Differential Protection Sensitivity Enhancement Scheme for AC Transmission Lines Connecting to VSC-HVDC Station

With the vigorous development of renewable energy and the popularization of HVDC transmission, the structure of power sources has changed a lot. The output current amplitude of power electronic devices is limited, the phase angle of current is controlled, and the characteristics of the sequential component are affected by the converter control strategy, which are different from fault characteristics of SGs. When the AC power system is connected to a large-capacity cross-area VSC-HVDC station, the sensitivity of the conventional current differential protection is reduced during fault on AC transmission line connecting to VSC-HVDC station. To solve the problem of insufficient sensitivity of conventional differential protection on AC transmission line connecting to VSC-HVDC station, this paper analyzed the fault characteristics of AC transmission line connecting to VSC-HVDC station during fault and proposed a current differential protection sensitivity enhancement scheme applicable to AC transmission line connecting to VSC-HVDC station. The scheme can improve the protection performance of the AC transmission line connecting to VSC-HVDC station, supporting the construction of a new type power system.

I. Introduction

With the gradual scarcity of fossil energy and global warming environmental problems becoming more and more prominent, human beings pay more and more attention to the development and utilization of new energy sources. Modular Multilevel Converter (MMC) based Voltage Sourced Converter based High Voltage Direct Current (VSC-HVDC) has the advantage of independent adjustment PQ, low level in the output harmonic, no commutation failure problem and flexible transmission mode. As a result, it has been widely used in the fields of asynchronous networking, grid-connection for large-scale renewable energy generation and long-distance DC transmission [1], which greatly facilitates the optimization of energy allocation in power system. The AC transmission line connecting to VSC-HVDC station as a direct link between the VSC-HVDC converter and the AC power grid, it may resulting in larger fault area when the protection is unable to be removed fault timely, endangering the safe and stable operation of the HVDC transmission system.