Kp Training Report

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TRAINING REPORT

RAJASTHAN RAJYA VIDHYUT PRASARAN

NIGAM LIMITED

23.05.2011-25.07.2011(60 DAYS)

UNDERTAKEN BY:

KIRAN PRAKASH JANGID

EC-1, 2008UEC120

MALAVIYA NATIONAL INSTITUTE OF TECHNOLOGY JAIPUR


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Introduction to Power Line Carrier Communication (PLCC)

Communication between various generating and receiving stations is very essential for

proper operation of power system. This is more so in the case of large inter connected systems,where a control load dispatch station has to coordinate the working of various units to see that

the system is maintained in the optimum working condition, Power Line Carrier Communication

has been found to be the most economical and reliable method of communication of medium and

long distance in power Network. For short distance the ordinary telephone system is used. Open

wires or underground cables and in some cases VHF wireless communication are found to be

more economical as they do not involve the use of costly high voltage coupling equipment.

In early days of generation and utilization of electric power, the generating station was invariably

a thermal one located within or very near a city having industries acting as the consumers of the

power. However, with the introduction of hydroelectric generating stations and extension ofelectricity to suburban and rural areas, the picture radically changed .The various generating

stations, located at a great distance among them, and could no longer remain isolated and self-

sufficient entities. On the other hand, they soon become interconnected giving rise to what is

known as the power grid. This necessitated has economical and dependable means of

intercommunication, between various generating stations, substations and control rooms.


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LCCS Equipment is used for point to point communication over high voltage power lines.

PLCC equipment are used send/receive speech/data/teleprotection signals by using HF carrier

signals raging from 50KH.

1) Speech signals

2) Data/telemetering

3) Teleprotection

1. SPEECH SIGNALS:

(i) An input signal of 300-2000HZ band width can be used depending upon the customer

requirements.

(ii) PLCC has got provision for 2 wire / 4 wire speech from telephone exchanges / other

switching equipment , 2 wire/4 wire express telephone communication ( hotline from controldesk tc ) and communication through emergency jack telephones to be connected directly to the

PLCC terminals.

2. DATA/TELEMETERING:

PLCC terminals can be used for sending/receiving data signals for telemetering and etc. The

input signal for this channel will be between 2000-3000 HZ.

3. TVLEPROTECTION:

i) Protection coupler equipment can be used along with PLCC terminals for tele protectionrequirements.

ii) During line fault/other fault occurring in sub stations. Trip signals can be transmitted or

received by the protection coupler through PLCC terminals for activating the distant protection

relaying equipment.

In PLCC the higher mechanical strength and insulation level of high voltage power lines for

communication and lower attenuation over long distance. The idea of using power lines as

transmission lines for communication purpose was the first thought of at about the beginning of

the century and the practical applications were made in several countries from 1920 onwards.

These systems have now developed into extremely sophisticated and complicated PLCC systems

and widely used in all modern power systems.

When the distances involved are large, it will not be economical to provide separate wires

for communication purpose. In fact, for such large distances, the power lines themselves provide

a very good medium of transmission of information. So the POWER LINE CARRIER

COMMUNICATION (PLCC) is mostly used


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Basic principles of PLCC:-

Telephone communication system cannot be directly connected to the high voltage

power lines, therefore we have to suitably design the coupling devices. These usually consist of

high voltage capacitor or capacitor with parasitical devices and used in the conjunction with the

suitable line matching unit. For matching the line impedance to that the impedance of the coaxial

cable connecting the PLCC equipment.

In PLCC system the following Equipment are used:-

PLCC station

Line matching Unit

CVT/CC

Earth switch

Lightning Arrestor

Wave trap Co axial Cable

PLCC Station:-It is the station where (modulation) Transmitting, receiving (demodulation),Amplification, Filtration are performed.

Line Matching Unit: - The output of PLCC is connected to the line matching unit before to

the power lines to achieve the proper impedance matching in between PLCC Equipment and

power line.

CVT/CC (Control voltage transformer/Coupling capacitors):-It is connected to the line matching unit and the power line this is used for blocking the high

voltage entering to the PLCC Equipment.

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

Lightening Arrestor: -This is used for arresting any A.C. high voltage spike entering to the

L.M.U. PLCC unit.

Co-Axial Cable:-This is used for inter connection between PLCC & L.M.U for carrying the

high frequency signal.


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THE BASIC ARRANGEMENT OFCONNECTING THE WAVE

TRAP AND COUPLING CAPACITOR IN PLCC AS SHOWN

As can be seen from the sketch the power frequency and radio frequency component are sorted

out by the arrangement. The RF signal is prevented from entering the station bus & the power

frequency is blocked by coupling capacitor.

COUPLING DEVICES

A modern coupling capacitor consist of stack of flat elements of pure cellulose paper and

aluminum coils held between insulating roads under optimum pressure to minimize the

capacitance that changes with the time and pressure. The interconnection are designed to obtain

highest possible range withstand capacity and highest cut off frequency.


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TYPES OF COUPLING:

1. PHASE TO GROUND COUPLING

LMU-line matching unit

PLCC-panel-power line carrier communication equipment.

CC- coupling capacitor.

In this type of coupling out of three phase wire we use only one wire for communication. This is

the oldest type of coupling to connect the PLCC & circuit wire in which we use the wave trap to

stop HF signal to go in the yard. The coupling capacitor is used for connecting the LMU to the

LINE. LMU provides the impedance matching between the line and PPLCC station. PLCC paneldoes the modulation, filtration, amplification and then transmit the signal to the carrier and to the

opposite work at receiving end.

