ABB EasyDry RIS bushings make old transformers new again

2014-09-15 - ABB has won orders from PSE (Polskie Sieci Elektroenergetyczne) S.A., the state-owned transmission system operator in Poland, to replace about 150 transformer bushings. Around 90 will be EasyDry products using advanced Resin-Impregnated Synthetics (RIS) paper-free technology, supplied by ABB Micafil in Switzerland.

PSE operates about 13,519 km of electrical line in total and 103 ultra-high voltage substations of 750 kV, 400 kV and 220 kV, as well as a 254-km long 450 kV DC subsea connection between Poland and Sweden.

One of the key areas of activity of PSE as the Transmission System Operator is to ensure a high level of reliability and safety of the transmission network operation. This is, among others, achieved by the elimination of the factors affecting its efficiency, including the reduction and elimination of risks of failures, as well as the standardization of materials, equipment, devices and systems installed in the transmission network. These activities include a project concerning the preventive replacement of oil bushings in porcelain jackets, which have been operated for more than 25 years, for safer oil-free (dry) insulators in composite jacket. In a public tender procedure conducted by PSE, the ABB offer was found most favourable. ABB offered a delivery and installation of bushings in the RIS technology for 110 kV and lower voltage insulators.

High and dry
RIS technology not only provides oil-free but also fine capacitive graded, paper-free bushings. Instead of using conventional paper insulation, the bushing's core is wound with polymeric (or synthetic) fabrics, and encase in resin. EasyDry bushings do not contain any water-absorbent materials, while maintaining the fire-resistant, explosion-proof characteristics of traditional dry bushings.

The estimated life cycle of EasyDry bushings exceeds 30 years, so PSE will still be able to use the newly ordered devices even after the old transformers have been decommissioned, turning them into reserve stock, or installing them in new transformers.

“New PSE`s orders for bushings fit nicely into a program of preventive replacement in the oldest transformer units of its fleet. The customer`s decision to switch from oil bushings to dry-type bushings - RIP or RIS - puts Poland inside a worldwide trend favoring the use of these types of products,” said Eligiusz Hasiak, director of sales and marketing for ABB`s transformers business unit in Poland

Easy storage, reliable performance

Climatic chamber tests show RIS material absorbs almost no water, and dielectric loss is not dependent on long exposure to extremely high humidity, enabling easy transportation, uncomplicated storage during installation and reliable performance in service.

ABB is currently executing the first part of the order, which includes about 100 bushings; around 40 of the RIS type will be installed in ten power autotransformers. The second part includes delivery of 50 RIS bushings and comprehensive technical service for twelve 160 megavolt ampere (MVA) power transformers. The project is scheduled for completion by October 2015.
A big challenge is replacing old bushings that contain surge protection systems no longer in production. By accessing original transformer designs and the knowledge and experience of its designers, ABB developed a solution to replace the old bushings with advanced IRS technology, and minimal interference. ABB will also inspect the switch and provide advanced transformer diagnostics, including measuring moisture content in the windings.

Transformers are the most critical parts of the electric power grid, and transformer components such as bushings and tap changers are crucial for ensuring the reliability and safety of transformers in service. The main function of a transformer bushing is to take the current on high potential through the transformer tank. ABB has been producing high voltage transformer bushings for more than 100 years and today manufactures bushings in seven countries on four continents.