Technical characteristics of resistor-capacitor voltage divider electronic voltage transformer

Author： GOZ Electric Time：2024-05-20 09:26:22 Read：19

Whether it is a capacitor voltage divider type or a resistor-capacitance voltage divider type electronic voltage transformer, the requirements for the voltage divider are particularly high. At present, only a few companies with strong technical strength can meet product performance requirements.

1. High precision

1) The voltage sensor uses a resistor-capacitor parallel voltage divider. In the design, the resistor shunt only accounts for less than 0.03% of the capacitive current. At the same time, it ensures that the discharge time constant meets the discharge requirements. Therefore, the voltage dividing ratio is mainly determined by the capacitor and the temperature characteristics are consistent. Therefore, the error band range in operation is very small.

2) The capacitor uses a metallized film, and its electrodes are evaporated on the medium, which eliminates the influence of the air gap between the medium and the plate and improves the temperature stability of the capacitor. In order to avoid capacity loss caused by self-healing of metallized high-voltage capacitors and low-voltage capacitors during operation, a series of anti-oxidation measures are taken, which can not only effectively avoid capacitance loss and service life problems, but also ensure the long-term operation accuracy of the voltage divider.

3) The load impedance is converted into the low-voltage capacitor discharge resistance of the voltage divider, which reduces the load error.

2. There is no hidden danger of transient retained charge

The national standard GB/T 20840.7-2007 points out: "In this transient situation, the best solution is to use a resistor-capacitor hybrid voltage divider to transmit the correct signal." Since each capacitor unit is connected in parallel with a discharge resistor, transient errors are eliminated.

3. The measured voltage signal does not need to be restored by an integrating circuit, reducing errors.

  Resistor-capacitor voltage divider type electronic voltage transformer

The electronic voltage transformer is the core device of the smart substation, and the parallel connection of resistors and capacitors as high-voltage sensors not only takes advantage of the small loss in capacitor operation, but also achieves the purpose of discharging transient charges through parallel resistors. This improves the measurement accuracy of the transient process of the electronic voltage transformer.

1. Design of resistor-capacitor parallel voltage divider

The high voltage of CVT is mainly borne by the capacitive voltage divider. The voltage resistance strength of the capacitor dielectric is crucial not only for the reliable operation of the equipment but also for the accuracy of voltage measurement. Similarly, whether from the perspective of insulation or measurement accuracy, developing high-quality resistor-capacitor voltage dividers is an unavoidable primary task in the research and design of electronic voltage transformers.

2. Analysis of error temperature characteristics of resistor-capacitor parallel voltage divider electronic voltage transformer. The measurement process of voltage transformer is a dynamic test, and the measurement error is a dynamic test error. Since the errors of digital converters are generally small and relatively stable, they can be eliminated by improving the circuit structure, selecting high-quality components, and through software correction. Therefore, we focus on analyzing the error temperature characteristics of the resistor-capacitor parallel voltage divider.

Summarize

1) Among various active electronic voltage transformers, it is a relatively complete method to use a resistor-capacitor parallel voltage divider with a large capacitance as a high-voltage sensor. It can not only eliminate the influence of transient stagnant charges, but also does not require integration circuit restoration, which improves the reliability of long-term operation. 2) The resistor-capacitor voltage divider is the "throat" of the electronic voltage transformer. The reasonable selection and correct design of the basic components capacitance and resistor are the cornerstone of ensuring the quality of the voltage divider and the prerequisite for ensuring the long-term reliable operation of the electronic voltage transformer. Assure. High-voltage and low-voltage capacitors are designed with metallized film structures, which can not only improve the insulation level, but also improve measurement accuracy. The correct selection of high-voltage and low-voltage resistors and the reasonable determination of time constants can ensure the correct conversion and transmission of signals.

3) The long-term stable operation of the digital converter is an important guarantee for ensuring the correct transmission of secondary signals. Reasonable selection of the technical parameters of each component and component, reasonable design of circuit parameters, and taking appropriate protective measures can meet the requirements of the climate and electromagnetic environment.