08-07-2014, 12:52 PM
SEMINAR ON PLCC
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INTRODUCTION TO PLCC
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 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.
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.
Control Voltage Transformer/Coupling Capacitors
It is connected between the line matching unit and the power lines to block the high voltage entering to PLCC equipment.
It couples high frequency carries with power line.
WAVE TRAPS or LINE TRAPS
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.
ADVANTAGES
. 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.
DISADVANTAGES
1. Proper care has to be taken to guard carrier equipment and persons using them against high voltages and currents on the lines.
2. High voltage lines have transformer connections, attenuate carrier currents. Sub-station equipments adversely affect the carrier currents.
3. 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, corona and switching processes.
4. The noise is also introduced in the signal due to bad weather conditions.