Power Line Carrier Communication
Er. Vishwesh Kumar Sharma
PLCC system uses the same High Voltage transmission line connecting
two sub-stations for telecommunication purpose too.
PLCC is used in all power utilities as a primary communication service to
transmit speech, telemetry and protection tripping commands. This is
economic and reliable for inter grid message transfer as well as low bit
rate RTU signals.
The voice/data are mixed with radio frequency carrier (40-500kHz),
amplified to a level of 10-80W RF power and injected in to high voltage
power line using a suitable coupling capacitor. The power line as a rigid
long conductor parallel to ground, guides the carrier waves to travel along
the transmission line. Point to point communication takes place between
two SSB transceivers at both ends.
Power Line Carrier Communication System
PLCC Terminal = Translates Voice and data into High Frequency Carrier. Output
Power =10 to 80W
LMU = Line Matching Unit = For impedance matching between line and coaxial
cable, includes high voltage protection devices like drainage coil(20mH), lightening
arrestor(500V) and an earth switch.
Coupling Capacitor (C.C) = Couples high frequency carrier with Power Line (
Line Trap (L.T) = Do not allow the transmitted HF carrier to enter inside the substation. (L = 0.5 to 2mH) With out Line trap HF carrier get by- passed to some
other line on the same bus bar and may leak to ground ( a earth switch inside the
yard provided for each bay is kept closed during maintenance)
Line Trap function = PLC signal Blocking
Line Trap = High Impedance for PLC signal
Low Impedance for Power energy
Line Trap is a parallel LC circuit
Line Traps Mounting Options
LMU = impedance matching Transformer + high voltage Protection
To prevent dangerous potential on the PLCC connection
To match PLCC set & transmission Line
ABB PLCC terminal ETL- 41
System data -- complies to IEC 495
Operating mode : Single side band Suppressed carrier
Frequency range: 40 to 500kHz (programmable in 4 kHz
AF Bandwidth: 4 kHz (Speech band=300 – 3400 Hz)
Transmitter RF output power : 40W ( +46 dBm)
Receiver Selectivity : 70dB ( 300Hz from band limit)
Receiver Image rejection > 80 dB
Typical PLCC Installation
MS = Master station
PAX = Private automatic exchange
PR = Protection relay
PC = Computer
M = Modem
PR= Protection relay
FAX = Facsimile equipment
M = Modem
RTU = Remote terminal unit
PLCC work on rectified AC or main supply, when supply
goes off, we make use of a device for proper functioning of
PLCC called battery charger.
This is the device that provide supply to the PLCC
equipment for uninterrupted working.
It provide DC to the panel by battery.
No separate wires are needed for communication
purposes, as the power lines themselves carry power as
well as communication signals. Hence the cost is less.
Power lines have appreciably higher mechanical strength
compared with ordinary lines. They would normally remain
unaffected under the conditions, which might seriously
damage telephone lines.
Power lines usually provide the shortest route between
the power stations.
Power lines have large cross-sectional area resulting in
very low resistance per unit length. Consequently carrier
signals suffer much less attenuation than when they travel
on telephone lines of equal lengths.
Power lines are well insulated to provide only negligible
leakage between conductors and ground even in adverse
Largest spacing between conductors reduces
capacitance, which results in smaller attenuation at high
frequencies. The large spacing also reduces the cross talk
to a considerable extent.
Proper care has to be taken to guard carrier equipment
and persons using them against high voltages and
currents on the lines.
Noise introduced by power lines is far more than in case
of telephone lines. This is due to the noise generated by
discharge across insulators, switching processes.