Related Topics

  What can be the causes of damage to PVC cables and paper insulated cables?  What precaution should be taken while taken a cable through trenches in the following locations (a) Road crossing, (b) Railway crossing & (c) Crossing of water mains ?  What is called “Barrier joint” of cable ?  What is called “Heat shrinkable joint” of cable?  What are the procedures to be adopted for determining the types of cable faults ?  What is proximity effect ?  What is soil thermal resistivity ?  What are the methods of cable laying ?  what special cares are to be taken for storage of cable drum ?  What are the load conditions of an underground cable ?  What do you mean by thermal resistance of a single core cable ?  What do you mean by the term “Dielectric losses” ?  What is the procedure of reducing the sheath losses in sheaths of the three single core cables in a 3-phase system ?  What do you mean by the term “Sheath losses” ?  What do you mean by MIND cable and where is it used ?  What do you mean by XLPE cable and what are its advantages over conventional cables ?  What are varnished cambric insulated cables ?  Interview Question of Underground Cable

Index

SymbolsTransformerRelayPower-SystemBasic-electricalACSR-ConductorCircuit-BreakerInterview-questions-of-Basic-ElectricityInterview-questions-of-transformerInsulatorCurrent-TransformerMCQMCQ-powersystemThermal-power-stationInterview-questions-of-Power-SystemPower-ElectronicsInterview-questions-of-Underground-CableInterview-questions-of-IlluminationIlluminationMCQ-of-ElectronicsMCQ-of-Basic-ElectricalMCQ-of-Transformers MCQ-of-D.C-motor MCQ-of-D.C-generators

What is soil thermal resistivity ?

Soil thermal resistivity is defined as “the difference in degrees centigrade between opposite faces of a centimeters cube of soil caused by the transference of one watt of heat and is expressed in thermal ohm/cm or °C cm/watt. When the cables are buried in the ground the heat transmitted through the cables passes into the surrounding soil. The ground surface above the cable is a plain isothermal of the ambient temperature so that all the heat generated is ultimately transmitted to the ground surface which remains at a constant temperature. In general, soils having a higher percentage of moisture will have a lower thermal resistivity and consequently the best heat dissipating qualities, whereas porous or well-drained soils have a higher thermal resistivity. Soil resistivity varies over a period of 12 months. Lower resistivity occurs in the rainy season when the moisture content is high and ground temperature low and the converse occurs in the summer. In water logged area the soil thermal resistivity will tend to be reduced.

Soils vary enormously in their thermal resistivity from as low as g = 30°C cm/watt in certain water logged soils to a very unfavorable ground which may approach g = 400 °C cm/watt. The current rating of the cable should then be based on the highest value of soil thermal resistivity observed. Therefore, soil thermal resistivity should be an essential preliminary to the determination of the correct current for a given cable.

Related topics :



Recent Post

Multiple Choice Question (MCQ) of Electronics page-17:
241. Which of the following statement is true? a) The saturation voltage VCF of silicon transistor is more than germanium transistor.
b) The saturation voltage VCE for germanium transistor is more than silicon transistor.
c) The saturation voltage VCE for silicon transistor is same as that for germanium.
d) The saturation voltage VCE for silicon transistor is lower than germanium transistor.

Read more...

Multiple Choice Question (MCQ) of Electronics page-16:
226. Which of the following statement is correct? a) Inner electrons are always present in the semiconductor.
b) Bound electrons are always present in the semiconductor.
c) Free electrons are always present in the semiconductor.
d) Inner and bound electrons are always present in the semiconductor.

Read more...

Multiple Choice Question (MCQ) of Electronics page-15:
211. The materials whose electrical conductivity is usually less than 1 × 106 mho/m are a) Semiconductors
b) Conductors
c) Insulators
d) Alloys

Read more...

Multiple Choice Question (MCQ) of Electronics page-14:
196. In which of the following device the base resistors are not added in the package but added externally? a) UJT
b) CUJT
c) PUT
d) None of the above

Read more...

Multiple Choice Question (MCQ) of Electronics page-13:
181. The conduction in JEFT is always by the a) Majority carriers
b) Minority carriers
c) Holes
d) Electrons
e) Holes and electrons simultaneously

Read more...


Name :   

Comments: