Investigation of the Frequency Dependency of Phase Angle Error in a Zero-flux Current Measuring System

Abstract: An important technique for traceable measurement of electrical current utilizes magnetic zero-flux current transformers. The technique is well established, but much remains to be understood regarding its practical upper frequency limit. Typically, zero-flux systems consist of a measuring head mounted around the primary current carrier and an electronic unit creating a balancing current in the compensation winding. In this paper the phenomena responsible for the frequency dependency of the phase angle error in zero-flux systems in the span 5 Hz – 10 kHz are described using two-channel power measuring systems as reference systems. The aim was to find out which part of the zero-flux systems that contributes most to the phase angle error. It was found that the error increases linearly with frequency between 22 Hz and 2500 Hz. At higher frequencies, the error passes a maximum in transition between the normal operation and the work regime as an ordinary transformer. It is shown that the electronic unit introduces the most significant contribution. A comparison is made between two reference systems using one zero-flux system as a transfer standard. The coincidence between the two reference systems is good