Investigating the Effects of Adding Distributed Generation Resources to the Distribution Networks on their Protection System Performance

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.…”

“…Existing SCC solvers are differentiated mainly with respect to the computation time as well as the modeling of DGs and loads [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In this paper, the loads and fault are modeled as constant impedances inside the Y BUS matrix [9,12].…”

“…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. Finally, in [20], the authors study all the problems arising from the connection of DGs to distribution networks, such as blinding, islanding, and miscoordination. For their analysis, they apply the superposition rule, ignoring the loads prior to the short-circuit, that is, they simplistically assume a flat pre-fault voltage profile, while the DG currents are superimposed on the flat voltage profile using the network impedance matrix.…”

“…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].…”