THE INSULATING OF ARMATURE CONDUCTORS 249 



Insulation Specification for 500- Volt Tramway Motor 

 Armature Slots. 



The conductors are first finely spun with a double cotton 

 covering. This, of course, is generally done by the firm supplying 

 the copper wires. 



The wound coils are dried for three hours in a vacuum oven at 

 90 C., and are then impregnated with a good and preferably 

 plastic insulating varnish to render them moisture-proof. 



A 



Co Horn Fibre 025 



J<xcor>et Lbfx. O'lbmm ^o/er/A^j 

 imprtGf&Ced with J<>)<WA n 

 V^rn/sh ToO&l OriicKneSS 35'n 



VC C&pe 0/3 mmi over /aya 



eorvxt/ed wj,fch //. V^rnisA 



ic<<ness 0*35 mm 



pper - 



FIG. 286. Section through Slot of Strip- Wound Continuous-current Armature. 



In making up the compound coil, pieces of very thin shellac'd 

 presspahn l are placed between the component sections. The two 

 straight sides (i.e. the slot portion) are then placed in a steam or 

 electrically heated mould, thus compressing the whole group of 

 conductors into a solid compact form. 



The slot portion is then wrapped over with from two to four 

 layers of varnished cambric, and then the whole coil is served with 

 "jaconet" tape (cotton tape), 0'13 mm. thick and 16 mm. wide, 

 wound with half overlap. 



1 Shellac'd presspahn has the advantage for this purpose that the shellac 

 is pressed laterally out between the wires, filling up the interstices and 

 cementing the whole into one compact mass. There is not enough shellac 

 present to be harmful. 



