Heating is the main factor in the vacuum heating equipment during the preheating stage.

The vacuum drying equipment is divided into four stages: preheating, dewatering, final drying and end-point judgement.

In the preheating stage, heating is the main factor, and the air ballasting effect is used to keep the drying tank in a low vacuum state. At the same time, the air in the tank and the evaporated steam are fully utilized to transfer heat from the heater to the transformer body through convection and conduction, so that the temperature of the winding and core can be raised quickly. The evaporated water vapor can be pumped out and the temperature in the dryer can be uniformly distributed by means of the stirring action filled with air. When the air temperature, winding temperature and core temperature in the tank reach the set value, it can enter the stage of pressure swing dehydration.

Insulation drying of power transformer is a very important process in the process of transformer manufacturing, which has a great impact on the final quality of transformer. Some of the residual water in the insulating material will form electrodes under high electric field and produce free discharge, which will gradually destroy the insulation characteristics of the insulating material. At the same time, in the normal operation of the transformer, the aging process of the insulation material itself will be accelerated, and the life of the transformer will be shortened. If excessive drying results in crystalline water escaping from the insulating material, it will lead to premature aging of the insulating material and reduce the mechanical strength.

When the vacuum degree in the drying tank reaches the final dry pressure, and the temperature and leakage rate of each monitoring point meet the judging conditions, the vacuum drying terminal point judgment can be carried out to determine whether the drying of the transformer has met the requirements.

The drying equipment consists of four parts: vacuum drying tank, heating system, air extraction system and automatic control system. The automatic control system takes the programmable logic controller PLI as the core, has various control and protection functions required by the pressure-swing method, can automatically control the pressure-swing drying process and complete the whole process and end-point judgment. Break. And more than 20 different programs can be stored to suit different capacity transformers.

The main characteristics of vacuum drying by pressure swing method are as follows:

It is a new gas drying technology which uses dry and dehydrated steam as heat carrier. It makes full use of the heat of vaporization to improve the heating efficiency, and uses the method of controlling the pressure change in the drying process to correctly deal with the relationship between heating and vacuum, breaking through the traditional concept, so it can use simpler equipment with high heat transfer efficiency, energy saving, short drying cycle, uniform heating and energy saving. Advantage.