A method for field verification of the precision class of inductive voltage transformers

It is shown here that the precision class of an IVT-inductive voltage transformer-can be verified in the field, using the results obtained in the usual tests of no-load loss and current, short circuit and winding ohmic resistances, performed with common meters. A graphic diagram-the Mollinger and Gewecke diagram-is employed together with the results of an accuracy test previously carried out in order to determine the exact value of the winding turns relation and of the primary winding dispersion reactance. These values are used to calculate phase and magnitude errors, that must obey standards and must lie between definite limits, defined by the precision class of the instrument. Some commercial IVTs were tested in order to check the validation of the procedure. The errors were compared with the ones obtained with the Shering-Alberti method (CA bridge and comparison with standard IVT)