Electrical Knowledge

Underground Cable – Introduction and Construction An underground cable essentially consists of one or more conductors covered with suitable insulation and surrounded by some protective layer. Normally, electric power can either be transmitted using over head lines or underground cables. But the use underground cable offers a variety of advantages. Some of the advantages are listed below. It is less liable to damage during storm or bad whether condition. Offers low maintenance cost. Less voltage drop during normal operating condition and less chance of fault. But the main disadvantage of underground cable is its cost of installation. For higher voltage the cost of cable increases due to greater requirement of insulation as compared to overhead lines. Therefore, it is installed in area or localities where overhead lines cannot be installed. Requirements of Underground Cable There are various types of cable available but the choice of particular type depends on the operating

Types Of Underground Cables We have already seen what  Underground cables  are, and where they’re used. Moving forward, we must understand  various types of Underground cables  available to us. Classification Of Underground Cables The  classification of Underground cables  can be done on the basis of several criteria. Various aspects are taken into account while classification and these include: Number of conductors in the cable Voltage rating of the cable Construction of cable Type and thickness of insulation used Installation and Laying of the cables Classification Based Upon Number Of Conductors In The Cable Single core cable Three core cable Typically, an Underground cable has either one, three or four cores. These cables are of course, constructed accordingly. Underground cables are usually employed to deliver 3 phase power. A 3 cored cable is preferred up to 66 kV. Beyond that, insulation required for the cable is too much. For higher voltages, 3 cored constru

Types of Neutral Earthing in Power Distribution:  Introduction: In the early power systems were mainly Neutral ungrounded due to the fact that the first ground fault did not require the tripping of the system. An unscheduled shutdown on the first ground fault was particularly undesirable for continuous process industries. These power systems required ground detection systems, but locating the fault often proved difficult. Although achieving the initial goal, the ungrounded system provided no control of transient over-voltages. A capacitive coupling exists between the system conductors and ground in a typical distribution system. As a result, this series resonant L-C circuit can create over-voltages well in excess of line-to-line voltage when subjected to repetitive re-strikes of one phase to ground. This in turn, reduces insulation life resulting in possible equipment failure. Neutral grounding systems are similar to fuses in that they do nothing until something in the system g

Here is one most helpfull webpage for this topic http://marinenotes.blogspot.in/2012/12/underground-or-isolated-neutral-system.html http://www.ece.mtu.edu/faculty/bamork/EE5223/Ground%20Fault%20Protection%20isolated%20neutral.pdf http://202.74.245.22:8080/xmlui/bitstream/handle/123456789/112/Ch-26.pdf