Phase-shifting transformers play an important role to control the power flow within our modern networks that include more and more renewable energy sources. The most important protection principle for transformers is differential protection, but an additional phase-shift has to be considered by the differential protection to fulfil the requirements for selectivity. In addition to this, the different relay manufacturers use different approaches how the relays will ensure stability for phase-shifting transformers. This makes testing the protection relays for phase-shifting transformers not trivial.
In this paper different approaches for different types of phase-shifting transformers (e.g. one-core and two-core versions) are discussed and evaluated. Further, a solution approach is presented using a simulation-based test software, which is capable to simulate the detailed behaviour of the phase-shifts for the individual tap positions of the transformer. This approach makes protection testing for phase-shifting transformers very convenient.