POWER LINE CARRIER COMMUNICATION

RAJASTHAN RAJYA VIDHUT PRASARAN NIGAM LIMITEDNAVEEN KUMAR SHARMA 2008UEC407EC-4, FINAL YEARMNIT ,JAIPUR

ACKNOLEDGEMENTI am very grateful to shri MOHD. FAROOQ NIRBAN (Additional executive engineer) for his guidance & useful lectures. I would also like to express my sincere thanks towards PLCC staff of 132 KV CHAMBAL G.S.S for their coordination & trouble shooting.

INTRODUCTION OF R.S.E.B. * RSEB started from 1 July 1957It is a big organization and it functions under provisional electricity actThe aim of RSEB is to supply electricity to entire Rajasthan state in most economical wayThe target of board is to distribute energy in new areas as soon as possible

CONTENTSINTRODUCTION OF PLCCGENERAL DISCRIPTION OF PLCCSPECIFICATIONSBASIC PRINCIPLE OF PLCCCONSTRUCTION OF PLCCTYPES OF COUPLINGWAVETRAPS BATTERY CHARGERADVANTAGES AND DISADVANTAGES OF PLCCCONCLUSION

INTRODUCTION OF PLCCPOWER LINE CARRIER COMMUNICATION

Power line carrier communication has been found to

be the most economical and reliable method for

communication in a medium and over long distance

in a power system.

For sending speech or other signals from point to point in an interconnected power grid many communication methods can be used. Some of them are as following: . Public Telephone Network . Direct Lines . Radio Circuits . Power Line Carrier Communication(PLCC)

MODE OF OPERATIONPLCC Unit Provide Five type of operation:

1:TELEPHONE FACILITES2:COMPRESSOR & EXPANDER3:EMERGENCY CALL4:SIGNAL BOOSTING5:SUPERVISION & ALARMS

GENERAL MODULATION PRINCIPLESINGLE SIDE BAND TRANSMISSION CARRIER FREQUENCY IS SPACED ON A 4-KHZI.F. FIXED AT 16-KHZFULL DUPLEX MODE IS USEDLOWER SIDE BAND IS USED THROUGHOUT ALL COMMUNICATION

SPECIFICATIONS OF PLCC1)GENERAL - Carrier frequency range :- 40 to 512 KHZ Useful AF band :- 300 to 3,700HZ2)TRNSMITTERR.F.TRANSMITTING POWER;-peak envelope power:- 25w-side band power :- 15w

-I.F. CARRIER FRIQUENCY : 16 KHZ-PILOT TONE : 3600 HZ-TEST TONE : 1000 HZ-DUMMY LODE : 20 OHMS 3)POWER SUPPLY-DC SUPPLY : 24 V-CAPACITY : 800 AH- POWER CONSUMPTION :< 80 W

BASIC PRINCIPLE OF PLCCIn 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.

Since telephone communication system can not be directly connected to the high voltage lines, suitably designed coupling devices have to be employed.

Coupling devices consists of high voltage capacitors in conjunction with suitable line matching units(LMUs) for line impedance matching to that of the co-axial cable connecting the unit to the PLC transmit-receive equipment.

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 communication signals when earthed at isolator.

To prevent loss of communication signals, 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 usually have one or more suitably 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 RF is prevented from entering the stations bus(yard) and the power frequency is blocked of coupling capacitor.

The basic arrangement of connecting the WT and coupling capacitor in PLCC communication is shown in the figure below

(a) PHASE TO GROUND COUPLING

(b) PHASE TO PHASE COUPLING

(c) PHASE TO PHASE COUPLING

(d) INTERLINE OR INTER CIRCUIT COUPLING

WAVE TRAP

WAVE TRAPSWave traps (WTs) 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 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.

LIGHTNING ARRESTERThe ground wires running over the towers provides an adequate protection against lighting called L.A.It reduced the induced electrostatic or electromagnetic voltage.A good light arrester must posses the following properties:1:It should not absorb any current during normal operation, but during over voltage surge it must provide an easy way to the earth. 2: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.

DIAGRAM OF L.A.

TUNING CAPACITORUsed 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 usedFor higher voltage class of tuning units with impulse test voltage rating upto 150 KV, capacitors with mineral oil impregnated paper dielectric are used

THE DRAIN COILThe drainage coils has a pondered iron core serves to ground the power frequency charging to appear in the output of the unit. The coarse voltage arrester consists of an air gap, which sparks over at about 2 KV and protects the matching unit against line surges. Firstly it isolates the communication equipment for the power line. Secondly it serves to match the characteristic impedance of the power line 400-600 ohms to that of the co-axial vacuum arrester, which sparks, is over at about 250 v is provided for giving additional protection to the communication equipment.

BATTERY CHARGERPLCC (Power Line Carrier Communication) works on rectified AC or main power supply. When supply goes off, we use BATTERY CHARGER for proper functioning of PLCC, which provides supply to the PLCC equipment for uninterrupted working. It provides DC to the panel by battery of 48V. In this type 24 batteries are connected in series and individually per battery has approximately 2V capacity. Battery charger mainly consists of 4 sections 1. Float charger2. Boost charger section3. Control section4. Alarm section

TECHNICAL SPECIFICATIONSNORMAL INPUT :415 V AC 3-PHASEINPUT VARIATION : +/- 20%

FLOAT CHARGER : DC OUTPUT :50 V OUTPUT CURRENT :20 TO 40 AMP EFFICIENCY : >70%

BOOST CHARGERDC output- 43.2 to 67.2 VOutput current- 25-70 Amps.Efficiency- >80%

ADVANTAGES2

1. No separate wires are needed for communication purposes, as the power lines themselves carry power as well as communication signals. Hence the cost is less.2 Power lines have appreciably higher mechanical strength compared with ordinary lines. 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 area resulting in very low resistance per unit length. Consequently carrier signals suffer much less attenuation than when they travel on 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.

DISADVANTAGES1. 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 problem.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 difficulties.

CONCLUSIONA practical training for a period of 60 days provided me with an in-depth knowledge about POWER LINE CARRIER COMMUNICATION (PLCC).

THANK YOU

QUERIES ?

*