Plcc Report(Rohit Choudhary
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Transcript of Plcc Report(Rohit Choudhary
A
PRACTICAL TRAINING SEMINAR REPORT
ON
POWER LINE CARRIER COMMUNICATION
TAKEN AT:
132 KV CHAMBLE GSS, HAWA SARAK
JAIPUR
DURATION: 16 june 2011 to 15 July 2011
Submitted in partially Fulfillment of the Requirements for the Degree of
Bachelor of Technology
In
Electronics & Communication Engineering
SUBMITTED TO: SUBMITTED BY:
MISS PRAGYA KHAGWAL ROHIT CHOUDHARY
(Dean & H.O.D.) B.Tech. 7THSEMESTER
(Department of Elec. & Comm.)
DEPARTMENT OF ELECTRONICS & COMM. ENGINEERING
VIVEKANANDA INSTITUTE OF TECHNOLOGY(EAST), JAIPUR
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ACKNOWLEDGEMENT
We are over helmed in all humbleness and gratefulness to acknowledge our depth to all those
who have helped us to put these ideas, well above the level of simplicity and into concrete
something.
We are very thankful to all the instructors of PLCC, Jaipur for their valuable help. With the
help of their valuable suggestions, guidance and encouragement, we were able to
perform this project work.
I would also like to thank to our institution VIVEKANANDA INSTITUTE OF
TECHNOLOGY(EAST), Jaipur and faculty members of the department, who often helped
and gave me valuable guidence to prepare my presentation. Last but not the least, I would
like to thank my parents who helped me a lot in gathering different
information, collecting data and guiding me from time to time in making this project .despite
of their busy schedules ,they gave me different ideas in making this project unique.
ROHIT CHOUDHARY
B.Tech.7THSemester
VIT/ECE
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PREFACE
Summer Training is an important part of our Engineering Curriculum. The B. Tech. course
helps a student in getting acquainted with the manner in which his/her knowledge is being
practically used at a large scale. Hence, when the student switched from the process of
learning to that of implementing his/her knowledge, he/she finds an abrupt change. This is
exactly why summer training during the B. Tech. curriculum becomes all the more important.
Summer Training is prescribed for the student of Technical College as a part of the four-year
degree course of Engineering by the AICTE.
We are required to do training and it has to be completed within a particular period of time
before completion of the 3rd year and in VI semester. This training report describes each and
every detail of the work we performed to make a successful completion of project. This
report also give us a brief idea of how we move ahead step by step reaching to specific height
and ultimately completing the goal.
ROHIT CHOUDHARY
B.Tech.VII Semester
VIT/ECE
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OFFICE OF ASSISTANT ENGINEER
(PLCC)
RAJASTHAN RAJYA VIDYUT PRASARAN NIGAM
LIMITED
132KV G.S.S CHAMBAL POWER HOUSE
JAIPUR
TO WHOM SO EVER IT MAY CONCERN
This is certify that ROHIT CHOUDHARY student of B.TECH 3rd
year of Electronics & communication from VIVEKANANDA
INSTITUTE OF TECHNOLOGY (EAST), JAIPUR has attended
practical training program from 16-06-2011 to 15-07-2011
(30 working days) in this organization connected with power
line carrier communication (PLCC).
His performance during the practical training period
remained good/ very good/excellent and completed his
training with full devotion.
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Date:-03-08-2011 (MOHD. FAROOQ NIRWAN)
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CONTENTS
S. No. Topic Page
1. Acknowledgement I
2. Preface II
3. Certificate III
4. Company profile 1
5. Introduction to PLCC 2
6. Basic principle of PLCC 4
7. General description of PLCC equipment (ETI) 14
8. Applications of ETI equipments 15
9. Construction 18
10. Modes of operations 19
11. Specification of PLCC 21
12. Precautions and maintenance 23
13. Battery Charge 25
14. Advantages and Disadvantages 30
15. Conclusion 31
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COMPANY PROFILE
INTRODUCTION OF RSEB
"Rajasthan state electricity board" started working from Ist July, 1957. This is the body of big
organization and is to function under provision electricity act, like public limited companies.
The board does not have article and memorandum of association.
In order to carry out its function, its rules & regulation and his mad other necessary
administrative arrangement. After the acting of RSEB six dimensions along with 64 offices &
about 300 employees were transferred to its control by the state Govt.
The aim of RSEB is to supply electricity to entire Rajasthan State in the most economical
way. There are no possibilities of staking or electricity so the target of board is to distribute
the energy in the new area as possible. The board has to carry the business on profit without
losses.
After an efficient starting, for the better service privatization of RSEB has been done
recently, it has been divided in five main parts, they are:
1. Electricity production authority: RRVUNL
2. Electricity transmission authority: RRVPNL
3. Distribution authority for Jaipur: JVVNL
4. Distribution authority for Jodhpur: JDVVNL
5. Distribution authority for Ajmer: AVVNL
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INTRODUCTION OF PLCC
(POWER LINE CARRIER COMMUNICATION)
As electronics play a vital rote in the industrial growth, communication is also backbone of
any power system. Communication between various generating and receiving stations is very
essential for proper operation of power system. This is more so in the case of a large
interconnected 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 for medium and long-distance in a power network. For short distance the
ordinary telephone system is using. 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 the 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 him introduction of hydroelectric generating stations
and extension of electricity to suburban and rural areas, the picture radically changed. The
various generating stations, located at great distances among themselves could no longer
remain isolated and self-distances among themselves could no longer remain isolated and
self-sufficient entitles. On the other hand, they soon became interconnected giving rise to
what is known as the power grid. This necessitated an economical and dependable means of
intercommunication, between various generating stations, sub-stations and control rooms.
