Calculation of the frequency response of inductive medium voltage transformers

Inductive voltage transformers in the electrical grid are normally used for frequencies of 50/60 Hz. This is reasonable, because they have natural frequencies which lie considerable above 50/60 Hz. On a 20 kV voltage transformer the first natural resonance is about 5 kHz which obviates a dependable measurement of harmonics up to 9 kHz. However, as the measurement of harmonics becomes more important, the development of an inductive voltage transformer with an extended frequency range up to 9 kHz is expedient. It is therefore necessary to be able to calculate the relevant frequency response. The determination of frequency response can be accomplished by using three techniques, which are analytical or numerical calculation, or measurement. Finally, the influence of the burden on the inductive voltage transformer will be analyzed. Here a distinction is made between resistive, inductive and resistive-inductive burdens. The effects are explained in a basic example.