New paper-free insulation technology for dry high-voltage condenser bushings

A new Resin-Impregnated Synthetics (RIS) paper-free technology of high-voltage, dry, fine-graded condenser bushings is presented. In RIS technology, paper is replaced by polymeric fiber fabric which does not attract nor absorb humidity. The core is directly coated by a silicone insulator. A family of oil-air bushings based on the new RIS technology for voltages from 24kV to 170kV, has been developed and tested. The design tests have proven that the dielectric, thermal and lifetime properties of the RIS bushings surpass or are at least as good as those of the RIP cores. Climatic chamber test has shown that the RIS material absorbs almost no water and that its dielectric loss is not dependent on long exposure to extremely high humidity. This allows for easy transportation, uncritical storage in the period of installation and reliable performance in service. Type tests for the RIS bushings according to IEC and IEEE standards have been passed (however, bushings are not manufactured to the IEEE dimension standards) and first pilot installations have been agreed with electrical utilities for which the bushings have been commissioned in 2011. The developed family of RIS bushings covers oil-air bushings but the technology can be used for other fields of applications also.