LA LAES

ES


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1. PHASE TO PHASE COUPLING

In this type of coupling out of three phase wire we use two wires for communication. Theadvantage of using such way is that if one wire gets damaged then communication will be

carried out by the other wire. We use the wave trap to stop HF signal to go in the yard. The

coupling capacitor is used for connecting the LMU to the LINE. LMU provides the impedance

matching between the line and PLCC station. PLCC panel does the modulation, filtration,

amplification and then transmit the signal to the carrier and do the opposite work at receiving

end.


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INTER LINE OR INTER CIRCUIT COUPLING:

This is the same as phase to phase coupling but with the difference that the two conductors

used for communication belong to two different power circuit carriers on common towers. This

type of coupling is not employed where the two circuits are carrier on two separate sets of towers

as it then behaves more like a double phase to ground coupling &id found as in then behavesmore like to ground coupling &is found to be impractical.

This type of coupling is more reliable than phase to phase coupling on the same circuit in that it

permits operation with one of the two circuits opened out & founded for maintained purpose

.Inter Phase or inter systems coupling are always employed on 220 KV& 440 KV lines where the

interface levels &attenuation problem. This type of coupling permit higher reliability of

operation under breaker conductors conditions& are always employed where carrier line

protection are employed.


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COMPARISON BETWEEN PHASE TO GROUND AND PHASE

TO PHASE COUPLING:-

1. The phase to ground coupling has higher attenuation &unlike phase to phase coupling,

attenuation & varies with station conditions.

2. Reflections 7echoes due to mismatch difficulties are much greater in phases to ground

coupling.

3. S/N ratio is poor due to longitudinal noise voltage induced in line in phase to phase coupling;

the noise voltage cancels them because equal voltages are induced in each one conductor which

opposes each other in the circuit.

4. Radiation in phase to ground coupling is twice than p-to-p coupling.

5. A break or fault of some other kind in p-to-g coupling much more seriously than in p-to-p

coupling.

Hence p-to-g coupling is used due cheapness especially when frequency used and distances to

covered are suitable and radiations are not having much harm effect.

Construction:-

Wave trap is constructed by taking the parallel combination of the inductor and the variable

capacitor this will form the tank circuit which form the tuned circuit, which tuned the frequencyat 50Hz known as power frequency. The inductors which we are used having the range of 0.5

mH to 500 mH. The capacitors having the range of 4400pfarad to 5500pfarad.the choke coil

having the main role in that.

This coil may be a single layer or a multi layered coils made of special aluminum alloy and

designed to carry the full load current.

Lightening Arrestor:-

Ground wire over the tower provides an adequate protection against lightening and reduces the

induced electrostatics or electromagnetic voltage but such a shield is inadequate to protect anytravelling wave which reaches the terminal of the electrical equipment and such a wave can

cause the following damage.

1. The high peak of the surge may cause flash over in the internal wiring. Thus it may spoil

the insulation of winding.

2. The steep wave font may cause internal flash over between their turns of the transformer.


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3. The stop wave front resulting into resonance and high voltages may cause internal and

external flash over causing building up the oscillators is the electrical operations.

A Good lightning Arrestor must possess the following properties:-

It should not absorb any current during normal operation but during the over voltage surge it

must provide an easy way to the earth. After the first discharge of the current has taken places

through then must be capital of carrying the discharge current for same interval of time without

any damage to them. After the over voltage is discharge it must be capable of interrupting the

normal frequency of current from flowing to ground as soon as voltage reaches below the break

down voltages. In addition to the tuning devices which usually consist of capacitors and

inductors. A lightning arrestor is invariable connected across the choke coil of the wave trap. The

lightning arrestor used may be as a vacuum type arrestor, over voltage of which lies below the

rated value of the tuning capacitor but about the voltage which produce across the coil during a

short circuit surge. The lightning arrestor therefore protects the tuning capacitor against themomentary over voltage caused by the travelling wave.

Sustained over voltage resulting from the short circuit are not high enough to cause the lightning

arrestor to be over voltage. Hence consequent destruction of the arrestor is avoided.

4. The tuning capacitor

For lower voltage class of tuning units polystyrene capacitors are used while for high

voltage class tuning unit capacitor with mineral oil impregnated paper dielectric is used

which are similar in construction of coupling capacitor. Signal frequency trap have a

signal & double frequency trap have a double tuned parallel circuit. All the elements

belonging to tuning circuit are usually mounted in a common housing.


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5. Transmission system

There are three different transmission methods, which can be employed for PLCC, they are

given below:-

1.) Amplitude modulation with carrier and double side band transmission.

2.) Amplitude modulation with a single side band suppressed carrier transmission.

3.) Frequency modulation

The earlier system used the first method. The speech frequencies transmitted were between 300

to 2400 HZ when the carrier modulated with this frequency, the resulting side band took up a

maximum band width of 4800 HZ thus the available HF band was divided into no, of channel

each having the band of 5 KHZ. Some countries allotted 8 KHZ for each channel. And these

channels could naturally transmit the higher voice frequencies up to 3.4 KHZ instead of 2.4

KHZ. This resulted the better voice quality.

