Analysis of the method for AC withstand voltage test of the terminal of zigzag transformer

The Line Terminal Alternating Current Withstand Voltage Test (LTAC) is a critical test item for inspecting the insulation performance of transformers. For transformers with fully insulated high-voltage windings, it mainly assesses the electrical strength of longitudinal insulation such as that between turns, between layers of the windings, and between different windings; for transformers with graded insulated high-voltage windings, it primarily evaluates the electrical strength of insulation between turns, between layers, and between sections of the windings, as well as the insulation between the windings and the ground, between the windings and other windings, and between different windings.As specified in GB/T 1094.3-2017 Power Transformers - Part 3: Insulation Levels, Insulation Tests and External Insulation Air Gaps, this test is classified as a special or routine test for transformers with a maximum system voltage (Um) exceeding 72.5 kV.Taking the zig-zag transformer with a connection group designation of YNZN11 as an example, this paper analyzes the voltage, current,magnetizing magnetomotive force and induced multiple of turn voltage in the internal windings of the zig-zag transformer under different voltage application wiring methods during the Line Terminal Alternating Current Withstand Voltage Test (LTAC), considering its special winding connection mode.