INCREASING THE OPERATING FREQUENCY OF PAPER-FOIL CAPACITORS BY USING TWO WATER COOLED COILS
The creation of powerful thyristors with small times of restoration of properties allows to increase the switching frequency of the converter, including the paper-foil electrothermal capacitors up to 20 kHz. This can be done using two water cooled coils. Water cooled condensers are known in which the collecting tires of all the plates of one polarity are brought out through the lead-in insulator, and the other polarities are also brought out through the lead-out insulator mounted on the condenser cover. The disadvantage of this capacitor is that the output of the first coil serves as the input of the second coil. Therefore, overheating of water up to 5...10 ℃ is permissible. In order to eliminate this drawback, two additional insulators are installed on the cap of the capacitor, which serve as outputs for two coils. The coils outside the condenser are connected in parallel in water. To calculate electrothermal capacitors with paper-foil plates at known voltages, frequencies, capacities and cooling surfaces, it is also necessary to determine the value of the heat transfer coefficient αT. The purpose of the experiment is to determine the heat transfer coefficient αT in the presence of two cooling coils. For this purpose, prototypes of condenser-type models cooled with water have been created. For a comparative analysis, heating elements were created, simulating losses in paper with one-sided and two-sided winding. At the inlet and outlet of coils, temperatures were measured using mercury thermometers with a division value of 0,1 ℃, and the temperatures were monitored by a China-made HCJYET HT-830 infrared thermometer, the results of which differed by 0,1...0,2 ℃. A comparative analysis shows that the maximum error in determining the heat transfer coefficient αT is 0,8...1%. An analysis of the experimental results shows that in the presence of two cooling coils, it is possible to raise the frequency of electrothermal capacitors to 20 kHz by a corresponding decrease in the active width of the capacitor by 10 mm.