A wideband current transformer bridge

The work progress on a new current transformer test set at PTB is described. The operation range for the ratio based bridge is intended for frequencies from 16.7 Hz up to 20 kHz. Equal setups of magnetically shielded current comparators with primary windings for currents from 100 mA up to 5 A convert the secondary currents of the standard current transformer and of the transformer under test (DUT) into proportional voltages. The errors of the DUT are calculated from the subsequent measurement of the complex voltage ratio. At 50 Hz, the measuring system offers a basic accuracy in the order of less than ± 2 ppm or μrad respectively.