2 Presentation at PLCC STU

POWER LINE CARRIER COMMUNICATION

S.T.U.USMANISENIOR ENGINEERPOWERGRID


The method involves superposition of radio frequency channel on a power circuit

without interference of / or from power system

Power Line Carrier Communication


Transmits and receives simultaneously speech and

multiplexed teleoperation and teleprotection signals in SSB

technique over high voltage lines

PLCC Equipment


• Economical

• Reliable

• Lower attenuation over long distances

• Convenient maintenance at line terminals

Advantages


Operates over band of frequencies between 30 Khz and 500 Khz.

Frequency Range


• Harmonics, switching & lightning surges and corona presents components in the frequency band between 100 hz and 30kHz

• Signal to noise ratio will be quite poor.

• Very difficult to separate power frequency and radio frequency components (mv)

• Cost of coupling equipment is high

Reasons for low Frequency Limit of 30 Khz


• Above 500Khz, The radiation losses are very high.

• Interference to and from other services increases

Reasons for high frequency limit of 500 Khz


• On-off mode (Used to block tripping in an unfaulted line Section)

• Frequency Shift Mode (Used for either blocking or transferring tripping)

• Sing Side Band Mode(Functions combined on a SSB Channel, Audio Tones are used to modulate the carrier

Mode of OperationMode of Operation


• Process whereby the amplitude or frequency or phase of a carrier wave is

varied as a function of the instantaneous value of another wave.

Modulation


• The Amplitude of the carrier wave is varied in accordance with the instantaneous value

of the signal.

Amplitude Modulation


AM WaveformAmplitude Modulation


• More Carrier channels can be accommodated in any given frequency range

• Better signal to noise ratio• Greater selectivity permitting closer channel

spacing.

Advantages of Single Side Band


• The instantaneous frequency of the carrier wave is varied as a function of the instantaneous value of the modulation signal.

Frequency Modulation


• Frequency Modulation by a square wave modulating signal. This method is extensively used in the system of pulse transmission employed in the teleprinting, telemetering, Line protection, Supervisory control, etc.

Frequency Shift


• Ratio of single power to total noise power at any point. Ratio above 10db is considered satisfactory for frequency shift operation.

Signal to Noise Ratio


• Propagation loss and increases in the propagation length of the line.

• Ratio between the voltages, currents or power at any two points is a measure of the attenuation between these two points.

Attenuation


• Phase to Phase Clearance

• Phase to ground clearance

• Humidity of Air

• Carrier Frequency

Attenuation of Line for Carrier Signal Depends on:


• Ratio of applied voltage to the resulting current, flowing into the line.

Characteristic Impedance


• For maximum power transfer the line should be terminated with a resistive load equal to its characteristics impedance when all the energy from the line is absorbed by the load

• If the terminated load is not equal to the characteristic impedance part of the energy traveling down the line will be reflected back.

Matched LineMatched Line


Major Carrier Components


PLCC System


• Phase to Ground• Phase to Phase for carrier by-passing• Phase to Phase (Inter Phase)• Phase to Phase (Inter Circuit)• Three Phase• Insulated earth wire coupling• Intra-bundle coupling

Methods of Coupling


• Radiation losses are high as earth forms part of the circuit

• Noise pick-up is higher • Increased cross talk

• Used for smaller line sections.• Used where noise level is low.• Most economical

Phase to Ground Coupling


• Grounding or opening the coupled phase wire at the end of the lined section will cause mark reduction in signal level.

• Use of outside phase wire for ground coupling results higher attenuation in long lines.

Disadvantage

Phase to Ground Coupling Carrier By-Pass


• Higher Dependability• Lower line attenuation• Less Radiation• Suitable for long lines

where carrier protection is involved

Advantage

Phase to Phase Coupling

• Initially Expensive

Disadvantage


One Circuit can be taken out of service and grounded

Advantage

Possible only when both circuits are strung on same structure

Phase to Phase Coupling Inter Circuit Coupling


• Additional Redundancy• Better performance

during system distributions

• Ideal for long series compensated EVH line.

