CONTENTS UNDER P.L.C.C.:-

1. Introduction 2. General concept of P.L.C.C3. Theory of P.L.C.C. Network4. Operating Principle5. Equipment Functional Description6. Associated Equipment configuration For P.L.C.C.7. Signal through P.L.C.C.8. Battery Charger9. Advantages & Limitation

INTRODUCTION:-

PLC i.e. Power Line Communication can be said as communication through power lines. These lines use power to carry the sound signals between the substations.

This means instead of using the line laid for the local use by the companies are not used rather these lines help in communicating between just the stations and their respective place of purpose i.e. it covers the whole system under it. PLC is used for various purposes like speech, telemetering, teleprotection, teleprotection etc.

The system can be basically divided into two i.e. outdoor and indoor equipments/systems where the Wave Trap, Coupling capacitor, LMU, Lightening Arrestor, Drainage Coil, and Earthing Switch comes under outdoor equipments and indoor. Equipments consist of the Exchange and the Carrier Terminals/Cabinets.

The PLCC offers optimum utilization for signal transmission conserves spectrum space and has large transmission. PLCC also provides various applications like voice communication, telemetering, teleprotection etc.

THEORY OF PLCC NETWORK:-

From the power line supply wave trap blocks 50 KHz-500 KHz for the power supply to the yard or panels of the substations.

The frequency band block by wave trap through it goes downloads to the coupling capacitor connected to it. Her condenser passes high frequency to the phase lines of the LMU where it matches the impedences between 300 ohm and 125 ohm & at a time one is also connected to the lightening arrestor which arrests the flashes of light to make them grounded so that to prevent the lighten equipment from burning or from sever damage, also the wire is connected to ES which is a earthling switch required to earth the leakage current if it flows through the circuit network. If there is any components LMU or in all Y device the earthling switch is used to make the unit grounded and change the defective part.

Now from LMU the signal goes through coaxial cable due its characteristic impedance, which remains always constant and does not demand upon the length of the wire.

GENERAL CONCEPT ON P.L.C.C.:-

The 6515 Power Line Carrier(PLC) Terminals are the transmission of speech telemetering, teleprinting, telecontrol and teleprotection signals in the carrier frequency range b/w 30KHz and 500 KHz over the following communication media with suitable line coupling equipment.

High voltage & Medium Voltage power Lines. Open-Wire Lines exposed to Power lines.

Message transmission is based on the single side band principle where the carrier purpose and one of the two sidebands, generated as a result of modulation, are suppressed. This mode of operation offers the following advantages:-

Optimum utilization of the available send power for signal transmission. Minimum channel width to conserve spectrum space. Large transmission range.

The carrier voltage for UP conversion is drawn from a binary freq. divider, which scales down the crystal freq. to the desired carrier in the range of 30-500 KHz. The stability of the crystal is such that the freq. is maintained with a stable of +5 or -5 ppm. Carrier voltage for modulation(IF) is similarly obtained after division of a crystal freq. 6.144 MHz. optimum even provides better stability.

A freq. modulated pilot channel (3600+30Hz/2580+30Hz) arrange above the speech band is provided for volume control in the receiver of the terminal. Pilot freq. is transmitted during rest condition and the other is keyed during dialing. Freq. Shifts during Dianne do not affect volume control operation.

6515 Terminals can be additionally equipped with optional commanders in order to improve the signal to noise ratio for speech communication.

The PlC terminals provide on the AF side 4-wired input and output for connection to telephone exchange through suitable automatic relay equipment. AH Hybrid provides 2-wire AF I/O. The terminals are also equipped with a jack-telephone module, which facilates point-to-point conversion from the terminal.

The terminals are supplied with a Power-Supply unit suitable for connection to a battery supply voltage of +20V or -10V DC

Operating Principle:-

The communication device for the PLC communication system is a built-in Power Line Modem (PLM), which transmits and receives data over the power line. Both the MIU and the DCU contain the PLM device. The binary data stream is keyed onto a carrier signal by means of the Frequency Shift Keying (FSK) technique. The central frequency is shifted +0.3KHz to represent 1 or 0 of the binary data stream. This signal is then coupled onto the power line by the PLM. At the receiving end, an identical PLM will detect the signal and convert it back to a binary data stream. The PLMs operate in a Half Duplex, two-way, Time Division Multiplex communication mode. Two-way communication between DCU and MIU is essential in establishing a proper communication channel, for system synchronization and status reporting. In AMRS, transmission speed is not a great concern but reliability is important. The data rate of the PLC channel is set at 600 bps, to ensure communication over a longer distance and reduced transmission error. Every MIU is also equipped with repeater function. If required, the DCU can designate any MIU in the sub-system as a repeater to enhance communication with a particular MIU. With the sensitive signal detection and sophisticated digital filtering technique, this PLC communication is highly immune to electrical noise and interference.

