The Development and Characterization of High Current and High Voltage Transducers

Metrology grade portable transducers have been developed and characterised in this project to ensure they are suitable for use on the medium voltage grid so that on-site measurements with uncertainties comparable to laboratory conditions can be achieved.

Coordinator: Paul Wright

Current and voltage measurements are required for power loss and power quality measurements on power generation and distribution equipment at the high magnitude levels typically found on the electricity grid. The present state-of–the-art uses well established methods which are laboratory based. For high voltage measurements, systems including compressed gas capacitors are used in national metrology institutes (NMIs) to obtain sufficient uncertainties (below 100 ppm). However, these transducers are heavy, and they contain pressurized gas.  As a result, they are sensitive to mechanical stress and temperature variation; hence they require special care during transport.  Resistive and capacitive (RC) high voltage dividers offer a portable alternative to compressed gas dividers, whilst maintaining the dynamic performance lacking in voltage transformers.  Although commercial RC dividers are available, the limited temperature stability, voltage linearity and long-term stability of these dividers, make their performances insufficient for calibration purposes.     

For currents much above a hundred amps, shunts are not practical for continuous measurement. For higher currents up to tens of kiloamperes, other types of current transducers, such as current transformers (CT), Hall effect probes, Rogowski coils or electro-optical systems based on Faraday effect, are used. CTs are well established, but they are heavy, invasive (they require the circuit to be broken) and have limited bandwidth. Rogowski coils systems overcome these problems; commercially available systems exist; however, they are generally designed as monitoring devices rather than accurate measuring instruments. 

As most of this high voltage equipment is bulky and expensive to remove from its service location, on-site measurements are an attractive, and often the only, alternative. Metrology grade portable transducers have been developed and characterised in this project to ensure they are suitable for use on the medium voltage grid so that on-site measurements with uncertainties comparable to laboratory conditions can be achieved. In addition, the understanding of higher current events such as short circuit transients and impulse currents are important for the management of power quality. This requires transducers of sufficient dynamic performance so as not to degrade the shape of the transient or pulse.   

These transducers are suitable for use at low power factor with an uncertainty low enough to calibrate the instrumentation used for verification of the contractual requirements between the manufacturer and purchaser of high voltage equipment. 

This research enables NMI grade measurements to be extended to real world environments and provide the necessary infrastructure for power quality/loss measurements on the electricity grid and at generation sites.  

For more information, see  the project webpage >>