Advanced procedures for calibration of instrument transformer burdens

Measurement of electrical power or energy in the area of electroenergetic, power systems and electric drivers is closely linked with use of instrument current or voltage transformers (ICT, IVT). Accuracy of these appliances substantially affects the resulting accuracy of the measurement. An important parameter which affects ICT or IVT accuracy is their burden. Therefore the calibration of instrument transformers (IT) must be performed at a desired value of the burden. It usually varies in the range (1 up to 75) VA. ICT burdens less than 5 VA are usually real or they have the inductive power factor 0.8 for greater values. IVT burdens have usually inductive power factor 0.8. A precise adjusting of the burden is important to achieve required IT calibration accuracy. Burden calibration is a necessary part of the calibration process. Procedures for burden calibration used at CMI are described in the paper. There is described a procedure using a standard transformer test set and also procedures with PC controlled measuring systems.