PLCC Training Ppt

5/5/2010 Sunildatta V Kulkarni AE TCSD Parli 1

Power line Carrier communication• PLCC is used for establishing communication

between two S/S using power line.

• For the smooth & efficient operation of power systems, reliable communication network is very essential.

• The signal that can be transmitted over the PLCC include

• Speech signals• Data/Telemetry signals• Signals required for Tele protection.


PLCC


Importance of PLCC in power system

• The concept of GRID has been developed for the effective utilization of available electrical energy.

• Load Despatch centre will be required to monitor & control the electrical network.

• The LD centre have to process & act upon data (MW,MVAR, KV etc).

• PLCC is used for conveying these information without any interference with normal power flow.


History behind PLCC• The first PLCC system was introduced

by an American company in 1920.

• The power line conductors were used for communication instead of separate telephone lines.

• In India PLCC system was introduced for speech & protection in 1950.


Line trap

� Line Trap or Wave Trap

�Name itself suggests that it traps the waves / frequencies of High magnitude.(50 KHz to 500 KHz)


Line Trap or Wave Trap• WTs are provided to block

the carrier signals from entering in the sub-station and to allow the power frequency current to pass through.

• Achieved by providing a suitable filter consisting capacitors & inductors.

• L. A. is provided across WT to protect it from high voltages surges.

Power Power Power Power

linelinelineline

CCCC1111

CCCC2222

LLLL2222

LLLL1111

RRRR

L.A L.A L.A L.A

Switch

Yard


Coupling Capacitor• Offers isolation between the high

voltage line and carrier equipment.

• It offers minimum impedance to carrier frequencies (50 KHz to 500 KHz)and high impedance to power frequency ( 50 Hz).

• The top end of C.C. is connected to the high voltage line and lower end is connected to the earth through LMU.


Specifications of WT & CC

• Wave Trap• 2000A/ 1.0 mH• 1250 A/ 0.5 mH• 630 A / 0.5 mH• Tuning pot• Freq. Band• Blocking impedance• Blocking Resistance

• Coupling Capacitor• Rated capacitance:-

– 400 kV-4400pf– 220 kV-6600pf

• Attenuation in dB:- 0.5 dB

• Pass Band- 50 to 500 kHz

8


Connection of WT & CC

Wave trap Wave trap

Coupling Capacitor


Coupling Device / LMU


Line Matching Unit• Name itself gives idea that this unit matches

something. This something is nothing but Line impedance.

• It is mounted at the base of the coupling Capacitor.• LMU consist of 2 units called unit A & unit B • Unit A consist of

– Balancing T/F– Matching T/F– Filter unit.

• Unit B consist of– Matching T/F– Filter unit.


LMU• Balancing Transformer

– It improvises better Ph. Splitting & couples the o/p of PLCT to the coupling filters.

– It ensures the carrier signals are in healthy condition even under the failure of any of the coupled phases & voltage isolation.

• Matching Transformer– Impedance matching & high voltage

isolation.• Capacitor Filter together with CC forms

a T section Band pass Filter.


Three element protective device

L. L. L. L. AAAA.... Earth Earth Earth Earth

switchswitchswitchswitch

To C.C.To C.C.To C.C.To C.C.

Drainage Drainage Drainage Drainage coilcoilcoilcoil


• Lightening Arrestor – Protects coupling device from high

voltage spikes from power line that appear at the bottom of coupling condenser.

• Drainage CoilOffers low impedance to power

frequency and high impedance to carrier frequencies, thereby power frequency current flowing through coupling condenser gets grounded and protects the coupling device.

• Earth switch– Normally this is kept open but is closed

whenever any work is to be carried out on LMU


Technical specifications• LMU

– Operating Band width- 80-500 KHz for CC 4400 pf.– Composite loss- < 2db.– Return loss > 12 db– Equipment side Impedance- 75 Ohm– Line side Impedance- 600 Ohm ph. to Ph.– Peak envelope power- 650 W

• LA– Rated Volt.- 850 V– P.F. spark Over Volt.- Twice rated Volt.

• Drainage Coil� Rated Inductance- 40 mH� Cont. Current rating- 1 Amp.� Short time current rating- 50 Amps.

• Earth Switch– insulation withstand Volt.- 10 KV AC– Rated current- 400 Amps


High Frequency Cable/ Coaxial Cable

• Connects the PLC terminal to the LMU in the yard.

