Nowadays, a clear trend of increase of system voltage to 800 kV AC and above can be observed in the world. This calls for the need of having test facilities to verify the fault current interruption performance of circuit breakers for such "super grids". Standard synthetic test-methods for fault current interruption verification cannot be applied to circuit breakers of 800 kV and above, and alternative solution must be searched for. The present contribution highlights the test-circuits and test-methods that the author's laboratories have developed in recent year to be able to carry out a full test-program of short-circuit tests on circuit breakers up to 1200 kV. For such tests, separate, well-synchronized sources for the supply of fault current and transient recovery voltage (TRV) are required, combined to synthetic test circuits. In this contribution, it is shown how this principle is stretched further to be applied for UHV (above 800 kV) switchgear. A recently commissioned system of a two-stage synthetic installation is demonstrated, with actual test examples of 800 and 1100 kV circuit breakers, for which TRV's in excess of 2000 kV are required. A key feature of the test-circuit is that the circuit breaker under test can remain on ground, which greatly facilitates efficient testing compared to test approaches in which the breaker must be installed on an isolated platform. In case of three poles of a circuit breakers being mounted in a single enclosure, the international standards require synthetic testing of each pole simultaneously. The expansion of the laboratory with a new synthetic installation enables full three-phase synthetic testing, even under effectively earthed conditions, examples of which will be shown. In addition, three-phase closing ('making') tests will be illustrated, including the full power testing of a switch, designed to activate closing resistors in an 800 kV GIS circuit breaker.
