Analysis of impulse voltage on distributed power transmission lines

Author： GOZ Electric Time：2024-08-12 09:31:39 Read：14

Abstract: The share of distributed power generation in the power grid is gradually increasing. The reclosing technology after a fault can ensure the reliability of the power grid operation. Compared with the three-phase reclosing technology, the reliability and safety of the single-phase reclosing are higher. This article analyzes the voltage and current components of the summer network when the distributed power generation is not in full-phase operation, and analyzes the voltage and current impact during reclosing. The simulation results show that the voltage and current components are consistent with the analysis results with high accuracy.

Keywords: distributed power supply; single-phase reclosing; impact voltage; impact current

1. Introduction

    Distributed power sources can alleviate the problems of traditional fossil energy shortage and environmental pollution, and are often connected to the power grid through inverters. However, due to the control strategy and topological structure of the inverter, when a fault occurs, the operating characteristics are quite different from those of the traditional synchronous generator system. The relay protection system of the distributed power source and the reclosing technology after the fault is removed are different from the traditional system. For the three-phase reclosing technology, due to the low equivalent inertia and low voltage regulation capability of the distributed power source, the quasi-synchronous closing requirements of the reclosing are relatively high. The single-phase reclosing technology of the distributed power source has a small impact on the system's current and voltage. When a single-phase fault occurs in the tie line, the distributed power source can operate in non-full phases, and the distributed power source will not fail. Disconnection from the power grid leads to power shortage and power outage of a large number of loads, affecting the reliability of power grid operation and the ability to absorb new energy generation. This study analyzes the positive sequence network, negative sequence network, and zero sequence network of the system when the distributed power source is not in full-phase operation during single-phase fault, and studies the voltage and current characteristics of the power supply system. Then, the characteristics of the impact current and impact voltage during reclosing after the fault is removed are analyzed. In order to verify the validity of the analysis results, a simulation model was built. The results show that the analysis method of this study can accurately calculate the voltage and current during single-phase reclosing. After the distributed power source adopts negative sequence current suppression technology, there is no impact voltage and impact current during single-phase reclosing.

2. Analysis

    In order to verify the reliability of the method proposed in this study, a simulation model was built. Before the fault occurred, the effective value of the grid voltage was 1pu, and the distributed voltage was fully loaded, that is, the output current was 1pu. The connecting line between the distributed power source and the large power grid had an instantaneous fault at 1.5s. After 100ms of isolating the fault, it was reclosed with a delay of 1s. The distributed power source adopts a negative sequence current suppression strategy. When the load level is 50% and the single-phase is closed, the waveforms of the voltage and current of each sequence are shown in the figure. It can be seen from the legend that when a single-phase fault occurs, the fault-cutting system is not in full-phase operation, the positive sequence component of the voltage is 1pu, and the negative sequence component and the zero sequence component are only 0.05 pu. When the 2.6s reclosing occurs, the system has basically no voltage shock. Due to the use of negative sequence current suppression control, the distributed power supply only outputs positive sequence components during full-phase operation and non-full-phase operation. During single-phase closing, the negative sequence current component and zero sequence current component of the system are close to 0pu. When the single-phase reclosing occurs, the system has no current shock. When the distributed power supply does not adopt the negative sequence current suppression strategy and the load level is 50%, the single phase is closed, and the waveforms of each sequence voltage and current are shown in the legend. It can be seen from the legend that when the faulty distributed power supply is not in full-phase operation, the positive sequence voltage rises to 1.21pu, the negative sequence voltage rises to 0.23pu, and the zero sequence voltage also rises to 0.23pu. At this time, the overvoltage protection is triggered, and the distributed power supply is disconnected from the large power grid. During non-full-phase operation, the positive sequence current drops to 0.83pu and the negative sequence current rises to 0.16pu. However, due to overvoltage, the reclosing fails and the system is disconnected from the large power grid.

3. Conclusion

    When a single-phase fault occurs in a distributed power supply, and the distributed power supply control system adopts the negative sequence current suppression control strategy, there is no current shock and voltage shock when the single-phase reclosing is performed after the fault is removed. If the negative sequence current suppression control strategy is not adopted, the single-phase reclosing will fail due to overvoltage.