• It provides shielding so that noise cannot get into the cable & cause interference.

• It is a constant impedance or HF cable.

• Now a days 75 Ohms Balanced Impedance Cable is used.


HF & LMU connections

• LMU ckt earth is connected to its body which is switchyard earthed. And PLCT connected to LMU thro’ HF cable having PLCC earth combines thro’ amphenol connector.

• The outer shield of HF cable is connected to LMU body which is switchyard earthed . It is to be disconnected in switchyard.

17presentation by S.V.Kulkarni MSETCL AE TCSD Parli


LMU Wattage

• Wattage of the LMU is calculated as follows-

W = n * n* pWhere ‘n’ is the number of PLCC s connected & ‘p ‘is the coaxial power of individual PLCCs

For 400 KV, W= 4*4*40= 640 Watts.


Coupling schemes• Coupling schemes ranked in order of

least losses are –– Mode 1 coupling ( out on 2 outer

phases, in on the center phase).– Center ph. to outer ph. ( Push-pull)– Center ph. to ground.– Outer ph. to outer ph. with ground return (push-push)

– Outer ph. to ground (only on short lines)


PLCC Panel

• PLCC Terminals or Panels are used as a Pair, One at each end of the power line between substations.

• Each terminal is designated for a set of Transmit & Receive Frequencies (Channel Frequencies)

• The corresponding PLCC at the other end will be designated for the reverse value of the transmission & Reception frequencies.


PLCC• The channel frequency will be either in 4 KHz Bandwidth ex. 176/172

KHz OR 8 KHz bandwidth ex. 408 /400

KHz

depending upon Single channel or Twin channel equipments


Working Principle

• PLCC works on Modulation & Demodulation.

• Modulation & Demodulation requires carrier frequency which is generated in in cabinet.

• Crystal Oscillator generates carrier frequency.

• PLCC panel/terminal/cabinet/set consists of

• Audio Frequency (AF )section• Intermediate Frequency (IF)section• High Frequency (HF) section


Transmit path• The speech signal along with other Voice

Frequency signals is fed to IF modulator.• IF modulator modulates the AF signals to IF stage.• Up converter converts IF to HF.• HF signal is fed to preamplifier & then to Power

amplifier t raise the output level t required value.• The amplified signals are then fed to HF hybrid.• Hybrid is used to provide isolation between Tx &

Rx path at HF stage.• HF signals are then connected to HF Cable.


Receive Path

• The receive section receive the signals from remote end through HF Hybrid.

• Down-Converter converts the signals from HF to IF in connection with a band pass filter which allow only the required signals having a certain band.

• Demodulator demodulate the signals from IF to AF.

• Speech, data & other superimposed channels are separated out with suitable filters,


Importance of Pilot• A pilot frequency is provided for self-monitoring &

Automatic Gain control (receiver volume control).• Pilot indicates the healthiness of cabinets.• Pilot freq.is transmitted during normal rest condition & shifted dial is transmitted during dialing for transmission of pulses.

• A dc signal whose amplitude is proportional to receive signal is fed to the amplifier in Rx section to control the gain of the amplifier.


Power supply & Amplifier

• Power supply & Amplifier are most important Modules / Prints of any PLCT.

• They are subjected to various surges through DC supply or surges through HF cable.

• Hence most vulnerable parts of any PLCT


Frequency allocation in PLCC

• HF band 50 KHz to 500 KHz• Voice Frequency 0.8 to 1 KHz.• Data channel freq. called as AF 1 to 4 KHz.

• Pilot freq. 2.5 to 4 KHz.• IF 24 to 28 KHz.• Bandwidth 4 or 8 KHz


Speech 2.0 kHz

Speech 2.2 kHz

Speech 2.4 kHz

Speech 2.6 kHz

Speech 2.8 kHz

Speech 3.0 kHz

Speech 3.2 kHz

Speech 3.4 kHz

0.3 3.6 4.0

0.3 3.6 4.0

0.3 3.6 4.0

2400 Bd

1200 Bd600 Bd300 Bd

200 Bd100 Bd50 Bd

Spee

d

Center frequency120 Hz steps

2.0

ProgrammableProgrammableProgrammableProgrammablespeechspeechspeechspeech bandwidthbandwidthbandwidthbandwidth

plusplusplusplus

ProtectionProtectionProtectionProtection CouplerCouplerCouplerCoupler4-4-4-4-commandcommandcommandcommand teleprotectionteleprotectionteleprotectionteleprotection

plusplusplusplus

DataDataDataData transmissiontransmissiontransmissiontransmission

kHz

kHz

kHz


Telephone Exchange• Telephone exchange

is used to connect speech between two ports

• Ports include Lines, trunks, tones,etc

• Electronic programmable automatic exchange


Telephone Exchange

�Telephone Exchange used for Dialing communication

�Microprocessor based version.

