The advent of the SF6 circuit breakers in the 1970s, got along with the rapid growth of short-circuit power in the power systems. In the earlier air-blast breaker era, multiple chambers had to be put in series to deal with the ever increasing voltage Thus it was feasible to test a single chamber with relatively low power as a scaled down test. Now, almost overnight powerful SF6 breaker became available that could rely on a much smaller number of chambers. This meant that direct testing (in which current and voltage are supplied from a single source) soon started to fall short to cope with these new powerful breakers.
To accommodate larger breaker in smaller laboratories, first J. Biermans (1931, Germany) and later W.F. Skeats (1936, USA) experimented with separate sources: one for the current before interruption, one for the voltage after interruption. In the 1940s F. Weil started to think about coupling the current and the voltage sources through a spark gap, an idea later refined by G. Dobke and E. Slamecka in the 1950s. When the interrupting power of SF6 chambers roughly tripled in a decade between 1975 and 1985, even KEMA, after the opening of lab 4 world’s largest direct test lab, could no long supply sufficient direct power, and “equivalent” or “synthetic” testing became the only way to keep ahead of the developments on the world market.
At KEMA G. Damstra and H. Kempen designed test-circuits and infrastructure in order to realize synthetic testing, to be commissioned in 1979, which raised the available testing power from 8400 MVA to a staggering 30000 MVA. Having already four generators at that time offered the additional advantage that sufficiently high voltage at generator side can be maintained to keep the current unaffected by any test-object. In order to provide sufficient arc duration, arc prolongation has to be applied, based on a unique application of triggerable vacuum switches that were at that time only available from a military supplier. Another innovation was the control and timing electronics, so-called three-phase injection timers, carefully taking care of the control of the multiple events in the critical synthetic test. In 1986 W. van der Linden and L. van der Sluis published a synthetic circuit that enable testing of three-phase circuit breakers for non-earthed applications.
A mile stone was the testing of the largest breaker in the world, based on a single breaking chamber, in 1996.
Another 20 years later, even the KEMA synthetic circuits reached its limits because of the development of UHV circuit breakers that operate in systems with rated voltages above 800 kV. After the construction (and decline) of a 1050 kV system in USSR mid 80s and a pilot 1000 kV system in Japan by 1990 (which did not reach full operation) the first commercial 1100 kV system was commissioned in China in 2009. Already two years earlier, KEMA set a world record by demonstrating the full-pole testing of a UHV breaker. Initially an improvised second synthetic installation was constructed in the test bay, in 2012 a completely new installation was commissioned. This meant not only also the “lower voltage” breakers at 800 kV could be dealt with more swiftly but also that full three-phase testing became possible for breakers designed for any earthing. In the mid 2010s, this appeared to be a major asset as it drew loads of 145 kV three-phase metal enclosed breakers to KEMA.