Underground cable

Every year there are thousands of incidents involving damage to buried cables, some of which result in burn injuries and a few (typically one or two) are fatal. Most of the incidents occur during street works where utility companies, construction companies and local authorities carry out excavations in the highway and damage an electricity supply company s underground mains. Other incidents take place on construction sites and other private property and involve a supply company s service cables or mains, or distribution cables belonging to the site occupier. 

The burn accidents invariably result from manual excavation when, for example, an operator using a pneumatic drill penetrates a concealed, buried cable with the tool. A short circuit will occur when the bit comes into contact with one or more of the live conductors and the metallic armouring and/or sheath of SNE cables or the CNE conductor where a PME distribution system is in use. The initial phase/earth or phase/neutral fault usually develops and involves the other phases, causing arcing which may emerge as a flame arc and blast from the hole made by the tool, injuring the operator. 

There are few reported accidents where the victim received an electric shock. This is probably because the fault involves an earthed conductor so the tool does not attain a significant voltage to the surrounding ground and 

In the past, there were fewer accidents because buried cables were better protected. Most of the supply authorities used paper-insulated, lead-sheathed, single-wire or steel-tape armoured and served cables and very often protected them with cable tiles. For economic reasons cable tiles are seldom used now and many of the mains laid in recent years are unarmoured CNE cables with plastic insulation and sheathing, such as PVC and cross-linked polyethylene (XLPE). The outer concentric conductor, which is the earthed neutral, is copper or aluminium tape and consequently more vulnerable to damage than a steel-wire-armoured cable. Every year more new mains cables of this type are laid so the resultant hazard to excavators is growing and more accidents can be expected to occur unless the construction industry becomes more effective at taking precautions against striking buried cables. 

---

Low Temperature Performance. The abihty of plasticized PVC to remain flexible at low temperatures is of great importance in certain apphcations, eg, external tarpaulins or underground cables. Eor this property the choice of the acid constituent of the plasticizer ester is also important. The linear aUphatic adipic, sebacic, and azeleic acids give excellent low temperature flexibiUty compared to the corresponding phthalates and trimeUitates (Pig. 3). 

Countries like the USA and Japan have adopted underground cabling tor tran.smi.s.sion of power up to 1000 MW al 550 kV. 

Electromagnetic (EM) Conductivity Measures the electrical conductivity of materials in microohms over a range of depths determined by the spacing and orientation of the transmitter and receiver coils, and the nature of the earth materials. Delineates areas of soil and groundwater contamination and the depth to bedrock or buried objects. Surveys to depths of SO to 100 ft are possible. Power lines, underground cables, transformers and other electrical sources severely distort the measurements. Low resistivities of surficial materials makes interpretation difficult. The top layers act as a shunt to the introduction of energy info lower layers. Capabilities for defining the variation of resistivity with depth are limited. In cases where the desired result is to map a contaminated plume in a sand layer beneath a surficial clayey soil in an area of cultural interference, or where chemicals have been spilled on the surface, or where clay soils are present it is probably not worth the effort to conduct the survey. 

Overhead transmission lines require that the area beneath them be cleared of trees or tall shrubs, which may result in erosion. When the transmission line right-of-way is not kept clear, the transmission line may come into contact with vegetation, causing a fault on the system and possibly starting a fire. Chemical contamination of soil may result from some types of transmission structures, such as treated wood. Burial of underground cables also can impact the environment due to erosion. 

Polarised Electric Drainage a means of electric drainage comprising the employment of metallic connections between the underground cable system and the traction return circuit, with the insertion of a unidirectional system (rectifier or contactor and relays) in the connections. 

Uses Nonsystemic contact and ingested insecticide and fumigant. Treating termites and other insect pests. Also used as a wood preservative, treating underground cables, and reducing earthworm populations in lawns (Worthing and Hance, 1991). 

In 2008, SuperPower, Inc., an electric power component manufacturer in Schenectady, New York, produced a 1,311 meter (.814 mile) length of HTS wire, a new record for the industry. SuperPower recently completed the Albany Cable Project in which a 350 meter (1,148 feet) HTS underground cable was installed in the National Grid power system connecting two substations in Albany, New York. 

Mirex 2385-85-5 1958 20-30% of mirex for termite control in structures of houses, dams and underground cable boxes. 1997 Same as above... 

In certain locales, power transmission is made by means of underground cables. In one example an 8.0-cm-diameter cable is buried at a depth of 1.3 m, and the resistance of the cable is 1.1 x 10 4 ft/m. The surface temperature of the ground is 25°C, and k = 1.2 W/m °C for earth. Calculate the maximum allowable current if the outside temperature of the cable cannot exceed 110°C. 

Power lines, underground cables, transformers and other electrical sources severely distort the measurements. 

Because of its chemical inertness, lead has also been popular as a covering for underground cables, such as buried cables that carry telephone messages, and for pipes through which liquids are transported. For many years, lead was the material of choice in the construction of water pipes since it was inert to most chemicals occurring in nature and easily shaped. With the recognition of lead s threat to humans, however, many of these applications have been discontinued. 

The application of the M — 1 philosophy is less complicated with incoming feeders e.g. underground cables, overhead lines. N is usually chosen as 2 because it is not usually economical to use three or more feeders for one switchboard. Both feeders are usually in service and so the spare does not usually exist. However, each feeder is rated to carry the full demand of the switchboard. Therefore with both in service each one carries half of the demand, and can rapidly take the full demand if one is switched out of service. This approach also enables a feeder to be taken out service for periodic maintenance, without distmbing the consumers. 

It may be noted that the simple treatment of the zero sequence impedances in the example would tend to be more appropriate to a remote switching station fed by an underground cable. 

Fig. 27.1 The NMR-MOUSE measuring the rubber insulation of a high-power underground cable sleeve. A defect is located at positions 1, 2, and 3 with an average of T2efr = 3.6 ms, while the regular material exhibits an average value at positions 4, 5, and 6 of 72eff = T8 ms. T2eff is defined in the text.

Cross-linking of the outer casing is achieved by grafting a vinyl silane to polyethylene by means of a peroxide as part of the cable extrusion process. The chemistry is shown in Scheme 2.1. When the cable is subsequently soaked in water, the alkoxy silanes hydrolyse and crosslink within the matrix. It is an unresolved question whether polymers that have been modified by a free radical mechanism will survive for the expected lifetime of underground cables (ca. 75 years). 

The arrangement form used in the electrode cables buried inside seam roof, electrical meter installed in the tunnel behind, linked ground monitoring station through the underground cable. 

Details of underground cables Motor and other drivers data sheets... 

---