Among many facilities that such means of communication are expected to provide, the
following are the important ones:
1. Speech transmission
2. Remote control and Tele-metering
3. Power line protection
4. Direct breaker tripping
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Many different methods are possible for sending speech or other signals from point to point
in an interconnected power grid. Some of them are as between:
1. Public Telephone Network
2. Direct Lines
3. Radio Circuits
4. Power Line Carrier Communication (PLCC)
In PLCC the higher mechanical strength and insulation level of high voltage power lines
result in increased reliability of communication and power 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 system.
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.
APPLICATION OF POEWR LINE CARRIER
COMMUNICATION
1) Protection
By using the PLCC equipment we can able to protect the power lines. If any problem occur in
the transmission of power, it will be informed to the main station by the using of power line
carrier communication.
2) Point To Point Communication
In power line carrier communication, communication occurs in between two stations. If we
want to communicate with the same station then a separate line is required. So in power line
carrier communication is a point to point communication and PLCC line never busy.
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3) Fault Indicator
If power line has any fault it will informed to power house to repair the fault. In power line
fault is very dangerous because it consists of very high voltage.
BASIC PRINCIPLE OF PLCC
In PLCC the higher mechanical strength and insulation level of high voltage power lines
result in increased reliability of 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 systems and widely used in all modern power systems.
Since telephone communication system can not be directly connected to the high voltage
lines, suitably designed coupling devices have therefore to be employed. These usually
consist of high voltage capacitors or capacitor with polaritical devices used in conjunction
with suitable line matching units 9LMU's) for matching the impedance of line to that of the
co-axial cable connecting the unit to the PLC transmit-receive equipment.
Also the carrier currents used for communication have to be prevented from entering the
power equipment used in GSS as the would result in high attenuation of even complete loss
of communication signals when earthed at isolator. To prevent this loss, wave traps or line
traps are employed. These consist of suitably designed choke coils connected in series with
the line, which offer negligible impedance to RF carrier currents. Wave traps also usual have
one or more suitable designed capacitors connected in parallel with the choke coils so as to
resonate at carrier frequencies and thus offer even higher impedance to the flow of RF
currents.
The basic arrangement of connecting the WT and coupling capacitor in PLCC
communication is shown in the above figure -
As can be seen from the sketch, the power frequency and radio frequency component are
sorted out by this arrangement. The RF in prevented from entering the stations bus and the
power frequency is blocked of coupling capacitor.
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Fig:- Basic PLCC circuit
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(1) COUPLING DEVICES
Earliest coupling devices used were antenna as similar to these used in radio work. This was
because capacitors capable of withstanding the high voltages used in transmission of
electrical power were not available at that time. The antennas used for coupling the PLC
equipment to the transmission lines were usually erected below the line and parallel to it.
They were usually more then 300 ft long and were tuned to the carrier frequency employed.
These were rather inefficient and the systems were affected but interference from nearby long
wave radio transmitters.
By about 1930, suitably paper and oil capacitors were developed which could withstand the
high voltage and serve as affectidive coupling units to PLC equipments.
A modern coupling capacitor consists of stack of flat would elements of pure cellulose paper
and aluminium coils held between insulating roads under optimum pressure to minimize
capacitance the changes with time and temperature. The interconnection is designed to
obtain.
Highest possible range withstands capacity and highest cut-off frequency. The entire stack
assembly as placed in a suitable pro claim insulating shall fill with insulation coils and
hemetically sealed by metallic flanges and gaskets of synthetic rubber with a dry nitrogen gas
cushion. The mechanical strength of the shell and flanges are carefully matched.
Coupling capacitors are designed for outdoors use and withstand normal atmospheric
phenomenon such as temperature and humidity rain, shown etc. The capacitor's used in
modern PLCC systems have a capacity between 2000 and 8000 ft. The usual value is between
3000 and 5000 ft. The units are designed to have a very low (<0.5dB). There are usually
mounted on pedestals below the line conductors.
In many cases the capacitive voltage dividers are used for communication system and voltage
is used for synchronizing purpose or voltage measurement.
Coupling is necessary because, if power of power line is flow through the communication
line it cause the burning of PLCC equipment. So overcome this problem a coupling capacitor
is used to block the flow of power into the carrier signal line.
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TYPE OF COUPLING
(A)Phase To Ground Coupling
As can be seen from the figure, the wave traps and coupling capacitors are all connected to
one conductor of the power line. The remaining two conductors, though not directly
connected to the.
Line carry a potion of the returning carrier current because these two conductors do not have
wave traps, a portion of the carrier energy is 1 lost. Also radiation losses are goes high as
earth forms a part of the circuit and the noise pickup is correspondingly higher. The method
of connecting is inefficient and the connection at the receiving and can not be made to match
the line perfectly. This is because the impedance of the line can not be calculated correctly as
it depends partly on the soil conductivity enrote the line which varies from place to place and
time to time and parity on station switching condition.
