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

Abstract

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.

Vulnerability assessment of line current differential protection in converter–dominated power systems

“…Using current distribution factors in (10), the relation between faulted path currents for AG fault can be expressed as:…”

“…Investigations of LCD protection in the presence of CIS have been presented in [8][9][10][11]. In [8,9], characteristics of the converter fault current using a dual sequence current controller with different control objectives are analysed, which demonstrate that fault conditions and control objectives could both influence the fault current angles.…”

“…[10] and [11] present mathematical expressions for representing fault contributions from the CIS and the grid into an LCD operating characteristic, under the assumption of a relatively strong grid-side fault contribution. In [10], the mathematical expression for the CIS current references under different control strategies are derived, while in [11] the controlled nature of CIS fault waveforms are represented as a voltage dependent current source in parallel with a variable impedance. It was demonstrated that the line length, CIS capacity, fault location and fault severity could all influence the performance of the LCD protection.…”

Impact of large-scale photovoltaic-energy storage power generation system access on differential protection of main transformer under symmetrical faults

“…Many studies have analyzed some fault current characteristics of GCPPPs, but most of them are studies on the fault analysis of the transmission line of GCPPPs and focus on line protection (Jia et al, 2018;Alsafasfeh et al, 2019;Liang et al, 2020). Both (Alsafasfeh et al, 2019;Jia et al, 2018) have calculated expressions of fault current under different control targets, which are suppressing negative sequence current, suppressing active power fluctuation and suppressing reactive power fluctuation respectively.…”

Advanced Protection Schemes of Modern Transmission Grids with Large-Scale Power Electronics

“…Ref. [73] outlines the influencing factors of a transmission system connecting FCGbased plant on the current differential protection. However, the FCG-based plant commonly operates according to a certain grid code during grid faults, and such reality is not directly mentioned.…”