The working principle and importance

In a vacuum (typically ≤ 133Pa), the boiling point of water is significantly reduced. The vacuum pump unit continuously pumps air to form a negative pressure inside the transformer body, and the moisture in the insulating material evaporates at low temperatures and is discharged by the vacuum system. Compared with atmospheric pressure drying, vacuum drying can avoid the damage of high temperature to the insulating material, and the efficiency is increased by more than 30%.

Transformer insulation materials (e.g. cardboard, pads) have an initial moisture content of 4%-8%, while the operating standard requires ≤ 0.5% (0.3% ≤for 500kV class). Moisture will reduce dielectric strength and increase dielectric loss, and vacuum drying is the core process to ensure the safety of transformers.

The Core Composition of Vacuum Pump Unit

Backing pump: oil sealed rotary vane pump or dry screw pump is mostly used, which can quickly establish rough vacuum.

Booster Pump: The roots pump is used in the medium vacuum stage, and in combination with the molecular pump, it can achieve a high vacuum (10⁻² Pa) and completely remove deep water.