(b) Phase To Phase Coupling
This type of coupling was formally being used to improve the reliability of communication
case of breakage of one of the coupled conductors the system used double the number of
wave traps and coupling capacitors used in phase to ground and hence is costlier. This
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coupling capacitor at each and have the line are connected in parallel to the LMUs as shown
in this sketch figure-
Through this type coupling increase the reliability of communication, the attenuation,
interference from radio transmission and monitoring possibilities are all-higher than those of
phase to ground coupling. Hence this type of coupling has been discontinued and super sided
by the phase to phase coupling system.
(C) Inter Circuit Coupling
This type is coupling uses the same number of wave traps and the capacitor as two
phase coupling but the capacitance are not connected in parallel as in the case of that type of
coupling. The two power conductors used in this case may be considered as metallic go and
return lines for the carrier currents. The conductor has no appreciable influences on the
carrier currents. The third has no appreciable influence on the carrier current transmission.
Hence the switching conditions attention is less because two conductors are used instead of
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one conductor and earth. This type of coupling is more reliable over longer distance and is
generally used load dispatch work, though is lightly costlier than the two phase system.
COMPARISON OF PHASE TO PHASE AND PHASE TO
GROUND COUPLING
The phase-to-ground coupling has the advantage of requiring only half the number of wave
traps and coupling capacitors in comparison to phase-to-phase coupling. But it is inferior to
many respects as would be evident from the following points:
1. The phase-to-ground coupling has higher attenuation and unlike phase-to-phase
coupling, the attenuation varies with station switching conditions.
2. The variation of attenuation function with changes in weather condition is greater in
phase-to-ground coupling.
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3. Reflection and echoes due to mismatch difficulties are much greater in phase-to-
ground coupling.
4. Signal-to-noise ratio is poorer due to longitudinal noise voltages induced in the line.
In phase-to-phase coupling thee noise voltages tend to cancel themselves as equal
voltages are induced in the coupled conductors, which oppose each other in the
circuit.
5. Radiation from phase-to-ground case is about double than that in the other case.
6. A break or fault of some other kind will hamper the transmission in phase-to-ground
coupling much more seriously than in phase-to-phase coupling.
Hence, phase-to-ground coupling is used due to its cheapness, especially when frequency
used and distances to be covered are suitable, and radiation not particularly objectionable, as
may be the situation in sparsely populated areas.
(2) WAVE TRAPS
Wave traps- (WT's) are used between the transmission line and the power stations to avoid
carrier power dislocation in the power plant and cross talk with other power line carrier
circuits connected to the same power station. WT’s also ensure proper operating conditions
and signal levels at the PLCC transmit receive equipment irrespective of switching conditions
of the power circuits and equipment in the station.
A wave trap must satisfy the following requirements :
1) It must block the carrier currents. By blocking, we mean that the track should
attenuate the H.F. signals by at least 8 to 10dB.
2) It must carry the power frequency current safely during normal operation as well as
during short circuit fault conditions.
Constructions of Wave Traps-
All wave traps have a choke as a main part. This choke may be a single layer or a multi-layer
coils made of special aluminum alloy and is designed to carry the full load current the power
circuit continuously and also to withstand normal short circuit current in the event of a fault
on that line for a short time until the current in the event of a fault on circuit breakers clears
the fault without suffering any mechanical or thermal damages. The inductance of the choke
kvaries from 100 Micro henry's to 2 milli-henrys depending on the pass-band required. The
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100 or 200 Micro Henry wave trap will in conjuction with a suitable tuning capacitor block a
band of a few tens of KHz, the blocked land width being dependent on the carry frequency.
The one willi Henry and 2 milli-Henry traps will clock periodically teh whole range of carrier
frequency employed in PLCC a 2.o mH traps can be used without a tuning capacitor across it.
It will still block almost all carrier frequencies in use effectively, but its inherent capacitance
of about 100PF, will cause it to resonate at the high end of the PLCC band (250 to 500 KHZ).
The low indutance respant types of traps are usually wound a narrow cylindrical single layer,
whereas the high inductance broadband traps are invariably wound as large diameter
discoshed coils.
The cost of the wave trap increased with the rated power current to be carrier by it as well as
with the inductance required. A trap with a nominal rated current of 1600n Amp. Designed to
withstand a short circuit current of look. A may cost 10 times as much as trap rated for a
nominal current of 400 Amp and a short circuit current of 50 KA. Similarly a 2.0 mH tap may
cost several times as much as 100 micro-henry traps for the same nominal power current.
Therefore, wherever the nominal load currents and expected short circuit currents are high
smaller inductances are used with tuning arrangement to obtain broadband trap.
Suspension mounting of wave trap is preferred to rigid mounting on coupling capacitors as
this arrangement enables it to withstand the dynamic stresses created by short circuits better
and because it is more economical but high current, high inductance traps, which are very
heavy may have to be mounted on pedestals insulators or coupling capacitors. Wave traps are
made in various is a standard sizes and rating and to various specifications.
Standard inductances for wave trap recommended by IEC are 0.2, 0.25, 0.4, 0.5, 1.0 and 2.0
mH.
3) LIGHTNING ARRESTER
Lightning is one of the most serious causes of over voltage. If the power equipment
especially at our door's is not protected, the over voltage will cause burning of insulations.
The ground wires running over the towers provides an adequate protection against lighting
and also reduced the induced electrostatic or electromagnetic voltage but such a shield is
inadequate to protect any traveling which reaches terminals of electrical equipment and such
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waves can causes internal flash over between inter-turns of transformers and the high peack
voltage of surge may causes external flash over between terminals of the electrical equipment
which results in damage of insulators.