Almost all the modern PLCC equipment is designed for an amplitude modulation with a single

band suppressed carrier transmission. Single side band having following advantages over the

double side band:-

1.) The band width required per channel is exactly half of the double side band transmission.

2.) As the receiver accepts only half band of frequency the noise input to the receiver is

correspondingly reduced resulting in better S/N ration.

3.) As the carrier one side band are not transmitted the power required for this also same.

6. Telephone network

Telephony implies both way of communication that is the person at each end of the line

must able to speak and listen. The cheapest and simplest way of achieving this working is to

have simplex working. Here only one frequency is allotted for given link. Both the terminals

issue the same frequency for transmitting and receiving. But in that case only one person can talk

or listen at a time. This is achieved by press to talk switch. For a duplex two different carrier

frequencies are allotted between two stations. In the system both the parties/persons can speak or

listen simultaneously. This arrangement is costlier then simplex and it is almost used in presentPLCC system.

7. Fixed frequency system

In the large network it may be necessary to provide the point to point communication

between a large no. of station. For this purpose each carrier link is designed a set send and

receive frequency. For duplex working in carrier frequency section between all model points are


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separated on 4-wire basis. All inter modulate station required two set of equipment such as

PLCC.

8. 4-wire group selectors or electronics switching devices

These are used to connect the PAX to PLCC equipment. A PAX cannot be directly

connected to PLCC terminals as the later work on 4-wire basis that is send and receive path are

in same that is only two are used for each correction.

9. TRUNKING CONNECTION FOR TYPICAL CLASS OF THE

NETWORK

The trucking connection between the heera pura and Ajmer as shown above. For calling

Ajmer from telephone no. 23 from heera pura the subscriber will left the telephone & he will dial

the direction no. for Ajmer that is 53 & if the line is not busy he will further dial the station no.

that is 52. Now the subscriber at the heera pura will receive the station tone of the Ajmer. Now

on further dialing the telephone no. 22 the link will be stabilized in between telephone no. 23 of

heera pura and if the number 22 of Ajmer in a slimier manner the Ajmer can contact Heera pura

by dialing the direction no. 33.The station no. 67 & subscriber no. 23 all the direction are having

different direction no. & all stations are allotted different station no.

10.Priority facility:-

If in the case of dialing the caller gate busy tone. We can use the priority facility if he is

provided with the same. This consist a button, which when posed really to send a priority pulse

over the carrier link and get himself connected across the channel in use. He can then request the

parties using the channel to hand up he as an urgent call to make after the parties using the

channel hand up. This can originate a call as usual to get the required party on phone.


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11.Carrier Protection:-

Carrier protection is employed in large power network to trip or block circuit breaker of

certain sections of line depending on the requirement for example when the protection relay is

faulty section of a line fed from both ends of a section. But if high speed resoling is to be

employed the breakers at the both end will have to trip simultaneously to clear the fault & than

resoled simultaneously after a few cycle this coordination is best achieved by using a carrier

protection scheme.

12.In Carrier Tripping Scheme:

The form of carrier tripping scheme ensures near simultaneous tripping of breakers at both

ends of a line even when a fault occurs very near one end of the line. In such a case at the station

nearest to the fault the protective relay operate the first one end trip the circuit breaker. The

relays at the other hand with how ever sense this fault as the second one fault and breaker at the

end would normally trip at the end of definite time delay set by a timer unit which will be inseries with M2 unit contact of distance relay. On the receipt of the power line carrier trip signal

however a carrier relay short the bypass the timer unit conductor and as the M1 unit contacts trip

the breakers as iron a first zone is faulty that is without the trip delay. This ones again ensures

simultaneously tripping and later simultaneous reclosing. This type of protective scheme is

called permissive carrier enter tripping or permissive under reading or accelerated distance

protected scheme.

In a carrier blocking scheme of an external fault occurs on a protected span the OM3 unit

of the mho distance relay will sense the fault as on the external fault and will in conjunction with

the carrier protection transmitter send the carrier signal to the other end of the protected span to

block the breakers at the end from tripping.

13.Carrier Blocking Scheme:-

EXAMPLE: Time line between two power stations the above line is fed from both end at A

and D. A fault between section B and C is sensed by the relays connected to the breakers 3 and

4. Which will trip these breakers to isolate them simultaneously? The OM3 unit of mho relay

connected to breaker 2 and 5 will sense the fault as an external fault & start the breaker 1 &6

respectively. Thus section of the line between station A and B and between the station C and Dwill be kept alive and there will be no interruption to any of the load.


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14.Carrier Telemetering:-

Telemetry of the information regarding voltage current and power are reactive power etc.

of each generating the station the etc. is absolutely essential for the load dispatch as the work. As

the load dispacting office is usually located in the grade and generating station may be quite far.

Quantities measured at these places had to be transmitted to the load dispatch office by the

telemetry over PLCC network.

For transmitting the information by telemetry all the measure ends have to be first

converted into the electrical quantities such as voltages, resistances, current and frequencies

pulse width etc. by using suitable transducer. Then these electrical quantities will have to be

transmitted by PLCC signal over the power line.

15.Digital Telemetring :-

Telemetry signals are send in the form of pulse train over PLCC channel measure ends

are first converted from analogue to digital form by suitable convertors called encoders and then

transmitted in the form of numbers in the binary system. The transmission of the binary pulses

that is affecting by keying the transmitter between the fixed frequency keying.

