Coming to Power
When industries came into being, there were no facilities for research other than the workshop offered. Later on research began to be concentrated in the universities and the engineers tried as best as they could to apply, in practice,the findings of the scientists. It is the aim of theory to reduce the varied phenomena of nature to the basic simplicity of a few but comprehensive laws of nature. The practical effect of this shows up, more than anywhere, in the high-voltage circuit breaker.
The electric arc, a plasma channel between the breaker contacts after a gas discharge in the breakers extinguishing medium, plays a key role in the current interruption process. At current zero, where current interruption takes place, the circuit theory based on Kirchhoff’s voltage and current laws meets the physics of gas discharges. In the 1920’s very little was known about the switching arc. Experiments were needed for better understanding and testing was a requirement to verify the interrupting performance of switchgear.
Circuit breakers are rated primarily with regard to their breaking capacity when interrupting short-circuits, the determining factors being the current on interruption and the recovery voltage. Usually the product of these, the breaking capacity in MVA, is written on the name plate. As this is based on RMS values the information it gives is incomplete, since experience has shown that not only the peak value of the recovery voltage, but also the rate of rise and the whole nature of the restriking transients, is of importance. These transient phenomena last only a short period of a few microseconds to one millisecond. The coming of sensitive voltage dividers and the cathode-ray oscillograph initiated current-zero research, brought a better understanding of the current interruption process and gave a boost to circuit breaker development worldwide.
KEMA entered the world of high power testing in 1937 with a three phase 660 MVA short-circuit generator driven by a 1000 horse power induction machine. There were also machines for super excitation. The nominal voltage of the generator was 11 kV and the stator had two windings per phase. Three single phase transformers, each having four 12.5 kV windings per phase, could bring the voltage up to 100 kV. KEMA operated, before the second world war, already one of the larger high-power test in facilities in the world.