A good light arrester must pass the following properties:
It should not absorb any current during normal operation, but during over voltage surge it
must provide an easy way to the earth. After the first discharge of current has taken place
through then must be capable of carrying the discharge current for same interval of time
without any damage to them. After the over voltage discharge, it must be capable of
interrupting the normal frequency of current from flowing to ground as soon as voltages
reaches below down value.
In addition to tuning devices, which usually consist of a capacitor or capacitors, a lightning
arrester is invariably connected across the choke coils of the wave traps.
The lightning arrester used may be vacuum type arrester whose are over voltage lies below
the rated voltage of the tuning capacitors, but about the voltage produced across the coils
during a short circuit current surge. The lightning arrester therefore protects the tuning
capacitors against momentary over voltage caused by traveling waves. Sustained over voltage
resulting from short circuits currents are not high enough to cause the lightning arrester to be
over. Hence, a sustained are and consequent destruction of the arrester are avoided.
(4) THE TUNING CAPACITOR
Used are high voltage, high stability mica capacitors with low losses. For lower voltage class
of tuning units (with impulse test voltage rating upto 40 KV) polystyrene capacitors are used
by some manufactures. For higher voltage class of tuning units with impulse test voltage
rating upto 150 KV), capacitors with mineral oil impregnated paper die electric are used
which are similar in construction to coupling capacitors. All types are moulded in epoxy
resin. Single frequency traps have a single and double frequency traps have a double tuned
parallel resonant circuit. All the elements belonging to the tuning circuit are usually mounted
in a common housing, which can be revolved and substituted with another similar tuning
device to reasonate trap to a different frequency.
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DIAGRAM SHOWING COPUPLING ARRANGEMENT
(5) TRANSMISSION SYSTEMS
There are three different transmission methods, which can be employed for PLC
communication. They are as 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 systems used the first method. The speech frequencies transmitted were between
300 HZ to 2400 HZ when the carrier modulated with these frequencies the resulting side
bands took up a maximum bandwidth of 4800 KHZ. Thus, the available HF band was divided
into a number of channels each 5 KHZ wide with the nominal to (carrier) frequency located
in the centre o the channel, some countries attlotted 8 KHZ for each channel an these
channels could naturally transmit higher voice frequencies upto 3.4 KHZ insisted of 2.4 KHZ
and this resulted in better voice quality. Later, some manufacture retained the 8 KHZ and
used the remaining part of the channel for transmitting the telemetry information etc.
Almost all the modern PLC equipments are designed for amplitude modulation with single
side band suppressed carrier transmission. Single side band transmission has the following
advantages over a double side band transmission.
1) The bandwidth requirements per channel is exactly half that of double side band
transmission. Hence, twice the number of channels can be accommodated in the
available band of frequencies of the speech.
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2) As the receiver accepts only half the band of frequencies the noise input to the
receiver is correspondingly reduced. This results in better signal to noise ratio and
intelligibility of the speech.
6) TRUNKING CONNECTIONS FOR TYPICAL CALLS IN
THE NETWORK
A Trunking connection between Heerapura and Ajmer is shown above. For calling Ajmer for
telephone number 23 from Heerapura, the subscriber will left the telephone and he will dial
the direction number for Ajmer that is 53 and if the line is not busy, he will further dial the
station number that is 52. Now he subscriber at Heerapura will receive station tone of Ajmer.
Now on further dialing the telephone number 22, the link will be established in between
telephone number 23 of Heerapura and if a number 22 of Ajmer, in a similar manner, Ajmer
can contact Heerapura by dialing direction number 33, the station number 67 and subscriber
number 23. All directions are having different direction numbers and all stations are allotted
different stations numbers.
GENERAL DESCRIPTION OF PLCC EQUIPMENTS (ETI)
The multipurpose equipment type ETI-21 and ETI-22 transmit simultaneously speech and
multiplexed tele-operation signals in SSB technique over high voltage lines of cables.
The transmitted intelligence is suitable for
Telephone Tele-operations: - Telemetry
- Remote control
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- Remote analogue metering
- Tele-printer
Tele-protection signals for: - High voltage power equipment
- High voltage power lines
While the telephone and Tele operations facilities are typically used for economic control and
supervision of energy network. The tele-protection channels are kept continuously on hot
stand by an are used only in rare cases of a power fault for the planning of new network and
the extension of existing equipment, the ETI series offers a complete range of variation made
possible by a combination of tiers and plug-in PCB.
The equipment is built of 3 main parts-
1. The low frequency multiplex section
With the speech and up to five Tele-operations channels, together with an optional speech
compander.
2. The Carrier Frequency Section
Designed for single channels duplex or double channel duplex working in a 4 KHz or 2.5
KHz raster. The carrier frequency ranges is from 24 KHz to 500 KHz and with transmitted
power of 20 watts of a variant 100 watts.
3. Power Supply Unit
This can be operated from 110/220v, 50/60Hz or a separate battery or charger unit of 24v,
48v or 60v.
The techniques of simple side band modulation with double conversion provides frequency
equalization, automatic gain control and frequency synchronization and ensures perfect
reproduction of the transmitted intelligence, proper distribution of the transmitting power in
normal operation and for the boosting of protection trip signals enables optimum distance to
be converted.
