Calculation of hydraulic friction losses in dc motors filled with liquid dielectric
Abstract
Hydraulic friction during rotation of the armature in a dc motor filled with liquid dielectric is a major source of power loss, up to 40% of all power losses in such a motor. These losses are usually reduced by impregnating the end turns of armature coils with a compound and smoothing their outside surfaces. Hydraulic losses are best determined experimentally on a model armature and then calculated according to the theory of similarity for any other motor. This was with the armatures of DPK83000, DPK081000 small motors and P42, Mu52 large motors as test models. For subsequent calculations the armature is treated as a structure consisting of three cylinders: (1) slotted wound active core rotating inside a stationary cylinder with a radial gap between them; (2) end turns of coils rotating in free space; and (3) slotted commutator rotating in free space. The back plate of the armature constitutes a rotating disk. Considering that the hydraulic drag coefficient is a function of the Reynolds number only, it is calculated for each component of the armature on the basis of semiempirical relations with length and radius, gap width between stator (field) bore and active rotor core, angular velocity or rpm, and density of the dielectric as parameters. The resultant hydraulic drag coefficient is found by weighted combining of the four partial ones, with use of diameter ratios and a lengthtodiameter ratio for the active core.
 Publication:

USSR Rept Electron Elec Eng JPRS UEE
 Pub Date:
 June 1984
 Bibcode:
 1984RpEEE.......49M
 Keywords:

 Dielectrics;
 Direct Current;
 Electric Motors;
 Losses;
 Viscous Drag;
 Accuracy;
 Armatures;
 Axial Flow;
 Coefficients;
 Computation;
 Flow Stability;
 Reynolds Number;
 Turbulent Flow;
 Viscosity;
 Electronics and Electrical Engineering