Standards Development

Scope

This document specifies requirements for rubber seals used in transformers with natural or synthetic esters as insulating liquid.

The requirements include:

- technical properties,

- test methods,

- applicable temperature conditions,

- marking,

- packaging, transportation, and storage.

Purpose

Sealing components are key fundamental components of electrical equipment. Failure of sealing will directly affect the safe and stable operation of power equipment. With the increasing global attention to the theme of environmental protection, natural esters (FR3®, DEEP®, RAPO®, etc.), synthetic esters (MIDEL®, DEEP®, etc.), and other insulating liquids are being rapidly adopted as insulating media in transformers instead of traditional mineral oils. Transformers using FR3 natural ester have been in service worldwide. A 420 kV transformer filled with FR3 natural ester manufactured by Siemens Germany was put into operation in 2013. In 2020, a 220 kV FR3 natural ester transformer produced by CHINT Electric (China) obtained KEMA certification. In 2023, a 132 kV high-fire-point insulating fluid transformer supplied by XD Group (China) to CLP Power adopted MIDEL 7131 synthetic ester. By 2023, more than 60,000 transformers around the world had been using natural ester and synthetic ester insulating fluids. In the same year, over 12,000 new transformers in the United States were filled with ester insulating fluids, and more than 18,000 ester-filled transformers were newly installed in Germany, the UK and France combined. In China, over 14,000 ester-filled transformers were installed in 2023. Statistics show that the number of transformers in operation in China was approximately 17 million in 2023. During the same year, three large-scale State Grid projects in Shandong, Guangdong and Henan provinces of China replaced more than 18,000 traditional mineral oil transformers with ester-filled transformers. In 2024, a 110 kV natural ester transformer developed by Shandong Electric Equipment Engineering Co., Ltd. (China) was filled with DEEP natural ester produced by domestic manufacturer Jiangsu Shuangjiang Energy Technology Co., Ltd. Also in 2024, a 500 kV vegetable oil transformer commissioned by Guangzhou Power Supply Bureau of China adopted RAPO natural ester from domestic manufacturer Guangdong Zhuoyuan New Materials Co., Ltd. In 2024, the Wells Hydroelectric Project in the United States replaced old mineral oil transformers from the 1960s with new transformers filled with MIDEL 7131 synthetic ester. It is expected that traditional mineral oil transformers will be gradually replaced by ester insulating fluid transformers in the future. However, there are significant differences in chemical structure, polarity, and physical properties between esters and traditional mineral oils, which pose new requirements for sealing materials. Traditional sealing materials (nitrile, acrylate, fluororubber, etc.) are prone to swelling, softening, and aging in esters, and this will also affect the acid value, loss factor, etc. of the ester, leading to sealing failure and a decline in transformer insulation performance. The compatibility between the traditional sealing materials and esters is poor, unable to meet the long-term durability requirements of transformers with esters as insulating liquid. This can affect the safety and stability of the power grid. At the same time, there are currently no specific requirements for rubber sealing components for transformers with esters as insulating liquid in China and abroad, resulting in a lack of unified basis for product design and selection, unclear testing and verification methods, and posing great risks for the development and later operation and maintenance of electrical equipment including esters as insulating liquid. Therefore, it is urgent to formulate technical standards for rubber sealing components for transformers compatible with esters, providing a foundation for the production and manufacturing of rubber sealing components for transformers with esters as insulating liquid, providing a unified technical basis for global power equipment manufacturers and sealing component suppliers, offering a basis for operation and maintenance, leading to the development of the industrial chain and upstream and downstream technologies of electrical equipment and sealing components. Based on the key research project of the Chinese Innovation Joint Body of the State-owned Assets Supervision and Administration Commission of the State Council, "Research and Development of High-Performance Sealing Materials for New- Type Environmental-Friendly Insulating Liquids Filled in Transformers", the main technical content of this proposal has been completed. Through communication and exchanges with representative producers of transformers, esters as insulating liquids, and sealing material producers and user units at home and abroad, and based on years of operation and maintenance experience from all parties, a proposal draft has been formed. The proposal unit has made full preparations and hereby applies for project approval.