Expansion of the Impedance and Frequency Measurement Ranges of AC Shunt Resistors

For expanding the impedance and frequency ranges of a calibration system for ac shunt resistors, a current bridge method with cascaded current transformers (CTs) has been developed. An ac shunt resistor with a nominal value of 10 mΩ is evaluated by the current bridge method using cascaded CTs and the results of the calibration system using this method are validated. It is demonstrated that the calibration system for ac shunt resistors using the current-bridge method with the cascaded CTs can be used successfully for both in-phase and quadrature components up to 3 kHz. Further, for expanding the frequency range, a voltage difference method is proposed. The measurement results obtained by the current-bridge method and the proposed method are consistent with each other within the measurement uncertainties. In addition, for expanding the impedance range at higher frequencies, a combination method with an inductive voltage divider and a current transformer is proposed. The measurement results using the combination method are consistent with the results of the current-bridge method within the measurement uncertainties. The test current in this paper was limited up to 10 A because of the specification of shunt resistors.