The Calculation of Can Losses in Canned Motors

Abstract

Most of the performance characteristics of these canned motors may be calculated by well-known methods. The most unique feature of these motors is the presence of a stator and rotor can in the air gap. Simple equations for the calculation of the losses, in watts, in these cans were derived and are repeated. W=15.5B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ltX10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-16</sup> /ρ (1) or W=0.7854(Vø/N) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (2) stator can loss = KS × W (3) rotor-can ripple loss = 1.3(bt/bs(Kcs-1)2 Kr×W (4) The summation of these two losses should be added to the no-load iron loss as part of the total no-load losses. In certain cases, it may also, be found desirable to calculate the no-load damper loss, particularly in cases where the number of rotor slots differs from the number of stator slots by more than 25 percent. At full load, both the can losses and the iron losses are reduced because of the drop in fundamental flux density in the air gap. However, a number of tests indicate that this reduction is approximately compensated by an increase in stray load losses. The effect of stator magnetomotiveforce harmonics on the notor can loss was calculated for a number of cases and found to be generally negligible at no load. The lower-order harmonics such as the fifth and seventh, which may have appreciable magnitude, are largely damped by induced currents in the rotor; since one pole pitch of these harmonics will generally span more than one rotor slot pitch.