A new solution for high-precision measurement of RC voltage divider

作者： GOZ Electric 时间：2024-12-01 09:54:00 阅读：12

As one of the key main equipment in AC/DC power grid system, voltage transformer plays an important role in power metering, power monitoring, relay signal transmission, fault recording, etc. With the extensive application of power electronic core equipment (converter valve, flexible DC valve, DC circuit breaker controllable lightning arrester, energy dissipation device, flexible AC transmission system equipment (FACTS), static synchronous compensator (STATCOM), etc.) in modern AC/DC power grid, the electromagnetic environment has become more and more complex, and transient waves such as AC, DC, harmonics, and fault traveling waves exist simultaneously. Accurate and fast measurement of the above voltage composite signals is the key to ensuring the safe and reliable operation of the power grid. At present, RC voltage dividers are widely used as voltage measurement equipment in both AC and DC fields in DC projects at home and abroad. Compared with traditional AC voltage transformers (electromagnetic voltage transformers, capacitive voltage transformers), they are characterized by wide measurement bandwidth, fast response speed, and technically capable of measuring DC operating voltage and harmonic voltage signals.

As the key performance indicators of the RC voltage divider, measurement accuracy and measurement stability have always been the key issues to be considered in its design process. The IEC61869-6 and IEC61869-15 standards have put forward clear requirements for the DC and AC broadband signal measurement accuracy of the RC voltage divider. The overall measurement error of the RC voltage divider mainly includes:

1) Measurement error caused by the stray capacitance of the primary voltage divider.

2) Measurement error caused by the temperature rise of the primary voltage divider.

3) Error caused by the secondary voltage divider.

4) Error caused by the transmission cable.

5) Error of the secondary acquisition system, etc.

Like the widely used capacitance voltage transformer (CVT) in the AC power grid, the primary voltage divider ratio of the group capacitance voltage divider is also affected by the stray capacitance on site. The project team conducted an in-depth analysis of the influence of stray parameters on the voltage divider ratio of the RC voltage divider and proposed the equipotential shielding technology. The research results provide support for the influence of stray parameters on the RC voltage divider when performing high-frequency measurements. As one of the key components of the RC voltage divider, the resistor will continue to generate heat during long-term operation. The heat accumulates in the sealed voltage divider casing, causing a large temperature rise inside the voltage divider, causing the resistance values of the high and low voltage arms of the voltage divider to deviate from the design values, resulting in measurement errors. At present, the main method is to improve the circulation of gas inside the voltage divider, improve the efficiency of heat dissipation, and reduce its temperature through structural optimization design. Current research mainly focuses on the simulation calculation and heat dissipation optimization of resistor heating, and there is no suppression design for the heat source. Based on the above situation, this paper proposes a method and design scheme that can effectively improve the measurement accuracy of the RC voltage divider, studies the influence of stray capacitance and temperature rise on the measurement accuracy of the RC voltage divider, compares and analyzes the measurement accuracy of the traditional RC voltage divider and the high-precision RC voltage divider, designs and develops a high-precision RC voltage divider prototype and conducts experimental verification, proving the effectiveness of the design scheme.

The influence of stray capacitance and temperature rise on the measurement accuracy of RC voltage divider was studied, and a technical solution that can effectively improve the measurement accuracy of RC voltage divider was proposed. The transmission principle and error influence of traditional RC voltage divider and high-precision RC voltage divider were compared and analyzed. The project team designed and developed a high-precision RC voltage divider prototype based on equipotential shielding technology and temperature rise control scheme, and verified the effectiveness of high-precision measurement technology and temperature rise algorithm through measurement performance comparison test. The technology is of great significance for guiding the main parameter design, key component selection and overall design of RC voltage divider.

The project team first proposed the equipotential shielding technology using RC circuit and successfully applied the technology to the development of high-precision RC voltage divider, which improved the measurement accuracy of AC signal by 2 measurement levels compared with traditional RC voltage divider.

In view of the problem of temperature affecting measurement accuracy, different from the traditional passive heat dissipation idea, an innovative technical solution was proposed and implemented by optimizing the design of main electrical parameters to reduce the thermal power of the RC voltage divider, which reduced the temperature rise by several times and effectively improved the measurement accuracy. Limited by the current testing methods and conditions, it is impossible to accurately test the surface temperature of the high and low voltage arm resistor/capacitor components of the RC voltage divider during the test, and it is impossible to accurately optimize the temperature rise calculation method. The calculated value of the resistance/capacitance change derived from the flange temperature data of the RC voltage divider and the classical heat transfer theory is close to the measured value, which provides a new idea for the main parameter design of the RC voltage divider for engineering and the selection of the resistance/capacitance components of the product.