A novel capacitor vacuum drying impregnation process

A novel capacitor vacuum drying impregnation process Ma Lihua (Wuxi Power Capacitor Co., Ltd., Wuxi, Jiangsu 214035) Judgment basis and judgment method for vacuum drying really finished. "Variable pressure method" vacuum drying impregnation process can be one-third of mine sister time, improve the partial discharge qualification rate of the capacitor, thereby improving the product quality, saving energy 1 Introduction Vacuum condenser drying impregnated power capacitor is to exclude the capacitor core Moisture and gas in the son, then impregnated with purified and tested infiltrant, filling all voids between the internal solids of the product to improve the electrical properties of the existing product. The existing power capacitor vacuum drying impregnation process is subject to heating The stages of low vacuum, high vacuum, cooling, oil injection and impregnation determine whether or not each stage is completed by measuring whether the vacuum degree meets the process requirements and stipulates a certain period of time, and whether it can enter the next stage. Its disadvantage is that it is impossible to judge whether the water in the condenser core has fully escaped before the oil injection stage. At a certain temperature, the degree of vacuum and time required for the process have been achieved, but the evaporation and condensation of the water molecules have reached a dynamic equilibrium. The moisture in the capacitor core may not be completely discharged and it will enter the pouring stage, which will affect the capacitor. Another case of electrical performance is that although the process time is not yet reached, the moisture in the capacitor core has fully escaped and the vacuum is still continuing, wasting a lot of energy. Therefore, we need to find a new process to judge whether the vacuum drying is really over. Instead, it can enter the pouring stage to improve the electrical performance of the capacitor and save energy.

Less than it combines the low vacuum and high vacuum into one. At this stage, the vacuum in the tank is changed by filling the vacuum tank with dry air so that the moisture in the capacitor core can fully escape. Through a certain method to find an end point to determine whether the vacuum drying really ended and enter the pouring stage 2 “Variation method” Principle of vacuum drying Traditional vacuum drying principle: The traditional vacuum drying of capacitors is to increase the heating capacity of the capacitors in the vacuum tank. The kinetic energy of the water molecules in the capacitor core (W=KT2 /2) makes it become water vapor to evaporate from the insulating material, increase the partial pressure of the water vapor in the capacitor core and then vacuum the vacuum tank. The pressure in the space around the capacitor is reduced, so that a pressure difference AP is formed between the capacitor core and the surrounding space, so that the water vapor diffuses from the capacitor core and diverts to the surrounding space and is pumped by the vacuum pump to eliminate the moisture in the capacitor core. With the role of gas, traditional methods should achieve the best drying effect. First, increase the temperature, so that the moisture in the capacitor core can get enough kinetic energy to become water vapor, but the temperature is too high, the insulation material will appear aging, damage The second is to increase the degree of vacuum insulation, in order to increase the Ap suction capacitor core moisture and gas; higher vacuum, The saturated vapor pressure of water vapor decreases, and water molecules easily become vapor escaped. However, the degree of vacuum cannot be increased indefinitely. It is limited by the ultimate vacuum of the vacuum pump. If the degree of vacuum is too high, the heat conduction of the gas molecules is reduced. The water molecules in the insulating material cannot obtain enough energy to evaporate, but it will affect. The evaporation rate of moisture in the capacitor core finally reaches a dynamic equilibrium under certain temperature and vacuum degree. The evaporation and condensation of moisture reach a dynamic equilibrium. The water molecules in the capacitor core cannot be completely discharged, affecting the electrical performance of the capacitor. Thirdly, the drying time is extended. , Wasting a lot of energy on the basis of the vacuum drying principle of the container. In the vacuum drying controlled temperature range, when a certain degree of vacuum is drawn, the evaporation and condensation of moisture in the insulating material reach a dynamic equilibrium, due to the vacuum tank The heat conduction of gas molecules is reduced. The moisture in the pores of the insulating material cannot obtain enough energy to turn into water vapor. Then, a certain amount of dry air is put into the tank through a gas release valve to increase the heat conduction of gas molecules in the vacuum tank. , Insulation material can get enough energy to become water vapor escaped by vacuum pump When drawn down and when a certain degree of vacuum, filling the tank must again air dried. This is repeated several times, which greatly increases the rate of evaporation of water molecules in the capacitor core, and completely eliminates the effects of moisture and gas in the capacitor core. Then through a certain method to find an end point to determine whether the vacuum drying really ended and enter the pouring stage 3 "Variation method" vacuum drying impregnation equipment to achieve "variable pressure method" vacuum drying impregnation process, first of all existing vacuum equipment Transformation 3.1 The existing vacuum tank heating system is reformed. In the existing vacuum tank, two pipelines are added to the bottom of the existing vacuum tank. Steam enters the bottom of the tank in two ways from the end of the tank. Each of the two pipelines passes through three rows. The tube introduces steam into the can jacket to heat the capacitor. To make the condensate in the jacket drain out of the jacket in time, add a drain pipe at the bottom of the vacuum tank and connect it to the tank jacket through three pipes. When the jacket water flows into the drain pipe, install it at the outlet of the drain pipe. The filter drain valve, steam trap, and a leveler are used. Usually, the trap works, and the accumulated water in the jacket can be drained in time. When the accumulated water reaches the red line position specified in the leveler, the drain valve is opened. Discharge water to ensure that there is no water in the tank jacket, so that the steam more efficient heating capacitor in the tank can be known from the experiment: by placing the platinum resistance temperature probe in the tank, tank, tank tail, tank left, tank right The analog capacitors with pin resistance temperature probes are placed in tank doors, tanks, and tank tails in the tank top, tank bottom, and three cores. They are led out of the vacuum tank using lead wires, and are connected to an automatic temperature meter. Printed once every 1 hour, the results found that the temperature rise of the capacitor core faster than before the transformation, the tank temperature is even than before the transformation, the temperature can be controlled within 2C.

