The utility model discloses a transformer substation is through -flow equipment once, through -flow equipment includes three phase current and the controlling display that is connected with three phase current, the controlling display passes through relay switch and is connected respectively with stepup transformer and current booster, current booster is connected to CT equipment, the stepup transformer is connected to PT equipment, CT equipment with PT equipment is connected to pincerlike looks bit map respectively, can perfect the back at secondary protection device current loop, it gos forward to go into operation works and accomplishes the detection of every winding current phase place and current loop integrality when class experimental, has avoided the possibility of current phase mistake behind the equipment belt electricity, has guaranteed security of system, steady operation, has improved the success rate that once puts into operation.