In one make of equipment an instrument with maximum of 256 scales division can

measure any small no of division and transmitted the no. A max of 8 pulses is required for

remitting a number up to 255 in a binary system a ninth pulse is added as an priority bit to check

the correctness of transmission.

These digital techniques give better accuracy and more reliable transmission of

information than simplex analog technique. As only presence or absence of pulse matter in this

technique & not their magnitude in digital telemetering system tolerate power signal to noise

ratio and ideally suited for long distance transmission of telemetry data.


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16. Telecontrol :-

By the same method of transmission on telegram transmission pulses over PLCC tone

channels the remote circuit breaker can be closed or opened, and the governor setting of turning

can be altered to adjust voltages, power reactive towards the frequency etc. of the system as

desired by the load dispatcher.

DISCRIPTION OF PANEL CARDS

PLCC section containing different cards which enable it to do its work properly. This card

is specified by some no and contained inbuilt circuit that performs accordingly.

Different card have different specification, these specification can be summed in the following

way :-

E3EC Rx RF filter

N3FLTEST Matter

P3EORF hybrid

E5EATransmitter filter

B5ECPower supply

B3EA

40 volt regulator

B3EB24 volt regulator

P5EAPower amplifier

O3EIsupervision

P3ECReceive IF demodulator

E3EDReceive IF filter

P3EDRF & AGC modulator

P3EFReceive IF modulator

O3EHSignal output pilot

O3EETelephone adaptor


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O3EGVoice amplifier

E3EFVoice filter

O3EATele operational input

O3EDExpander or compander

O3ECSignal adaptor

O3EDDial module pilot tone

P3EATransmit IF modulator

E3EATransmit IF filter

P3EB

Transmit radio frequency modulator

E3EBTransmit pre filter

APPLICATIONS:-

The ETI series has been designed to cater for a Varity of application where by AF

multiplexer section may be separated from the parent section PLCC equipment and operated

remotely over a cable connection.As a rule the power line carrier equipment and associated protection signaling units are

required to be situated in the area of high voltage apparatus there by facilitating connection to the

PLC line coupling equipment.

SPECIFICATIONS OF PLCC:

1.GENERAL

Carrier frequency range: 40 KHZ to 512 KHZ

Gross channel band width: 4 KHZ

Useful AF band: 300 to 3700 KHZ

2. PERMISSIBLE ROOM TEMPERATURE IN CLIMATES

Data guarantee within reliable 0 to 45 degree C.

Operations guarantees 20 to 45 degree C.

Frequently stabile of RF oscillator 5 KHz


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3. TRANSMITER (RF TRANSMITING POWER)

Peak envelop power 25 watt

Side band power 15 watt

Auxiliary carrier frequency

Pilot tone 3600 Hz

Test tone 1000 Hz

synthesizer reference frequency 8 KHz

Dummy load 20 ohm

4. TRUNK DIALING

Shifting the pilot oscillator frequency to 3600 Hz +/-30Hz

Transmit dialing criterion of a speed of normality 10 pulse per second

5. POWER SUPPLY

DC supply 48 volt to 60 volt

Capacity 800 AH

AC supply 220+/- 15%.50Hz

Power consumption:


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stage and HF stage is placed in erect position contrary to this channel 2 is opposite In the

following diagram circuit function of PLC equipment ETI 21 and 22 is explained with help of

attached block dial Apart from the details for the wiring level setting and control voltages the

diagram contains information of the type and position number of plug in units for e.g. Telephone

adaptor O3EE tier p7EG-N10. In addition details are given for isolating links all measuring

points strapping information and attenuator network specially importing plug in element is

shown it bold.

AF MULTIPLEXER-TRANSMITTER

Speech

When the speech circuit of the PLC equipment is switched into a trunk circuit of the PAX or into

PLC equipment the function of the control leads is as shown in table:-

2-WIRE TERMINAL WORKING /4 WIRES TRANSMIT WORKING

THE TELEPHONE ADAPTOR UNIT (03EE) provides via isolating links (8-13) the connection

between the telephone PAX equipment and the PLC equipment.

The so modulated pilot tone arrives at the output TX either over strap P or via the relay in the

protection signaling equipment NSD4041 various signaling arrangement are possible using the

strapping e and f and a, b, c and d(receive).

4 wire service and emergency call telephone By inserting the service telephone plug into the 4

wire jack HANDSET, the microphone receives a dc energizing current from the voice

amplifier the speech signal which is superimposed on the dc feed current is fed via the

summating amplifier 3 into the main speech path the CALL button initiates a 1kHz continuous

calling tone supplied by generator 12 in dial module and is also fed via amplifier 3 into the main

module The 2 wire send and receive speech traffic is separated by the hybrid into the send and

receive paths To adjust the input levels to the nominal values of the equipment ,an adjustable

attenuator ,is fitted directly after the hybrid and is associated with the measuring jack6 The

transmit 2 wire speech is fed via the normally closed contact of the level switching relay v1 to

the amplifiers 2 and 3 similarly the transmit 4 wire speech is taken via adjustable attenuator and

the normally open contact v1 dial impulse from the PAX are passed over amplifier 8 to the dial

module 03ED for further processing

To avoid any interference with the auxiliary carrier the speech signals pass via the 300 Hz high

pass filter 4 and similarly via the low pass filter 7 to avoid interference in the tele operation band.