The front panel arrangement of operational and servicing elements such as switches,
potentiometer, lambs etc. allows the non specialist to carry out maintenance of the equipment
with the aid of a built in test oscillator and handy audio test instrument, a quick test and level
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adjustment can be carried out so that with the local transmitter and receiver connected back-
to-back a complete stimulation of the PLC link in establish.
APPLICATIONS OF ETI EQUIPMENTS
The power line carrier (PLC) equipments and the associated protection signaling units are
required to be situated in the area of the high voltage apparatus, thereby facilitating
connections to the PLC' line coupling equipment. In contrast, the telephone exchange and
Tele control equipment are usually more conveniently situated in a control building some
distance from the high voltage equipment.
According to the type of installation various arrangements are possible. These are briefly
explained in the following:
1. PLCC equipment and AF Multiplexer as a Combined Unit
The majority of electricity authorities adopt this arrangement since the complete PLC is
contained in a single cabinet or rack and is easily placed in a suitable telecommunication
room. From this room the individual connections are taken directly to the associated HV
protection circuits and via an appropriate distribution frame, connections to the telephone and
Tele control equipments.
2. Remote at Multiplexer Connected by A long Cable
The case here is that the high voltage lines are terminated in the sub-stations as the edge of
the city while the associated control building or load dispatching office is situated some km.
way in the center of the city. A long 4-wire interconnection cable (Zo=600 chms) connects
the parent PLC equipment with the remote multiplexer.
Brief characteristics -
Cable Attenuation - Permitted 32 dB maximum
- Planning value 26 dB
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Frequency band - 300 to 3700 HZ
- 300 to 3400 HZ Optional
- Adjustable attenuation equalizes for loaded lines, located at both
ends.
The Facilities Available is -
- 4 wire duplex speech, from remote location.
- Duplex tele-operational channels, from remote location.
- Duplex pilot/signaling channel, from remote location.
- Possibilities for input and output connections of tele-operation
signals from PLC equipments.
- Optional: Service telephone from parent PLC equipment to opposite
PLC station.
3. Remote at Multiplexer Connected by a Short Line
When the distance between the PLC and remote multiplexer is relatively short, i.e. up to
about 3 km and in connected by a 4-wire pilot cable (Zo=600 ohm). Due to the lower cable
attenuation the line amplifier with line equalizer is unnecessary and the cable will be
terminated on the tele-operation input/notput circuit (03EA and 03EH/s respectively).
Brief Characteristics -
Remote AF Multiplexer - Cable Terminal Type KTI :
Cable attenuation:
Permitted </=7 dB with a cable distortion loss of /=2dB in the frequency band 300-
3700 Hz. This is equivalent to a distance of 3 Km. Maximum with an unloaded 600
ohms cable.
Frequency band - 300 to 3700 Hz
- 300 to 3400 Hz optional
4. Protection Signaling Over PLCC Equipments Where AF Multiplexer
Is Remote
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In addition to the remote AF multiplexer, tele-protection signaling equipment can be coupled
directly to the PLC equipment. Such an arrangement must of course be reliable and safe so
that even with a possible favour of the remote multiplexed or connecting cable the Tele
protection equipment continues to work perfectly.
This means the PLC equipment has to function fully independently of the transmit signals
from the remote multiplexer. This will be the case when a pilot signal P-1 is used from AF
multiplexer to PLC equipment. A further pilot tone P-2 of the same frequency is transmitted
from the PLC equipment to the opposite PLC station. The signaling impulses carried by the
pilot tones are looped from P-1 to P-2 in DC form at the PLC equipment. The pilot tone P-3
from the opposite stations is received directly at the remote multiplexer.
5. Repeaters
When several transmission are joined together to form a long transmission path, the ETI
equipment can serve as repeater at the intermediate stations. In each transmission section the
carrier signal will be individually regulated, syschronized and equalized and the transmitted
intelligence at each repeater station will be demodulated and passed on to the next section.
The method allows the insertion of tele-operation signals at the repeater station provided, of
course, free space in the 4 KHz band is available. The transit filter E3ET prevents the pilot
tone P-1 entering the neighboring section.
CONSTRUCTION
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The PLC equipment built in Module Electronic System (MES) is especially compact. For all
equipment variations, the single channel equipment ETI-21 can be accommodated in 3 tiers,
the double channel equipment ETI-22 in 4 tiers and the double channel, 40W equipment ETI-
22 (s) in 6 tiers. Further more, a mechanical coding system ensures all plug in units can be
inserted in their correct position.
The ABB free standing cabinet type E-35 can for example, accommodate two single channel
PLC equipments with the associated protection signaling units and an electronic trunk-dialing
unit for eight (8) telephone subscribers.
A nameplate on the front door of the carrier cabinet carriers relevant information of the PLC
link, such as equipment type, station names, carrier frequency etc.
To enable printed circuit boards to be exchanged without any readjustment being required,
there is on the rear side a strapping field for the initial programming of the system variant and
also for the system variant and also for the adjustment of the PLC equalizer. Further of
course, all terminal strips and connectors are easily accessible on the rear side.
MODES OF OPERATION
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The PLCC equipment is suitable for connecting to a telephone exchange and further more , a
4 wire remote and emergency call station can be created by operating it in parallel with the
built in service telephone equipment. The transmission facility for Tele operation working
use separate input and separate output circuit according to their classifications.
