Background

The drive for increased reliance on renewable or low carbon energy in Europe has led to more distributed energy sources such as wind farms and solar power being connected to the power network, leading to an increase in harmonics of the waveforms.
Instruments for measuring electrical power have undergone significant improvement since the introduction of sampling systems. For example smart meters for energy measurement, power analysers for power quality measurement, and phasor measurement units for power flow analysis have all opened up completely new possibilities to collect information about the state of the power grid. These modern instruments and protection devices are connected to the low voltage side of installed current or voltage transformers with limited bandwidth in order to observe the state of the power grid, to protect the grid, or to allow metering / billing. However, the performance of these setups is limited by the characteristics of the conventional transformers which are currently installed on power networks.
New, non-conventional technologies are being more and more widely applied e.g. optical Faraday effect based sensors, hybrid electrical/optical sensors and air core Rogowski coils for current measurement; and voltage dividers or optical Pockels effect based systems for voltage measurement or upgrading of conventional instrument transformers with digital or optical readouts. These solutions are potential replacements for traditional instrument transformers for power frequency measurement on medium and high voltage power lines, and they show great promise in enabling lightweight, accurate measurement systems for voltage and current, both for fundamental and harmonic frequencies. However, at present they lack the level of accuracy needed for metrological applications.