Additionally, momentary peaks in the speech signals are symmetrically limited by limiter 6. also

to reduce the sensitivity noise which may be picked up in the transmission path, the signals can


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be passed through COMPRESSOR 5 instead of via the strap D and the normally closed contact

ht of the BOOSTER relay

The 2-wire send and receive speech traffic is separated by the hybrid into the send and receive

paths. To adjust the input levels to the nominal values of the equipment , an adjustable attenuator

is fitted directly after the hybrid and is associated with the measuring jack6(-18 Dbr, printE3EF/h/l).The transmit 2-wire speech is fed via the normally closed contact of the level

switching relay v1 to the amplifiers 2and 3 . Similarly ,the transmit 4-wire speech is taken via

the adjustable attenuator (ENF-X157 potentiometer 4W) and the normally open contact v1.dial

impulse from the PAX are passed over amplifier 8 to the dial module 03ED for further

processing.

To avoid any interference with the auxiliary carrier the speech signals pass via the 300Hz high

pass filter 4 and similarly via the low pass filter 7 to avoid interference in the teleoperation band.

Additionally, momentary peaks in the speech signals are symmetrically limited by limiter 6 alsoto reduce the sensitivity noise which may be picked up in the transmission path, the signal can be

passed through COMPRESSOR 5 (03EB) instead of via the strap NC1 .the clearly defined

speech band passes via the strap D and the normally closed contact ht of the BOOSTER relay or

exceptionally via strap ND, (non-disconnect able) to the output of AF multiplexer. However with

the inclusion of the protection signaling equipment NSD 40/41, both straps are to be removed

because the speech path is taken via external contacts of the protection signaling equipment.

4-WIRE TERMINAL WORKING/4-WIRE TRANSIT WORKING:

This method of working is different from that described in 5.22; simply because the estrapping is soldered instead of f on the printed board and that via the attenuator (ENF -X156,

potentiometer 2W) the local 4-wire level is matched to the working level of the equipment.

SIGNALLING

The signaling pulses that serve to set up and release a telephone connection are fed to the

signaling input. The dc marking passes first to the fixed inverter stage8 and is then amplified by

the optional inverter stage 9. It is not, however, transmitted in this form but by the impulse

keying of the pilot frequency in the DIAL module 03ED/Q.

The 4-wire emergency call telephone set which may be used remotely from the PLCC equipment

is in practice, connected in the parallel with the service telephone and works in a similar manner.

Due to the switch hook contacts the microphone is only energized after the handset is lifted.

It can be used for ex; in emergencies as a direct end to end telephone independently from the

PAX circuit.


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TELEOPERATION SIGNALS:-

For the most application the various tele operation signals are connected separately and via

isolating links to each of the 5 TELEOPERATION inputs (03EA). Each input is fully decoupled

, and adjustable for level setting in the SIGNAL ADAPTOR (03EC),Apart from one resistor to

be soldered in (ENF-X) and a potentiometer , each input contains a measuring jack (18 Dbr),

On inputs 1 &2 an additional network of resistors is provided for the adjustment of the boosting

ratio and includes further measuring jacks a predetermined level will be set to achieve the correct

modulation index.

While disconnect able tele operation channel are taken via contact D of the boosting relay HT,

the non-disconnect able channels as well as the boost channels are taken via contacts ND and B

respectively.

With all protection signaling equipment, including the NSD40/41 equipment. The inputBOOSTER REALAY is used to operate relay HT during the trip condition. Never the less

input criteria form theNSD40/41 is taken via separate terminals for ex; VP1/VP16

5.3 Carrier Frequency sectionTransmitter

5.3.1 AF-IF conversion

The speech, tele operation and pilot signals enter the carrier frequency section collectively,

The summation amplifier 13 of the TRANSMIT IF MODULATOR (P3EA) these together free

of feedback before the multiplexed signal is transferred into the IF stage by AF-IF modulator 14.

By its modulation with the 16 KHZ IF frequency generated by the quarts controlled oscillator,

two side band are created and the carrier us strongly suppressed.

From the two side bands the IF filter 16(TRANSMIT IF FILTER E3EA) SEPARATES OUT

the lower one of 12.3 KHZ to 15.7KHZ the succeeding summation amplifier 17 (transmit RF

MODULATOR P3EB) pairs the IF signal with 16 KHZ auxiliary carrier which is used as

reference frequency for synchronization at the receiver it should be noted with the channelequipment ET122, that channel 1 operates exactly as above, however , in the 2 channel the upper

side band from 16.3Khz to 19.7Khz is filtered out (TRANSMIT IF FILTER E3EP) AND VIA

THE SECOND INPUT ENTERS the Transmit IF MODULAR (P3EB).with the attenuator

strapping CH2 (double channel equipment only) in place CH1 (single channel equipment) the

output level of the summation amplifier 17 is reduced by 6 DB.


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5.3.2 IF-HF CONVERSION

The resulting IF signal from 17 is mixed in the RF modulator 18 with synthesized HF

carrier 19 to place it in the desired position of the HF band. Furthermore, the TRANSMIT PRE

FILTER (E3EB/Q) filters out only the lower side band and gives it on to preamplifier 21. Here

with the aid of the adjustable attenuator network (straps 1-2 and 3-4, potentiometer TX level) theoutput of the POWER AMPLIFIER (P5EA) can be set to the desired level from the output stage

the signal goes via the TRANSMIT FILTER (E5EA).

And the RF hybrid (P3EO) for connection to the RF line various tapping of the unbalanced

output transformer (IMPEDANCE OF PLCC TERMINALS) and optionally and additional

balance transformer, ensures an optimum matching of the line.

