Power and renewables
KEMA Laboratories 90 years 2011

Ultra-high voltage
Most of the power plants are large industrial sites located at strategic locations, nearby a river or a lake for cooling water, and close to energy resources or supply routes. These large power plants are connected to the transmission network by step-up transformers and are controlled by the Transmission System Operator in order to take care of the voltage and frequency stability of the power system.

Remote sources of primary energy and increasing number of energy consumers, larger amounts of electrical energy have to be transmitted over large distances. Power systems operate at a certain voltage level, this is called the system voltage. In order to facilitate transmission with low losses, the system voltage needs to go up. Losses are proportional with the amperes that dissipate heat in the aluminium or copper conductors, so we keep the current in transmission lines low. The only way to still transmit bulk energy economically is to raise the voltage level. A doubling of the voltage reduces the ohmic losses by 75%.

In the nineteen twenties, when KEMA was founded, Germany was the first country in the world to erect a long distance 220 kV overhead line that came into operation in 1929. The line was designed for a future upgrade to 380 kV, but it was Sweden that first build a 1000 km power line at 380 kV operating voltage. The next major step was made by Hydro Quebec in Canada; a 765 kV overhead line connected the hydro power generated at James Bay in the north with the cities in South-Quebec.

Both the Swedish and the Canadian project emphasized the need for long distance energy transmission of distant hydropower to urban load centres. This was also the main driver for the next step: bringing the system voltage above 1 million volt. A 1100 kV transmission line came into service in the USSR in 1985. In the meantime, the economy in Japan boomed and Tokyo Electric Power designed a 1000 kV system to bring the energy, necessary to power the economic activity, into Tokyo. When the UHV equipment became available, in the early nineties, the Japanese economy declined and a nation-wide UHV transmission system was never realised. Then the Peoples Republic of China set off with the first commercially operated UHV transmission system at 1100 kV in 2009. India is aiming for an even higher level: 1200 kV. A grid connected test station is operational and preparations for a long distance UHV transmission line across the country are being made.

At each of these steps forward, KEMA was involved in testing the switchgear. When laboratory 2 was opened in 1958, the royal visitor could already have a look at a 380 kV breaker being prepared for a test, but it lasted until the availability of laboratory 4 and 5, together with the synthetic current and voltage injection circuits, before the 550 kV level could be dealt with. In the mid-nineties, KEMA tested the largest single break circuit breaker in the world, a Japanese 550 kV 63 kA design. Ten years later the Chinese 1100 kV system was planned and it became necessary to test complete UHV circuit breakers. Although such breakers have multiple interrupting chambers, the specific metal enclosed design requires testing of the full breaker. KEMA test engineers took the brave step to test the complete breaker as it is installed in service, namely  as a component fitted on the ground. This is a far more realistic approach and more efficient than putting the huge and heavy breaker on an insulated platform. This meant, however, that an alternative had to be found for the generation of the transient recovery voltage (TRV). The idea came to generate the first million volt of the TRV wave shape with the existing synthetic installation, and to superimpose an additional million volts with a mobile synthetic circuit. The tests were successful and reaching a TRV peak of 2050 kV is till now a world record.

One of the lessons learnt was that even laboratory 5, our largest test bay, was dielectrically speaking just large enough to house the test object with enough space around it to avoid flashovers to the walls. But ceiling lights had to be removed and the breakers bushings needed a lower inclination than in the original design in order to safeguard the ceiling from a flashover. This limitation gave the start to design a complete new installation that is now called “Synthetic East”. In 2012 this new synthetic test facility became available for commercial testing and this two stage synthetic installation allows circuit breakers up to 800 kV, to be tested “full-pole”. Also gas insulated three-phase common enclosed switchgear can now be tested in a real three-phase environment.

Combined with the existing synthetic installation, “Synthetic East” is versatile enough to act as a third synthetic in case of testing three-phase common enclosed switchgear under earthed system conditions. This opened a whole new market of three-phase testing of 145 kV GIS switchgear.

Synthetic East
Synthetic Hall East in 2011
Ultra-high voltage disconnectors in 2014
Ultra-high voltage disconnectors on the roof of the high power laboratory
Ultra-high voltage SF6 circuit breaker testing in 2013
The tests in 2013 of an UHV SF6 circuit breaker were successful and reached a TRV peak of 2050 kV which is up till now a world record