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POWER LINE CARRIER COMMUNICATION is the technology which is used to communicate between electric substations through existing electrical cables .
POWER LINE CARRIER COMMUNICATION is mainly used for telecommunication, tele-monitoring and tele-protection between electric substations through power lines at high voltages. The data can be transfer at 9.6Kbits/sec over many miles of electrical cable.
In PLCC the higher mechanical strength and insulation level of high voltage power lines result in increased reliability of communication and lower attenuation over long-distance.
Since telephone communication system can not be directly connected to the high voltage lines, suitably designed coupling devices have to be employed.
Coupling devices consists of high voltage capacitors in conjunction with suitable line matching units(LMU’s) for line impedance matching to that of the co-axial cable connecting the unit to the PLC transmit-receive equipment.
Carrier currents used for communication have to be prevented from entering the power equipment used in GSS as this would results in complete loss of power system.
Wave traps – (WT’s) are used between the transmission line and the power stations to avoid carrier power dislocation in the power plant and cross talk with other power line carrier circuits connected to the same power station.
WT’s also ensure proper operating conditions and signal levels at the PLCC transmit receive equipment irrespective of switching conditions of the power circuits and equipment in the station.
A wave trap must satisfy the following requirements:
1) It must block the carrier currents. By blocking, we mean that the track should attenuate the H.F. signals by at least 8 to 10 dB.
2) It must carry the power frequency current safely during normal operation as well as during short circuit fault conditions.
1. 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.
2. 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.
3. Power lines usually provide the shortest route between the power stations.
4. 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.
5. Power lines are well insulated to provide only negligible leakage between conductors and ground even in adverse weather conditions
6. 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.