Harsh environmental impact on performance of low voltage underground power cables in hot countries
It is a well-known fact that underground cable loads are affected by many factors such as depth of installation, number of parallel circuits of cables, ambient temperature, conductor size, duct size, size of backfill (or duct bank), and soil thermal resistivity. It is also recognized that resisti...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Online Access: | http://psasir.upm.edu.my/id/eprint/70985/1/FK%202017%2010%20-%20IR.pdf http://psasir.upm.edu.my/id/eprint/70985/ |
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| Summary: | It is a well-known fact that underground cable loads are affected by many factors
such as depth of installation, number of parallel circuits of cables, ambient
temperature, conductor size, duct size, size of backfill (or duct bank), and soil
thermal resistivity. It is also recognized that resistivity changes with moisture
migration under loading conditions. One important factor that is usually ignored is a
harsh environment. In hot countries, extreme environmental conditions exist, where
the air temperature during the summer season overrides 500C and the dry soil creates
very high thermal resistivity.
This dissertation takes a direct and comprehensive approach to study the effect of
harsh environment on thermal performance of the buried power cables to evaluate
the cable temperature rise as well as the effect upon life reduction under constant
loading conditions, using the dry zone formulation which provides a simple but
consistent framework to model cables and their installed environment.
In this thesis, the effect of a harsh environment on the current-carrying capacity (or
ampacity) of underground power cables is also presented.
The method is given to extend the use of a thermal circuit to cover the entire
environment rather than just the cable itself. This is because the nodal solutions in
the environment support the prediction of moisture migration in the steady-state
adaptation of the two-zone approach to moisture migration employed in the
standards, where the native soil surrounding cables is assumed to dry out when the
temperature overrides a predefined critical temperature rise above ambient. The main application of the FEM is to predict conductor temperatures in real time
from thermal resistivity measurements and a realistic knowledge of the thermal
environment of a cable. A full thermal analysis of the installed cable system can lead
to high accuracy in the finite element method and predict the conductor temperature
from thermal resistivity measurements.
The phenomenon of the formation of the dry zone around the cable related to three
types of soil is considered, when these types of soil are subjected to constant loading
conditions.
The IEC-60287 was taken as a reference, while ANSYS software was used to
calculate the temperature distribution at the cables with the surrounding environment
for different types of native soils with some experimental data. The results have
demonstrated that the ambient temperature in Iraq has a direct impact upon cable life
temperature and useful life. |
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