A

REPORT ON

132KV G.S.S.

PLCC SECTION

CHAMBAL POWER HOUSE

SESSION 2012 - 13

Submitted To : Submitted By:

Additional Executive Engineer JAYANT SINGH INDA

MOHAMMAD FAROOQ NIRBAN

PLCC SECTION

APEX INSTITUTE OF ENGGINEERING AND TECHNOLOGY

PREFACE

The objective of our practical training is to learn something about

industries, practically and to be familiar with the working style of a technical

worker to adjust simply according to industry environment.

As a part of academic syllabus of four year degree course in

Electronics and Communications Engineering, every student is required to

undergo a practical training for 30 days. We are student of third year

Electronics and Communications and this report is written on the basis of

practical knowledge acquired by our batch of 5 students during the period of

practical training taken of PLCC Section of RVPNL, Heerapura, Jaipur.

This report deals with equipments their relation and their general

operating principle.

For an easy way to understand the PLCC working a separate topic

named basic principle of PLCC is added in the report.

We hope, that this report will be use full for a person to get the basis

knowledge about the PLCC phenomenon.

ACKNOLEDGEMENT

I am very grateful to Shri MOHD. FAROOQ NIRBAN (Additional

executive engineer) for his guidance and useful lectures.

I would also like to express my sincere thanks towards PLCC

staff of 132 KV CHAMBAL G.S.S for their coordination and trouble

shooting.

INTRODUCTION OF R.S.E.B.

'Rajasthan state electricity board' started working from 1st 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, it has rules and regulations and has

made 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 Government.

The aim of RSEB is to supply electricity to entire Rajasthan State in

the most economical way. There is no possibility of staking or electricity so

the target of board is to distribute the energy in new area as possible. The

board has to carry the business on profit without losses.

After an efficient starting, as from last many years RSEB is not

earning profits. So far for betterment, 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

CONTENTS

TOPICS

INTRODUCTION TO PLCC

GENERAL DESCRIPTION OF PLCC EQUIPMENTS (ETI)

APPLICATIONS OF ETI EQUIPMENTS

CONSTRUCTION

MODE OF OPERATION

GENERAL MODULATION PRINCIPAL

SPECIFICATIONS

PRECAUTIONS & MAINTANANCE

BASIC PRINCIPLE OF PLCC

BATTERY CHARGER

ADVANTAGES & DISADVANTAGES

1. 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 co ordinate 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

the 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:

Power line carries schematic

LCC'S Equipments are used for point-to-point communication over

high voltage power lines. PLCC equipments are used send/receive

speech/data/teleprotection signals by using HF carrier signals ranging from

50 KH.

1) Speech signals.

2) Data/Telemetering.

3) Teleprotection.

1. SPEECH SIGNALS:

(i) An input signal of 300-2000Hz or 300-2400Hz bandwidth can be used

depending upon the customer requirements.

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

exchanges/ other switching equipments, 2 wire/4 wire express telephone

communication (hotline from control desk tc) control desk) and

communication through emergency jack telephones to be connected directly

to the PLCC terminals,

2. DA T A/TELEMETERING:

PLCC terminals can be used for sending/receiving data singnals for

telemetering and etc. The 'input signal for this channel will be between 2000-

3000Hz.

3 TELEPROTECTION:

i) Protection coupler equipments can be used along with PLCC

terminals for teleprotection requirements.

ii) During line fault/other occurring in substations trip signals can be

transmitted or received by the protection coupler through PLCC terminal for

activating the distant protection relaying equipments.

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 no 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 communications 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.

Basic Principles of PLCC:-

Telephone Communication system can be not directly connected to

the high voltage power lines, their for we have to suitably designed the

coupling devices. These usually consist of high voltage capacitor or

capacitor with parasitical devices & used in the conjunction with the suitable

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

the co axial cable connecting the PLCC Equipment.

In PLCC system the following Equipments are used:-

* PLCC Station

* Line matching Unit

* CVT/CC

* Earth Switch

* Lightening 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 out-put of PLCC is connected to the line matching unit before to

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

Equipments and power line.

CVT/CC (Control Voltage transformer/Coupling

capacitors):-

It is connected to the line matching unit to the line matching units 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.

C0-Axial Cable:-

This is used for inter connection between PLCC & L.M.U. for carrying the

high frequency signal.

THE BASIC ARRANGEMENT OF CONNECTING 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.