3.2 The vacuum unit still uses the spool type vacuum pump and the second-stage Roots pump, but the main valve adopts the high-vacuum pneumatic flapper valve with the position indicator bellows shaft seal to improve the sealing performance of the tank door sight glass window, etc. The total leak rate of the tank is controlled at 10Pa.L/s3.3 The use of the German Leybold TM TM21 vacuum gauge, anti-contamination TR216 regulation, with print control section, and signal output functions to supervise the manual operation and the entire vacuum drying The impregnation process is automatically controlled.

3.4 Install a condenser with good cooling effect in front of the Roots pump, and transfer energy a to the deep layer so that the moisture in the pores is cooled by the condenser and discharged into the water after the leM in the core of the container is pumped out of the vacuum pump. The vacuum system prevents the water vapor emulsification pump oil, increases the pumping capacity of the vacuum pump, and prolongs the service life of the vacuum pump.

4. Judgment on whether vacuum drying is truly finished in the "variable pressure method" 4.1 Basis for judgment When the high vacuum pneumatic diaphragm valve is closed for a period of time t, the degree of vacuum in the vacuum tank is determined by the following equation: the time between; close the high vacuum pneumatic gear The degree of vacuum in the vacuum tank after the plate valve t time; p vacuum degree in the vacuum tank before closing the high vacuum pneumatic flapper valve; (Qdt) the surface of the vacuum tank itself is deflated, the gas contained in the core of the tank capacitor and The amount of outgassing due to evaporation of water vapor after heating, etc. is negligible due to the deflation of the inner surface of the vacuum tank during t (t is small), and the gas and water vapor contained in the capacitor core at the end of vacuum drying. All are pumped away by the vacuum pump, that is, X (Qdt) 0 is obtained by the above formula: p = p + Q> tIV. When the total leakage rate of the vacuum tank is constant and the specified pt is a fixed value, t should be a fixed value. After closing the high vacuum pneumatic baffle valve, the vacuum degree shall be measured after t time. The actual measured vacuum degree shall tend to be pp (p is the minimum value). At this time, it can be judged that the vacuum drying of the capacitor is really over, and the temperature drop and the oil injection can be entered. , impregnation stage until the tank 4.2 Judgment method When the vacuum tank heated to the required temperature for the process began to vacuum, when the vacuum reaches p, close the high vacuum pneumatic damper t, observe the vacuum gauge measurement p, when P-, then open the air release valve to put dry gas into the tank to close the air release valve, then open the high vacuum pneumatic flapper valve to continue vacuuming, when the vacuum is reached, repeat the above process, after repeated several times When the high true value Pn is turned off to satisfy Pn-PP, it can be judged that the vacuum drying of the capacitor has been truly completed. The specific operation process of entering the cooling, oil filling and impregnation stage is shown in Table 1. What are the tQop and p parameters due to different vacuum drying impregnation equipment? Selection, to be determined through