polymer insulators. This is a peculiar nature of polymer insulators. Nowadays, silicone rubbers incorporated with alumina trihydrate (Al₂O₃•3H₂O) filler are representative housing materials of polymer insulators. One merit of using silicone rubbers is providing stable hydrophobicity, which can be quickly recovered even when it is lost as a result of discharges and/or deposits of contaminations, to insulator surfaces. Stable and recoverable hydrophobicity prevents water film to form, restricting leakage current passing through the water film and thus enhancing the capability of electrical insulators even in wet and contaminated conditions. Fundamental understanding is reviewed on the loss and the recovery of hydrophobicity of silicone rubbers in association with a formation of low molar mass cyclic silicone oligomers, a formation of silanol groups and an orientation of methyl groups. A correlation of the hydrophobic variation with the electrical insulating performances is also reviewed.

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Thermal and weather stability, water repellency, high surface resistivity and lightness have made silicone rubber very attractive materials for polymer insulator. Those features come from the nature of silicone polymer (polydimethylsiloxane). Silicone rubber has been used for high voltage insulation from 1960's and since then physical/electrical properties and durability have been modified. And processability and design of silicone insulator have also been investigated. Another advantage of silicone is the recovery of hydrophobicity on the surface and it can be used even in heavy environment. There are three different curing systems for silicone rubber i.e. peroxide cure, addition cure and condensation cure. A brief explanation for those is made.
High loading of aluminum trihydrate (ATH) is commonly used for silicone rubber to improve tracking and arc resistance. Silicone rubber with 50wt% ATH will pass 4.5kV tracking resistance and it also has good resistance to sea wind. Silicone rubber without ATH can be used where sea wind doesn't have much effect. Tracking resistance can also be strengthened by improving hydrophobicity of the surface. Low permanent set silicone rubber is used for indoor/outdoor cable accessories. Another application for silicone rubber for this area is the coating material to give water repellency on the insulator.

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EP(Ethylene Propylene) Rubbers are usable for various power cables, cable splices and terminations, as they have a high degree of electrical properties (breakdown voltage, volume resistivity, tracking resistance and so on) under ambient condition. But these products used for underground power distribution under water immersion or high humidity, in rare case, fall into breakdown in a few years. Therefore good electrical properties are also necessary to these insulating materials under the latter condition for very long term.
This paper introduces accelerated test method and gives the results obtained by the method for deterioration characteristics of insulating materials subjected to electrical stress under water immersion. Test results indicate that volume resistivities and relative permitivities of EP rubber deteriorate in short term depending on its formula. Since the selected materials show long lifetimes even subjected to high temperature and high electric field, they are available for developments of power cables and their related things as stable insulators under severe circumstances.

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In recent years, the PST* (CST**) has been adopted as a splicing material of an electric power cable.
This is because predominancy, such as ease of splicing by the PST, homogeneity, and long-term reliability, is applied.
This paper explains the fundamental structure of the PST, and the material characteristic required as the PST. Moreover, the example to which PST was applied as a splicing material of an electric power cable is shown.
*PST; Pre Stretched Tube **CST; Cold Shrink Tube

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Excellent characteristic of rubber materials is used for pressure sensitive cable sensors. These code-like sensors have plus and minus electrodes. When pressure sensitive cable sensors are sufficiently deformed by external pressure to cause a pair of electrodes to touch each other, these enters the"ON"state. Two kinds of rubber material, conductive rubber and insulation rubber, are used for these sensors. It is necessary for conductive rubber that low volume resistivity and durability. It is necessary for insulation rubber to have both of flexibility and durability.
We have developed the pressure sensitive cable sensor, which is a flexible cord-like sensors capable of sensing any pressure applied at any position or in any direction. These excellent characteristics are achieved by the special structure in which four conductive wires are spirally molded in the cable. Moreover this sensor exhibits good durability and reliability in the various environmental conditions. This sensor has been already used for several applications like automobile door sensors, and with its excellent characteristics, it can find other wide-range potential applications.

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Many kinds of rubber parts such as fusing roller, media handling roller, and cleaning blade apply to commercial electrophotographic copiers and printers. Recently, charging roller, developing roller, and toner transfer roller or belt composed of rubber materials have progressed remarkably. The cause of this progress is that electric resistance of rubber materials can be precisely controlled in semi-conductive region such. as 10⁶-10¹²Ωcm. Charging roller is used for providing charge to a photoconductor. The photoconductor is charged by micro space charging, i.e. directly contacting the DC or DC plus AC voltage applied semi-conductive rubber roller on the photoconductor. In a developing process using a non-magnetic one-component developer, charged toner particles are transferred from the developing rubber roller to the photoconductor by the latent image potential. In a transfer process, toner image created by a developing process is transferred to a recording paper by the transfer electric field generated between the voltage applied transfer roller and the photoconductor or the intermediate transfer drum/belt. This report focuses on applications of semi-conductive rubber for electrophotographic system, and explains the electrical and mechanical properties of semi-conductive rubbers in demand and the conditions for using in electrophotographic processes.

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