PURPOSE: To maintain appropriate quantity of air in the air duct as well as to obtain high cooling efficiency for the subject reactor by a method wherein a shielding material is provided along coils whereon a lead wire was wound in the direction of the coil, and when an air duct is formed between the coils, at least a part of the ventilative sectional area of the air duct is changed in proportion to the voltage used on the coils.

CONSTITUTION: The end section of the coil 1 consisting of a dry type air-cooled reactor is supported by a coil support 2, and the support 2 is fixed to the coil supporting frame 3 made of metal. Then, a shielding material 4 is provided along the axial direction of the coil 1 with its one end connected to the supporting frame 3, and an air duct 5 is formed between the coil 1 and the shielding material 4. Also, an air duct guide 7 is provided at the end section of the inner insulated cylinder 6 on the coil, and cooling air is sent to the air duct 5. In this constitution, the upper surface of the coil 1 and the inner surface of the shielding material are positioned facing the air duct 5 located in the center part of the coil 1, and then an air gap adjusting guide 8 is provided. Through these procedures, the shape of the guide 8 is determined appropriately corresponding to the circuit voltage, and the reactor having a well-balanced insulation and cooling can be obtained.