# Electromechanical energy conversion

Thread Starter

#### Sarilaci

Joined Dec 16, 2015
2
1-electromagnet with a relative permeability of 1000 and a uniform thickness of
10 cm has the dimensions as given in Figure . Calculate the limit value of the current in the
series-connected coils so that the electromagnet can lift the ferromagnetic bar having a relative
permeability of 300 and a mass of 20 kg (Earth’s gravitational constant g=9.81 m/s2). 2-
Consider the two-coil rotating electromechanical system shown in Figure. The
airgap is uniform and the iron core is infinitely permeable. The self inductance of the rotor and
stator coils are Lr = Ls = 0.6 H, and the mutual inductance between them varies with the angular
position (θ) as: Lrs(θ) = Lsr(θ) = 0.5 cos θ, where θ is in degrees. a) Calculate the torque induced on the rotor when θ = 30o, Is = 5 A and Ir = 2 A, where Is
and Ir are currents in stator and rotor coils, respectively.

b) The rotor coil is open circuited and the stator coil current is fixed to 5 A. Calculate
induced voltage between the terminals of the rotor coil when the rotor is revolving at an
angular speed of 100 rad/s.

#### crutschow

Joined Mar 14, 2008
27,237
So how's it going so far with your solution to the questions?
Or are you expecting us to do your homework? Thread Starter

#### Sarilaci

Joined Dec 16, 2015
2
So how's it going so far with your solution to the questions?
Or are you expecting us to do your homework? I have same examples with solutions but in this questions,electromagnet and ferromagnetic bar have infinite permeability.How do we solve that permeabilities are different as question 1.

In question 2b, I try to solve this question by using this formula: e2=Lr(Q)*di2/dt + i2*wm*dLr(Q)/dQ + Ls(Q)*di1/dt + i1*wm*Ls(Q)/dQ

I find -250sinQ, is it true?