An improved algorithm for the series step-up method based on a linear three-ports network

Capacitive leakage and adjacent interference are the main influence sources of the measuring error in the traditional series step-up method. To solve the two problems, a new algorithm was proposed in this study based on a three-ports network. Considering the two influences, it has been proved that response of this three-ports network still has characteristics of linear superposition with this new algorithm. In this three-port network, the auxiliary series voltage transformers use a two-stage structure that can further decrease measurement uncertainty. The measurement uncertainty of this proposed method at 500/ √ 3 kV is 6.8 ppm for ratio error and 7 μ rad for phase displacement ( 𝑘 = 2). This new method has also been verified by comparing its results with measurement results of the PTB in Germany over the same 110 /√ 3 kV standard voltage transformer. According to test results, the error between the two methods was less than 2.7 ppm for ratio error and 2.9 μ rad for phase displacement.