Electrical Machines Questions and Answers_pag3

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Explanation: f​e​=-(∂W​fld​ (φ,x))/∂x= -(∂W​fld​ (∅,x))/∂x and T​e​=-(∂W​fld​ (φ,θ))/∂θ=-(∂W​fld​(∅,θ))/∂θ. 
8. The developed electromagnetic force and/or torque in electromechanical energy conversion 
systems, acts in a direction that tends to ___________ 
(i) increase the co-energy at constant flux 
(ii) increase the co-energy at constant mmf 
(iii) decrease the stored energy at constant mmf 
(iv) decrease the stored energy at constant flux 
Which of the above statements are correct? 
a) (ii), (iv) 
b) (i), (iii) 
c) (ii), (iii) 
d) (i), (iv) 
View Answer 
Answer: a 
Explanation: f​e​=-(∂W​fld​ (φ,x))/∂x and f​e​= (∂W​fld​
1​(F,x))/∂x. 
9. A physical system of electromechanical energy conversion, consists of a stationary part 
creating a magnetic field with electric energy input, and a moving part giving mechanical energy 
output. If the movable part is kept fixed, the entire electrical energy input will be _______ 
a) stored in the magnetic field 
b) stored in the electric field 
c) divided equally between the magnetic and electric fields 
d) zero 
View Answer 
Answer: a 
Explanation: As the movable part is fixed, W​mech​=0, we know, W​elec​=W​mech​+ W​fld​,therefore, 
W​elec​=W​fld​. 
 
This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on 
“Singly Excited Magnetic Systems”. 
1. For a toroid to extract the energy from the supply system, the flux linkages of the magnetic 
field must be ________ 
a) zero 
b) changing or varying 
c) constant 
d) any of the mentioned 
View Answer 
Answer: b 
Explanation: dW​elec​=idφ=eidt, where dW​elec​= differential electrical energy to coupling field, and if 
the flux linkages are either constant or zero, i.e, dφ=0, then dW​elec​=0. 
2. Magnetic stored energy density for iron is given by ______ 
a) 1/2 B/μ 
b) 1/2 B​2​ μ 
c) 1/2 ∅​2​ Rl