1) Telephone Facilities
The associated automatic telephone exchange (PAX) is suitable for a network with a limited
number of subscribers. Between the PAX and PLC channels, controls circuits give out-
signals for the setting up , dialing and later releasing a telephone connection and the
switching criteria between PAX and PLC equipment is performed by potential free contacts.
The PAX sending contact will, via the PLC signaling channel close an output contact in the
PLC receive and the distant end of the link.
The dialing impulses are transmitted over the combined pilot and signaling channel which
has a maximum transmitted speech of 50band. It should be noted that because of the various
possibilities of telephone switching, more functions are built into the speech circuits than are
actually needed by some PAX types.
2) Compressor And Expander (Compander)
The inclusion of a compander improves the carrier signal quality of speech and in normally
reserved for use over lines with high noise. The improvement in the signals to noise ratios is
approximately 12 db. When the speech is carried over PLC links in series, it is recommended
that only one compande r be used, the compressor being installed at the sending end of the
line and the expander in the farthest station.
The ETI series is fully wired for a later inclusion of the compander equipment when required.
3) Service Telephone
With the help of the built in speech facilities, service calls be carried out in 4 wire from the
front panel associated equipment the DC belt and the plug in 4 wire handset are supplied.
4) Supervison And Alarms
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The channels plug in supervision unit give an alarm indication if there is a failure of the tx
path, the transmitter / receiver and the power supply. Both a collective and individual alarms
are given and are indicted on the equipment with light emitting diodes (LED’s).
5) Signal Boosting
The equipment offers the possibility of signal boosting of one or two especially important
signals, for example protection signals for high voltage lines or equipment. This is advantage
during unfavorable transmission conditions caused by perhaps faults conditions on the power
line. During boosting, the less importing channels, for example the speech are disconnected
(known as disconnected channels) whereas other channels can be allowed to work normally
(non-disconnected able channels).
6) Tele-Operation Signals
Individual and adjustable Tele operation inputs are the essential requirement of the PLCC
equipment for the interfacing with the various manufacturers’ low frequency transmission
channels and for PLC through switching/transit working. The 5input and 3output possibilities
each individually adjustable and fully decoupled together with the separated terminals. For
protection signaling equipment, offer the necessary flexibility. A strapping field is provided
for choosing the various modes of operation.
7) 4 Wire Hand/Emergency Call
The equipment, especially in the extension phases can, without addition units in the HF
equipment is equipped through out with hand/emergency call telephone. This telephone with
DC bell can be connected directly via a 6-wire extension cable. The calling of the opposite
station is accomplished lifting the handset and pressing the calling button in the opposite
station after a two second delay the bell rings as the push button is pressed. By lifting the
handset the called station, the bell is automatically disconnected. After the cell is completed
both handset must be replaced. The calling tone is fixed at 1 KHz in the speech band.
SPECIFICATIONS OF PLCC
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1. General
- Carrier frequency range :- 40 to 512 KHZ
- Gross channel bandwidth :- 4 KHZ
- Useful AF band :- 300 to 3,700 KHZ
2. Permissible Room Temperature In
Climates
- Date guaranteed within reliable
Centigrade
:- 0 to 45 degree
- Operation guarantee :- 20 to 45 degree Centigrade
3. Transmitter
R.F. Transmitting power :
- Peak envelope power :- 25 W
- Side band power :- 15 W
- Auxiliary carrier frequency :- 16 KHZ
At frequency 250 KHZ their power lower by 2 dB.
- I.F. carrier frequency :- 16 KHZ
- Pilot tone :- 3,600 HZ
- Test tone :- 1000 HZ
- Synthesizer reference frequency :- 8 KHZ
- Dummy load :- 20 OHMS
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4. Trunk Dialing
Shifting the pilot oscillator frequency of 3600 +/-30 transmits dialing criterions of a
speed of normally 1- pulses per second.
5. Power Supply
- DC supply :- 49 TO 60(-10/+25%), 180 W
Approximate maximum supply 2 percent
- Capacity :- 800 AH.
- A.C. Supply :- 220+/- 15%, 50 HZ
- Power consumption :- < 80 W
PRECAUTIONS AND MAINTENANCE
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In normal rooms the ETI equipment generally erected on an open rack on a frame of
freestanding cabinet.
The rooms for the erection of the equipment should have a dust free floor, which is washable.
The room should be well ventilated and of normal temperature & humidity and where
necessary provided with a ventilator fan having a dust filters.
The cabinets should be checked for damage before mounting.
Caution - before opening the hinged frame, make sure that the cabinet cannot tip forward.
Fault Analysis, Test Equipment And Test Procedure
(1)Test Equipments
(A) Test Oscillator
Test oscillator enables the commissioning of the PLC link without aid of external signals,
pressing the CALL button initiate a test tone of 1 KHZ which is fed to the voice amplifier and
passes through all transmit stages of the PLC equipment with the exception of the telephone
adapter. It is possible to check at any test point the DBR value printed in the front side of the
equipment is against the measured dB reading. It simplifies also the setting of the
transmitting (Tx) output power, which is measured by T (HF) on the transmitting level test
point.
(B) Dummy Load And Hf Loop Test
Faultfinding is much simplified when the HF output is connected to a definite resistive load
in place of the more or less ill defined characteristics of the power line. The ohmic load with
additional isolates the line, takes the form of a 50 ohms artificial load, which insert in place
of P3EO at the time of testing. Connecting back-to-back transmitter and receiver can test the
complete PLC equipment. This is achieved by to feeding a reduced transmitting voltage. The
dummy load automatically adjusts the receiver to accept the transmitter frequency.
