Page 153 - From Smart Grid to Internet of Energy

134 From smart grid to internet of energy

there are composed of overhead lines, and they only serve for 10–15 customers
[58]. In addition, there is main frequency differences throughout the world. For
instance, the main frequency is determined as 50 Hz in Europe and in many
parts of Asia while American countries utilize 60 Hz main frequency. One
another important factor affecting the PLC channels is that the characteristic
behaviors of electrical devices and components change over the years due to
varying impedances. Moreover, there are important differences among the
buildings as mentioned before. Generally, the buildings can be grouped as
multi-flat buildings with riser, multi-flat buildings with common meter room,
single-family houses and high-rise buildings [48]. The differences in wiring
topology of different buildings also cause diversity in signal attenuation and
interferences in the PLC channel [49].

4.3.2 Underground cables characteristics
Underground cables are composed of one or more conductors that are covered with
proper insulation materials, and are enclosed by a sheath. These cables present sev-
eral advantages such as less chance of damage from storm and/or lightning, more
reliable among faults and voltage drop issues and low maintenance costs. Nonethe-
less, main disadvantages of these cables are high installation cost and insulation
problems in high voltage transmission. Thermal capacity that limits overloading
in long-distance applications is an important characteristic of underground cables.
Several disruptive effects such as noise, electromagnetic interference (EMI),
impedance mismatch, and inter-symbol interference (ISI) may affect these cables
because of the multi-branched structure of underground wiring. In addition, heat
dispersion is a critical problem for underground cables and it may cause perfor-
mance degradation on power transmission [1, 59, 60]. Thermoplastic (i.e., Polyvi-
nyl Chloride (PVC)) or thermosetting (i.e., Ethylene-Propylene Rubber (EPR),
Cross-Linked Polyethylene (XLPE)) type materials are generally preferred as insu-
lation material for underground cables. Even though capacitive coupling among
ground and power cables causes performance degradation on NB-PLC technolo-
gies operating under 1 MHz, reliable communication over underground cables can
be performed up to 300 m distance [61, 62]. In addition, shielding of underground
cables according to electromagnetic interferences can decrease noise issues of
broadband applications. Several underground cable examples employed under-
ground network are listed in Table 4.3.

4.3.3 Overhead power-lines characteristics
The use of overhead cables for power transmission over long distances provides
two important advantages. The first one is related to installation costs whereas
the second is related to transmission requirements of electricity at high voltage
levels due to the economic reasons. These cables are widely utilized to deliver
or distribute electrical power in modern power systems. The service quality of