Development of a new type of large-size self-integrating Rogowski coils applied in TPG-series generators

Abstract

Different meter-class, thousand-turn, self-integrating Rogowski coils for the TPG-series generators are designed. The features of this type of coils are the extremely large turn number (several thousands) and the 50-Ω characteristic impedance of the cable used as the current viewing resistor. After calibrations for these large-size coils, it is found that the experimental sensitivities are larger than the theoretical ones and that the deviations range from 4% to 20%, which cannot be accepted. The deviations are analysed in perspective of coil size and cable length. It is concluded that the sensitivity deviations are mainly due to the increased coil size and partly due to the long cables. A modified theoretical sensitivity expression of the large-size, self-integrating Rogowski coils is presented based on the transmission-line model, which embodies the factors of coil size and cable length. A method to test the key parameter in the model, the characteristic impedance of the coil, Z, is also presented. With this expression and the method, the theoretical sensitivities for the TPG-series generators are re-calculated, which agree well with the experimental ones, only with a deviation around 2%. It is suggested that the modified theoretical sensitivity expression can be used to calculate the sensitivity of the self-integrating Rogowski Coils with a large size.