Moisture in the package is a leading factor causing inter-turn insulation failure of dry-type air-core reactor.In order to reveal the harmful effect of the moisture on the inter-turn insulation

we dissected a set of retired reactors due to inter-turn insulation failure

and carried out hydro-thermal aging test of the PET film

which is used as the inter-turn insulating material.Firstly

we used SEM

FTIR

and tensile testing machine to evaluate the physical and chemical properties of the specimens

and inferred the change of the insulation in the package after wetting.Then

hydro-thermal aging test was conducted on the PET film to obtain its breakdown voltage and elongation at break in different humidity conditions.The results show that:1) the package of the dry-type air-core reactor might have been seriously damped

and the moisture would cause hydrolysis of the insulation materials in the package;2) PET film has very poor hydrolysis-proof property

and is very easy to hydrolyze in humid and high-temperature condition

leading to significant reduction in mechanical strength or even to embrittlement

as a result

the film may split under the internal stress to damage the inter-turn insulation.So it is necessary to prevent the package from damp and reduce the damage of moisture to the inter-turn insulation.