.PowerGrids.Electrical.PowerFlow.SlackBus .PowerGrids.Electrical.PowerFlow.SlackBusSlack bus: prescribes voltage magnitude and phase (default zero).
Exactly one slack bus is required in each interconnected AC
system. If the system is isolated, the active and reactive power
flows port.P and port.Q should be small,
ideally zero; they are not if the system is not balanced in terms
of active and reactive power production and consumption.