Substation Pad Mounted Transformer

CONSTRUCTION

Core
Catalog Data CA202001EN Effective January 2018
The three-legged, step-lap mitered core construction is manufac- tured using a high-quality cutting machine. For maximum efficiency, cores are precisely stacked, virtually eliminating gaps in the corner joints.
Five-legged wound core or shell-type triplex designs are used for wye-wye connected transformers, and other special transformer designs.
Cores are manufactured with precision cut, burr-free, grain-oriented silicon steel. Many grades of core steel are available for optimizing core loss efficiency.

Coils
Substation transformers feature a rectangular coil configuration with wire-wound, high-voltage primaries and sheet-wound secondaries. The design minimizes axial stress developed by short circuits and provides for magnetic balancing of tap connections.

Core and coil assemblies
Substation transformer core and coil assemblies are braced with heavy steel ends to prevent the rectangular coil from distorting under fault conditions. Plates are clamped in place using presses, and welded or bolted to form a solid core and coil assembly.
Core and coil assemblies exceed ANSI® and IEEE® requirements for short-circuit performance. Due to the rigidity of the design, impedance shift after short-circuit is comparable to that of circular wound assemblies.

Transformer tanks
Transformer tanks are designed for high strength and ease of handling, installation, and maintenance. Tanks are welded using precision-cut, hot rolled, pickled and oiled steel. They are sealed to protect the insulating fluid and other internal components.

Tank finish
An advanced multi-stage finishing process exceeds IEEE Std C57.12.28TM-2014 standard. The eight-stage pre-treat- ment process assures coating adhesion and retards corrosion. It converts tank surfaces to a nonmetallic, water insoluble iron phosphate coating.
The paint method consists of three distinct layers of paint. The first is an epoxy primer (E-coat) layer which provides a barrier against moisture, salt and corrosives. The two-component urethane final coat seals and adds ultraviolet protection.

Vacuum processing
Transformers are dried and filled with filtered insulating fluid under vacuum, while secondary windings are ener- gized. Coils are heated to drive out moisture, ensuring maximum penetration of fluid into the coil insulation system.

Cooling system
Less flammable fluid filled-Air cooling (KNAN) is provided with transformers rated 500 kVA. A choice of KNAN/ Future KNAF (Future Forced-Air) or KNAN/KNAF (Forced-Air) cooling is provided with units rated 750 kVA and above.

Insulating fluid
Hengfengyou offers EnvirotempTM FR3TM fluid or electrical grade mineral insulating oil in its Cooper Power series transformers. The highly refined fluids are tested and degassed to assure a chemically inert product with minimal acid ions. Special additives minimize oxygen absorption and inhibit oxidation. To ensure high dielectric strength, the fluid is re-tested for dryness and dielectric strength, refiltered, heated, dried, and stored under vacuum before being added to the completed transformer.