3 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;s line coupling equipment. In contrast,

the telephone exchange and Tele control equipments 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) PLC 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. away 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 26dB

- Frequency band :- 300 to 3700 HZ

:- 300 to 3400 HZ Optional

Adjustable attenuation equalizes for loaded lines, located at both ends.

The Faciliities Available are-

- 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 Kms. 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/output circuit (03 EA and 03

EH/S respectively).

Brief Characteristics-

Remote AF Multiplexer - Cable Terminal Type KTI:

- Cable attenusation:

Permitted </=7 dB with a cable distortion loss of ,/=2 dB 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 PLC EQUIPMENTS WHERE AF

MULTIPLEXER IS REMOTE

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 multiplexer 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 station is received

directly at the remote multiplexer.

5) REPEATERS

When several transmission sections 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, synchronized

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 neighbouring section.

4. CONSTRUCTION

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 only 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 adjustment of the PLC equalizer. Further of course, all terminal

strips and connectors are easily accessible on the rear side.

5. MODE OF OPERATION

The PLC equipment is suitable for connecting to a telephone exchange and

further more, a 4 wire remote/emergency call station can be created by operating it

in parallel with the built in service telephone equipment. The transmission facilities

for Tele operation working (telemetry, tele-control & protection signals) use

separate input and separate output circuits according to their classifications.

When 4-kHz equipment carries simultaneously the speech and Tele

operation signals, they are transmitted in frequency multiplex and accordingly the

audio frequency band is divided into two parts. The lower part of the band is used

for speech and the upper part for Tele operation signals.

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 receiver 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 50 baud. 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 the speech and

in normally reserved for use over lines with high noise. The improvement in the

signals o noise ratios is approximately 12 dB. When the speech is carried over

several PLC links in series it is recommended that only one compander be used,

the compressor being installed at the sending end of the line and the expander in

the farthest receiving station.

The ETI series is fully wired for a later inclusion of the compander equipment when

required.

3) 4 WIRE HAND/EMERGENCY CALL

The equipment, especially in the extension phases can, without additional units in

the HF equipment is equipped throughout with hand/emergency call telephone.

This telephone with DC bell can be connected directly via a 6wire extension calbe.

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

long as the push button is pressed. By lifting the handset the called station, the bell

is automatically disconnected. After the Call is completed both handsets must be

replaced. The calling tone is fixed at 1 kHz in the speech band.

4) SERVICE TELEPHONE

With the help of the built in speech facilities, service calls can be carried out in 4

wire from the front panel associated equipment, including the DC belt and the plug

in 4 wire handset are supplied.

5) TELE-OPERATION SIGNALS

Individual and adjustable Tele operation inputs are the essential requirement of the

PLC equipment for the interfacing with the various manufacturers' low frequency

transmission channels and for PLC though switching/individually adjustable and

fully de-coupled 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.

6) 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 advantageous during unfavorable transmission conditions

caused by perhaps fault 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-disconnect able channels)

The period of disconnection by which more power is switched to the boosting

channel, occurs for an extremely short period of time and is typically of the order of

approximately 100 milli-seconds.

The arrangement of speech and Tele operation falls into one of three categories

and is achieved by connecting to one of the following input:

- The disconnectable burs (D)

- The non-disconnectable bus (ND)

- Signal boosting bus (B) with a predetermined amplification

6 GENERAL MODULATION PRINCIPLE

The carrier frequency technique with single band transmission is due to the high-

quality band filters and converters, free from disturbing by products and spurious

signals. Optimum selectivity is achieved only in the intermediate frequency (IF)

stages by the filtering are out of the required side band,. here, therefore lines the

task of the carrier frequency section to move the AF intelligence from its low

frequency position of 300 to 300 HZ (respectively 300 to 2200 and HZ) first to the IF

stage and then into carrier frequency (HF) band. The carrier frequencies are

spaced on a 4 KHZ (respectively 2.5 KHZ) raster.

This arrangement requires the use of two conversion in each of transmit and

receive direction so that the intermediate frequency is fixed at 16 KHZ and the

carrier channel has a variable frequency which can be programmed to provide a

large number of HF carriers.

In the single channel equipment and channel 1 of the twin channel equipment, the

lower side band is used throughout all frequency conversions. The useful band is

inverted in the IF stage and in the HF stage placed in the erect position. Contrary to

this, channel 2 of the twin channel equipment is erect in the IF stage and inverted in

the HF stage.

