World’s Largest High Power Laboratory
The increase in consumption of electrical energy leads not only to higher voltage levels, but also to higher short-circuit powers. In December 1973 KEMA commissioned its new High Power Laboratory with four generators and a total available short-circuit power in the test bay of 8400 MVA.
A high-power laboratory is designed to test interrupting devices, such as fuses and circuit breakers, but also load break switches and disconnectors, and other apparatus that needs to face over-voltages or encounter short-circuit currents like transformers, surge arresters, and bus bar systems.
Based on the difference of the power supply, two types of high-power laboratories can be distinguished. One is the testing station directly supplied from the network and the other is the specially built short-circuit generator test station. The network testing station is located close to a high-voltage transmission substation and uses the network to provide the short-circuit power directly.
The generator testing station is equipped with specially designed short-circuit generators, which supply the short-circuit power. A motor is used to spin the short-circuit generator to its synchronous speed before the test takes place. During the short-circuit test, the excitation and the kinetic energy of the rotor mass, supply the power.
For high-voltage circuit breakers a means to overcome the shortage of test power was, for many years, the unit testing method. In this method, units, consisting of one or more interrupting chambers, are tested separately at a fraction of the rated voltage of a complete breaker pole. This technique, however, retains some problems such as the thorough understanding of the influence of the post-arc conductivity on the voltage distribution along the units.
Modern SF6 puffer circuit breakers have a high interrupting rating per break and this interrupting rating surpasses the short-circuit power of the largest high-power laboratories. The synthetic testing method was being developed during the 1930’s to overcome the problem of insufficient direct test power.
In 1942, F. Weil introduced a synthetic test circuit, which was later improved by G. Dobke and others and is now used worldwide, as the parallel current-injection circuit often referred to as the Weil-Dobke test circuit. The synthetic testing method applies two source circuits to supply the high current and the recovery voltage separately. The short-circuit generators serve as current source and the recovery voltage comes from capacitor banks.
In 1980 KEMA’s High Power Laboratory, located at the banks of the river Rhine was extended with a synthetic test facility. Full pole testing of 550 kV - 63 kA breakers was now possible.