Characterisation of AC and DC MV instrument transformers in extended frequency range up to 150 kHz

The increased use of renewable energy has placed a strain on electricity networks. Solar, wind, or other sources produce electricity often of a different magnitude, frequency or type than that already present in the AC medium voltage (MV) grid. Power electronics, such as DC to AC converters, are used to match or synchronise levels but operate at high frequencies. This can generate ‘harmonics’ of up to 150 kHz leading to degraded power quality, damage to network components, and grid instabilities.

Instrument transformers (ITs) allow network stability to be monitored by reducing voltage and current to measurable levels. However, there are no documentary standards that cover the performance of these instruments in the presence of high-frequency disturbances. This lack, highlighted by standardisation bodies such as IEC TC 38, may mean initial network instabilities go undetected, limiting the uptake of renewable energy.

This project will determine suitable calibration conditions, procedures and performance requirements for ITs and share this with standardisation committees to contribute to new or improved international guides and standards. Good practice on superimposing high frequency signals on currents and voltages will be produced to ensure the accuracy of future IT calibrations.
Reference measuring systems for AC and DC voltage and current will be characterised, validated and reported, and new calibration services developed.

This will not only help the uptake of green sources of energy, it will also be possible to operate ITs more efficiently, saving around 5 % of global electricity consumption annually - equivalent to 450 million tonnes of greenhouse gas emissions by 2040.