practice to determine the 5 process test First, the vacuum tank and tanker oil accumulated with a dry cloth to wipe clean, then close the tank door heating vacuum, the drying of the internal surface of the product Let it be turned into steam by a vacuum pump until the inner surface dries up. Stop the heating and vacuuming. Prepare the process test 334-1 with 28 capacitors in the tanker, connect them by single oil injection and close the tank door. After the vacuum tank is heated to 80~90C, open the slide valve to pump vacuum and the temperature is controlled at 80 ~ 90C. When the vacuum reaches 1kPa, open the second Roots pump to continue vacuuming. When the vacuum reaches 1Pa, close the high. Vacuum pneumatic flapper valve and Roots pump, after 5min, the vacuum drying end of the judgment curve (from = outside Q) tIV calculated 1.35Pa, the provisions of the reed is 0.1), then open the valve to the vacuum tank filling dry atmosphere To vacuum 70kPa, close the air release valve, and then open the high vacuum pneumatic flapper valve to vacuum up to 1kPa, then open the second Roots pump to continue vacuuming up to 1Pa, repeat the above process until the high vacuum pneumatic flap valve is closed for 5min , Vacuum degree decreased 1.42-1.35 Test data Compared with the previous similar products, there is no abnormal vacuum drying time, and the increase of the capacitor can be seen, the use of "variable pressure method" for vacuum discharge rate of capacitors ,Saving of energy is saved Judgment of vacuum drying No. of dryness between bundles Drying of strands Drying of knots Number of times of discontinuation Times of original vacuum Vacuum drying of dipping Dry dipping (h) Time (h) Partial rate of one time (%) Drying time between dry and dry stains % dry-down impregnation Partial discharge Local discharge starting voltage Electrical extinction ratio average voltage ratio (kV) Average dry impregnation method is feasible, not only can shorten beam curve see time (h ) Vacuum degree (Pa) Temperature (°C) t When the vacuum degree is judged by the end of the drying Remarks Not a fixed value Open high vacuum Pneumatic flapper valve Open H- Open high vacuum Pneumatic flapper valve Open H- 150 Class 2 Z pump Close the high vacuum pneumatic damper valve t after the time measured vacuum p1, when p1-pt>pi, open the air release valve to fill the tank dry air to pb, close the air release valve to open the H-150 pump, off the second Z Original p wide open high vacuum pneumatic flapper valve open H- open high vacuum pneumatic flapper valve open 150 secondary Z pump closed high vacuum pneumatic flapper valve t time after measuring vacuum factory 2, when p2 -pi, open put The valve fills the tank with dry air to pb, closes the purge valve to open the H-150 pump, closes the second stage Z pump to close the high vacuum pneumatic damper After the valve t time measured vacuum pi, when the pn-pi, it can be judged that the vacuum drying really ended the pump cooling 45 open high vacuum pneumatic flap valve open H-150 2 Z pump open high vacuum pneumatic flap valve table 1 vacuum Dipping process specific operation Table 2 Three types of capacitor process test results Pressure method "Vacuum drying impregnation process is characterized by: vacuum drying impregnation time per tank capacitor is not a fixed value

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