# Overhead Lines vs Power Cables - Question on Insulation

• Fjolvar
In summary, insulation in power cables is important because it prevents short circuits and reduces power losses. Overhead power lines do not need insulation because the distance between the wire and ground provides enough resistance. This also allows for higher voltage levels to be transmitted compared to power cables.
Fjolvar
Hello I have a very basic question.

I'm studying power cable engineering right now and I've learned about the role of insulation in a cable to reduce dielectric losses and charging current losses, but I don't understand what this means exactly. Here are my questions..

1. Is the insulation basically reducing the voltage from building up outside of the conductor and creating leakage current?

2. I'm trying to understand what would happen without insulation in a power cable. Why do we need insulation? And why do overhead power lines just have bare wires without any insulation? How does this effect power losses?

3. Why can overhead transmission lines transmit at higher voltage levels that power cables?

Any help would be greatly appreciated. I am preparing for an exam and this is my weakspot :(

Last edited:
Fjolvar said:
I'm trying to understand what would happen without insulation in a power cable. Why do we need insulation? And why do overhead power lines just have bare wires without any insulation? How does this effect power losses?

With no insulation, the wires would short circuit to Earth ground (soil or water.) Insultation provides high resistance (ideally infinite resistance) to current flow. In a cable, it is provided by the jacket. For overhead lines, it is provided by the air in the long distance between wire and ground.
Fjolvar said:
Why can overhead transmission lines transmit at higher voltage levels that power cables?

If the overhead wire is say, 20 meters in the air, the electric breakdown voltage is 20* 3 x 10 6 V/m, or 60 MV. The actual voltage is much less than that, probably more than 100 times less than that.

Compare the 3 x 10 6 V/m breakdown strength of air with the cable insulation. Then consider the thickness 20m overhead versus 0.02 m for cable.

## What are overhead lines and power cables?

Overhead lines and power cables are two methods for transmitting electricity from a power plant to homes and businesses. Overhead lines are typically visible above ground and consist of wires suspended on poles, while power cables are buried underground and consist of insulated wires.

## What is the difference between overhead lines and power cables?

The main difference between overhead lines and power cables is their location and method of insulation. Overhead lines are exposed to the elements and use air as insulation, while power cables are buried underground and use a solid or liquid material as insulation.

## Which is more efficient, overhead lines or power cables?

Overall, power cables tend to be more efficient than overhead lines. This is because the insulation used in power cables reduces energy loss and interference from external factors, resulting in a more reliable transmission of electricity.

Overhead lines have a lower installation cost and can be easier to maintain compared to power cables. They also have a higher capacity for transmitting electricity, making them suitable for long distance transmission.

## What are the advantages of using power cables?

The main advantage of power cables is their reliability. Being buried underground, they are less vulnerable to external factors such as weather and animal interference. They also have a lower risk of electrical faults and require less maintenance compared to overhead lines.

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