Abstract
Legacy protection schemes face new challenges as Inverter Interfaced Distribution Generation (IIDG) significantly changes the transient fault response of the distribution grid. The performance of the protection near the IIDG side is adversely affected by Low Voltage Ride Through (LVRT) and the negative sequence current suppression control characteristics of the IIDG. The operational characteristics of the protection are very different from those of the legacy protection schemes used in the distribution grid. Traditional overcurrent protection schemes cannot meet the requirements of selectivity and sensitivity. This paper analyses the influence of the IIDG on the protection schemes used in the distribution grid. Based on the positive sequence voltage polarization impedance criterion this study proposes a polarizing impedance criterion based on the fault component of positive sequence voltage, which can adaptively follow the fault resistance variation to satisfy the requirements of grid operation. The simulation results show that: (a) the proposed criterion is immune to the adverse effects of the transient characteristics of the IIDG; and, (b) it can adaptively follow the change of fault resistance making it suitable for application in short distribution lines. Using specialized System-on-Chip technology, a new distance protection device has been developed and tested on an industrial site. Simulation results and field tests showed that the new distance protection meets the requirements of the distribution grid with IIDGs.
Highlights
With the rapid developments in new generation technologies in recent years, various forms of new energy sources have been connected to the grid in the form of the Inverter Interfaced Distribution Generation (IIDG)
For the protection system installed on the near-IIDG side, due to the Low Voltage Ride Through (LVRT) control characteristics of the IIDG, the current fed to the fault point was closely related to the busbar voltage of the IIDG, and the maximum short-circuit current was limited to a low level
The negative sequence current suppression control strategy changes the transient characteristics measured by the protection scheme
Summary
With the rapid developments in new generation technologies in recent years, various forms of new energy sources have been connected to the grid in the form of the IIDG. The transient characteristics of the positive sequence voltage polarized impedance relay used for the grid-connected wind power plants are analyzed in a study (Li et al, 2012).
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