20-12-2012, 05:55 PM
PLCC OVERVIEW
1PLCC.ppt (Size: 3.75 MB / Downloads: 90)
PLCC Technology
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.
Components
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 = Couples high frequency carrier with Power Line ( 4000 to10000pF)
Line Trap = Do not allow the transmitted HF carrier to enter inside the sub-station. (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)
Elements of Coupling Device
Drain coil for draining of HV leakage currents to earth.
Lightning arrester at the line terminals of coupling device for transients protection
Transformer for impedance matching and galvanic isolation between line and PLCC terminal.
Earth switch for grounding of line terminals during maintenance.
High-pass or band-pass filter elements for efficient matching.
connectivity to equipment room through coaxial cable.
Effect of bad weather on PLCC communication
Losses increase for all inclement weather conditions
The worst offender is when heavy frost is formed on the line
Because of the skin effect, the carrier signal tries to propagate on the ice instead of the conductor.
The attenuation can change as much as 4:1 depending on the frequency.
The contaminats (on the insulators) have a larger effect when it is raining than when the line is dry.
The worst condition is a light rain with the presence of contaminants on the insulators