1.

Which of the following is the correct equation for DC series motor ________(a) [ Vt / kφ]- [ Rse +Ra / kφ] Ia(b) [ Vt / kφ]- [ Ra/ kφ2] Ia(c) [ Vt / kφ^2]- [Rse +Ra/ kφ^2] Ia(d) [ Vt / kφ^2] + [ Ra/ kφ^2] IaI have been asked this question during an interview.The question is from Operating Characteristics of DC Series Motor in division Characteristics of DC Motors of DC Machines

Answer»

Right choice is (a) [ Vt / kφ]- [ Rse +Ra / kφ] Ia

To explain I would SAY: Speed-torque characteristic equation is obtained by back emf = (Vt -IaRa-IaRse) and back emf= kφn. Thus, by combining these EQUATIONS and by assuming all CONSTANTS equal to k we get, the final equation shown above.



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