(C) Audio Test
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For a quick and simple check of the equipment and audio test circuit is provided. The audio
test (voice amplifier) is to patch on the front side of the equipment to any desired signal path
and the received signal will be heard in the handset of the service telephone via amplifier.
The following signals can be checked in the AF section of the equipment: -
Speech, Tele operation/data dialing.
(2) Fault Analysis
In fault analysis the faulty devices are checked in this serial or manner:
- Telephone or Tele operation signals
- Cabling-low frequency circuits or DC power supplies
- PLC equipments
- HF transmission path
Comparisons with the transmission levels and working voltages measured under health
conditions are valuable aids to fault analysis. The back-to-back testing of the equipment using
the dummy load is also a very useful aid.The presence of AF signals in the various stages of
the equipment can be checked using the telephone handset and test load connected between
the associated measuring point and audio testing.
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BATTERY CHARGER
PLCC (Power Line Carrier Communication) works on rectified AC or main when supply
goes off. We make use of a device for proper functioning of PLCC, called BATTERY
CHARGER. this is the device that provides supply to the PLCC equipment for uninterrupted
working. It provides DC to the panel by battery of 48 V. In this type 24 batteries are
connected in series and individually per battery has approximately 2 V capacities.
1. General Description
Battery charger mainly consists of 4 sections -
1. Float charger
2. Boost charger section
3. Control section
4. Alarm section
All the four sections are situated in mounted sheet steel. The sides and tops of the frame are
provided with removable panels suitable recess has been provided in front panel to prevent
the compenent from projecting out. All meters indicating lamps, push buttons have been
mounted on front panel.
2. Technical Specifications
- Normal Input - 415 V AC 3 phase
- Input variation- +/20% of voltage
Float charger -
DC output - 50 V +/-1%
Output current - 20 to 40 ampere
Line regulation & load regulation - +/-1% individual
Ripple - 0.6 Vpp (peak to peak)
Efficiency - > 70%
Boost charger -
DC output - 43.2 to 67.2 V
Output current - 25-70 Amps.
Over load - 10%
Efficiency - > 80%
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1. Float Charger -
The float charger is basically static type 3-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. This amplified voltage control the triggering signals of all
the 3 phase bridge control rectifier, as the output voltage tends to decrease than it's selected
value, it makes the triggering signals of each thyristor of all 3 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 triggering pulses of these thyristors of all 3
phase are delayed in firing operations in such a way so that the output dc voltage is again
brought back to its stabilized voltage.
Circuit Description -
The 3-phase AC input is applied through the 3 poles 2 way switch (RS-I) and fuse F-18 to F-
20 to the float input contractor (CON-1).
The AC voltage is applied after CON-1 to the float transformer TX-1. The pilot lamp LED 4
To LED 6 indicates 'ON' condition of the float charger. The secondary of the TX -1 is
connected to the 3-phase full wave half controlled bridge rectifier, which consists of silicon
diodes D-2 to D-4, and SCR-1 to SCR-3, D-1 is the free wheeling diodes. HRC fuses F1 to
F7 protect all diodes and SCR's, Special surge circuits have also been provided to protect
SCR's.
The rectified output is filtered by the choke XL-1 and KL-2 and the capacitor bank C-1 and
C-2, which are protected by the HRC fuse F-8. The filtered DC output is protected by the
HRC fuses F-9 and LK-1. BR-1 is the bleeder is the resister for the capacitor bank.
Control Circuit of Float Charger -
The output of the charger is controlled through the electronic controller. Using phase control
of the SCR's feedback control the output. The control circuit has plug in type cards with hard
type connectors for external connections. The control circuit consists of following functional
circuits:
1. Power supply
2. UOT firing for SCR phase control
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3. Amplifier
4. DC under voltage/over voltage sensing
5. Auxiliary circuits
Power Supply:
This card provides regulated power supplies of +/-12% and u unregulated24 V used for ICs
and relays respectively, regulated output is 200 (maximum)., Auxiliary transformer TR-5 gets
supply from main transformer's phase and neutral points. The two identical secondary circuits
consisting of bridge rectifier, filter and IC regulator provide +/- 12V stabilized output and
24V unregulated DC output. The output of the bridge is filtered using L-C filter comprising
of filter Choke CH-1 and capacitor bank consisting of capacitor C-1. The capacitor is
protected by HRC fuses. BR-1 is bleeder resistance dummy load connected across the DC
output; the filtered output is then connected to the load circuit or to the battery through a
rotary switch. Shunt SH-1 is used for current limit control, which is also used for measuring
output current on ammeter. A DC volt- meter indicates the DC output voltage. An indicating
lamp indicates DC 'ON' condition. Blocking diodes are used to prevent reverse current
flowing from the battery to the charger when the charger voltage goes below the battery
voltage or charger is 'OFF'. The DC voltmeter V-2 reads voltage across the load bus.
UOT Firing Card:
There are three (3) identical firing cards, each for triggering one SCR in the main bridge.
Zener diodes DZ-1 to DZ- 6 and resistance R-15, R-16, R-17 connected to the secondary of
the TX-2, TX-2 and TX-4 clamp the positive half of the input sine wave to the Zenor voltage.
