Introduction of a High Accuracy Active Compensation Voltage Divider

作者： GOZ Electric 时间：2024-06-25 09:18:27 阅读：17

The high accuracy of active voltage dividers places high demands on the performance of components used in electronic circuits and the design capabilities of researchers. In order to improve the error accuracy requirements of the existing power frequency voltage ratio standard and reduce the complexity of electronic circuit design, a high-accuracy active compensation voltage divider is proposed, which greatly reduces the error and instability caused by active devices. The compensation method of active capacitive voltage divider is mainly explained, and the main voltage divider, compensation capacitive voltage divider and test methods of each part of the active compensatory voltage divider are introduced in detail.

Capacitive voltage divider is a commonly used metering equipment in high voltage measurement test. In applications with an accuracy of more than 0.1%, the high-voltage arm of the capacitive voltage divider mostly uses compressed gas capacitors, which have the advantages of good stability, small temperature coefficient and low dielectric loss. However, since the gas capacitor has a capacitance of tens of pF, the capacitive voltage divider has poor load capacity. In use, the voltage divider ratio is adjusted according to the input impedance of the secondary measuring meter as the actual ratio, but after replacing the measuring meter, the voltage divider ratio will change. Therefore, in practical applications, the secondary of the capacitor voltage divider often uses electronic units to realize the impedance transformation between the voltage divider and the secondary meter to improve the load-carrying capacity of the voltage divider. The high-voltage standard voltage divider 4860 produced by the Swiss Hafele Company is based on the above principle. This question describes a compressed gas standard capacitor voltage divider that places the high and low voltage arm gas capacitors in a shell; in order to reduce the influence of the rear-end electronic unit, the rear-end follower circuit of the voltage divider has an input impedance of more than 5GΩ. The design uses a multi-stage bootstrap circuit and a multi-operational amplifier (hereinafter referred to as "op amp") feedback follower circuit to achieve the above high input impedance and high accuracy requirements; the voltage divider has good frequency characteristics, and the measurement error is less than 0.1% in the range of 50~2500 Hz. A standard capacitor voltage divider based on a precision inverter is designed. The high-voltage arm capacitor uses a compressed gas standard capacitor, and the inverter low-voltage arm capacitor uses a ceramic capacitor, which has a lower temperature coefficient and dielectric loss. This design avoids the requirement of the voltage divider for the electronic unit to have a high input impedance. At the same time, the voltage divider shielding potential is zero potential, and the differential pressure with the shielded line is only microvolts, so the shielding effect is good. The T-type equivalent circuit is used in the design to reduce the influence of the low-voltage arm parallel resistance on its voltage divider ratio error. Its measurement accuracy can meet 0.01% under power frequency conditions.

At present, there are many products of traditional passive capacitor voltage dividers, and their error levels are also public and do not need to be measured. The overall error level is up to 0.2%. The traditional passive capacitive voltage divider uses capacitors in series to complete the conversion of the primary high voltage to the secondary output voltage based on the high and low voltage arm capacitor voltage division principle. The voltage division signal is obtained from the high and low voltage arm voltage division point, and the corresponding shielding means are used to prevent external interference with the measurement signal and the influence of the distributed capacitance of the measurement cable on the capacitance of the low voltage arm. The traditional passive voltage divider is affected by the distributed parameters. When the frequency changes, its measurement error also changes. It also has poor load capacity and is not suitable for use in metering situations with high requirements for measurement accuracy. The active voltage divider has good load capacity. In order to obtain high measurement accuracy under power frequency conditions, a large number of compensation circuits are required. The active compensation capacitor voltage divider proposed in this paper not only has the advantage of improving input impedance, but also improves the voltage measurement accuracy level under power frequency.