7 SPECIFICATION OF PLCC

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 CLIMAES

- Data guaranteed within reliable :- 0 to 45 degree Centigrade

- Operation guarantee :- 20 to 45 degree Centigrade

- Frequency stability of R.F. oscillator:- 5 HZ

3) TRANSMITTER

R.F. transmitting power:

- Peak envelope power :- 25W

- Side band power :- 15W

- 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

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%), 180W

Approximate maximum supply 2 percent

- Capacity :- 800AH.

- A.C. supply :- 220+/-15%,50 HZ

- Power consumption :- <80 W

8 PRECAUTIONS AND MAINTENANCE

In normal rooms the ETI equipment generally erected on an open

rank or on a frame of freestanding cabinet.

The room for the erection of the equipment should have a dust free

floor, which is washable. The room should be well ventilated and of a normal

temperature & humidity and where necessary provided with a ventilator fan

having a dust filters.

The cabinets should be checked for damage before mounting.

Cabinets should prevent from tilting when opened.

Caution- before opening the hinged frame, make sure that the cabinet can

not tip forward.

FAULT ANALYSIS, TEST EQUIPMENTS AND TEST PROCEDURE.

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 following singles 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 healthy 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.

9 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 externally 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 consists 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 this would

result in high attenuation of even complete loss of communications 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 suitably designed capacitors

connected in parallel with the choke coils so as to resonate at carrier

frequencies and thus offer higher impedance to the flow of RF currents.

The basic arrangement of connecting 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 is presented from

entering the stations bus and the power frequency is blocked of coupling

capacitor.

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 than 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 affect dive coupling units to

PLC equipments.

A modern coupling capacitor consists of a stack of flat would elements of

pure cellulose paper and aluminum coils held between insulating roads

under optium pressure to minimize capacitance the changes with time and

temperature. The interconnection are designed to obtained to obtain highest

possible range withstand capacity and highest cut-off frequency. The entire

stack assembly as placed in a suitable pro claim insulating shall fill with

insulating coils and hermetically 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, show 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 loss (<0.5dB). They 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.

TYPE OF COUPLING

(A) PHASE TO GROUND COUPLING

(a) PHASE TO GROUND COUPLING

WT= wave trap. LMU= line matching unit. TR= transmission and receiving

equipments. CC= coupling capacitor

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 portion 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 o the soil conductivity enrote the line which varies from

place to place and time to time and partly 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 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) PHASE TO PHASE COUPLING

This type of 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 influence on the career currents.

The third conductor has no appreciable influence o the carrier current

transmission. Hence the switching conditions attention is less because two

conductors are used instead of one conductor and earth. This type of

coupling is more reliable over longer distance and is generally used load

dispatch work, though it is lightly costlier than the two phase system.

(D) ITERLINE FOR INTER CIRCUIT COPULING

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

two conductors used for communication belong to two-difference power

circuit's carrier 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 and is found to be

impracticable.

This type of coupling is even more reliable than phase-to-phase coupling on

he same circuit in that it permits operation with one of the two circuits

opened out and founded for maintenance purposes.

Inter phase or inter systems coupling are always employed on 220 KV and

400 KV lines where the interference levels are therefore also used on very

long 110 KV lines where attenuation becomes a problem. This type of

coupling permit higher reliability of operation under breaker conductor

conditions and are always employed where carrier line protection systems

are employed.

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.

3. Reflections 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 10 dB.

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 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 100 or 200 Micro

Henry wave trap will in conjunction 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 milli Henry and 2 milli Henry traps will clock

periodically the whole range of carrier frequency employed in PLCC a 2.0

MH traps can be used without a tuning capacitor across it. It will still blocked

almost all carrier frequencies in use effectively, but its inherent capacitance

of about 100 PF, will cause it to resonate at the high end of the PLCC band

(250 to 500 KHZ).

The low inductance respant types of traps are usually wound as 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 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 trap 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 10 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.

LIGHTING ARRESTER

Lightning is one of the most serious causes of over voltage. If the power

equipment especially at out door's is not protected, the over voltage will

cause during 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 waves

car cause internal flash over between inter-turns of transformers and the

high peak voltage of surge may cause 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 break 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.

THE TUNING CAPACITORS

Used are high voltage, high stability mica capacitors with low losses. For

lower voltage class of tuning (with impulse test voltage rating upto 40 KV)

polystyrene capacitors are used by some manufacturers. 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 resonate trap

to a different frequency.

