Temperature rise distribution at the drawlead cables in the condenser bushings was studied with a thermal model and actual thermal tests. Temperature rise of the hottest spot at the cables from the model is consistent with that from the tests within a 10% deviation. Factors that influence working current and overload capacity of the cable were studied. Current-carrying capacities of the drawlead cables with index 105 insulation are presented based on thermal basis of rating.Index Terms-Bushing, Current-carrying capacity, drawlead cable, temperature rise, thermal model, thermal test.

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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.Index Terms-Condenser bushing, critical current, current carrying capacity, heat run, temperature rise, thermal siphon.

s u r e range o f 5-200 t o r r , amplitude range o f 6-15 kv, p u l s e d u r a t i o n o f 5-80 n s , t h e v e l oc i t y l i e s i n t h e r a n g e of 10'-2x10q cm/s.I t is n o t i c e d t h a t t h e d i s c h a r g e s h e a t h does n o t t u r n i n t o a plasma s h e a t h w i t h l o w r e s i s t a n c e a f t e r a luminous s h e a t h o f i n i t i a l d i s c h a r g e b r i d g e s b o t h electrodes.