7/29/2019 Kp Training Report
1/32
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
7/29/2019 Kp Training Report
2/32
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.
7/29/2019 Kp Training Report
3/32
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
7/29/2019 Kp Training Report
4/32
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.
7/29/2019 Kp Training Report
5/32
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.
7/29/2019 Kp Training Report
6/32
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
7/29/2019 Kp Training Report
7/32
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.
7/29/2019 Kp Training Report
8/32
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.
7/29/2019 Kp Training Report
9/32
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.
7/29/2019 Kp Training Report
10/32
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.
7/29/2019 Kp Training Report
11/32
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
7/29/2019 Kp Training Report
12/32
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.
7/29/2019 Kp Training Report
13/32
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.
7/29/2019 Kp Training Report
14/32
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.
7/29/2019 Kp Training Report
15/32
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
7/29/2019 Kp Training Report
16/32
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
7/29/2019 Kp Training Report
17/32
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:
7/29/2019 Kp Training Report
18/32
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
7/29/2019 Kp Training Report
19/32
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.
7/29/2019 Kp Training Report
20/32
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.
7/29/2019 Kp Training Report
21/32
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.
7/29/2019 Kp Training Report
22/32
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.
7/29/2019 Kp Training Report
23/32
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.
7/29/2019 Kp Training Report
24/32
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
7/29/2019 Kp Training Report
25/32
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.
7/29/2019 Kp Training Report
26/32
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%
7/29/2019 Kp Training Report
27/32
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
7/29/2019 Kp Training Report
28/32
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
7/29/2019 Kp Training Report
29/32
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.
7/29/2019 Kp Training Report
30/32
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.
7/29/2019 Kp Training Report
31/32
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.
7/29/2019 Kp Training Report
32/32