Loop Tests in Underground Cables: There are several methods for locating the faults in underground cables. However, two popular methods known as Loop Tests in Underground Cables are : Murray loop test Varley loop test These simple tests can be used to locate the earth fault or short-circuit fault in underground cables provided that a …
Types of Cable Faults: Cables are generally laid directly in the ground or in ducts in the underground distribution system. For this reason, there are little chances of faults in underground cables. However, if a fault does occur, it is difficult to locate and repair the fault because conductors are not visible. Nevertheless, the following …
Thermal Resistance to Heat Flow: The Thermal Resistance to Heat Flow between two points in a medium (e.g. insulation) is equal to temperature difference between these points divided by the heat flowing between them in a unit time i e. In SI units, heat flowing in a unit time is measured in watts. Clearly, the …
Capacitance of 3 Core Cables: The Capacitance of 3 Core Cables is much more important than that of overhead line because in cables (i) conductors are nearer to each other and to the earthed sheath (ii) they are separated by a dielectric of permittivity much greater than that of air. Fig. 11.18 shows a system …
Grading of Cables: The process of achieving uniform electrostatic stress in the dielectric of cables is known as grading of cables. It has already been shown that electrostatic stress in a single core cable has a maximum value (gmax) at the conductor surface and goes on decreasing as we move towards the sheath. The maximum …
Capacitance of Single Core Cable: A Capacitance of Single Core Cable can be considered to be equivalent to two long co-axial cylinders. The conductor (or core) of the cable is the inner cylinder while the outer cylinder is represented by lead sheath which is at earth potential. Consider a Capacitance of Single Core Cable with …
Laying of Underground Cables: The reliability of Laying of Underground Cables network depends to a considerable extent upon the proper laying and attachment of fittings i.e., cable end boxes, joints, branch connectors etc. There are three main methods of Laying of Underground Cables viz., Direct laying, Draw-in system and the Solid system. 1.Direct laying: This …
Three Phase Service Cable: In practice, underground cables are generally required to deliver 3-phase power. For the purpose, either three-core cable or three single core cables may be used. For voltages upto 66 kV, 3-core cable multi-core construction) is preferred due to economic reasons. However, for voltages beyond 66 kV, 3-core-cables become too large and …
Classification of Underground Cables: Classification of Underground Cables may be in two ways according to the type of insulating material used in their manufacture the voltage for which they are manufactured. However, the latter method of Classification of Underground Cables is generally preferred, according to which cables can be divided into the following groups : …
Insulating Materials for Underground Cables: The satisfactory operation of a cable depends to a great extent upon the characteristics of insulation used. Therefore, the proper choice of Insulating Materials for Underground Cables is of considerable importance. In general, the insulating materials used in cables should have the following properties : High insulation resistance to avoid …