Towards Higher Voltage Levels
In the early days of KEMA, the High-Voltage Laboratory was the largest building on the premises: 270 square meters and 15 meters high. Three single phase transformers of 200 kVA each could produce 175 kV. When connected in cascade the highest single phase voltage was 525 kV and in delta connection the three phase output voltage could reach up to 300 kV.
There has been a steady increase in the consumption of electrical energy since 1900, accompanied by a steady rise of the transmission voltage. The danger to high-voltage apparatus and lines arises less from the normal service voltages than from occasional over-voltages, which may reach values of several times the service voltage. These over-voltages can have steep wave fronts that impose severe stresses on the equipment in service. In order that these stresses may be simulated in a modern High-Voltage Laboratory it is necessary to have suitable sources of voltage and measuring equipment. For lightning impulse testing 72 capacitors of 0.54 microfarad each and a charging voltage of 45 kV could supply a voltage surge of 300 kV. When the capacitors are connected in parallel they serve as a DC source capable to produce 300,000 Amperes.
The primary purpose of a High-Voltage Laboratory is to measure the insulation strength, i.e. to determine the breakdown or flash-over voltages of the object under test, but also temperature rise test carried out on busbars and cables are of great value for the utilities, because a power system is designed and build to be in service for many years.
High-voltage testing of newly designed power system equipment will always be necessary. When we want to increase the voltage for the transmission network, we face the fact that nature does not scale: not all physical laws scale linear, some scale quadratic and some by the cube. From the design desk the engineers are forced to test on prototypes and to verify whether mother nature accepts their new ideas in design.