EQUIPMENTS FUNCTIONSAL DESCRIPTION:-

Transmission Path:

The speech signal with a level of -16 db at terminals P1/p2 enters the system via the 65 AF HYB modules. The four wire output of the Hybrid then is passed through the 65HYB REL module,65 COM REL modules, 65 COMP and 65TEJK modules. The 65 COM REL and 65 COMP is optional unit. The HYB REL in associated with 6565 AF HYB facilitates 2 wire to 4wire conversion. The output of the 65 TEJF is taken via the 65 Mod and 65 TX/RX/REL to the 65 MOD for modulation.

The 65 TX/RX/REL enables the trip signal from protection coupler to have precedence over the signals like speech, superimposed channels etc,The 65 MOD converts the input signal to the IF range (20-24khz) is taken as the output of the 65 MOD. The modulated signal is then fed to the 65 UPCONV which translate the incoming frequency band to the upcoming frequency range within 30-500 kHz. A channel filter which is the part of the 65 UPCONV, allows the required sideband to pass through the next change.

The 65 HF PRE is the high frequency preamplifier which rises the level of the signal. The output of this is fed to the 65 LA, which rises the output power to the required value. The 65 LA, which is tuned to the carrier frequency, receives the 65 LA output. The 65 HYB-H enables adjacent channel band working of transmission and receiver.

The 65 FS-SIG in the terminal generates pilot frequency for continuous supervision of the system. Frequency shin keying is employed for continuous supervision of the system .Normally a Frequency of 3570/2550 Hz if transmitted as pilot signal and is shifted to 3630/2610 by extending earth to R6 tag of the PLC terminal.

Receiver path:-

The HF signal arriving from the distant end are fed to the plc terminal through the 65 HYB-H to the 65 DNCONV through the group channels filter tuned to particular frequency. The output of the DNCONV is passed on to the 65 DEMOD which in turn translates the IF frequency to the composite AF band.

The various constituents of the composite audio band, speech data and other signals are separated out. The 65 DLPF filters out the speech band.

Pilot/Dial frequency is separated out by the receive filter in 65FS-SIG.IF the pilot signal is lost the relay contact of k201 extends earth to relay KE in 65 TX/RX/RELAY module. Operation of relay KE disconnects the speech signal and other superimposed channels. Similarly KE relay removes earth from the pole of relay KI thus effecting dial blocking during pilot failure condition.

65 FS-SIG modules gives a DC signal whose amplitude is proportional to the input to its receiver section, This voltage is extended to the 65 DEMOD module for the A.G.C. operation. Signal is fed to the photo coupler in the DEMOD, which in turn controls the gain of the VF section. AGC operation limits the variation in VF level to +1,-1 db for a Variation of +26,-26 db in HF receive signal.

In case of 40 W terminals, two 20w sections coupled together with the help of Amplifier Interface Card65AI are made use of each section consists of one lime Amplifier 65LA, one Power Supply Unit 65 BPSU and line filter 65 LF.

ASSOCIATED EQUIPMENTS FOR P.L.C.C. :-

Outdoor Equipments:-

1. Wave Trap2. Coupling Capacitor3. Line Matching Unit4. Lightening Arrestors5. Drainage coil6. Earthing Switch 7. Chopping Connections between different units8. Coaxial Cable

Indoor Equipments:-

1. Carrier Communication and associated equipment housed in cabinet E35C.2. Telephone Equipment EP AX 2003 and PBX equipments configuration.3. PLCC Cabinets.4. Battery Charger

Boost Section Float Section

5. Battery6. Interconnection Cables.7. Comparison between Analog and Digital PBX

OUTDOOR EQUIPMENTS:-

1. Wave Trap:- A wave trap consists of a tuned capacitor and lightening arrestor. Only one wire is wound around it. Its working is same as that of indicator. It trap or block high frequency signals like 200khz and pass low frequency signal like 50hz. Because it blocks a range of high frequency signals that are why it is also called as band block filter.

