FEM analysis and design of a voltage instrument transformer for digital sampling wattmeter

A voltage instrument transformer (VIT) or a voltage divider is needed if a National Instruments PXI 4461 Dynamic Signal Analyzer is used in a digital sampling wattmeter application. They assure that the input voltage is lowered to the allowed level of the acquisition card, and VIT also gives the galvanic isolation. This paper discusses possible types of sectionalized windings of a VIT with primary and secondary interleave, which result in lower leakage inductances. On the basis of a detailed finite element method (FEM) analysis, a prototype VIT is designed and produced. The ratio error and the phase angle error are measured on the prototype using a digital calibrator, digital multimeter (DMM) and a phase-angle meter. As well, the performance of the transformer over the wider frequency bandwidth and under the harmonically rich excitation is experimentally investigated.