Harmonic Measurements in a Capacitive Voltage Transformer: Improvement Considering the Transformer's Design Parameters

The power quality studies made for the deployment of renewable power farms consider the harmonic interaction between the existing grid and the corresponding farm. An accurate computational model describing the grid must consider the background harmonics at the point of common coupling before the commissioning of the renewable energy farm. Consequently, there is an increasing trend of measuring the harmonic distortion of electrical current and voltage across an instrument transformer to characterise the external grid. The use of the Capacitive Voltage Transformer (CVT) is a common practice in substations with voltage greater than 100 kV. It results to be a very cost-efficient solution in terms of accuracy, but its frequency response makes itself unsuitable for harmonic measurements due to its filter behaviour. The impact that this alteration has on the harmonic susceptibility, resonances, and emissions between the farm and the grid is studied and an alternative in the transformer industry sector is suggested to mitigate this problem. With that purpose in mind, the design parameters of the CVT are taken into consideration to obtain its transfer function and establish an enhancement on the harmonic voltage measurements.