Stepper motor It is required to predict the magnitude of the torque from the var

Question

Stepper motor It is required to predict the magnitude of the torque from the variation of inductance with angle. The diagram below shows the angle of overlap. If the radius of the rotor pole is r, the arc length of the overlapping part is r Assume that the field, with flux density Bg is confined to this arc, so the flux is dr0Bg where d is the axial depth of the rotor. The inductance of the two coils in series with 2N turns is: N 200 2.5 A, d 50 mm, r 20 mm, Ig-1 mm Calculate the torque from the following list a) 0.314 Nm b) 0.157 Nm c) 0.628 Nm d) 0.126 Nm

Explanation / Answer

torque is given by (i^2/2)*(dL/d(theta))

here dL/d(theta)=2*mu*N^2*d*r/(l_g)

=2*4*pi*10^(-7)*200^2*0.05*0.02/0.001=0.10053

then torque=(i^2/2)*dL/d(theta)

=(2.5^2/2)*0.10053

=0.31416 N.m

so option a is correct.

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