VACUUM DRYING OVEN FOR TRANSFORMER WINDINGS

A vacuum drying oven is a multipurpose device. It is used to dry transformer windings, electric motor rotors, powders and pastes, adsorbents, metal ceramics, wood etc. In this article we focus on the vacuum drying oven for transformers.

When drying of transformer windings becomes necessary

Drying of transformer windings is important at all stages of transformer life cycle. This is due to the fact that moisture reduces the dielectric strength of the insulation and accelerates its aging. Moisture can enter the windings even during transformer assembly, making it necessary to dry the wingdings. The dielectric strength of a well dried oil-impregnated cardboard is 20-25 times higher than that of untreated cardboard.

Contamination with water also occurs during operation of the transformer, again, demanding action. The drying process can be performed in a vacuum drying oven. While it is not the only method of winding drying, it is still one of the most popular due to simplicity and the uniformity of moisture removal from the entire volume of the insulation.

Vacuum drying oven: how it works

A vacuum oven dries transformer windings in several stages. First, the insulation is heated, releasing water from the internal layers to the outside as vapor. The vapor is then carried from the surface of the insulation to the outside. the The motion of water inside the insulation is due to the different concentrations of moisture and temperature at different points of the windings. Moisture moves from high concentration spots and hotter points to the portions with lower temperature.

Water migration from the internal layers of the windings is facilitated by thorough heating of the transformer core.

GlobeCore vacuum drying ovens

GlobeCore manufactures vacuum drying ovens for transformer windings and many other materials. Each oven is produced for specific conditions and capabilities available on customer site. Here are the things that can be select:

• oven dimensions;
• the heating method: oil, steam, IR etc;
• door drive: mechanical, pneumatic or hydraulic;
• core loading method.

The GlobeCore vacuum drying oven operates as follows. The winding is loaded into the oven and subjected to 100-110°С. Then air is evacuated from the oven to reduce boiling temperature, accelerate drying and remove water vapor from the chamber, keeping relative humidity low. The vapor is collected in a condensation chamber.

Using GlobeCore vacuum dry ovens during assembly and maintenance of transformers extends their lifetime by improving the dielectric strength of the insulation.