Removing islands causes issue with radial reductions

[acostarelli]

In the Argentina system if we attempt to remove the islands in some form like so:

set_available!.(get_components(x -> !get_available(x), ACBranch, sys), true)

for g in get_components(x -> get_bustype(x) == ACBusTypes.ISOLATED, ACBus, sys)
    set_bustype!(g, ACBusTypes.PQ)
end

for g in get_components(ACBus, sys)
    set_available!(g, true)
end

There is an error later when trying to do radial reductions:

Ybus(sys, network_reductions=NetworkReduction[RadialReduction()])

Inspecting the subnetwork matrices of the Ybus without network reductions shows a lot of isolated buses. Something to do with 3W transformers, which are marked available but their windings are not -- and setting their windings to available doesn't fix this, nor does in addition skipping the step of setting Isolated buses to PQ.

@SebastianManriqueM
@m-bossart

[m-bossart]

According to the debugging by @acostarelli the root cause of this error is a closed breaker/switch which meets the zero impedance line reduction criteria in parallely with a line that is set to available. The fix for this specific case is probably to not make those lines available or to re-examine the modification of component availability.

However, this case should still be able to run without error. This requires a refactoring of the zero impedance line reduction. This refactoring is in the works already to address #299