Simulation study on transient characteristics of short-circuit fault in high-voltage arm of RC DC voltage divider

Author： GOZ Electric Time：2024-07-03 09:24:34 Read：18

The development of high-voltage direct current transmission technology has been more than 60 years, with the advantages of large transmission capacity, long transmission distance and high stability. As an important device in the measurement link, the RC DC voltage divider has the functions of electric energy metering, operation status monitoring and signal transmission, ensuring the safe operation of the power system. The measurement results of the RC DC voltage divider directly act on the measurement and protection system, determining whether the power system protection device is activated. In actual operation, accidents of false operation of the protection system due to the failure of the RC DC voltage divider occur from time to time. In May 2011 and February 2012, the Tuanlin converter station had two DC line voltage mutation protection actions. After detection, the actual DC line was fault-free, which was caused by the grounding short circuit of the low-voltage arm circuit of the RC DC voltage divider. In September 2015, a UHV DC project in Southwest China was falsely locked. After analysis, it was found that the discharge circuit of the low-voltage arm of the RC DC voltage divider of the UHV rectifier station was instantaneously broken down. Related literature analyzes and optimizes the secondary voltage abnormal faults of the RC DC voltage divider in the Fu and Feng converter stations. The relevant literature studies the dynamic response of the high-voltage and low-voltage arms of the RC DC voltage divider when the high-voltage arm and low-voltage arm are short-circuited. The relevant literature proposes that the fault diagnosis is easy to be inaccurate only based on the overall SF6 gas decomposition of the equipment, and the internal structure of the equipment should be understood. The relevant literature takes the secondary voltage abnormality of the RC DC voltage divider used in a ±800kV DC project as an example, and according to the parameters of the RC DC voltage divider and the simulation experiment, the cause of the voltage abnormality is obtained, and the cause of the discharge is found. The relevant literature uses ANSYS finite element simulation software to simulate the potential and electric field distribution of the RC DC voltage divider under different working conditions.

In terms of the operating characteristics of the RC DC voltage divider, an expert Zhang et al. proposed a new matching method to make a high-precision high-voltage RC DC voltage divider. An expert ELG et al. took a 1000kV resistor-type RC DC voltage divider as an example to study the traceability of the RC DC voltage divider. Han Minxiao, an expert, found that the RC DC voltage transformer is suitable for DC harmonic voltage measurement. Experts Teng Yufei and others studied the influence of the secondary voltage divider topology and the cutoff frequency of the low-pass filter on the transmission characteristics. At the same time, they also analyzed the characteristics of the isolation amplifier and believed that increasing the cutoff frequency of the isolation amplifier can improve the protection sensitivity. Expert Li and others analyzed the influence of two types of RC DC voltage dividers on voltage traveling wave protection. Expert Li Dengyun and others proposed an improved DC voltage summation method to evaluate the voltage divider ratio error of 1000kV DC resistor voltage divider.

When studying the operating characteristics of RC DC voltage dividers, the existing content is mostly focused on harmonic measurement, transmission characteristics and the accuracy of RC DC voltage dividers. The RC voltage divider model used equates the high-voltage arm to a parallel connection of a resistor and a capacitor. When the high-voltage arm of the RC voltage divider fails, this model has great limitations. Therefore, there is a lack of establishment of a more accurate model of the RC DC voltage divider, and there is also a lack of research on the short-circuit fault of the high-voltage arm of the RC voltage divider.

The high-voltage arm of the actual RC DC voltage divider is composed of multiple voltage-dividing RC units connected in series. This article equates the high-voltage arm of the RC DC voltage divider to three sections, derives its transfer function under normal operation and high-voltage arm short-circuit fault, builds a model of the equivalent RC DC voltage divider in the simulation software, simulates and calculates and observes its transient response under different conditions when it works alone.

This paper establishes a model of a three-level high-voltage arm RC DC voltage divider, and derives the transfer function of this model. The mathematical waveform and simulation waveform are drawn using simulation software to verify the correctness of the mathematical model, and the transient characteristics of the RC DC voltage divider under different conditions are studied. The following conclusions are drawn:

1) In the normal unlocking state, t=0s, a 500kV DC impulse voltage is added to the primary side of the RC DC voltage divider, and a normal voltage surge occurs; after the voltage stabilizes, the low-voltage arm outputs a lower stable voltage, and the control and protection device of the system will not operate.

2) Since radial discharge often occurs in the high-voltage arm, the high-voltage arm of the RC DC voltage divider is prone to short-circuit faults. If the fault disappears by itself, the system will go through two full response processes. The voltage surges during a short circuit, but the DC system is in a normal state at this time. If the fault time and output voltage level of the DC voltage divider exceed the setting value of the control and protection system, it will cause the system control and protection device to malfunction, which will bring difficulties to the subsequent troubleshooting work. The staff should strengthen the detection of the internal insulation of the DC voltage divider, and pay attention to the selection of the setting value of the control and protection system.