Question

What is the product of the ratio of the current and the useful flux per pole?

(a) product of ratio of current and  useful per pole = (useful flux per pole due to upper limit current * upper limit current) / (useful flux per pole due to lower limit current * lower limit current)

(b) product of ratio of current and  useful per pole = (useful flux per pole due to upper limit current + upper limit current) / (useful flux per pole due to lower limit current + lower limit current)

(c) product of ratio of current and  useful per pole = (useful flux per pole due to upper limit current – upper limit current) / (useful flux per pole due to lower limit current – lower limit current)

(d) product of ratio of current and  useful per pole = (useful flux per pole due to upper limit current * lower limit current) / (useful flux per pole due to lower limit current * upper limit current)

The question was posed to me in an online quiz.

My question is taken from Motor Starters, Calculation of Resistance Steps & Design of Field Regulators topic in section Design of Small Electrical Machines, Starters and Field Regulators of Design of Electrical Machines

Answer 1

Correct option is (d) product of ratio of current and  useful per pole = (useful flux per pole due to upper limit current * lower limit current) / (useful flux per pole due to lower limit current * upper limit current)

Easiest explanation: First the product of useful flux per pole due to upper limit current and lower limit current and then the product of useful flux per pole due to lower limit current and upper limit current. On substitution the product of ratio of current and useful per pole is obtained.