Thai, You cannot aproximate unbalanced system consited of branches and loads with 3W+N+G (three-phase, neutral and ground) via positive sequence solver like MATPOWER. The principle of methodology (NR) assumes symmetry in the system. Symmetry in branch impedances, loads and generation sources.
Best Regards, Robert Spiewak > On Jun 19, 2015, at 08:18, Ray Zimmerman <[email protected]> wrote: > > MATPOWER does not model unbalanced 3-phase systems, and without a lot of work > to refresh my memory, I’m not comfortable commenting on the possibility of a > good single-phase approximation in your case. > > Maybe someone else can comment. > > Ray > > > >> On Jun 18, 2015, at 8:24 PM, Thai Tran <[email protected]> wrote: >> >> Hi Dr.Zimmerman, >> >> I'm new to matpower so please excuse me if this is a silly question. >> >> I'm trying to use matpower to calculate power flow for a distribution grid. >> This circuit has power coming from a substation on 12.47 kV three phase >> line. Single phase transformers tap off the three phase line and step the >> voltage down to 120V to serve houses in the circuit. In matpower, >> transformers are modeled as a branch, how should I model the connections in >> my circuit? >> >> For example: >> substation is connected to transformer 1 which is then connected to 5 loads. >> In the circuit model it would be >> substation -> transformer >> transformer -> load 1 >> ... >> transformer -> load 5 >> >> Should I model this in the branch matrix as >> >> substation(node 1) -> load 1 (node 2) >> ... >> substation(node 1) -> load 5 (node 6) >> load 1(node 2) -> load 2 (node 3) >> ... >> etc. >> >> >> Also since the transformer step the voltage level from 12.47kV to 120V, >> which level should I use to calculate my p.u impedance? >> Thank you >> Thai > > > >
