NMI is responsible for maintaining and disseminating Australia's standards of voltage, i.e. electric potential or electromotive force (the volt) and current (the ampere). Specialised techniques are required to disseminate these quantities at high voltages and, for these tasks, NMI has a purpose-built high-voltage laboratory and a mobile laboratory. Using the High Voltage Laboratory, NMI can undertake research and development to solve problems associated with the electrical supply industry. Presently, research is focussed on high-voltage measurement systems, high-voltage insulation, impulse voltage measurement systems and applied dielectrics.
NMI's High Voltage Laboratory is used in the research and development of digital impulse measurement systems. Recent developments include establishment of system for performance tests of impulse digitisers, construction of impulse calibrators used for calibrating dividers and digitisers and construction of precision digital filters for impulse waveform processing. A reference measurement system for lightning impulse up to 350 kV, with overall accuracy of 0.4% for peak voltage and 1% for time parameters, has been established. Impulse calibrators with output peak voltages up to 1 kV have been built.
NMI is also an active organiser and participant in international comparisons of impulse calibrators, dividers and software, as well as complete measurement systems. NMI is also involved in collaborative work in relevant CIGRE and IEC working groups.
NMI develops and manufactures high-voltage resistive dividers of high precision and stability, for use in Australian and overseas standards laboratories. A 100 kV model and a 150 kV model are currently available. Dividers of higher voltage ratings can also be built by stacking the modular high-voltage resistors. A reference divider with a rated voltage of 1 000 kV is currently under development.
Critical performance parameters of the most accurate 150 kV model built in the laboratory are as follows:
A total of 17 precision dividers have been supplied to metrology laboratories in the US, Canada, New Zealand and other countries in the Asia–Pacific region since 1995.
NMI has also organised a number of international multi-laboratory comparisons of DC high-voltage dividers, and is continuing its collaboration with other national metrology laboratories in further improving the accuracy of DC high-voltage measurement.