The transmit filter has the function of suppressing any spurious emissions and, above all through

its output impedance characteristic , allows perfect working of several PLC equipment connected

in parallel to tjr same line side which can be dangerous to equipment and person .

5.4 CARRIER FREQUENCY SECTION RECEIVER

HF-IF CONVERSION

The incoming wide band line signal passes first over the RF hybrid 24 (P3EO) which serves

to decouple the receiver section from the adjacent transmitter output. with the aid of associated

attenuator network RF Rx ATTENUATOR , (straps LP,HP1 , HP2 and potentiometer Rx level)

the working point for the level regulation circuit will be sat to -5.0 volt measured on jack AGC

AMPLIFIERE(P3ED).

The receive RF FILTER B (E3EC/R) separates out the required HF band , and additionally the

filter together with the adjacent attenuator will attenuate by 40 DB any high voltage peaks

coming in the from the power line.

In the RECEIVE RF DE-MODULATOR (P3EC) the programmed HF carrier 27 puts the pre

filtered receive frequency back into the IF stage, but, however, without carrier suppression.

The main function of the RECEIVE IF FILTER (E3ED) 28 is to be determine the receiver

selectively in channel 1 the lower side band 12.3 KHZ to 19.7 KHZ is extracted .

Only in channel 1 is the 16 kHz carrier for synchronizing purpose allowed to pass through in

channel 2 it is blocked.


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5.4.2 IF-HF CONVERSION

After the filter 28, the signal passes to the IF and AGC AMPLIFIER (P3ED) which has a

uniform gain control as soon as its nominal working point is set (-5.0 v on measuring jack AGC),

the circuit equalizes perfectly all the level variations in the range +14 DB/-26Db in order to

prevent any over controlling effect , the amplifier rapidly increase , conversely any sudden dropin the level is restored slowly and uniformly ,since any uncontrolled swings of the AGC

regulation must not , for example , disturb further a protection trip signal originated as a result of

power line fault.

After conversion by the IF DE-MODULATOR (P3EF) and its associated pre filter 30, the upper

side band is removed by the low pass filters 32 and 34 and then finally the transmitted

intelligence is restored to its original frequency position. Never the less, it is recommended to

compensate frequency dependent level variations caused by the characteristic of the line, by the

PLC equalizing amplifier 33. Both speech and tele operation output signals are taken to their

respective terminals via a normally closed contact AF BLOCKING .This contact is opened by

the SUPER VISION (O3E1/P)circuit if the receiver level is too low or distorted due to noise .

From the output of the equalizing amplifier 33, a feedback path is provided via the SIGNAL

OUTPUT (03EH/S) where the pilot frequency is separated out by filter 35 and passed to the IF

and AGC AMPLIFIER (P3ED). The pilot tone is rectified and amplifier35before being

connected to the AGC AMPLIFIER 29.

Straps a and b serve to make slight adjustment to the gain of amplifier 29. These are set in the

factory test and normally do not require further adjustment.

AF MULTIPLEXER-RECEIVER

Speech

2-wire terminal/ 4-wire terminal transit working

The multiplexed signal enters the AF section via the Rx lead and from here the low pass filter

(E3EF/H/1) separates out the speech band the potentiometer 12 together with amplifier 38

(COMPANDER O3EB) when the compander is not fitted, the level is adjusted with straps

NC1,NC2 connected. This level is also measured at output of the amplifier 40 on measuring jack7, immediately before the attenuator network (strapping c, d potentiometer 4 watt). The

attenuator network its self-allow the 2 wire & 4 wire output levelss to be set independently from

each other.


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The received speech signal passes over the 2/4 wire selection relay output V2, amplifier 41, and

contact GA of the hybrid switching relay to the 2 wire output. From here the speech passes via

the connected PAX to the telephone subscriber.

Relay V2 switches from 2 to 4 wires working according to the criteria signal given out by the

PAX. Similarly the relay is operated from the PAX but after the telephone call end to end hasbeen setup .this arrangement prevent any danger of hybrid singing during the setup of the call.

4-wire terminal/ 4-wire transit working:-

This method of working is slightly different to that describer above because the hybrid

switching criteria (GA) is missing & the attenuator network,(straps C, d potentiometer 2 watt)

together with strap E is arrange for terminal or transit working.

SIGNALLING:-

The received dialing signals enters the AF Multiplexer via input R1 & passes to detector 42

(pilot/dial module o3ed/q) where it reforms the dialing impulses. The inverting stage 43 impulses

output relay DL which has a potential free contact available (signaling input) for impulse the

PAX circuits. Various signals arrangements are possible using a combination of strapping A, B,

C & D (receive) & E, F transmit.

If the incoming signal is disturbed due, for example, to serve noise on the power line, the

supervision unit (o3EI/P) will block the signaling detector 42 via the R3 lead.

4-wire service & telephone is plugged into four wire jack handset. The handset is connected

respectively to the output of the receive amplifier 40 , & the output of the transmit amplifier 3, an

incoming calling signal of 1000 Hz is delivered in the TELEPHONE ADAPTOR by the

frequency selective amplifier 47 to sound the built in buzzer 48.

A remote 4-wire telephone set connected to the PLCC equipment & is in effect connected in

parallel with the service telephone. Its function is therefore, similar to that described above

except that the buzzer is operated via the current amplifier 49.

