Analysis of the influence of temperature on the measurement performance of RC voltage divider

作者： GOZ Electric 时间：2024-12-05 09:57:43 阅读：15

The high-voltage arm of the resistor-capacitor voltage divider has a closed structure, and key components such as the high-voltage arm resistor and capacitor are packaged inside the hollow insulator. Capacitor oil or SF6 gas is used as the insulating medium inside the insulator. The low-voltage arm is arranged in the voltage divider base outside the insulator to facilitate on-site debugging and replacement: According to actual measurements, the surface temperature of the primary voltage divider insulator of traditional resistance-capacitance voltage divider products can reach more than 80°C, and the temperature rise exceeds 40°C, which means The temperature rise of its internal resistance/capacitance components will be greater. Therefore, resistor/capacitor components with high resistance/capacitance value accuracy and small temperature coefficient must be selected during the development process to reduce the impact of temperature rise on the measurement accuracy of the resistor-capacitor voltage divider. However, the high requirements on the temperature coefficient of RC components mean that the material selection, manufacturing process, cost and other aspects of RC components will be significantly affected, which increases the difficulty of component selection and product development, and also increases the cost. At the same time, the problem of high temperature rise still exists. The long-term exposure of the resistance-capacitance voltage divider to high temperature environment will accelerate the aging of its key components, reduce the operational reliability, and reduce the service life. The high-voltage arm resistor is in a closed environment, and the difference between SF6 gas and composite insulators The heat transfer characteristics are poor, and long-term operation results in a large temperature rise inside the voltage divider insulator. The low-voltage arm resistors and capacitor components of most resistor-capacitor voltage divider products are located outside the hollow insulator, and have good heat transfer conditions with the outside world. It can be considered that the temperature of the low-voltage arm resistor/capacitor components is close to the ambient temperature. Due to the large temperature difference between the high and low voltage arm resistors/capacitors, the actual voltage dividing ratio of the resistor-capacitive voltage divider deviates from the ideal voltage dividing ratio. resistance/

The temperature coefficient of capacitance changes as the ambient temperature changes, and there is also a large deviation due to different materials. The premise for the analysis and calculation in this section is as follows:

1) It is believed that the resistance/capacitance materials of the high and low voltage arms of the resistance-capacitance divider are consistent, that is, the material temperature coefficients are consistent.

2) During the temperature rise test described in this article, the temperature range of the resistor/capacitor element is between 20 and 50°C. The temperature coefficient of the resistor/capacitor element is relatively stable within this temperature range, so this article assumes that the temperature coefficient remains constant.

3) Calculate the error using the average temperature rise as the input condition.

4) It is assumed that the resistance/capacitance temperature of the low-voltage arm of the resistor-capacitance divider is consistent with the ambient temperature.

The calculation results of the temperature rise additional error of the resistor-capacitor voltage divider under different temperature coefficients and average temperature rise conditions are shown in the figure.

By analyzing the relationship curve between the temperature rise and the additional error shown in the figure, it can be seen that the material temperature coefficient and temperature rise of the resistor and capacitor components have a significant impact on the measurement accuracy of the resistor-capacitor voltage divider. The greater the temperature rise of the high-voltage arm resistance/capacitance or the greater the material temperature coefficient, the greater the deviation between the actual resistance/capacitance value and the rated design value, which in turn leads to a greater measurement error of the resistance-capacitance divider.

A 200kV high-precision resistance-capacitance divider thermal simulation model is established in the Fluent simulation environment. The ambient temperature is 20°C, and the air convection heat transfer coefficient is 20W/(m°C). Calculate the average temperature rise of the high-voltage arm resistor, capacitor and flange after the high-precision resistor-capacitor divider reaches thermal equilibrium under different heat loss conditions. The calculation results are shown in Table 3 and Table 4. The resistance thermal current of the 200kV high-precision resistor-capacitor divider is 1mA. When , the average temperature rises of the top flange, resistor and capacitor components relative to the ambient temperature are 5.4, 25.3 and 14.5°C respectively. When the resistance thermal current is 2mA, the average temperature rises of the top flange, resistance and capacitance components relative to the ambient temperature are 10.2, 38.9 and 18.6°C respectively.

Combining the relationship curve between the temperature rise and the additional error shown in the figure, it can be obtained that the temperature coefficient of the resistance element is 15ppm/℃, and when the average temperature rise is 25.3 and 38.9℃, the calculated additional error of the resistance temperature rise is about 0.04% and 0.06%. Similarly, assuming that the capacitive element is 200ppm/℃ and the average temperature rise is 14.5 and 18.6℃, the calculated additional error value of the capacitor temperature rise is about 0.3% and 0.4%.

The above comparison illustrates:

1) Reducing the temperature rise can effectively reduce the additional error caused by the temperature rise of resistors and capacitors.

2) After reducing the temperature rise, the selection requirements for RC components can be relaxed. The selection range of parameters such as resistance/capacitance accuracy and temperature coefficient of RC components is wider, which effectively reduces the difficulty and cost of component manufacturing and improves technical economy.

3) Reducing the temperature rise can extend the service life of the resistor-capacitor components and ensure the operational reliability of the resistor-capacitor voltage divider throughout its life cycle. Therefore, the design idea of a high-precision resistor-capacitor voltage divider should focus on reducing the internal temperature rise of the resistor-capacitor voltage divider. Specific measures include:

1) The main measures are to optimize the design of main electrical parameters, reduce the thermal power of the resistor-capacitor voltage divider, and fundamentally reduce the internal heat generation of the resistor-capacitance voltage divider.

2) Auxiliary measures are to improve the overall heat dissipation design of the resistor-capacitor voltage divider, strengthen the convection of the internal insulating medium, and increase the internal and external heat exchange speed.