Kai Xie

On-Line Evaluation of Voltage Transformer Accuracy

The accuracy of voltage and current transformer (VT and CT) is a key factor in electric power metering. Ratio error and phase displacement calibration of VT and CT is traditionally carried out off-line. As a result of the expansion of the power grid and the increasing metering quality requirements from customer side, the off-line metering of VT and CT becomes more and more difficult. In this paper, a VT accuracy on-line evaluation system is developed, which can evaluate the accuracy of VT under on-line operating status. The principle and adopted key techniques in the development of the VT accuracy on-line evaluation system is introduced. Some on-site test results are also presented and analyzed as application demonstration.

The Current Transformer Accuracy On-Line Evaluation System

The accuracy of current transformer (CT) is important guarantee of power system protection, monitoring and measurement. A new method based on live working technique for CT accuracy evaluation is proposed in this paper. Through constructing standard part, which is on-line insert into power lines, and comparing the data of standard part with the data of the measured part, the system can calculate the ratio error and phase displacement of the measured CT. The results of on-line test have shown that the proposed method is feasible and effective, and the accuracy of proposed system achieves 0.1 grades.