Determining correction factor of power cable sizing under nonlinear load condition
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Date
2008-12
Authors
Azizan, Muhammad Mokhzaini
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Abstract
The invention of electronic equipment has lead to a serious power quality problem in
harmonics. The equipments, also known as the nonlinear loads have the ability to distort
parameters such as voltage and current. Distortion of current, particularly, is lethal to power
system and among the power system parameters to be having direct impact of harmonic in
current is power cables. Component of harmonics might increase RMS value of current, thus
jeopardizing insulation of cable. The conducting part of cable might be exposed and in a
confined cable trunking pipe; contact with other cable is possible and short circuits would
cause power system break down. Looking at the possible solution, this thesis has come up
with a correction factor for power cable sizing, particularly under nonlinear load condition.
Few power cable samples are to be undertaken series of tests involving harmonic content in
current, for both single phase and three phase power system. The increment of THD; is
measured as well as its corresponding increase of temperature. The result of the thesis is the
constant that relates power cable operating temperature and content of harmonic (THD) in
current. For single phase power system, K value obtained as variation of THD; from 0% to
80%, equals 0.40 ± 0.015. More complicated power cable solution reserved for three phase
power system where neutral cable plays a big part in sizing method. For injection ofTHD; at
phase ranging from 0% to 40%, the constant value is 0.41 ± 0.009 where mostly the sizing
would be referred to phase cable's size. However, as harmonic content at phase amounted
from 50% to 80%, a different constant is obtained due to the influence of neutral cable
current loading, which yields constant is 0.47 ± 0.004. Another finding is the current
reduction rate for both single and three phase power system which it to be applied in inverse,
so that equivalent load current can be determined. A relation between power cable sizing and
THD; has been established; through power cable's operating temperature parameter. Power
cable sizing solution under nonlinear load condition has been successfully determined.
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Keywords
The nonlinear loads have the ability to distort , parameters such as voltage and current