Two Channels Opto-Isolation Circuit for Measurements of the Differential Voltage of Voltage Transformers and Dividers

Abstract

In this paper the design of the two channel opto-isolation circuit for measurements of the differential voltage is presented. It is used to ensure high impedance of the measuring channel(s) in the differential system to ensure the rated operation of connected voltage divider(s). Its conversion accuracy tests are oriented to determine the ratio and phase errors introduced by a tested device under three test conditions. The opto-isolation circuit is tested for the internal noise at various levels of common voltage. In the next step the calibration of the zero output voltage at zero differential voltage is tested. In the last step of the testing procedure, the values of conversion ratio and phase errors are determined. In the first case the analysis is performed during an operation with an additional common voltage divider when both inputs ensure high impedance. In the second case the values of the conversion ratio and phase errors are tested in conditions when only one input ensures high impedance. In this paper the application of the opto-isolation circuit to determine the values of the composite error of the tested voltage divider with the rated voltage ratios equal to 15 kV:100 V, 10 kV:100 V, 5 kV:100 V is presented. Moreover, its usage to determine the values of the composite error of the inductive voltage transformer with voltage ratio (15 kV/√3)/(100 V/√3) is shown.