Question

The arc length voltage characteristic of a DC arc is given by the equation V = 24 + 4L where V is the arc voltage and 'L' is the arc length in mm. The static volt ampere characteristic of the power source is approximated by a straight line with no load voltage of 80 volts and the short circuit current of 600 amperes.

The optimum arc length is

• A. 3 mm
• B. 5 mm
• C. 4 mm
• D. 2 mm

Answer 1

The correct option is C 4 mm

$V=24+4LEq-1OCV=80VSSC=600A\frac{V}{OCV}+\frac{I}{SSC}=1\therefore \frac{V}{80}+\frac{I}{600}=1P=VI=600V(1-\frac{V}{80})P=600(V-\frac{V^2}{80}){\text{For P =P}}_{max}\frac{dP}{dV}=0\therefore 600(1-\frac{2V}{80})=0\Rightarrow V=40Volts$

$\text{By putting value of V in Eq -1 L = 4 mm}$