At the core of VTC’s flawless execution pyramid is our people – Trained and Certified Technicians. Professional overseeing and receiving tools and materials in a timely manner allow our trained and certified technicians to perform at their best.

Our technicians are essential to the process and their training must be continuous and current.

Experienced supervisors are continuously “overseeing “and analyzing the product and the process from all angles to ensure efficiency and effectiveness. We also have a dedicated team in place to prevent process interruptions because of late or missing tools and materials.

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When building power transformers the goal is to suppress the water content of cellulosic-based materials to <0.5 % (by weight) prior to shipment. We employ processes to ensure a complete dry out before shipping. Cellulosic kraft materials, such as: high-density pressboard, papers, tapes, crepe tubes and spacers are used in the paper/oil insulation system of a transformer to support windings and leads and to maintain dielectric clearances. These materials organically retain of 8 – 10% of moisture by weight at ambient temperature, which threatens the longevity of any power transformer It reduces the electric strength and resistivity of the product and accelerates deterioration of the solid insulation. At VTC we ensure all moisture is removed from the insulation to maintain its critical insulating properties. Conventional drying costs more, requires more energy, and has yet to achieve optimal process parameters.

VTC’s Process Summary

VTC employs a Vapor Phase Drying (VPD) process to completely extract moisture from the core and the coil. Final dry out beings by loading the entire core and coil assembly into one of our vapor phase vacuum chambers. The cycle begins by removing the majority of oxygen from the atmosphere of the chamber. At this point, solvent vapor is introduced which beings to condense on the core and coil. As the vapor condenses, it transfers its latent heat which results in a consistent and even heating of the transformer internal assembly.

Once process temperatures have stabilized, the system beings its high vacuum cycles, further reducing the pressure below 0.5 torr. Moisture removal begins during the heating cycles and progresses through the remaining vacuum cycles.

The chamber is then flooded with transformer oil to impregnate and seal the pores of the insulation materials and prevent further moisture absorption.

The core and coil are removed from the chamber for processing. After a thorough inspection, the assembly unit is immediately tanked and covered with transformer oil to inhibit moisture absorption. The oil is again drained and the transformer is placed on high vacuum to remove any surface moisture The transformer is once again vacuum-filled with hot, processed transformer oil for its final impregnation. After the appropriate sit time, electrical testing beings.

The VPD process provides many advantages in the manufacture of power transformers: Reduced oxygen levels minimize oxidation and thermal aging of materials, and it’ excellent heating characteristics transfers heat to all parts of the core and coil assembly uniformly, quickly, and more efficiently than can be achieved with hot air or radiation processes.

All of our facilities are equipped with VPD ovens. Our Rincon, GA plant has three independent 430.5 sq ft (13345 cubic foot) ovens for large and extra-large power transformers. Each oven is PLC operated to allow for precise temperature, vacuum, time control and for adjustable isostatic pressing of the transformer winding to ensure proper calibration and sizing of the coils.

If a transformer is too large for VPD, then a Hot Oil Spray (HOS) method is used for drying. In this method, the transformer is placed under the vacuum and sprayed with heated transformer oil to remove moisture. HOS is continued until the desired moisture levels are achieved.

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