PLCC.

[attachment=16881]

Outdoor equipment:-

1. Wave trap:- These are used for blocking the HF signals of PLCC entering into substation. Wave traps will allow only high voltage power signal of 50Hz frequency.

2. Line matching (LMU):- The output of PLCC is connected to the LMU then to the power lines to achieve proper impedance matching between PLCC equipment and power lines.

3. Capacitance voltage transformer/Capacitor coupling (CVT/CC):-
(CVT/CC) is connected between the LMU and power lines. These are used for blocking the high voltage entering into the LMU/PLCC.

4. Drainage coil/Lightening arrestor:- These are used for arresting any AC high voltage spikes entering into the LMU/PLCC.

5. Earth switch:- This is used at the time maintenance of LMU.

6. Coaxial cable:- This is used for interconnection between PLCC and LMU for carrying HF signals.


COUPLING EQUIPMENT:-
The most important technical problem in a power line carrier is to device methods and equipment to couple the low voltage and high frequency carrier set to the high voltage and low frequency power line.
During the initial stages of carrier operation on power lines, and aerial wire of more than 300 feet length, supported on power line structure, was used. On one end of it was connected the output from carrier equipment. While the aerial coupled the signals to power lines mainly due to capacitance between them.


(a.)Phase to Ground Coupling:-
Carrier terminals are connected between one phase conductor and ground. The wave traps and coupling capacitors are all connected to one conductor of the power line. The remaining two conductors do not have wave traps. A portion of carrier energy is lost and also radiated losses are high as earth forms a part of the circuit inefficient as the connection at the receiving end cannot be made to match the line perfectly.

(b.)Two-Phase Coupling:-
It provides reliability of operation in case a coupled conductor develops some fault. It needs twice the coupling equipments and wave traps. For this reason, this method is not used in practice.

(c.) Phase to Phase Coupling:-
It provides metallic go and return paths to the carrier currents. In this case the uncoupled conductor does not have any appreciable influence on the transmission.