For a quick and simple check of the equipment an audio test circuit is provide. It is only

necessary to patch input 11 of the audio test on the front side will be heard in the handset of the

service telephone via amplifier 40.


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TELEOPERATION:-

The complete incoming 4 KHz AF band enters the AF multiplexer section via R2 lead &

passes via amplifier 45 (signal output O3EH/S) to the tally operation output. Two types of output

impedances are available (low


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AUDIO TEST:-

For a quick and simple check of equipment and audio test circuit is provided. The audio

test(voice amplifier) is to patch on the front is of the equipment to any desired signal path and the

received signal will heard in the headset of the service telephone via amplifier.

The following signals can be checked in the AF section of the equipment: - speech, tale

operation data dialing.

FAULT ANALYSIS:-

In fault analysis the faulty devices are checked in this serial or manner:-

1. Telephone or tale operation signal

2. Cabling low frequency circuit or DC power supply

3. PLC equipment

4. HF transmission path

Competition with the transmission levels & working voltages measured under the healthy

condition are voluble aids to fault analysis. The back to back testing of equipment using the

dummy6 load is also a very useful aid.

The presence of AF signals in the various stages of the equipment can be checked using a

telephone headset and test load connected between the associated measuring point and audio

testing.

BATTERY CHARGER:-

PLCC works on rectified AC or main, when supply goes off we can make use or a device

for proper functioning called battery charger. This is the device that provides supplied to the

PLCC equipment for uninterrupted working. It provides DC to the panel by battery of 48 volt. In

this type 24 batteries are connected in series and individually per battery has approx. 2V

capacity.


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GENERAL DESCRIPTION:-

Battery charger consists of four sections

1. Float charger

2. Boost charger section3. Control section

4. Alarm section

All the four sections are situated and mounted in steel sheet. The sides and tops of the frame are

provided with the removable panel suitable recess has been provided in front panel to prevent the

component from projecting out. All meters indicating lamps, push button have been mounted on

front panel.

TECHNICAL SUERVISION:-

1. Normal input - 415V AC, 3 phase

2. Input variation - +/- 20% of voltage

FLOAT CHARGER:-

DC output -50 V +/-1%

Output current -20 to 40 Amps.

Line regulation & load regulation - +/- 1% individual

Ripple -0.6 Vpp

Efficiency ->70%

Boost charger

DC output -43.2 to 67.2 V

Output current -25 to 70 Amps.

Over load -10%

Efficiency ->80%


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1. FLOAT CHARGER

The float charger is basically static type three phase charger with stabilized output DC

voltage. The charger output dc voltage is constantly compared with standard DC reference

voltage and error voltage is again amplified. The amplified voltage control the trigging signal of

all the 3 thyristor of 3 phase bridge control as the output voltage tends to decrease than its

selected value, it makes the trigging signal of each thyristor of all three phase to advance for

firing them, so that the output voltage remains within the specified accuracy. If the output

voltage tends to increase more than the selected value the trigging pulse of these thyristor of all

three phase are delayed in the firing operation in such a way so that the output DC voltage is

again bought back to the its stabilized value.

CIRCUIT DESCRIPTION:-

The three phase AC input is applied through the three poles two way switch (RS1) & fuses

F18 to F20 to the float input contractor (CON1). The AC input voltage is applied after CON1 to

the float transformer TX1. The pilot lamp LED4 to LED6 indicates ON condition of the float

charger. The secondary of the TX1 is connected to the 3 phase full wave half controlled bridge

rectifier, which consists of a silicon diode D2 to D4 & SCR1 to SCR3, D1 is the freewheeling

diode. Fuse F1 to F7 protects all the diodes & SCR special serge circuit has also been provided

to protect SCR.

The rectified output is filtered output is filtered by the choke XL1 to XL2 & the capacitor bank

C1 to C2 which are protected by the HRC fuse F8. The filtered DC output is protected by HRC

fuses F9.

CONTROL CIRCUIT OF FLOAT CHARGER

The output of the charger is controlled through the electronic controller using phase control of

SCR feedback. The control circuit has plug in type card with hard type connector for external

connection. The control circuit consists of following functional circuit

1. Power supply

2. UJT firing for SCR phase control

3. Amplifier

4. DC under voltage lower voltage sensing

5. Auxiliary circuit


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POWER SUPPLY:-

This card provides regulated power supply of 1 to 12 % & unregulated 24 V used of IC &

relays respectively. Auxiliary transformer TX5 gets supply from main transformer phase &

neutral point. The two identical section circuit consisting of bridge rectifier, filter. & IC regulator

provides 1 to 12 volts stabilized output & a 24 Volt unregulated DC output. The output of the

bridge is filter using LC filter, compressing of filter chop CH1 & a capacitor C1.The capacitor is

protected by HRC fuses. Dummy load connected across DC output the filtered output is than

connected to the load circuit or to the battery through a rotary switch. Shunt SH1 is used for

current limit control which is also used for measuring output current on ammeter. A DC

voltmeter indicates a DC output voltage & indicating DC ON condition. Blocking diodes are

used to prevent the reverse current flowing through the battery to the charger. When the charger

voltage goes below the battery voltage or charger is off. The DC voltmeter V2 read voltage

across the load bus.

UJT FIRING CARD:-

There are three identical firing cards, each for trigging one SCR in the main bridge. Zener

diode DZ1 to DZ6 and resistance R15, R16, R17 connected to the secondary of the TX2, TX3,

and TX4 clamped the positive half of the input sine wave to the zener voltage.

