I need to find out the advantages and disadvantages of overhead and underground cables please? The comparisons? Help would be appreciated
Underground cables are expensive. It is expensive to dig, and if you ever have to repair them, you have to dig up the whole section to find the break, etc. There is concern that living too near overhead power cables (don't know about telephone or cable TV), can cause health problems. Now-a-days, you often have to do underground cables in city neighborhoods, but your higher power lines (like 345 KiloVolt lines) tend to be overhead cables strung across areas that aren't too near to houses. The buried local neighborhood lines aren't typically buried because the power company wants to; they are buried because the city mandates it. In the country - isolated farm houses here and there, underground lines just aren't pratical. In cities, sometimes you can put the power lines through say some underground tunnels (like sewers - though not necessarily the sewers themselves). If the tunnels already exist, it may be only slightly more costly to put the power lines there, and really shouldn't cost more to maintain than overhead lines (as the lines are accessible to the crews - no digging in most cases).
The situation is different for distribution and transmission. Underground distribution pros: - esthetically preferable - requires smaller right-of-way - right-of-way can be shared - fewer problems with vegetation, automobile accidents, lightning, or vandalism Underground distribution cons: - higher cost of construction - higher repair cost - potential risk from careless digging In general, underground distribution is a practical option for new construction and in some jurisdictions, is required (eg, all new construction in New York must be underground). There are three major factors with underground transmission: - the cost is FAR greater than overhead. Underground transmission is almost always reserved for situations where right-of-way is extremely limited - eg, metropolitan areas - or for water crossings. - reactive control - this can be a big problem. The shunt capacitance is greater with underground cables than it is with overhead, and at the same time, the series reactance is lower. That's a consequence of the spatial physics. As a result, the use of underground cables for transmission can result in significant reactive control problems at the transmission level. That in turn means that additional equipment is required to address those reactive control problems, further increasing the effective cost of underground compared with overhead. - on the other hand, undgrounding transmission means that it is not visible. There is no evidence that exposure to transmission has any demonstrable health effects, but there still people who are fearful. If the transmission lines are underground, they won't see then and will therefore worry less (or, more lik ly, find something else to worry about)
Buried power cables lose some power by inductance to the surrounding soil [sort of like the soil being the secondary winding in a transformer]. How much power is lost depends on the soil and especially on how wet it is. Also important are the length of buried cable, and whether the cable is high voltage/low current [more insulation problems] or low voltage/high current [more induction loss]. I sort of recall a friend saying [decades ago] that their local power company told them that if the wire to their cabin were buried [a couple of hundred feet] they would lose 1/3 of the power. Don't take that as gospel, though; I might misremember, or the friend might have misspoke, or the power company guy could have. Underground cables are usually less troubled by lightning and high winds. Squirrels probably gnaw on them less, too.
