Abstract
When a pole-to-pole short-circuit fault occurs in an LCC-MMC hybrid DC transmission system, the fault characteristics are affected by the distributed capacitance and the transition resistance that cause a dead zone in the fault location and poor accuracy in determining the fault location. In view of this, this paper proposes a fault location method for the LCC-MMC hybrid DC transmission system. By analyzing the fault characteristics of the rectifier station and inverter station, the fault circuit equation of the rectifier side is analyzed, and the relationship between the fault distance and the transition resistance is deduced. The fault circuit of the inverter side is isolated by blocking CDSM-MMC, which can clear the fault current on the inverter side and thus eliminate the influence of the transition resistance. The steady-state fault information of the LCC DC outlet is used to eliminate the effect of distributed capacitance and achieve an accurate fault location. The LCC-MMC hybrid DC transmission system model is built on the PSCAD / EMTDC simulation platform. Simulation results show that the proposed fault location method can effectively avoid the transition resistance and distributed capacitance influences and thus obtain high fault location accuracy. Moreover, an accurate fault location can be achieved with a narrow fault data window length.
Highlights
The problem of commutation failure in DC transmission systems based on line commutation converters (LCC) is difficult to solve [1], [2] and limits the development of DC transmission systems
The faults that occur in DC systems are basically nonmetallic faults, and transmission lines cannot ignore the characteristics of distributed capacitance [5] because the characteristics of pole-to-pole short-circuit faults are affected by the transition resistance and distributed capacitance; the accuracy of determining the fault location is reduced
Reference [11] proposes a high-frequency impedance-based fault location method and uses double-ended measurement information to eliminate the effect of transition resistance; the effect of the line distributed capacitance will be amplified at high frequencies
Summary
The problem of commutation failure in DC transmission systems based on line commutation converters (LCC) is difficult to solve [1], [2] and limits the development of DC transmission systems. Reference [11] proposes a high-frequency impedance-based fault location method and uses double-ended measurement information to eliminate the effect of transition resistance; the effect of the line distributed capacitance will be amplified at high frequencies. After a pole-to-pole short-circuit fault occurs, the LCC is not blocked to obtain enough useful fault information to realize accurate fault location in the following research. According to the above analysis, after the CDSM-MMC is blocked, it can be seen from Fig. 8 that the voltage and current measured by the rectifier side protection m have the relationship shown in (1). The average algorithm (as shown in Fig. 9) is used to obtain the stable DC component to eliminate the influence of fluctuations and improve the accuracy of the fault location results. Through a sliding window calculation, it is possible to obtain approximately constant DC voltage and current measurement values
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