PURPOSE: To minimize installation space at stepwise area and provide an inspection passage, by a method wherein a switching device field of low-tension side is installed at upper stage, and a plurality of three-phase transformers of dividing type are installed at area of the same level as installation field of high-tension side.

CONSTITUTION: At lateral side of single-phase transformers 3, 4, 5 in three-phase transformers 1, 2 opposed with each other, high-tension leads 6 are drawn towards a space between the three-phase transformers 1, 2. Low-tension leads 7 are drawn at uppe side thereof. The high-tension leads 6 and the low-tension leads 7 are connected respectively to high-tension gas insulation bus bars 8 and low-tension gas insulation bus bars 9 arranged in a space between the three- phase transformers 1, 2. The high-tension gas insulation bus bars for three phases are overlaid in the vertical direction to the ground surface and then extended to a high-tension switching device field 12. The low-tension gas insulation bus bars 9 are extended to a low-tension switching device field 13 at higher level than a transformer installation field 14 by one step.