RV1 and RV2 are adjusting to equals the conduction angle of the SCRs resulting in low ripples.

All SCR at the same conduction angle +1-10% input and output is adjusted to 5 volt. RV2 again

adjusted in full load to keep conduction angle of SCRs equal.

C1 begins charging at the start of the cycle through current supplied by the R2, RV2 and TR1

when voltage across C1 reaches the threshold value, UJT fires and C1 discharge through the

pulse transformer. This pulse fire the main SCR via auxiliary transistor.

Output voltage control obtained by varying the base emitter bias of TR1. An increase or decrease

in charging currents leads to decrease or increase in firing angle and the corresponding increase

or decrease in the output voltage. Zener OZ1 limits the gate voltage of the main SCR to the zener

voltage.

AMPLIFIER CRAD:-

This card consist of two operational amplifier IC1 and IC2 reference zener diode

OZ1,emitter follower TRJ and buffer amplifier TR3 and TR4,IC1 is error detected amplifier.

A negative reference by a zener diode OZ1 and voltage sensing signal are given to the inverting

input of op-amp ICI the output is taken through diode OJ2 to the base of the transistor Tr1 from


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whose emitter, the output is taken to the UJT driver card. Ratio of R$ and R5 determine the

voltage gain of op-amp and RV1 is used offset mulling.

The voltage sensing input is supplied to the op-amp IC2 through an OR gate formed by diode

OZ2 and OJ5, which ever signal is higher the amplifier will responded to that signal. OZ2

accepts the battery current signal while OIS accepts the float voltage limit signal at any time onlyone of the above signal will be commanding the amplifier.

The overall working of the feedback control can be explained as follows:-

If the inverting output is tends to rise in the loading during current limit the output of op-amp

IC1 decrease which in turns makes the emitter voltage TR1 lower. This reduces the bias on

transistor TR1 on firing cards so that charging current supplied by them to the capacitor is

reduced. Hence the triggering pulses are reported and make the output lower. Thus the negative

feedback is complete so that increase in output voltage will reduce or if the unit is in the load

limit condition. The increase in output will also be reduced to bring the current to the originalcondition.

R3, capacitor C2 and resistance R2, capacitor care incorporated to remove the instability like

hunting. Op-amp IC2 linear amplifier, the mV drop across shunt. The ratio of R14/R15

determine the gain of amplifier and RV2 0.1 subassembly sets the charging current. When

charging current increases the mV drop across pin no2 and 3 will be increase. This voltage is

applied to the base of TR4 through R11 transistor TR4 will be base current of TR3 and TR4 will

increase the voltage from D2 will control the voltage correcting amplifier IC1.

It is desired that the output of rectifier attains its steady state values slowly rather than by step.

FUSE FAIL ALARM

Fuse fail alarm is also available in float charger in the invent of any HRC fuse failure

corresponding type fuse blows and trip corresponding relay.

BOOST CHARGE SECTION

The battery can be charged by using two rotary switches provided on the front panel for

coarse and fine control the charging current can be read by emitter A3 provided at the front

panel. The operator must ensure that the rotary switches are in minimum position before

switching on the boost charger.


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OPERATION OF CHARGER:

The flow or boost charger can be switches ON by means of selector switch RS1. Thus at a

time only charger either float or boost we can operate.

When the charger is operated in the float mode the battery is on float charger all the VDDs areby passed through the connects of DC contactor. This enables complete voltage appearing on the

load. In case of mains fail also the entire battery voltage is available on the load through the

contacts of DC contactor when the charger is operated in boost mode, the contacts of DC

contactor opens.

MAINTANCE AND FAULT TRACKING PROCEDURE

1. All connection should be checked. The control circuit boards should be inserted far firmly in

their respective socket before energizing the battery charger.

2. All mounting bolts should be checked before energizing as loose mounting will causes

vibrations.

3. The charger should be switched off. Once in every month connection and mounting should be

checked.

4. The battery terminals should be connected first and the AC input after that.


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ADVANTAGES AND DISADVANTAGES OF PLCC

ADVANTAGES:-

1. No separate wires are needed for communication purpose. As the power lines them carry

power as well as communication signal. Hence the cost of constructing separated telephone line

is saved.

2. When compared with ordinary line the power line having higher mechanical strength. They

would normally remain unaffected under condition, which might seriously damage the telephone

line.

3. Power line usually provides the shortest route between the power stations.

4. Power lines have long cross sectional area resulting in low resistance per unit length

consequently the carrier signal suffered much less attenuation than they travel in ordinary

telephone line.

5. Largest spacing between conductors reduces capacitance which resulting smaller attenuation

at high frequency. The largest spacing also reduces the crosstalk to a considerable extent.

6. Power line is insulated to provide only negligible leakage between conductor and ground even

in adverse weather conditions.

DISVANTAGES:-

1. Proper has to be taken to guard carrier equipment and persons using them against the voltages

and currents on the line.

2. Reflection is produced on spur lines connected to high voltage line. This increases the

attenuation of other line.

3. High voltage line has transformer connections which attenuates the carrier signal.

4. Noise introduce by power line is far more than in case of telephone line. This is due to noise

generated by the discharge across the insulators and switch process. So it is obvious that an

effective power lines carrier system must overcome these and many difficulties also.


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Kp Training Report