ESTABLISHING TRACEABILITY OF SYNCHRONISED PHASOR MEASUREMENTS AT THE NATIONAL LABORATORY LEVEL

Working quietly behind the scenes, standards laboratories at the national level (such as the National Institute of Standards and Technology in the USA) and in the offices of our industry work together to make sure that all voltmeters are calibrated to a universal reference. As technology advances, newer and better standard devices are developed at the national laboratories, providing the possibility of ever-improving fundamental accuracy. Over the years, for example, the national standards for frequency and time have changed from highperformance ovenised quartz oscillators, to the socalled ‘atomic clocks’ based on cesium-beam oscillators, to hydrogen masers. Standards for length were once based on a metal metre-bar stored at the International Bureau of Weights and Measures (known by its French acronym BIPM) in Paris; length is now defined in terms of the wavelength of a specific spectral line of an isotope of krypton. For voltage, batteries of electrochemical cells have been superseded by solid-state Josephson-junction arrays.