Advantage

• Initially Expensive

Disadvantage

Three Phase Coupling


• RF hybrid loss

• Coupling loss (Line Tuner loss + Coupling Capacitor loss)

• Shunt loss caused by carrier power flowing back through the line trap and station bus and ground

• Transposition loss

System Losses


• Inherent dissipation of signal power (3.5 db)

•Also small transformer loss and a mismatch loss

RF Hybrid Loss


Caused by resistive component of line tuner and coupling capacitor impedances ( 3 dB)

Coupling Loss


Carrier loss through the line trap impedance and any shunt path to ground (3 dB)

Shunt Loss


Carrier losses for the system


• Offers high impedance to carrier signal• Offers nil impedance to power frequency• To minimize loss of carrier energy• To minimize mutual interference between adjacent

line sections

ProposePropose

Wave Trap:Provided in the Coupled Conductor


• Single-frequency Traps

• Double-frequency Traps

• Broad-band Traps

Wave TrapTypes


C1 – Tuning capacitor

LA- Vacuum type arrester

Wave Trap(Double frequency

resonant type)


Mounted in the base of coupling capacitor

Provides low-impedance path for power frequency current and high-impedance for carrier frequency signal

Carrier loss introduced by drain coil is <0.5db

Drain Coil


• Coupling carrier Equipment to EHV line

• Offers high impedance at power frequency

• Offers very low impedance for high frequency

Coupling Capacitor

PurposePurpose


One end of the coupling capacitor must be securely earthed to prevent over voltage up to the magnitude of the operating voltage on the equipment side of the capacitor.

Capacitor voltage transformer used for measurement of voltage are used for carrier coupling.

CautionCaution

Coupling Capacitor: Provided with the coupled Phase


• To match the carrier equipment output impedance and the overhead line impedance with a view to ensure maximum power transfer from carrier equipment to the line.

Line Matching Unit


Ensures maximum power transfer from the carrier set to the line.

Provides an impedance match with low losses between the coaxial cable and the transmission line

Line Matching Unit


• Low loss concentric cable to connect the line matching unit and carrier transmitter – receiver assembly

• Generally grounded at terminal equipment end.

Coaxial Cable


• Consists of drainage coil, arresters, grounding switch.• Provides protection of carrier equipment & personnel

against undesirable high voltage• Drainage coil connected between carrier current lead

and ground to present low impedance path to ground only to power frequency current passed by the coupling capacitor.

• Drainage coil prevents loss of carrier frequency energy

Protective Device


• Teleprotection required for high speed relaying which is facilitated by:

• Comparing fault conditions at line terminal

• High speed simultaneous clearing of faults from both ends of the faulty section

• Blocking unwarranted isolation in the event of fault in the line section.

Teleprotection


• Carrier is employed to compare the phase relation between current entering one terminal of a transmission line section and leaving another

Teleprotection

Phase Comparison SchemePhase Comparison Scheme


• With the initiation of tripping of a line at one end, a signal is sent out over the carrier simultaneously to the other end and cause remote end beaker also to trip.

Trip Transfer SchemeTrip Transfer Scheme

Teleprotection


• A Blocking signal is sent out in the opposite direction of fault to prevent tripping of the remote end circuit breaker which is also sensing the fault.

Directional Comparison SchemeDirectional Comparison Scheme

Teleprotection


• Improved transient stability of the system• Reduced line damage & possible melting of

conductor• Minimum outage time with the help of high

speed autoreclosing

High Speed Relying ProvidesHigh Speed Relying Provides

Teleprotection


• Reliability

• Security

• Transmission Time

• Information signal should be of sufficient strength to overcome any line disturbance

Criteria for Selection of TeleprotectionCriteria for Selection of Teleprotection

Teleprotection


Fc-60 Fc+60Fc-30 Fc+30Fc

F2F1

A typical tone channel

Utilisation of Audio Frequency Band

2 Presentation at PLCC STU

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