2. Coupling Capacitor:- It works in opposite manner to that of wave trap. It passes the high frequency signals of 200 kHz and blocks low frequency signal of 50 kHz.

3. Light Matching Unit:- It consists of some air core transformer and some condensers. Its function is to match the impedance of the lines i.e. it matches impedance of 300D and 12 in order for the proper functioning of the unit.

4. Lightning Arrestor:- During working operation a flash of light is produced by electric discharge between clouds or between clouds and ground and this equipment catches all the flashes of lightning to ground them for the protection of unit, because it may cause danger or destroy the whole network.

5. Drainage coil: When supply is given, all equipments start working. Wave trap block high frequency signals like 200khz and pass low frequency signal like 50hz and coupling capacitor passes the high frequency signals of 200 kHz and blocks low frequency signal of 50 kHz. During all this process if any leakage current flows due to any distortion, then this drainage coil arrests all leakage current and ground it so that it does not cause any harm to the network.

6. Earthing Switch: In case when there is any fault in the LMU or in, any component, then this switch is used in order to ground the LMU. So that we can repair the faults or change the defective components.

The PLCC network consists of two major equipment:-

1 .Exchange

2. Cabinets

EPAX 2003(PLCC):-

The EPAX system 2003 (PLCC version) is an andvanced, state of art, stored program microprocessor controlled exchange, using 8-bit microprocessor. The control function are implemented with digital hardware and voice switching is done with TDM technique. The microprocessor control ensure most reliable switching because the system employs only electronic circuit. It eliminates periodic preventive maintenance and makes system noiseless unlike conventional electromechanical exchanges. The PA2003 (PLCC) system accepts decading dialing pulses and is therefore compitable with rotary dialing instruments or pulsing type button telephone instruments.

The PA2003 (PLCC) system has been specially designed to be connected to be connected to another PAX through power line carrier communication equipment. this system is intended to be a direct replacement for the electromechanical exchange now in use in power generation system and industries. The exchange can interface directly with PLCC terminal on one hand and the existing telephone sets all the others. Hence the exchange software has been designed to meet all the existing needs of the presently used electromechanical exchange.

The block diagram consist of following :-

1. PSU

2. PI

3. RING

4. CONF

5. CPU.

6. SCC

7. LIC

8. SPIC

9. TIC

CPU (central processing unit):-

The CPU module consists of the 2-80 CPU with associated memories. The memories include both EPROM and RAM data. The program are stored in the EPROM of about 14K bytes and the scratch pad database for all subscriber is in the ram of about 8K bytes. The CPU data address and control bus are bought out through buffers. The CPU data bus is referred as DRECT bus. Tile SCC, SPIC module are sitting on the CPU buses referred to as system bus. Some of the programmable parameters are stores in 2K bytes of EPROM that can be changed by dialing special numbers from control lines.

SSC (switching circuit controller):-

This module is controlled by CPU through system bus. The SSC accepts tile CPU commands and stores the talk and listen address in network memory gives out network talk and listen bus to all module presents information at various points for diagnostics by CPU samples only the required no time slots as dicted by CPU.

SPIC (scanner and peripheral interface controller):-

The SPIC module collects the hook state information, debouches it and make it available for the CPU, generates the system interrupt at 8ms, act as the source for various tones; interface the direct and indirect buses; generate the ring modulation waveforms as directed by CPU.

LIC(Line Interface Controller):-

LIC act as the interface between the line side & exchange side; presents the hook state information to CPU gives ring to the line, If desired by the CPU; presents card information& Ringer Rely register output for diagnostic purposes.

TIC (Trunk Interface Controller):-

This line act as the interface between the trunk lines and exchange side; presents line ON/OFF condition information to the CPU; accepts commands from the CPU to seize the trunk,and repeats the digits over trunk.

PSU (Power Supply Unit):-

Here the DC/DC converter 48v DC to -5 ,-12 and +12 volts; they are rectified and regulated with respective rectifier and regulator and then brought out .The 48V SC is straight away given for lines and ringer.

