Extending test methods for electrical measurements
The EC has highlighted that to meet energy targets for 2030 a reduction in the power lost in electricity networks will be required. Electricity travels over the transmission grid at high voltages (HV) of 115 kV or above as this is more efficient for transmitting electricity than lower voltages. At the distribution grid, which supplies end-users, this voltage is stepped down by power transformers. Significant losses occur at this stage and improving transformer efficiency alone could save 16 TWh per year, equivalent to 3.7 Mt of CO2. For this reason efficiency requirements for transformers are included in the Ecodesign Directive. For large transformers however, there were no calibration services available with the required accuracy for loss measurements meaning transmission system operators and transformer manufacturers struggled to show compliance to this directive.
To improve efficiency ultra-high voltages (UHV) are being introduced which requires improved tests on grid components to verify robustness to voltages exceeding 2500 kV. Current methodologies are detailed in the IEC 60060 international standards, which include lightning impulse tests to ensure component resilience to rapid voltage or current surges. Voltages were already increasing to levels higher than those covered by some standards however, thus there was an urgent need to extend tests into the UHV range. Furthermore, reference systems for on-site work were limited to 500 kV, which was insufficient to prove linearity to full test voltage levels for UHV applications thus there was an urgent need to extend tests into the UHV range.
This project focused on the research required to demonstrate the quality of products developed to enable higher efficiency electricity grids. A novel, highly accurate system was developed for measuring losses in large capacitors, large inductors and very low-loss power cables with an uncertainty 3-10 times better than previously available.
Calibration for UHV impulse testing was extended from 500 kV to 2700 kV and new facilities were developed to characterise environmental and other on-site influences on measuring very fast transients. Improved voltage dividers for lightning impulse tests were designed and built and used in a EURAMET comparison for impulses greater than 200 kV. These have now been validated and have had commercial uptake.
The project also showed that losses at HVDC convertor stations can be calculated by the difference between AC and DC power, demonstrating that converter losses as low as 1 % are measurable. As a result of the work performed new and extended internationally recognised Calibration and Measurement Capabilities now exist in Europe. These include measurement of losses at high voltage, high current and low power factor, measurements for fast current transients and calibration of lightning impulse systems at UHV. For the latter a best practice guide has also been published.
Not only will project outputs benefit manufacturers of instrumentation for the UHV grids and lead to more cost-effective solutions for UHV power transmission, the higher efficiency grid components will also reduce CO2 emissions and support the implementation of the Ecodesign Directive.
EMPIR project 17NRM01 TrafoLoss builds on this work.
CIRED - Open Access Proceedings Journal
Proceedings of the 23rd International Conference and Exhibition on Electricity Distribution (CIRED), Lyon, France