Influence of Unbalanced Secondary Burden on Voltage Error of Voltage Transformers in Distribution Power System

Abstract

Voltage errors of three voltage transformers in three-phase four-line metering devices in ungrounded distribution power system are interrelate with each other, however, the error characteristics of each voltage transformer under unbalanced secondary burdens have scarcely been studied. In this paper, three-phase three-element combined transformer is taken as an example to analyze the influence of unbalanced secondary burdens on voltage errors of its three voltage transformers. Firstly, equivalent circuit of the three voltage transformers taken as a whole is established, and then voltage error is analyzed theoretically and tested to verify the validity of theoretical analysis. Results show that the change of the secondary burden of voltage transformer will results in the error of each voltage transformer changing linearly when the secondary burdens of two other voltage transformers remain unchanged, the primary current has some influence on the error of voltage transformer, however, the influence is much smaller compared with the influence of unbalanced secondary burdens on voltage error, the characteristics that unbalanced secondary burdens have a great influence on voltage errors can be utilized to optimize the power metering error of electric energy metering device.