Active V/I conversion capacitor voltage divider weak output voltage sensor error calibration system

作者： GOZ Electric 时间：2024-07-19 09:20:57 阅读：12

Introduction

With the continuous construction of smart grids, the State Grid is vigorously promoting the deep integration of primary and secondary electrical equipment to realize functions such as feeder status monitoring and control, fault location processing, and improve the level of distribution network automation. As an important device in the integration of primary and secondary distribution networks, AC voltage sensors should meet the requirements of measurement and protection at the same time, and take into account miniaturization, and can be integrated with primary equipment such as pole switches. The primary and secondary fusion voltage sensors that are currently being gradually promoted and applied are all small signal output-related technical requirements, and the output voltage of the primary and secondary fusion AC voltage sensors is 3.25/3V. In comparison, the standard voltage transformer outputs of metrological institutions such as provincial companies and national high voltage metering stations are all 100V or 100/3V. In order to establish an error calibration system for weak output voltage sensors and realize their value traceability, this paper uses an active V/I conversion capacitor divider with the same weak output as a standard device, which has excellent frequency characteristics and high measurement accuracy, and has no high input impedance requirements for the rear load. However, its rated output is a 5V reverse voltage signal. In order to match the output voltage of the standard and the sensor and make the dual-channel error test unit work in the best performance state, the paper designs a precision voltage matching unit with a two-stage electromagnetic coil for feedback compensation to achieve the inversion and proportional voltage division of the output signal of the standard, and conducts error analysis and testing. Finally, a weak output sensor error calibration system including an active standard, a precision voltage matching unit and a dual-channel error test unit was established, and the error test of weak output voltage sensors based on different principles was completed.

1. Weak output voltage sensor error calibration system

The active standard is a capacitive voltage divider based on the weak output active V/I conversion principle. Its voltage division point is 0 potential, and there is no input impedance requirement for the rear load. The rated output voltage of the active capacitor voltage divider is 5 V, and the active V/I conversion principle determines that its output is an inverted voltage. The output of the weak output primary and secondary fusion voltage sensor is 3.25/3 V, and the two-channel input voltage ratio of the dual-channel error test system based on Labview and NI PXI-5922 is controlled between 0.5 and 1.0 to achieve its optimal performance. At this time, its measurement error is less than 0.5 ppm. In order to achieve the matching between the output voltage of the weak output sensor and the active standard, a precision voltage matching unit is designed to perform inversion and proportional conversion on the active capacitor voltage divider voltage, and the error calibration of the weak output primary and secondary fusion voltage sensor is realized in conjunction with a high-precision dual-channel error test system.

2. Active V/I conversion standard capacitor voltage divider

A capacitor voltage divider based on the active V/I conversion principle is used as a standard. Its schematic diagram is shown in the figure. The high and low voltage arm capacitors are compressed gas standard capacitors and low-loss solid dielectric capacitors, respectively. The corresponding auxiliary circuit is used to complete the accurate measurement of voltage.

Compared with the traditional capacitor voltage divider, the shielding potential of the capacitor voltage divider based on the active VI conversion principle is the ground potential, which is the same as the 0 potential of the high and low voltage arm capacitor connection point, and will not generate additional errors caused by leakage current, and the rear-end load will not be equivalently connected in parallel to the low voltage arm capacitor, thereby causing errors in the voltage divider ratio.

3. Precision voltage matching unit

3.1 Basic principle

Since the active standard is rated for inverted 5V signal output, a precision voltage matching unit needs to be designed to match the output of the weak output sensor with the output of the standard.

3.2 Error analysis

For the main circuit, the existence of G greatly improves the open-loop voltage gain of the main circuit. Assuming that the open-loop voltage gains of the main circuit op amp are Av, and Av2, respectively, the error introduced by the main circuit is reduced from △3 to A4.

4. Error verification of weak output voltage sensor

By developing high-precision active standards, precision voltage matching units, and cooperating with dual-channel error test units, the error verification system of weak output voltage sensors is developed.

The developed error calibration system is used to perform error calibration on 10kV capacitive and RC weak output voltage sensors at 2%, 5%, 20%, 100%, 120% and 190% rated voltage.

5. Conclusion

The error calibration system of weak output voltage sensor is established with the active V/I conversion capacitor voltage divider with good measurement accuracy and load capacity as the standard. In order to achieve the output voltage matching between the standard and the voltage sensor, a precision voltage matching unit with inverting and proportional voltage division functions is designed. Through error analysis, parameter design and testing of the precision voltage matching unit, its ratio error is less than 21.8 ppm and the angle error is less than 14.1urad. Finally, with the high-precision dual-channel error test system, an error calibration system suitable for weak output voltage sensors is established, and error calibration is performed on voltage sensors of different principles. The precision voltage conversion unit designed in this paper will improve the applicability of the active proportional standard. The developed error calibration system has engineering practical significance for the value traceability and error calibration of weak output sensors.