Question

A single core cable has inner diameter of 5 cm and a core diameter of 1.5 cm. If paper dielectric has a working dielectric stress of 60 kV per cm, the maximum permissible line voltage when such cables are used on a 3-$\varphi$ power system is _____kV.

• A. 93.84

Answer 1

The correct option is A 93.84
Given,
Diameter of core (d) = 1.5 cm
Radius of core (r) = 0.75 cm
Inner diameter of cable (D)= 5 cm
Inner radius of cable (R) = 2.5 cm



Maximum working dielectric stress $\left(g_{max}\right)=60kV/cm$
$V_{ph}=r.g_{max}ln\left(\frac{R}{r}\right)kV$

$=0.75\times 60ln\left(\frac{2.5}{0.75}\right)kV$

$V_{ph}=54.18kV$

When such cables are used in 3-$\varphi$ power system, then
$V_L=\sqrt{3}.V_{ph}=93.84kV$