Why is the surge impedance in overhead lines more than in underground cables?

It is because of the difference between the capacitance in them. is the positive sequence capacitance. Since, per line length capacitance for cable systems are much more than of overhead lines, the surge impedance is less for cable systems.

What is the difference between underground cable and overhead cable?

Overhead electricity lines are usually held up by wooden poles or steel towers. Typically overhead lines are more common in rural areas as they are used to cover greater distances. Underground electricity cables are laid below the ground and are usually found in built up areas such as cities.

What is an advantage of using underground power cables rather than overhead power cables?

The underground cables have several advantages over the overhead lines; they have smaller voltage drops, low chances of developing faults and have low maintenance costs.

What is the main drawback of underground cables as compared to overhead transmission lines?

➨Cost of underground cables (e.g. HVDC) are three times higher compare to overhead lines (e.g. 400 KV). ➨Moreover laying or burying cost of underground lines are greater compare to overhead lines. ➨It is difficult to find and repair the wire breaks in case of failure of system.

What are the ranges of surge impedance for overhead lines and underground cables Why the surge impedance values are different in these two cases?

The value of Surge impedance for overhead transmission line is around 400 ohm, whereas surge impedance value for underground cable is around 40 ohm.

What is the range of surge impedance for an underground cables?

around 40 ohms
An impedance which renders the line as the infinite line is known as surge impedance. It has a value of about 400 ohms and phase angle varying from 0 to -15 degrees for overhead lines and around 40 ohms for underground cables.

What is the main disadvantage of underground cables?

Disadvantages of a Underground Cables: The Cost of underground cables are very high (e.g. HVDC). We can say that underground cables cost is three times more compare as to the overhead lines (i.e. 400 KV). Moreover placing or inter cost of the underground cable lines are much greater as compare to the overhead lines.

What are the advantages of underground cables?

Section 3 – Advantages of Underground Cables

• Longer Life Expectancy. Underground systems normally last much longer than overhead wiring.
• Reduced Maintenance Costs.
• Service Uninterrupted by Storms.
• Conserve Valuable Land.
• Reduced Fire Fighting Hazards.
• Prevention of Accidents.

What is the major advantage of underground cables?

Underground systems normally last much longer than overhead wiring. Components of underground systems, not being exposed, require less maintenance. Underground systems are protected from ice storms, lightning, and high winds. Land is a valuable resource, particularly in urban areas.

What is surge impedance in underground cable?

An impedance which renders the line as the infinite line is known as surge impedance. It has a value of about 400 ohms and phase angle varying from 0 to -15 degrees for overhead lines and around 40 ohms for underground cables.

What is the ratio of surge impedance of an underground cable to an overhead line?

Hence, such an impedance which renders the line as infinite line is known as surge impedance.It has a value of about 400 ohms and phase angle varying from 0 to –15 degree for overhead lines and around 40 ohms for underground cables.

Why do we use underground power cables instead of overhead?

Because underground line capacitance for power cables is far higher than overhead line capacitance. Wires are closer to each other. Wires are closer to the earth (within a few inches). The inductance is lower as well.

Why is the capacitance of power cables higher underground?

Because underground line capacitance for power cables is far higher than overhead line capacitance. Main reasons for this: Wires are closer to each other. Wires are closer to the earth (within a few inches).

What is the difference between O/H cables and overhead cables?

Overhead, O/H cables are much cheaper per km to buy and install but frequency of repairs is higher due to lightning, hurricane, and tree exposure. But then they are also faster and cheaper to repair.

What is an extruded cable?

Extruded cables are so called because the insulation material (XLPE or EPR) is shaped by passing heated polymers, which are vulcanized, through a die to provide the required insulation thickness over the conductor. A metallic shield, if present, of tape or, wire of copper or aluminum may be applied over the insulation.