RV-1 and RV-2 are adjusted to equalize the conduction angle of the SCR's resulting in law
ripple. All SCR's at the same conduction angle +/-10% input and output adjusted to 5V. RV-2
again adjusted in full load to keep conduction angle of the SCR's equal.
C-1 beings charging at the start of the cycle, through current supplied by the R-2, RV-2 and
TR-1. When voltage across C-1 reaches the threshold value, UOT fires and C-1 discharge
through the pulse transformer. This pulse fires the main SCR via auxiliary transistor.
Output voltage control is obtained by varying the base ammeter bias of TR-1. An
increase/decrease in charging current leads to a decrease/increase in firing andgle and a
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corresponding increase/decrease in the output voltage. Senor DZ-1 limits the gate voltage of
the main SCR to the Zenor voltage.
Amplifier Card:
This card consists of two operational amplifiers IC-1 and IC-2 reference Zenor diodes DZ-1,
emitter follower TR-1 and buffer amplifier TR-3 and TR-4; IC-1 is the error detector
amplifier.
A negative reference by a Zenar diode DZ-1 and voltage sensing singles are given to the
inverting input of operational amplifier IC-1 the output is taken through a diode D-1 to the
base of transistor TR-1 from whose emitter the output is taken to the UOT driver cards. Ratio
of R-4 and R-5 determine the voltage gain of the operational amplifier and Rv-1 is used for
offset nulling.
The voltage sensing input is supplied to the OPAM IC-2 through an 'OR' gate formed by
diode D-2 & D-15. Whichever signal in higher the amplifier will respond to that signal. D-2
accepts the battery current signal while D-15 accepts the float or voltage limit signal at any
time only one of the above signals will be commanding the amplifier.
The overall working of the feedback control can be explained as follows :-
If the inverting input tends to rise or increase in loading during current limit, the output of the
operational amplifier IC-1 decrease which in turns makes the emitter voltage or TR 1 lower.
This reduces the bias on transistor TR 1 on firing cards so that charging current supplied by
them to the capacitor are reduced. Hence the triggering pulses are retarded and make the
output lower. Thus the negative feedback is complete so that the increase in output voltage
will reduce or if the unit is in load limit condition. The increase in output current will also be
reduced to bring the current to the original condition.
Resistance R-3, capacitor C-2 and also resistance R-2, capacitor C-1 are incorporated to
remove the instabilities like hunting. Operational amplifier IC-2 l liner amplifier the mv drop
across shunt. The ratio of R-14/R-15 determine the gain of the amplifier and RV-2 on sub
assemble sets the charging current. When charging current increases the mv drop across pin
No. 2 & 3 of IC-2 will increased. This voltage is applied to the base of TR-3 and TR-3
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through R-11. Transistor TR-4 will be the base current of TR-3 and TR-3 will increase the
voltage from D-2 will control in DC output voltage to keep the battery current at set level,
which can be adjusted by potentiometer RV-2.
It is desired that output of the rectifier attain its steady state value slowly rather than by step.
Fuse Fail Alarm:
Fuse Fail alarm is also available in float charger. In the event of any HRC fuse failure.
Corresponding types fuse blows and trip the corresponding relay.
2. Boost Charger Section
The battery can be charged by using the two rotatory switches provided on front panel for
coarse and fine control and that charging current can be read by ammeter A-3 provided on the
front panel. The operator must ensure that the rotatory switches are in minimum position
before switching on the boost charger.
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ADVANTGES & DISADVANTAGES OF PLCC
1. Advantages -
1. No separate wires are needed for communication purposes, as the power lines
themselves carry power as well as communication signals. Hence the cost of
constructing separate telephone lines is saved.
2. When compared with ordinary lines the power lines have appreciably higher
mechanical strength. They would normally remain unaffected under the
conditions, which might seriously damage telephone lines.
3. Power lines usually provide the shortest route between the power stations.
4. Power lines have large cross-sectional areas resulting in very low resistance
per unit length. Consequently the carrier signals suffer much less attenuation
then when they travel on usual telephone lines of equal lengths.
5. Power lines are well insulated to provide only negligible leakage between
conductors and ground even in adverse weather conditions.
6. Largest spacing between conductors reduces capacitance, which results in
smaller attenuation at high frequencies. The large spacing also reduces the
cross talk to a considerable extent.
2. Disadvantages -
1. Proper care has to be taken to guard carrier equipment and persons using them
against high voltages and currents on the lines.
2. Reflections are produced on spur lines connected to high voltage lines. This
increases attenuation and creates other problems.
3. High voltage lines have transformer connections, attenuate carrier currents. Sub-
station equipments adversely affect the carrier currents.
4. Noise introduced by power lines is far more than in case of telephone lines. This is
due to the noise generated by discharge across insulators, corona and
switching processes.
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CONCLUSION
The Practical training has proved to be knowledge buster for me and I have acquired a good
practical knowledge of the field which can’t be gained nearly by reading books. As PLCC is
the power line carrier communication that is used to transmit the signal with power line
network for such large distances, the power line themselves provides a very good medium of
transmission of information. So the power line carrier communication (PLCC) is mostly used.
The training has proved me with a good knowledge of working of PLCC and base for relating
the theoretical knowledge with the practical one. It was a very exciting adventurous and
exhaustive training which has raised my practical skills to a great extent.