High-precision DC standard voltage divider vehicle integrated platform simulation

Author： GOZ Electric Time：2024-07-23 09:19:03 Read：12

3. Design of standard voltage divider

Imported resistors are selected, with a resistance accuracy of 0.01% and a temperature coefficient of 5ppm/°C. Considering the multiple series connection and heat dissipation of components, the theoretical temperature coefficient of the entire system is 10ppm/°C. Within the range of 20°C±20°C, the theoretical maximum change of the voltage divider ratio is 0.02% due to changes in ambient temperature. A 50kV test voltage divider was designed with this resistor, and the overall temperature coefficient test of the voltage divider was carried out (placed in a constant temperature box, and the temperature coefficient test was performed at 4 points from 20°C to 60°C). The test results showed that the temperature coefficient of the voltage divider did not exceed 5ppm/°C. Under the action of high voltage, leakage current also flows through the insulating bracket of the voltage divider. If this current does not affect the voltage divider ratio, its size should be limited to the order of 10~9A. The voltage divider bracket uses organic glass and polytetrafluoroethylene materials with good surface state characteristics, and the surface resistance is sufficient to meet the above requirements. However, the insulating surface is prone to static electricity, adsorbing dust and moisture, so the inside of the voltage divider must be kept highly clean and free of dust and impurities.

4. Electric field simulation calculation and parameter optimization design

The high-stability DC voltage source designed in this paper is applied to the field calibration experiment of DC transformer. The output parameters of the DC voltage source and its own corona have a close relationship with the reliability of the test results. The corona of the high-stability DC voltage source mainly depends on the field strength distribution on the surface of the voltage source. If no voltage equalization measures are taken around the voltage source, the corona current and leakage current of the voltage source will increase, affecting the test results. The designed 1300 kV high-stability DC high-voltage system has a three-capacitor column structure, which is mainly composed of three capacitor columns, high-voltage silicon stack, flange, voltage equalization ring, base and cover plate.

Due to the complex actual structure of the high-stability DC voltage source, it is reasonably simplified in the calculation model, and the support rod of the voltage equalization ring is ignored. The capacitor column is filled with simulated dielectric, with a relative dielectric constant of 4 and a resistivity of 7.5×10 (12th power) Ω·m; the relative dielectric constants of air and SF6 gas are 1. In the calculation model, it is considered that air and SF6 gas are ideally insulated and there is no current inside. During the calculation, a voltage of 1300kV is applied to the voltage-equalizing ball at the top of the capacitor column, and a potential of 0 is applied to the boundary between the chassis and the air. The maximum field strength on the generator surface appears at the top of the capacitor, with a value of about 1.14×10 (6th power) V/m. In addition, the area with a larger field strength is above the bottom pillar, with a value of about 1.08×10 (6th power) V/m. This maximum field strength is much smaller than the critical field strength of air (25kV/cm), so the electric field distribution and intensity fully meet the design requirements.

5. Key technologies of DC voltage standard for field use

DC transformers can be divided into analog output and digital output DC transformers according to the output type. According to the output type of DC transformers, there are two DC transformer calibration schemes, including DC transformer analog calibration scheme and DC transformer digital calibration scheme. The developed DC transformer calibrator has the calibration function of DC transformers with both analog output and digital output. DC transformers are generally calibrated by direct measurement.

5.1 Analog quantity calibration scheme For DC transformers with analog output, such as zero flux DC current transformers or traditional DC voltage dividers, the DC transformer calibrator adopts the analog quantity calibration scheme "double meter method", that is, two digital multimeters are used to synchronously sample the secondary outputs of the standard side and the test side, and then the error data is calculated. The "double meter method" is used for on-site calibration of DC transformers with analog output. High-precision digital multimeters are used for analog sampling on both the standard side and the test side. The digital multimeter uses Agilent's 34461A, with an input range of 0~1000 VDC, a sampling rate of up to 100kHz, and an annual voltage reference stability of 8ppm for DC voltage measurement. By using the software synchronization trigger function, the trigger accuracy reaches the sub-microsecond level, ensuring strict synchronous sampling on the standard side and the test side.

5.2 Digital quantity calibration scheme For DC transformers with digital output, such as all-fiber DC current transformers or DC voltage dividers with digital output, the DC transformer calibrator adopts a digital quantity calibration scheme. The simulated output signal is sampled, and the test product side uses a protocol conversion device to sample the digital output signal of the test product. After the digital protocol is parsed, it is sent to the verification system for error calculation. In the DC transformer digital verification scheme, the standard side and the test product side use the second pulse or B code output by the clock synchronization device for synchronous sampling. The clock synchronization accuracy reaches the nanosecond level, which can ensure the strict synchronous sampling of the DC transformer secondary signals on the standard side and the test product side.

6. Conclusion

This paper can realize the automatic deployment of the vehicle-mounted integrated platform of the field verification equipment of the high-voltage DC standard voltage divider through experiments and related simulations, and develop a hydraulic support platform for the standard voltage divider. The research results of this paper can be applied in the subsequent planning of DC projects, and provide a positive role in the development and promotion of my country's independent DC measurement device technology. At the same time, the field standard source integrated verification system developed in this project can provide support for field error verification and equipment performance evaluation.