Transformer is a complex unit, and the processes of its manufacturing, servicing and repairs involve many operations and require a number of different machines. This article is about one of the most important machines, namely, a transformer evacuation system.
What is evacuation?
In general, evacuation is the process of pumping out gases or vapor from a vessel to achieve a negative pressure (below the standard atmospheric). Beside creating vacuum, evacuation involves keeping that vacuum for a necessary duration of time.
When is transformer evacuation necessary?
The first evacuation is performed at the assembly stage, the so called pre-evacuation. Its objective is to remove air from the transformer tank and to check vacuum seal reliability. Pre-evacuation removes moisture from the surface of transformer core and improves insulation performance.
Microscopic bubbles of air in the paper and oil insulation can cause partial discharges, which later lead to intercoil or interlayer short circuits and burning of the windings. This is why evacuation is also performed when the transformer at or above 150 kV is filled with new oil. To eliminate the risk of insulation breakthrough due to air bubbles, the transformer is also evacuated after the filling. In the process of filling, the evacuation is performed to the residual pressure specified in the transformer manuals.
Evacuation is also performed in the following stages of the transformer life cycle, for maintenance and repairs (adding oil, opening the tank etc).
GlobeCore transformer evacuation system
GlobeCore manufactures the BV transformer evacuation systems. They include two groups of vacuum pumps. The two backing pumps reach preliminary vacuum, whereas the booster reaches the highest vacuum in the transformer tank. The combined effect of the pumps improves process efficiency. The geometric rate of air or vapor extraction, depending on the model of the equipment, is in range from several hundred cubic meters per hour to several thousand, with the ultimate vacuum of 0.01 mbar.
The benefits of GlobeCore transformer evacuation systems
The benefits of GlobeCore transformer evacuation systems are:
- suitable for application at every stage of transformer life cycle (assembly, servicing and repairs);
- easily integrated into the important transformer servicing processes. The systems can be used as stand-alone plants, or in combination with transformer oil drying and purification plants, and can also be in important part of other equipment, such as transformer winding drying ovens;
- the evacuation system not only removes air, non-aggressive gas, vapor etc, but also dehydrate the upper layers of solid insulation.
- depending on customer requirements, the evacuation system has several construction options (skid on wheels, on trailers etc), which, along with the control cabinet, makes the transformer evacuation system convenient in operation.