DESCRIPTION OF THE PANEL CARDS

PLCC section contains different cards which enable it to do its work properly.

This card is specified by the some number and contains inbuilt circuit that

performs accordingly.

Different card have different specification these specification can be summed in

following way:-

E3EC RXRF Filter

N3FL Test matter

P3EO RF hybrid

E5EA Transmit filter

B5EC Power supply

B3EA 40 volt regulator

B3EA 24 volt regulator

P5EA power amplifier

O3EI supervision

P3EC receive IF demodulator

P3ED receive IF filter

P3ED RF&AGC amplifier

P3EF receive IF modulator

O3EH signal output plot

O3EE Telephone adaptor

O3EG Voice amplifier

E3EF Voice filter

O3EA Tele operational input

O3ED Expander or compander

O3EC Signal adaptor

O3ED Dial module pilot tone

P3EA Transmit IF modulator

E3EA Transmit IF filter

P3EB Transmit radio frequency modulator

E3EB Transmit pre filter

APPLICATIONS

The ETI series has been designed to cater for a variety of application

where by AF multiplexer section may be separated from the parent

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 ion the area of high voltage

apparatus there by facility connection to the PLC line coupling

equipment.

Figure: Standard TPg Traction Battery

(Courtesy Standard Batteries Limited)

BATTERY CHARGER:

PLCC (Power line carrier Communication) works on rectified AC or main, when make supply goes off. We 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 component 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%

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 thyristors of 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 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 do 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-I).

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 I 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 assembly sets the

charging current. When charging current increases the mv drop across pin

no. 2 & 3 of IC-2 will increased. This voltage is applled to the base of TR-4

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 the voltage correcting operational

amplifier IC-1. This will result in decrease 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

Description of Circuit-

Boost charger is used to charge the batteries after power resumption. The

input supply is switched on mains of rotatory switch RS-1, three numbers

HRC fuses.

F-21 to F-23 has been provided for over current protection. AC contractor

CON-2 has also been provided. Transformer-6 steps down the input AC

voltage to suitable level. Necessary taps are provided in the primary of

transformer to cater for varying input voltage that may prevail at sub station.

The secondary voltage of transformer-6 is applied to a bridge rectifier, which

consists of 6 silicon diodes D-6 to D-11 for rectification of AC to DC. These

diodes are mounted on individual heat sinks for cooling so that junction

temperature of the device is within specified limit. The diodes are protected

by capacitors and resistances against have storage effects and transit over

voltage in also by HRC fuses F-10 to F-15.

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.

3. OPERATION OF CHARGER

The float or boost charger can be switches "ON" by means of selector switch

RS-1. Thus at a time only one charger either float or boost can be operated.

When the charger is operated in float mode the battery is on float charge

and all the VDD's are bypassed through the contacts of DC contractor. This

enables complete voltage appearing on the load. In case of mains fall also

the entire battery voltage is available on load through contacts of DC

contactor. When the charger is operated on boost mode, the contacts of DC

contractor opens.

Load voltage can be adjusted by VDD switch RS-8 as per the requirement

main switch RS-9 have been provided to isolate the charger from load and

battery. When the selector switch RS-9 is in charger mode then it will

supplying load as well as trickle charger. The batteries in float and boost

charger, the batteries mode when the switch RS-9 is in main mode, then the

load will be supplied by the battery and the charger is totally isolated from

battery for charger main purpose.

4. MAINTENANCE AND FAULT TRACING PROCEDURE

1. All connections should be thoroughly checked. The control circuit boards

should be inserted far firmly in their respective sockets before energizing the

battery charger.

2. All mounting bolts/screws should be checked before energizing as loose

mounting will cause vibrations.

3. The charger should be switch off once in every month and the

connections and mounting should be checked.

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

that.

11. ADVANTAGES & DISADVANTAGES OF PLCC

ADVANTAGE

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 than 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 DISADVANTAGE

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.

It is obvious that an effective power lines carrier system must overcome

these and many other difficulties.

1. PRINCIPLE OF CARRIER COMMUNICATION-

-N N. BISWAS

2. MANUAL OF ETI EQUIPMENTS-

-ABB(ASEA BROWN BOVERI)

3. MANNUAL OF BATTERY CHARGER-

-R.S.E.B.