�Programmable feature available.

�Improved stability & quality of dialing carriers communications.

�Separate earthing is very important for stability of power supply of EPAX,


48 V DC Battery

• 24 No. of cells

ForForForForChargedChargedChargedCharged BatteryBatteryBatteryBattery

ForForForFor fullyfullyfullyfully dischargdischargdischargdischargedededed BatteryBatteryBatteryBattery

Specific Gr.

1210 1180

Voltage 2.15 1.85


48 V DC Battery Charger• These are SCR

control having Float & Boost operation,

• Normally charger should be kept on Float & Voltage of charger should be kept on 51.5 V.

• Boost charging is constant current charging.


48 V DCDB

• To provide separate switch for Individual panel.


48 V DCDB


A.C.Supply

Exhaust Fan

Illumination

Testing equipments


Air Conditioner


Exchange to PLCC panel connection


Emergency Jack Telephone

• PLCC terminals has got provision for– 2 wire speech from

EPAX.– 4 wire Express

telephone communications (hot line from control desk to control desk) &

– Communication through emergency Jack telephones.


Protection Coupler

• Protection coupler equipments can be used along with PLCC terminals for Teleprotection requirements.


Protection coupler

• During line fault / other fault occurring in S/s, trip signals can be transmitted or received by the protection couplers through PLCC terminal for activating the distant protection relaying equipment.


Disconnecting TB


“AL: COMMON ALARAM (Red)

This LED lights on all the units that the alarm concerns. “RDY” Ready (Green)

The "transceiver ready" signal (TRY) “TRP” Trip (Green)

The tripping signal has picked up.“GRD” Guard(Green)

Lights whenever the guard signal is being received.“SNR” Signal to Noise Ratio(Red)

Lights whenever the signal-to-noise ration is too low. “LEV”” Level Alarm (Red)

The signal strength of the guard signal is not within the permissible limits.“TX-A”-----”Tx-D” (Green)

Lights whilst the corresponding signal is being transmitted.“RX-A”-----”Rx-D” (Green)

Lights whilst the corresponding signal is being Received“TX-A/B”-----”Tx-C/D” (7 segment Display)

The number of commands transmitted is displayed (00 ... 99).“RX-A/B”-----”Rx-C/D” (7 segment Display)

The number of commands received is displayed (00 ... 99).CONTROLSCONTROLSCONTROLSCONTROLS

„Loop Test“ (black pushbutton) for manually initiating a loop test. “RESET” (Red Pushbutton) for reinitialising the signal processor (outputs are blocked for approx. 10 s).„Tx“ Stand-alone NSD 50 transmitter signal (0.3 ... 4 kHz, 0 dBr)„Rx“ Signal received (0.3 ... 4 kHz, 0 dBr)„COM1“ Standard serial interface for the connection of a terminal. “DISPLAY” Switches for selecting commands A and B or C and D for display.„RESET COUNTER“" (black pushbutton) For resetting the trip counters.

Protection coupler NSD 50


PLCC counter Reading

• Note down PLCC counter readings (Tx & Rx) regularly.

• Note down PLCC counter readings after each tripping of line/ operation of Protection coupler.


PLCT connection


PLCC earthing


Earthing of P.L.C. C. equipmentEarthing of P.L.C. C. equipmentEarthing of P.L.C. C. equipmentEarthing of P.L.C. C. equipment

– Separate earthing system to be provided.

– The same not to be interconnected with switchyard earthing. Otherwise, high voltage due to GPR may damage PLCC’s electronic components.

– 48 volts. D. C. Battery charger to be earthed to P. L. C. C. earthing system.


Level Meter & Level Oscillator

Level Meter is used for dB level measurement.

Level Meter is used for dB level measurement.

Level Oscillator is used for generation of dB level for measurement


dB (Decibel)• The dB (Decibel) is a unit for

measuring relative levels of I, V, P.

• It shows the ratio between I/P & O/P.

• dB = log 10 (Input /Output)• - sign before dB indicates a Loss• + sign before dB indicates a Gain

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