The cable connection
The peaty and sandy soil in the Netherlands and the relatively short distances between the loads make underground cables ideal for the countries electrification. The first 10 kV mass impregnated cable was put into service in 1909. These cables gave at first many problems and a breakdown of the insulation occurred frequently, resulting in local black outs. Research combined with laboratory testing was therefore needed and this became one of the main activities of KEMA after its foundation 1927. The KEMA high voltage laboratory opened its doors in 1938 and was specially designed for testing of high voltage mass impregnated cables. For several decades KEMA and the Dutch cable manufacturers developed test methods and took part in standardization activities that lead to more reliable cables.
Medium voltage cables with XLPE insulation came on the market in the late nineteen seventies and KEMA developed new methods to test for partial discharges, a phenomenon that led to frequent breakdowns in high-voltage cables. A second critical weak-spot of XLPE cables were the so-called water trees. After many years of research KEMA developed test methods to determine the mechanism of water treeing and this resulted in better XLPE material and improved cable designs.
Since 2000 the KEMA High Voltage Laboratory is a world player for testing and certification of medium- and high-voltage cables systems. Special testing techniques have been developed for efficient testing. In 2009, the HVL left the original building, built in 1938, and moved to a new laboratory next door to the High-Power Laboratory.
Cable drums as high as 5 meters now come from all over the world to Arnhem by ship. Cable accessories are fitted either by the cable or the accessory manufacturer at the premises of the HVL. Confidentiality is important when different cable systems are under test at the same time.
Experience from utilities learned that cable networks, even after a successful type test, were experiencing frequent breakdowns. KEMA, participating in up-dating of the IEC standards, developed a prequalification test to be able to test a cable connections under normal service conditions. An outdoor test site was laid out for cables with voltages up to 400 kV. At this site, high-voltage cables and their accessories can be buried either directly in the soil or in cable ducts. The test duration is one year with, every two days a heating cycle to raise the conductor temperature to 90 degrees Celsius.
The high voltage DC-cable is relatively new on the market, but with the renewable energy sources coming up they will soon become an important player in the cable field. The first DC-cable had a nominal voltage of 320 kV, but within a few years the voltage went up to 500kV and in the future it will even reach 800kV. KEMA laboratories have developed a special test facility for type testing and prequalification testing of DC cables. History repeats itself as standards are not available yet while the cables are already in service.