RING (Ringer Circuit):-

The -48 v is given t the oscillator, which gives out 25hz to 75v AC ringing voltage output.This is taken out via transformer .The ring control Information coming from SPIC module controls the oscillator, in accordance with ring Modulating Waveform such that ringing voltage is generated or ceased.

CONF (Conference Circuit):-

This is used for establishing conference circuit between two subscribers.

2. Cabinets:-

PLCC is composite equipment or panel having transmission and receiving cabinets.PLCC are of following types:-

1 BPL(6515 model)SQ In BPL,there are separates cabinets. R

2 ETBA 3 ETI-21 & 224 ETL-41 & 42

SIGNALS THROUGH P.L.C.C :-

There are four signals working under P.L.C.C. All the four signals work in AF section.

These signals are :-

1. Voice Communication signalsa. Lift and talk signalsb. Dialing signal

2. Telemetering signal3. Teleprotection signal.

1) Voice Communication: It has two sections:a) Lift and talk section: In this section when we dial the telephone instrument on the

send side,the ring tone directly rings on the other side.

b) Dialing: In this section 2-3 digit numbers are used .This means that the exchange design is based on 2-digits for local and 3-digits for outstation(trunk) numbers. Like 20,21,_ _ _ _etc.for local and trunk, the number starts from 0 like 031,032, _ _ _ _etc.

2) Telemetering: In telemetering data like line voltage,current,breaker, frequency etc is controlled by a unit called RTU(Remote Telemetering Telemetering Unit)i.e. data is controlled and telecommunicated through PLCC network.

3) Teleprotection :It is also known as distance protection. It is used to prevent thefaults between two or more substations.For this purpose, high sensitive relays are used which sease the failure of power line of the nearer substations and trips the power lines having defects.Now through PLCC network, after 9 mS it senses another relay circuit of other substations and trips the same power line having defects. This rotects the whole network from severe damage.

BATTERY CHARGER:-

Battery charger is equipment by which we can recharge the batteries. Battery charger is used at many places. It is also used in industries:-

Battery charger is of two types:-

1) Boast charger

2) Float charger

Boast charger is that type of charger in which we can charge the battery on variable voltage. In boast charger the supply can be variable in magnitude and we can control it by a variac. Variac is a equipment which is connected before transformer. In the boast charger mainly nine equipment are used-

1. Switches

2. Fuses

3. Connectors

4. Variac

5. Transformer

6. Rectifier

7. Battery

8. Load.

9. Alarm

In all above equipment switches are provided for protection at circuit. We can also switches off the equipment when it is not in use. Fuses are also safety equipments.

Connectors are that which short the charger the charger from main supply. In the circuit three electric lines R, Y, B are connected and when we use connector then all three connectors opened at same time.

Variac is that equipment by which we can control the voltage at transformer end. By this we can control the over voltage or under voltage condition.

Transformer is that equipments which transfers the voltage from one side to another side. It is of two type step up or step down. Here we use step up transformer which converts 415 volt 48 volt ac. Rectifier is that circuit which converts AC to DC and it is made up of diodes. In this charger the rectifier uses six diodes.

After that we use load circuit, in which any kind of load can be connected.

Alarm and annunciator are that equipment which indicates about any fault in circuit. In this any fault like fuse, trip mains failure, over voltage or other types of fault can be indicated. We can find faults in circuit easily with the help of this. And we can save our circuits.

Hence all above equipments are used to make a good boast charger.

In float charger all above equipment are connected in same way. The only change is that float charger produced constant voltage for charging the battery. For providing constant DC voltage in float charger we use thyristors in rectifier circuit. In rectifier circuit of float charger we use three diodes and three thryistors, in the form of coupling of one diode and one transistors.

Use of battery charger:-

For PLCC EPAX and other indoor equipments power supply requirement is 48 volt DC. And this power supply is given by battery. When any battery is used in circuit, it losses the power and hence for to use it again we charge the battery with the help of battery charger. Battery charger is very useful part of communication system.

Operation:-

Boast charger-

1. Put switches in on position. Lamps (1, 2, 3) will glow. If not, check HRC fuses and glass fuses. Check AC input voltage by meter and by voltage selector switches.

