Thermal issues in operating large motors outside their rated power and speed range

Effective Thermal Conductivity Calculation and Measurement of Litz Wire Based on the Porous Metal Materials Structure

“…R litz =R m -2*(R ab +R contact )-2* R covering (15) Measurements were taken at a mean interface temperature ((Thigh + Tlow) /2) of 50C, by adjusting the chiller and PID thermal controller to maximize Q, and a constant pressure of 3MPa to minimize the contact resistance between the test sample(s) and heat flux meter bars. Measurements last until steady state conditions are satisfied, when a temperature variation of ≤ 0.15K is successively recorded for each thermocouple over a 15 minutes period.…”

“…Assuming that the aluminum blocks in each sample are identical, firstly, the thermal resistance of the aluminum blocks are measured independently, i.e. without the Litz wire, where the thermal resistances of the aluminum blocks are approximated by 2*(R ab +R contact ) as described in ( 13) and (15). The measurement assumes that the thickness (and surface finish) of all Al blocks are constant at 2.25 mm, where the bulk thermal resistance and contact resistance of 2x aluminum blocks are calculated to be 407.75 K/W.…”

“…The main methods in researching the thermal field of electrical machines are lumped thermal resistance network methods, computational fluid dynamics (CFD), or finite element method (FEM), depending on the type of problem in hand. Combined all-numerical FEA electromagnetic/thermal coupling is applied in [13], while in [14], [15] coupling with lumped thermal resistance networks is adopted. Irrespective of the thermal analysis method used, the accurate thermal properties of the materials that are used in the machine are needed, especially within the slot section, where the majority of losses are typically located [16] , and where hotspots leading to machine failures occur.…”