Page 152 - From Smart Grid to Internet of Energy

Power line communication technologies in smart grids Chapter 4 133

red solid line, communication network that is included into the conventional
power grid for evolving it to SG is illustrated with blue dotted line.
The HV lines are utilized to deliver electricity in the range of 110–380 kV at
transmission stage of power grids. Since they are composed of long overhead
lines without branches, the HV lines can be regarded as wave-guides due to less
attenuation features when compared to MV and low-voltage (LV) lines. Arcing,
corona noise and coupling costs are appeared the most important problems of
the HV lines when they are considered for the PLC applications. Therefore, the
BB PLC applications of HV lines have been limited until today.
The MV lines that transfer electricity in the range of 10–30 kV are con-
nected to HV lines over primary transformer substations. This type of transmis-
sion lines that may be overhead or underground cables are employed to
distribute power among industrial customers, towns and cities. In the event
of mixed installation of overhead and underground cables at MV level, an
increased attenuation may be occurred due to impedance mismatch. In addition,
the MV lines can directly linked to intelligent electronic devices (IED) because
of containing a small number of branches. Since monitoring and automation
applications are generally required low data rates, NB PLC applications can
be efficiently realized over MV lines.
The LV lines that deliver electricity in the range of 110–400 V are connected
to MV lines over secondary transformer substations, and they are last stage of
power network reaching customers. If a communication signal on MV lines
passes to LV lines over secondary transformers, it suffers from an extreme atten-
uation, approximately in the level of 55–75 dB [57]. Channel characteristics of
LV lines are extremely dynamic than that of the HV and MV lines since there
exist many randomly connected/disconnected loads with different impedance
values. The noises in the LV lines are unpredictable because of the dynamic
impedance variations. Therefore, well-designed repeaters and coupling devices
are widely needed to ensure a reliable PLC system with high data rate.
On the other hand, network connection topology, used electrical cables and
other electrical devices and characteristics of power networks lead differences
throughout the world. It is important to note that there are remarkable differ-
ences between power networks of countries that closely affect PLC channel
behavior. The comparison of European and North American power networks
is a good example to understand differences among countries. The European
MV levels can change in the range of 10–24 kV by using overhead and under-
ground distribution systems. Typically, the LV lines are connected over second-
ary transformer substations in the Europe. The secondary transformer stations
are constituted in star topology with 400 V phase-to-phase and 230 V phase-to-
neutral features. While a secondary transformer substation is composed of two
or three transformers, these transformers may approximately serve for 150–300
customers. When the North American model case is considered, the MV levels
are in the range of 4 and 34 kV. The secondary transformers in North America
feed LV lines with 120 or 200 V according to load types. Most of LV lines in