New methodology for on-site measurement of Voltage Transformer magnitude and phase ratio as a function of frequency

Abstract

Inductive Voltage Transformers are commonplace in low and medium voltage power distribution networks and are important for network monitoring and protection. Their performance at frequencies above 50Hz, defined as maintaining transformer ratio and input/output phase relationship, is often completely unknown. It is also a challenge to remove VTs from existing installation points to test thoroughly for VT ratio and phase frequency response using the standard swept-sine variable frequency testing. To meet this challenge, the Power Networks Demonstration Centre (PNDC) has developed a technique which relies on a harmonic analysis of the relationship between the transformer input and output. In laboratory testing it has a speed and safety advantage over conventional techniques, while in the future it may allow comparison with known levels of harmonics distortion on the distribution network to calculate the performance at higher frequencies of VTs in-situ.