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Concept & PrincipleElectricalBasic Electrical

Option D

Any of above

Quick Summary: Cables are insulated using various dielectric materials depending on voltage levels, environmental conditions, and cost. Varnished cambric, rubber, and impregnated paper are traditional insulation materials used in electrical cable engineering.

💡 Explanation

Cables are insulated using various dielectric materials depending on voltage levels, environmental conditions, and cost. Varnished cambric, rubber, and impregnated paper are traditional insulation materials used in electrical cable engineering.

🔢 Key Formulas

$E_{max} = \frac{V}{r \ln(R/r)}$ — Electric stress calculation for a single-core cable

⚙️ Working Principle

Insulation works by providing a high resistance path to prevent leakage current and electrical breakdown. The dielectric material must withstand the electric stress $E = \frac{V}{r \ln(R/r)}$ and thermal heating while maintaining its structural integrity.

📌 Key Points

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Varnished cambric is used for high-voltage cables due to its high dielectric strength.
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Rubber is flexible and used in low-voltage domestic cabling.
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Impregnated paper is widely used in high-voltage oil-filled cables.
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Insulation resistance $R_{ins} = \frac{\rho}{2\pi L} \ln(\frac{R}{r})$

✅ Advantages

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High dielectric strength
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Flexibility for installation
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Thermal stability

❌ Disadvantages / Limitations

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Moisture sensitivity in paper insulation
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Degradation over time due to oxidation

🛠️ Applications / Uses

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Power distribution systems
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Industrial control wiring
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High-voltage transmission

📄 Additional Information

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Varnished cambric consists of cotton cloth coated with insulating varnish.
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Paper insulation must be kept dry; hence, it is often used in lead-sheathed, oil-filled cables.

📊 Diagram / Illustration

✅

D is correct — All listed materials (varnished cambric, rubber, and paper) are standard insulating materials used in different types of electrical cables.

Core Concepts Used

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Dielectric materials Electric stress in cables Cable construction

💡 EXAM TIP

Remember that the choice of insulation depends heavily on the operating voltage; paper is common in HV, while rubber/PVC is more common in LV.

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