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Seminar on, Power Line Career Communication
DEPARTMENT OF ELECTRICAL ENGINEERING
Dr. Abhimanyu Mohapatra,
& Dr. Ranjan Ku. Jena
Lecturers , Dept of
Fast and efficient communication is a
prerequisite for the management of modern
To maintain a large power grid in optimum
working condition,the central load despatcher
has to have at his command a large battery
of communication systems.
For this the load dispatcher may use the
commercial P&T telephone system using
underground cables or open wires or VHF
But for communication over medium and long
distances in a power network,Power Line
Carrier Communication is the most
economical and reliable method of
communication. This is because of :
The higher mechanical strength and
insulation level of HV powerlines.
Lower attenuation over longer distances.
Absence of additional communication lines.
Like any other communication system in PLCC
the three basic blocks of communication are:
1) transmitter 2) Channel and 3) Receiver
In PLCC we use wired channel of
The idea of Power line communication came
into picture in 20th century and practically
this idea came into operation in several
countries after 1920.
In early time antennae similar to those used
in radio work were being used to couple
telephone systems into powerline systems.
But due to their inefficiency owing to their
length and interference with nearby long
wave radio transmitters they were replaced by
oil and paper capacitors by about 1930.
These coupling capacitors could withstand
high voltages and serve as effective coupling
devices for power line carrier communication.
These early PLC communication systems
today handle not only speech communication
The various components of PLC
The line matching unit
The carrier signals used in modern PLC
systems are audio frequency currents of
frequencies between 24khz to 500khz.
The use of audio frequency carrier currents
enables several channels of communication
to be held over a single physical circuit.
The frequency limits are decided basing on
the following points:
Ease of separation between power frequency
and radio frequency
Cost of coupling equipments
Signal to noise ratio in the communication
Interference to and from other services
We use the word modulation to mean the
systematic alteration of one waveform, called
the carrier, according to the characteristic of
another waveform, the modulating signal or
In Continuous Wave (CW) modulation
schemes, the carrier is a sinusoid.
The various advantages of modulation are:
Ease of radiation
Improvement of signal to noise ratio
The four important types of linear modulation
1) Double Sideband, Suppressed Carrier
2) Double Sideband, Large Carrier (DSB-LC)
(also called conventional AM or simply AM)
3) Single Sideband (SSB)
4) Vestigial Sideband (VSB)
Let gm denotes the amplitude sensitivity (or
gain constant) of the modulator, with the
units per volt (we assume that m(t ) and Ac
are in volts). Then the modulator output s (t )
s (t ) = gm m(t ) (Ac cos(ωc t ))
For convenience, let gm = 1. Then,
s (t ) = Ac m(t )cos(ωc t )
There are two popular methods for
generation of single side band sinals:
Frequency discrimination method
Phase discrimination method
Frequency discrimination method
Conceptually, it is a very simple scheme.
First generate a DSB signal an then filter out
the unwanted sideband.
This scheme requires:
two product modulators
two π/2 phase shifters and an adder.
One of the phase shifter is actually a Hilbert
transformer (HT); it should provide a π/2
phase shift for all the components in M(f ) .
The received SSB signal is multiplied by the
local carrier which is of the same frequency
and phase as the carrier used at the
In the output we get the spectrum centered at
± 2fc which will be eliminated by the LPF
following v (t ).
Wave traps prevent the carrier currents
from entering into the power equipments in
the stations removing the chances of:
Complete loss of signals
These wave traps consist of choke coils
connected in series with the power lines and
Negligible impedance to power frequency
But a suitably high impedance to the radio
frequency carrier currents.
Modern coupling capacitors are designed to
Highest possible surge withstand capacity
Highest cutoff frequency
Lowest series resistance at carrier
The drainage coil serves to ground the power
frequency charging current of the capacitor
and allows the carrier frequency current to
appear in the output of the unit.
The line matching unit:
It consists of the matching transformer and
tuning capacitors and is generally tuned to a
wide band of carrier frequencies(100450khz).
Phase to ground coupling
Phase to phase coupling
Inter line or inter circuit coupling
More economical than all others.
Loss of carrier current.
Carrier energy & radiation losses are more.
Noise pick ups are correspondingly higher.
Short or unimportant lines where carrier
protection is not essential.
The third conductor has no appreciable effect
on carrier current transmission.
Switching conditions have little effect on
Signal attenuation is less.
More reliable over longer distances.
Used in load dispatch work.
It is more reliable than phase to phase coupling
on the same circuit as it permits operation with
one of the two circuits opened out & grounded
More reliable under broken conductor conditions.
In 220kv and 400kv lines where interference
levels are high.
In long110kv lines where attenuation is a
Now a day PLC communication is finding
application in domestic and many corporate
Spread spectrum is the main field of research
Very soon this system will have a wide range
of applications due to its reliability, fastness
and more economic features.