Whole‐line fault analysis method for unbalanced distribution networks with inverter interfaced distributed generators

Abstract

The integration of the inverter interfaced distributed generators (IIDGs) challenges the conventional fault analysis in distribution networks. However, the existing analysis methods mainly focus on the fault occurring at the network buses and little research has been done to analyse the whole-line faults. To extend the fault analysis methods, this paper proposed a phase domain estimation method. The new method was designed to analyse the whole-line faults in unbalanced distribution networks, considering the control strategy and fault-ride-through (FRT) capability of IIDG. A canonical method was developed and a compensation method was utilised, avoiding constructing the entire bus matrix and predefining the fault boundary conditions. Moreover, the new method is robust and can be used to analyse the simultaneous faults as well. Finally, the proposed method was programmed in MATLAB and different scenarios were tested on an unbalanced network. The calculation results were examined by the simulations, which verified the effectiveness of the new method. The new method can analyse whole-line fault in unbalanced networks with IIDGs connection, extending the current fault analysis methods and providing foundations for relay protection.

Incorporating Modern Fault Ride-Through Standards into the Short-Circuit Calculation of Distribution Networks

“…In order to incorporate FRT codes into the fault analysis, three basic steps must be iteratively executed: (a) SCC using a conventional algorithm such as [12][13][14][15][16][17][18][19][20][21][22][23], (b) two algorithms computing, respectively, the injected current and disconnection time of DGs, according to the FRT standard of each country, and (c) a formula that should accurately estimate the tripping time of protective devices, accounting for the time-varying fault current. All these steps are analyzed in the next sub-sections.…”

“…In fact, in reference [17], a modification is made to the formulation, disregarding the effect of a slack bus on fault currents, as is often the case in islanded microgrids. In [18], a whole-line fault analysis method for distribution networks with DGs is proposed, enabling the SCC in faults occurring not only at the location of network buses but also along the lines. In [19], the blinding effects caused on the overcurrent relay of a German low-voltage (LV) feeder are studied, using a tool for stationary short-circuit current calculations, based on the currentsource superposition method.…”

“…All the aforementioned SCC methods assume that either all DGs remain connected, injecting a constant current throughout the whole period of the fault, such as in [12][13][14][15][16][17][18][19][20][21][22][23], or they are disconnected once the fault occurs, as in [9][10][11]. Therefore, the short-circuit current is assumed constant, examining only one time instant (snapshot) of the fault.…”

“…Since DGs are connected to different locations, they experience different voltages and thus different disconnection times, causing the short-circuit current to be varied during the fault. As the DG penetration keeps growing, existing SCC methods [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] may lead to incorrect estimation regarding the sensitivity and tripping time of protective devices due to their assumption of a constant fault current profile. To the best of our knowledge, only one paper exists in the literature that incorporates into the SCC the disconnection order and time-varying current of DGs [24].…”

Relay protection sensitivity integrated optimal placement and capacity of inverter interfaced distributed generators in distribution networks

“…The characteristics of IIDGs differ from the traditional synchronous machines [ 33 ], prompting researchers to investigate fault analysis and fault current estimation methods in DNs with IIDGs [ 34 , 35 ]. The connection of IIDGs influences the magnitudes and phase angles of fault currents in the lines, thereby adding complexity to the fault analysis in DNs.…”