Analysis on turn-to-turn insulation of the secondary winding in Tesla transformer

A criterion to describe the turn-to-turn discharge of the secondary winding in Tesla transformers is presented. Factors which have influences on the turn-to-turn insulation of the winding such as the wire diameter, the wire distance, the void size, the purity of transformer oil and the insulation strength of the wire are researched based on this criterion. By theoretical calculation, the electric field enhancement factor (FEF) dependent on the wire diameter and the wire distance is presented. It is found that an optimum ratio of the wire diameter to the wire distance exists which corresponds to the minimum FEF. Via the Paschen's Curve, the electric breakdown strength (E
b
) for voids with different sizes is deduced, and it is found that the existence of voids makes the discharge occur more easily due to void's lower E
b
but if the size of a void is smaller than a certain value, it cannot affect the winding's turn-to-turn insulation. Through experiments, E
b
of the traditional enamel wire and that of the three-layered insulation (TLI) wire are compared. The results show that E
b
of the three-layered wire is basically two times of that of an enamel wire. Based on the results, suggestions to improve the insulation of the secondary winding in Tesla transformers are summarized.