Comparison of methods for measuring zero sequence impedances in 3-phase core-type transformers

This paper deals with two topics about the measurement of zero sequence impedances in 3-phase core-type transformers. The first topic is a comparison of 3 methods to perform the measurement in a 3-phase winding: a) parallel connection of windings; b) series connection of windings; and c) measurement of elements of the phase impedance matrix. A brief theoretical discussion about these methods is included. The second topic is a comparison of 2 methods for measuring the zero-sequence impedance for the Dyn connection: a) with all the delta branches short-circuited; and b) without short-circuiting the delta branches. The results for the Dyn connection are compared with the obtained ones for YNyn connection, by using the standardized method for this test (parallel connection of star windings). A discussion about the results is included.