2. Put variac to zero position by moving it anti clockwise. Trip by-pass toggle switch is provided inside the cabinets. Put rotary switch (S2) in on position to switch-on boast charger. In case the contactor (CN1) does not get on, check HRC fuses and circuitry of contactor (CN1). Lamps will glow.

3. Put Trip by-pass toggle switch to off position. Put DC voltmeter selector switch to Boast charger position.

4. Press push button (pb4). The servo meter will move variac clockwise to increase voltages. DC indicator indicator lamp will glow. If DC voltage is not indicated by voltmeter, check HRC fuses and HRC fuses of bridge rectifier circuit.

5. Check dc voltage at load terminal by selector switch and DC voltmeter and confirm that load is connected to tap cell of battery through blocking diode and rotary switch. Adjust position to get desired voltage at load terminal.

6. Check gravity of battery. When gravity reaches the proper level switch off the boast charger.

Float charger-

1. Put Trip by-pass toggle switch to on position. Put rotary switch in on position to switch on the float charger. Indicator lamp will glow. One control card is provided inside the unit red and green led’s.

2. VR-1 potentiometer is provided is provided in the unit. Move VR-1 anticlock wise to set it zero position.

3. Put switch (s-6) in on position. Put DC voltmeter selector switch to float charger position. We can change the voltage by moving potentiometer knob in anticlockwise or clockwise direction.

4. Now since boast charger contactor (cn1) is off, DC contactor (cn3) will switch on. Battery gets connected to float charger through contactor. Adjust potentiometer to get proper trickle charging current. It is indicated by indicator (T.R).

5. Check DC voltage at load by DC voltmeter and Selector switches(s-8). Now adjust DC voltage at load terminal by VFB potentiometer.

In case of any malfunctioning of float charger boast charger can be used to feed the load.

Metering:-

1. AC voltmeter to ensure AC input between any two phases by selector switch.2. DC voltmeter (M-4) to measure DC voltage at battery. Battery taping, boast charger , float charger and load by a five position selector switch.3. DC AMMETER to measure floats charger current.4. Dc ammeter, center zero ammeter to measure to measure charge/discharge current of battery.

5. DC ammeter to measure DC current of boast charger.

6. For trickle charge indication one indicator (t1) is provided which will indicate trickle charging.

Protection:-

1. HRC fuses at AC input.2. HRC fuses at DC input.3. HRC fuses in series with each device of rectifying bridge.4. Radio frequency interference (R.F.1) and AC surge suppressor at AC input circuit .5. Single phasing prevention trip at AC input side in float charger and boast charger

separately 6. DC under voltage and over voltage alarm.7. DC over voltage trip in float charger.

Milking charger:-

One built-in milking charger is provided. This charger can be utilized for parallel charging of any weak cell. The circuit consists of step down transformer, rectifier diode and HRC fuses.

SCOPE AND APPLICATION OF THE INSTRUMENT:-

The LEVEL METRE ET-71/v and LEVEL OSCILLATOR ET-71/A form a measuring sot covering frequencies from 200 hz to 620 hz for the measuring of carrier frequency system up to 120 channel capacity. Owing to the compactness and light weight as well as the versatile power supply, the level meter tends itself to use in places where no mains is available e.g. measurement of hardly accessible remote supplied repeater stations/.The Selective Level Meter is equally for wide- band and selective measurement. The input circuit switched over the measurement of level and overall attenuation interoperated in terms of power and voltage. The adapter supplied as an accessory permits the measurement of impudence, balance attenuation and active return loss.

In measurement involving the level metre ser up in the vicinity of the level generator the synchronous –tuning /tracking / mode will be valuable aid .The wide frequency range and wide sensitivity range of the level meter permits the measurement of transmission characteristic as well as crosstalk and other interference signals. At selectivity measurement distinction can be made between low distortion and noise modes to obtain the maximum intrinsic harmonic ratio or signal/noise ratio. The level metre has two bandwidth determining filter: --a wide filter with an effective bandwidth of 3.1 khz for noise measurements; --a narrow band filter with a bandwidth of 20 hz for measuring of carrier leak, crosstalk and non linear distortion.

Furthermore, the level meter is suitable for modulation measurement of multi-channel microwave and VHF relay chains.Owing to the low inherent distortion ,wide range of overdrive and high selectivity ,the unit can well used as the indicator of measuring bridges.