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Performance Problem of Current Differential Protection of Lines Emanating from Photovoltaic Power Plants

by Yingyu Liang 1,*, Wulin Li 1 and Guanjun Xu 2
1
School of Mechanical Electronic and Information Engineering, China University of Mining and Technology, Beijing 100083, China
2
NARI Group Corporation (State Grid Electric Power Research Institute), Nanjing 211000, China
*
Author to whom correspondence should be addressed.
Sustainability 2020, 12(4), 1436; https://doi.org/10.3390/su12041436 (registering DOI)
Received: 14 January 2020 / Revised: 4 February 2020 / Accepted: 11 February 2020 / Published: 14 February 2020
The amplitude and phase angle of the fault current in photovoltaic power plants (PVPPs) are significantly influenced by the control system of the grid-connected inverters, unlike in a conventional synchronous source. Hence, PVPPs may adversely affect the performance of the current differential protection designed for synchronous sources-based power grids. In order to study the performance problem of current differential protection on AC transmission lines, an analytical expression of the fault current in the PVPPs was deduced, and the fault current characteristic was extensively analyzed. Based on this analysis, the ratio of differential current over restraint current was initially derived in this study; this ratio is observed to be affected by the control system parameters, power grid system parameters, fault resistance, and fault types. Moreover, the dynamic characteristics of this ratio can be clearly observed based on a three-dimensional diagram. Furthermore, the operating performance of the current differential protection was analyzed under different influencing factors. The mathematical analysis presents that the amplitude ratio of the fault current on both sides of the line is larger than nine and that current differential protection will operate reliably in any case. Meanwhile, the theoretical analysis and simulation results show that the current phase angle difference may become an obtuse angle in case of an ungrounded fault, which will cause inaccurate operation of the current differential protection. The results of this study will provide guidance for the engineering application of current differential protection in case the PVPPs are connected to a power grid. View Full-Text
Keywords: current differential protection; fault current behavior; performance problem; photovoltaic power plants current differential protection; fault current behavior; performance problem; photovoltaic power plants
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Liang, Y.; Li, W.; Xu, G. Performance Problem of Current Differential Protection of Lines Emanating from Photovoltaic Power Plants. Sustainability 2020, 12, 1436.

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