ABSTRACT
Advancements in smart grid technology have created a need for reliable
forms of data transmission to be able to provide the various intelligent features
associated with smart grids. One means of data transmission is Power
Line Communication (PLC), which transmits data via the power cable with
the cable simultaneously performing its normal function of carrying electric
power. This is made possible by using suitable coupling interfaces. Attenuation,
phase constant and propagation velocity are important characteristics
of High Frequency (HF) signal transmission that need to be considered when
understanding a power cable’s data transmission capability. This research
report investigates the extent to which the outer semiconducting layer of an
Medium Voltage (MV) power cable a↵ects the HF transmission characteristics
by quantifying and comparing HF characteristics. Simulations were
performed based on an established HF cable model. The simulations indicated
that the outer semiconducting layer has an e↵ect, although marginal,
on the HF characteristics. The mean di↵erence of attenuation between 1 to
10 MHz is 2.849⇥104 db/m (3.08%). In the same frequency range the mean
di↵erence between the phase constant is 3.82% and the propagation velocity
is 4.2%. Physical experimentation was carried out using a Time Domain Reflectometry
(TDR) based measurement system. The resultant measurements
further confirmed that the outer semiconducting layer has an influence on the
HF transmission characteristics of the power cable. Time domain analysis,
showed that the outer semiconducting layer has an e↵ect on the velocity
factor of the cable with a di↵erence of 5.15%. Frequency domain analysis
showed that the mean attenuation di↵erence for the range of 1 to 7 MHz
was 0.0054 dB/m (1.14%), which is relatively small when compared to the
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simulation value. The outer semiconducting layer has a greater influence on
the phase constant and propagation velocity with mean di↵erences of 31.11%
and 41.18%, which are significantly larger when compared to the values obtained
through simulations. It was also determined that the length of the
cable has an e↵ect on the attenuation and usable bandwidth of the power
cable with a shift of the peak attenuation from 55 to 45 MHz. In comparing
the power cable with a communication (RG-58) cable of the same length it
was seen that the RG-58 was better suited for HF transmission within its
designated bandwidth and further showed the limitations of PLC. Design of
communication channels in MV power cables should take cognisance of the
power cable HF transmission limitations caused by components such as the
outer semiconducting layer
