What are the benefits and drawbacks of underground vs overhead power distribution lines?

For the same conductor size, overhead line could transmit powers more than underground cables. In overhead lines less shunt capacitance and more inductance, while in underground is the opposite. overhead line dose not exposed to addition heat and good ventilated, while underground cables are exposed to grouping heat affects and poorly ventilated. Wave radiation influence increase in underground cables trenches and ducts, while decrease in overhead lines.

I have different opinion for this question. There is always benefit for both overhead and underground distribution Lines. Because an engineer design according to requirements.

One of the primary advantages of overhead lines is the ease in finding faults. Inspectors can easily identify overhead lines that are prone to failure or those that have failed already. This can significantly reduce outage times which helps the utility maintain its service standards.

UG construction is expensive but more reliable. UG takes longer to repair after the fault. UG construction is desirable in urban settings.

In my experience, fault location of underground cables is more complex than overhead lines. It requires trained staff and special instruments. Underground cables do not require any clearance as the cables are already insulated, but the overhead lines require clearance. Hence special attachments like insulators, cross arms, poles and towers are required. Underground cables have several different layers other than the conductors which are built for specific tasks. Hence joining of UG cables require special jointing kits and trained labor. Whereas, overhead cables do not require any jointing kits and specially trained labor.

From the point of view of power system expansion, the underground line might be a good solution when you have a high load density. In this case, the cost of building an overhead line is more expensive than underground because you will have a high cost of the expropriation of land. Another important consideration is the installation of a dry underground line parallel to the oil-filled underground line. The impedance of these cables can be different to the extent that it can impact load flow, with the oil-filled cable carrying more load than the dry cable. Therefore, it is important to pay attention to this detail during the project.

In my experience, as fault location and repair time of underground cable is high due to excavation and road traffic constraints, it is recommended to use UG cables in ring formation or with a redundancy formation.

Some of the less commonly understood problems associated with underground lines are issues with switching overvoltages. As the capacitance of underground cables are higher than that of overhead lines, they are more prone to overvoltages when switched. These overvoltages can rise up to 4 p.u. in some instances which can be dangerous to operators and equipment. This leads to limitations in the length of underground cable that can be switched when compared to overhead lines. Underground cables are also generally more aesthetic than exposed overhead lines (although electrical engineers seem to disagree). This is why underground distribution systems are often used in new residential developments and CBDs.

I agree with most of the particles except for one minor thing: the word losses in this context is not associated with a fault or theft. If there is a fault or theft, you lose generation, but your loss does not change because of those 2 events. Loss is a product of design flaws and/or running conditions.

Losses are most affected by the voltage of the system and the conductor size relative to the load being supplied. Many utilities have done voltage conversions to improve capacity and reduce losses. There is no significant advantage to underground or overhead for losses. You can get bigger conductors underground than overhead, but due to heating of the conductors, you need bigger conductors for underground. The end result is approximately no advantage for either option.

I agree, but I don't consider leakage losses due to insulation breakdown as non-technical losses. Also, the line loss due to the resistance of the conductor is the same for UG cables and OH lines. Line loss due to resistance varies with the cross-sectional area, the material of the conductor, and the length only. I do not agree with the fact that UG cables are shorter than OH lines. Capacitive loss in UG cables are higher than the OH lines.

I do not agree with the fact of installing protective devices to reduce losses. To reduce the losses of UG cables, the cable system design and laying shall be done perfectly. Also for longer cables methods like transposing and using surge voltage limiters (SVL) can be used.

What i think is , there is no any strong points to explain advantage and disadvantage of overhead and underground lines . It depends on requirements and availability of clearance and condition of that particular area where the line is to be constructed. 🤗

For the same conductor size, overhead line could transmit powers more than underground cables. In overhead lines less shunt capacitance and more inductance, while in underground is the opposite. overhead line dose not exposed to addition heat and good ventilated, while underground cables are exposed to grouping heat and poorly ventilated. Wave radiation influence increase in underground cables tranches and ducts, while decrease in overhead lines.

The suitability for overhead vs underground distribution infrastructure is also dependent on the region and its weather patterns. For example, bushfire prone areas may benefit from underground infrastructure as overhead lines may pose a fire-start risk.