An experimental thermal siphon bushing

An experimental thermal siphon bushing was constructed and tested. The thermal siphon was made from the hollow conductor of a paper-resin bushing with water as heat transport fluid. The test shows that this bushing has almost uniform temperature distribution under its critical current and the temperature of its hottest spot is close to the boiling temperature of water. The current carrying capacity of this thermal siphon bushing is 50% more than that of the same bushing without thermal siphon. Simple formulas are proposed to determine the critical current of a thermal siphon bushing and estimate the temperature of the hottest spot if the bushing with thermal siphon is operated above the nameplate rating.