A 66 kV concentric cable with two inter-sheaths has a core diameter 1.8 cm. Dielectric material 3.5 mm thick constitutes the three zones of insulation. Determine the maximum stress in each of the three layers if 20 kV is maintained across each of the inner two.

Question

Accepted Answer

Refer to Fig. E.9.4.

The overall radius of the cable

0.9 + 3 × 0.35 = 0.9 + 1.05 = 1.95 cms.

Let [latex]g_{1 \mathrm{max}}[/latex] be the maximum stress on the surface of the conductor,

[latex]g_{2 ext { max }}[/latex] the maximum stress on the first intersheath,

[latex]g_{3 \max }[/latex] the maximum stress on the second intersheath.

[latex]\begin{gathered}V_{1}-V_{2}=g_{2 \max } r_{1} \ln \frac{r_{2}}{r_{1}}=0.3085 g_{2 \max }=20 \V-V_{1}=g_{1 \max } r \ln \frac{r_{1}}{r}=g_{1 \max } imes 0.9 \ln \frac{1.25}{0.9}=0.2956 g_{1 \mathrm{max}} \V_{2}=g_{3 \max } r_{2} \ln \frac{r_{3}}{r_{2}}=0.3165 g_{3 \max }\end{gathered}[/latex]

Now [latex]\quad V-V_{1}=20 \mathrm{kV}=0.2956 g_{1 \max }[/latex]

[latex] herefore \quad g_{1 \max }=\frac{20}{0.2956}=67.6[/latex] kV/cm

Also, [latex]\quad V_{1}-V_{2}=20 \mathrm{kV}=0.3085 g_{2 \max }[/latex]

[latex] herefore \quad g_{2 \max }=\frac{20}{0.3085}=64.83 [/latex] kV/cm

and [latex]\quad V_{2}=66-40=26 \mathrm{kV}=0.3165 g_{3 \max }[/latex]

[latex] herefore \quad g_{3 \max }=82[/latex] kV/cm.

Question 9.4: A 66 kV concentric cable with two inter-sheaths has a core d...

Related Answered Questions

Determine the economic overall diameter of a 1-core cable metal sheathed for a working voltage of 85 kV if the dielectric strength of the insulating material is 65 kV/cm. ...

Verified Answer:

If the lead sheath resistance in the previous problem is 2.14 ohm per km and that of the conductor is 0.1625 ohm/km, determine the ratio of sheath loss to core loss of the cable. ...

Verified Answer:

Verified Answer:

Verified Answer:

The capacitance of a 3-core lead sheathed cable measured between any two of the conductors with sheath earthed is 0.19 μF per km. Determine the equivalent star connected capacity and the kVA required to keep 16 kms of the cable charged when connected to 20 kV, 50 Hz supply. ...

Verified Answer:

Verified Answer:

A single core lead covered cable is to be designed for 66 kV to earth. Its conductor radius is 0.5 cm and its three insulating materials A, B and C have relative permittivities of 4, 2.5 and 4.0 with maximum permissible stresses of 50, 30 and 40 kV/cm respectively. Determine the minimum internal ...

Verified Answer: