Calibration of instrument current transformers at low currents using lock-in amplifier

A system for evaluating instrument current transformer errors using a lock-in amplifier is described in the paper. The difference between the standard and the transformer under test is evaluated as the ratio error and the phase displacement. The attention is focused to measurement of errors at the range of primary currents less than 20% of the nominal value. The measurement accuracy of current and energy in smart grids is important particularly at the time when the majority of appliances are in the standby mode