Corrosion protection of core steel in dry-type transformers
Anticorrosion coting: some dos and don’ts
This article demonstrates how corrosion of core steel starts, presents its negative effect on transformer’s efficiency, talks about the types of coating used on core steel material as well as the methods used in applying those layers of coating. It also provides a collection of data and best practices useful to identify the proper method for anticorrosion painting of the stacked iron core in dry type distribution transformers including the difficulties that may be encountered during this operation and the measures to be taken to eliminate the mentioned difficulties. In addition, this paper also presents the quality control checkpoints for final verification of an operation that is so simple, yet so important in preserving a fundamental part of the transformer which helps increasing its lifetime and decreasing the need for future maintenance.
Dry-type transformers are often exposed to corrosive environments in both indoor and outdoor applications such as industrial or marine environments. Industrial and environmental factors such as rain, snow, wind, dust, pollution, ultraviolet rays, and sea salt contribute to the degradation of protective of coating applied to the transformer. The core steel laminations within the active parts of the transformer are especially susceptible to corrosion due to the aforementioned corrosive agents in combination with the high operating temperatures and vibrations of the core that occur while the transformer is in service. Therefore, there is a need for putting a spotlight on corrosion-resistant coatings for dry-type transformer cores. ABB is a pioneer in the field of dry-type transformers manufacturing. For over 40 years ABB has provided continuous innovation, research and development for their production and engineering methods which offer the technologies necessary for achieving high reliability performance and lifetime. The processes described in this article, developed along the years of research, are just one example of ABB’s leading technology in the transformers industry to deliver high quality products.
2. Properties of core steel
Electrical steel (also called silicon steel, core steel or transformer steel) is special steel tailored to produce certain specific magnetic properties. The magnetic domain can be easily aligned in one or the other direction. The magnetic permeability is high i.e., the material allows easy formation and accumulation of the magnetic field within the core. Also, electrical resistance is high enough to prevent eddy current losses.