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The project FutureEnergy has provided new calibration services for ultra-high voltages and a good practice guide on Lightning Impulse dividers

Electrical networks are facing increased demands for energy to power such things as electric cars and heat pumps, along with an increase in the integration of often remote renewable sources, this has driven electricity transmission levels to ever higher voltages.

Conventionally electricity is transmitted over the network as alternating current (AC) at high voltages (HVAC). High voltage improves efficiency as the same power can be transmitted using lower currents, so energy is not lost due to electrical resistance. To further reduce losses - currently equivalent to 150 million tons of CO2 per year - ultra-high voltage (UHV) level direct current (DC) transmission lines of 1000 kV or above are being introduced  (UHVDC) as they are more efficient over long distances.

A crucial factor for the success of ultra-high voltage transmission lines is the need for dielectric testing of the UHV equipment.  Testing verifies the strength of materials, such as grid components and instruments, can take the stress caused by these extreme voltages. Although methods for testing and calibration are outlined in the International Electrotechnical Commission standard IEC 60060-2 High-voltage test techniques, voltages are now increasing to levels higher than covered by this standard and thus extended test methods are required for traceability up to 2000 kV for DC and 2800 kV for Lightning Impulse (LI) measuring systems.

The now completed EMPIR project Metrology for future energy transmission (19ENG02, FutureEnergy) has addressed these problems.

Good practice guide

An early output from the project was the construction of seven new 200 kV HVDC divider modules at RISE, the National Metrology Institute (NMI) of Sweden and PTB, the NMI of Germany.
This allowed the launch of a new 1200 kV HVDC calibration service for European HV industry.  Seven calibrations have already been performed for customers.

Voltage dividers are needed to reduce the extremely high voltage levels, such as those used in lightning impulse tests, to a level allowing measurements and for protection of personnel. The consortium has produced a Good Practice Guide on characterisation methods for UHV lightning impulse (LI) dividers including recommendations such as how to handle front oscillations, corona, proximity and signal cable effects. Although mostly targeted to engineers performing tests, the guide also contains annexes of technical details for interested readers.

New or improved Calibration and Measurement Claims (CMC)

The project has demonstrated CMC claims for UHVDC and UHVAC with unprecedented low measurement uncertainty:

• A shielded precision modular HVDC divider was extended from 1000 to 1200 kV by RISE (six 200 kV modules). One design spin off is a divider that also has traceability for HVAC to 660 kV, Switching Impulse (SI) to 1000 kV and Lightning Impulse (LI) to 1400 kV (in the current two HV module configurations). The third module for 1600 kV UHVDC is now in preparation, with an increase of AC, SI and LI to 1000,1300 and 2100 kV respectively.
• A shielded precision modular HVDC divider was also extended by PTB from 200 to 1200 kV and from 200 to 400 kV for TÜBITAK-UME, the NMI of Turkey. 
• RISE and PTB now have new CMC claims for procedures of up to 1200 kV for UHVDC, with an expanded measurement uncertainty of < 20 µV/V. TÜBITAK-UME have similarly new claims for their system.
• PTB has developed a new type of a shielded divider and updated their calibration procedure for UHVDC of up to 1600 kV (four 400 kV modules) with a CMC claim for an expanded measurement uncertainty of < 40 µV/V. A fifth 400 kV module is also available for an increase to 2000 kV.  
• RISE designed and built a new compact and lightweight modular universal RCR divider which is currently reaching 1000 kV HVDC (two HV modules) with an expanded measurement uncertainty of < 40 µV/V. This divider is extendable to 1600 kV (three HV modules) and 2000 kV (four HV modules) with future claims.
• PTB, RISE, VSL the NMI of the Netherlands and VTT MIKES the NMI of Finland now have calibration capabilities for UHVAC of 800 kV with an expanded measurement uncertainty of 20 µV/V.
• PTB, RISE, VSL and VTT MIKES have also submitted updated CMC claims for UHVAC calibration related to HV capacitors. These have now been submitted to EURAMET TC-EM.

The work of this project in developing the instruments and techniques for both UHVDC and UHVAC transmission networks – including on-site applications – will improve measurement uncertainty in this important area. This will not only allow energy operators to minimise electricity losses, but also improve monitoring of critical grid components.

Alf-Peter Elg who coordinated the project said about the work:

“It has been an honour to coordinate this project having such skilled project partners at my disposal. Apart from several new calibration services for the European industry and grid operators this also now feeds into a new EU financed EPM project 23IND01 ENSURE starting in June 2024”.

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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