Precision Two-Stage Voltage Transformer for a Wide Voltage Range of 5–40 kV

A two-stage voltage transformer (VT) with several rated transformer ratios and with a rated maximum voltage of 40 kV and a rated minimum voltage of 5 kV has been designed. To guarantee high accuracy over the full medium-voltage range, the primary winding has been split into four primary windings, which can be configured in three different series and parallel connections. With five windings of the secondary, 15 different voltage ratios can be accomplished. This connection scheme, which is already used in older commercial standard VTs of the error class 0.02, achieves a very low effective output resistance, which in turn results in very small additional errors of less than0.5× 10⁻⁶due to the loading by the input of the transformer bridge. According to the measuring results, for all the 15 different ratios, the error is less than20~μ V/V for ratio error and20~μrad for phase displacement.