Electrical Measurement* Digital Pressure Transmitter Application in Air Compressor Lin Hexiu (Jiangxi Copper Co., Ltd. Chengmenshan Copper Mine, 332100, Jiujiang) Chengmenshan Copper Ore Dressing Plant Filter Press Workshop 4L -20 The /8 air compressor mainly supplies air source for the filter press. The rated working pressure is 0.8MPa, and the normal working pressure is 0.4MPa~0.7MPa. The air pressure is controlled by the YWK-50-C pressure controller installed on the air compressor tank. Control, when the air pressure is higher than 0.7MPa, the pressure controllers 1 and 2 are connected, the electric control valve acts, the compressed air enters the lower part of the unloading valve, and the valve center of the unloading valve is closed upwards, the air compressor Stop inhalation, the air compressor stops running under no-load operation; when the air pressure is lower than 0.4MPa, the pressure controllers 1 and 3 are connected, the control signal is released, the intake valve is opened, and the air compressor starts to inhale, air pressure The machine load is running, re-compensation to 0.7MPa. The schematic diagram of the YWK-50-C pressure controller is shown. The electric control valve YWK-50-C type pressure controller principle has problems. The -50-C type pressure controller adopts the spring mechanical mechanism's pressure measuring method, and its own pressure measurement error is large, plus the vibration of the air compressor during operation. Large, pressure controllers are installed on the air compressor body, often causing the pressure controller to malfunction. When the air pressure is higher than 0.7MPa, the pressure controller does not operate, the air compressor continues to pressurize, and finally the air pressure rises to the working pressure of the safety valve, causing the safety valve to be opened and relieved, and a great pressure relief noise is emitted. If the pressure controller fails, the electrician needs to adjust according to the pressure value displayed on the pressure gauge, and there is a large error in the displayed value. 2 Solution The pressure measurement error of the mechanism is large, which is easy to cause the failure of the pressure controller. Therefore, it is decided to replace the YWK-50-C pressure controller with a digital pressure transmitter. The structure of the digital transmitter is as shown in the figure. The pressure controller is consistent with the pressure controller of type -50-C. The pressure measurement increases the number of turns of the field winding. The equivalent capacitance and inductance are connected in series, and the equivalent capacitance is reduced. Small, the inductance increases. On the other hand, the ratio between the field winding and the high voltage winding is reduced, and the equivalent capacitance from the high side is significantly reduced. The combined effect of the two aspects can effectively reduce the external equivalent capacitance of the low-voltage side of the transformer, so that the existing compensating reactor can fully compensate the capacitive current of the low-voltage side of the transformer at a frequency higher than 100 Hz. 4 Conclusion (1) Three-phase common-mode transformer, when the pressure between the neutral point and the terminal winding of the test phase is pressed, the non-tested two-phase winding will still induce a voltage due to the flow of the magnetic flux in the core, causing the The voltage between the pilot phase and the non-test phase is increased. When the phase excitation is simultaneously pressurized, the voltage between the two phases will greatly exceed the phase insulation level of 510 kV. This test scheme should be strictly prohibited. (3) When the induced voltage is tested, the low voltage side of the transformer winding is external. (The equivalent capacitance of 2013 is related to the voltage rating of the low-voltage side, the rated capacity, and the ratio between the high and low voltage windings. (4) For the double-star and three-star transformers, if the scheme of pressurizing between the neutral point and the terminal of the tested phase is adopted, when the existing reactor compensates for a lower resonant frequency, the non-tested phase winding can be used in parallel to assist the excitation. Scheme to reduce the equivalent capacitance and increase the resonant frequency of the test loop.
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