Instrument transformers (ITs), or transducers, are used to accurately reduce the relatively high levels of voltage and current used in the electrical power grid to lower levels that are useable by instruments such as energy meters or system monitoring instruments. The ratio error and phase error of the instrument transformers are the figures of merit for performance and these are sometimes obtained from calibrations of the ITs and used to correct results. 

Fitting or removing ITs from the power system is often disruptive and expensive as it may require a system interruption. Some technologies of current transducers can be split and fitted around the conductor in a non-invasive manner.

National Metrology Institutes (NMI) provide calibration facilities for voltage transformers (VT) using high voltage facilities in the range of tens of kV.  High current facilities are used to calibrate current transformers (CT).  Traditionally, grid ITs are optimised for accurate performance the 50 Hz power frequency, however recent interest in power quality, requires acceptable accuracy at higher frequencies leading to the ned for increased frequency calibration facilities.

On-site calibration facilities are also available at some NMIs which have the advantage that the IT can be calibrated in-situ without the extra inconvenience and expense of transporting a heavy and large transformer, that for some VTs can be filled with pressurised gas that must first be emptied.