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The direction of rotation of a DC series motor shaft can be changed by _____________(a) Interchanging supply terminals(b) Interchanging field terminals(c) Not possible(d) Cannot be determinedI have been asked this question during an online interview.My doubt is from Operating Characteristics of DC Series Motor -1 in portion Characteristics of DC Motors of DC Machines

Answer»

The correct ANSWER is (b) Interchanging field terminals

Explanation: From speed current CHARACTERISTICS for a DC series motor, we get that speed is inversely proportional to FLUX. If flux direction is REVERSED, same flux will be available with negative sign in VECTORS, thus, speed will remain same but with the other direction.



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