Known Problems and Caveats

Voltage Controlling Elements

It is generally possible to have several generators and external grids in one network. Buses also might have several bus-elements (ext_grid, load, sgen etc.) connected to them:

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It is however not possible to connect multiple ext_grids and gens at one bus, since this would convergence problems in PYPOWER:

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The pandapower API will prevent you from adding a second voltage controlling element to a bus, so you should not be able to build the networks pictured above through the pandapower API.

It is also not allowed to add two voltage controlled elements to buses which are connected through a closed bus-bus switch, since those buses are fused internally and therefore the same bus in PYPOWER (see switch model):

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Zero Impedance Branches

Branches with zero impedance will lead to a non-converging power flow:

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This is due to the fact that the power flow is based on admittances, which would be infinite for an impedance of zero. The same problem might occur with impedances very close to zero.

Zero impedance branches occur for:

  • lines with length_km = 0
  • lines with r_ohm_per_km = 0 and x_ohm_per_km = 0
  • transformers with vsc_percent=0

If you want to directly connect to buses without voltage drop, use a bus-bus switch.