These links have some good basic explanations. Did you have specific questions about either one?
Neutral reactors are fairly common. "Phase shifting transformers" are fairly rare, assuming you don't mean the normal phase angle shift do to the specific transformer connection such as 30 degrees for a delta/wye transformer.
Hello Steve14,
neutral reactors are installed in order to modify the zero sequence impedance of the system in that node. They are quite common in Europe in medium voltage networks (petersen coils). In the HV and EHV networks they are less common; I think here in Italy there is only a couple of them connected between the neutral point of a single phase shunt reactors bank installed at the end of a mixed aerial-cable 400 kV line.
PSTs are used to control power flow along the lines to which they are connected to. In Europe they are not so rare, there are several 400 kV PSTs up to 1800 MVA, often installed on interconnection lines.
Phase shifter transformers windings arrangement differs from quadrature boosters. The latter modify both phase and amplitude, while symmetrical PSTs change only the phase of the voltage.
