A large number of field FRT tests are already carried out with the test setup "Transformer Cut-In". As part of the OptiTransient research project, experiments have been carried out as an example on a grid forming inverter and compared with other possible test facilities. In addition to the usual amplitude changes or vector angles jump by coupling a length impedance the angle jump were also generated by the triangular switching of the coils. At no load, the voltage have a clean characteristic. Under load, the impedances influence the test subject. Until now, steps function tests for "Transformer Cut-In FRT-Tester" can not be feasible as a limit. Analyses from the OptiTransient research project show that real grid drops often followed by an over voltage event after grid recovery. Step tests can realized with "Transformer Cut-In FRT-Tester" and additional impedances which limited circular current. The tests will be challenging if no further additional impedances are to be used from financial and practical considerations. Such tests can be carried out in the limited area with previously excluded turning closure. Results will be shown to the various test facilities. The respective limits of the test facilities will also be discussed. For some test cases the integrated coil of the Transformer Cut-In FRT-Tester a 4 connection equivalent circuit diagram is required. A optimized grope for estimation such impedances are present. The OptiTransient research project is funded by the Federal Ministry of Economics Affairs and Energy of the Federal Republic of Germany.
Klosse et al. (Sun,) studied this question.