Design of voltage sensor based on resistor divider principle

作者： GOZ Electric 时间：2024-05-26 09:23:32 阅读：18

    At present, electromagnetic voltage transformers and capacitive voltage dividers are mostly used to collect voltage signals on power systems. Since the electromagnetic voltage transformer contains inductive windings and magnetic materials, its measurement range is limited by the magnetic saturation of the core, and the transmission frequency band is not wide enough. As an inductive component, there is the possibility of ferromagnetic resonance and poor reliability. Capacitive voltage dividers are capacitive components and may resonate with inductive components in the system, causing overvoltage and endangering the normal operation of the equipment and system. The voltage sensor studied in this article adopts the resistor divider principle. There is no ferromagnetic resonance, which overcomes the shortcomings of core magnetic saturation. There is no longer load sharing. Short circuits and open circuits are allowed. It has high reliability. Compared with traditional electromagnetic transformers, it is small in size and weight. With the advantages of light weight, simple structure, wide transmission frequency, and no resonance point, a voltage divider can meet the requirements of measurement and protection. Also, it performs better than a capacitive voltage divider because there is no ringing problem. The resistive voltage divider studied in this article is designed for a voltage level of 10kV. We performed a computational design of a resistive voltage sensor, built a resistive voltage divider prototype, and performed experiments and error analysis on it.

Design of structural parameters of resistor divider

     The most important thing about the voltage sensor is the error problem, and the determination of its structure and parameters must be considered from the perspective of reducing the error. Since there is an inherent electric field between the resistive voltage divider and the surrounding objects at ground potential, it will inevitably cause the voltage divider to generate stray capacitance to ground. On the other hand, there are also stray capacitances between the high-voltage lead and high-voltage end of the voltage divider and the voltage divider body. It is precisely due to the existence of stray capacitance that the resistive voltage divider has errors. Therefore, by changing the stray capacitance of the high-voltage lead of the voltage divider and the high-voltage terminal to the voltage divider body, the ratio difference of the voltage divider can be reduced to a certain extent. and phase difference.

    The shield on the high-voltage end of the voltage divider can partially compensate the influence of the voltage divider's stray capacitance to ground on the error. At the same time, considering that the shielding cover at the ground end can control the stray capacitance of the voltage divider to ground, a low-voltage shielding cover was also added during the design. The designed voltage sensor structure is as shown. 1 is the high-voltage lead, which is directly connected to the high-voltage terminal; 2 is the high-voltage terminal, which is made of metal material and is connected to the high-voltage shield. On the other hand, it serves as the upper sealing cover of the entire device. ; 3 is a high-voltage resistor, and the resistor divider structure uses glass glaze resistors. Its resistance value is very high; 4 is a high-voltage shield (copper or aluminum material with high conductivity); 5 is a low-voltage shield; 6 is an insulating shell; 7 is a low-voltage lead, which is led out through a metal ring on the container wall; 8 is grounding. The end is made of metal material, connected to the low-voltage shielding cover 5, and serves as the base of the entire device; 9 is a low-voltage resistor; the outer cylinder arm of the device is made of insulating material, and the sealing performance of the entire device must be guaranteed. The device is filled with transformer oil to Reinforced insulation. The selection of parameters includes the selection of operating points and resistance points. Select the rated current in milliamps.

     The selection of resistors must also be based on reducing errors. Resistor instability is an important cause of voltage divider error, and its size depends on the temperature coefficient of the selected resistor. In addition, according to the national standard GB311.1-1997, a 10kV voltage transformer must be able to withstand a 75kV full-wave impact and a 1-minute power frequency voltage of 42kV. Therefore, the selection of voltage should be considered from three aspects: temperature coefficient of resistance, voltage resistance performance and resistance value. Finally, choose a glass glaze resistor that can withstand high voltages. Select the resistor element to have a capacity greater than the required power rating of the voltage divider. Reducing the temperature rise is also due to the consideration of reducing errors.

Determination of optimal structural parameters of resistor divider

     The shield is a structural method to solve the voltage divider error. To determine the optimal structural parameters of the resistor divider, theoretical calculations must be performed using numerical methods from a field perspective. Since the field to be studied is neither a simple electrostatic field. It is not a simple current field, so we can only start from Maxwell's equations, derive the electromagnetic field equations of the field under study, and then study and calculate it.

    This paper calculates the maximum field strength and its error characteristics by compiling a simple harmonic field finite element program. Use parametric design to change structures, parameters, harmonic frequencies, etc. By comparing the ratio difference, phase difference, maximum field strength value and the frequency characteristics of the ratio difference of several structural schemes, an optimal scheme is obtained... Based on this scheme, a resistor divider prototype was produced.

Conclusion

     The resistive voltage sensor studied in this article adopts the resistive voltage divider principle, and combines the traditional resistive voltage divider structure with emerging electronic and digital technologies to replace the traditional instruments with measurement and protection windings in the power grid. The use of transformers fundamentally overcomes its inherent disadvantages. The sensor has compact structure, low cost, simple processing technology, wide measurement range, and has both measurement and protection functions. Therefore, it can replace the electromagnetic transformer in the power grid. It is suitable for various indoor and outdoor circuit breakers and pole-mounted switches. , high and medium voltage switch cabinets and other electrical equipment. The development of this sensor provides technical support for the development of intelligent electrical systems.