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Power line carrier communication

PLCC PROJECT REPORT

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Power line carrier communication

  1. 1. A Training report On Power Line Carrier Communication (PLCC) Taken at PLCC SECTION 132KV G.S.S. CHAMBAL POWER HOUSE,JAIPUR Submitted in Partial fulfillment of Bachelor’s Degree in Technology. Rajasthan Technical University, Kota. Session: 2014-15 Submitted to: Submitted By: Ms. Garima Mathur RAHUL KUMAR Head, Deptt. Of ECE 11EJEEC072 Department of Electronics & Communication Engineering Jaipur Engineering College, Kukas, Jaipur-303101
  2. 2. PREFACE The objective or main motive of this practical training is to getting a true practical knowledge about the industries, that how their industrial setups are held, and their communication techniques used in industry technologies to be made or used in the environment. This report is presented on the basis of practical training acquired at PLCC SECTION of 132 KV, CHAMBAL G.S.S. (GRID SUB-STATION). This report is on PLCC with relevant diagrams & by their proper description & explanation. In spite of all my best efforts some unintentional errors might have eluded, it is requested to abrogated them.
  3. 3. Acknowledgement It is my privilege to express my deep sense of gratitude towards all those who helped me to take this training. I would like to express my sincere thanks to Dr. Sanjay.A. Pujari (Director Academics) and Ms. Garima Mathur (Head Deptt. of ECE). For giving us permission to take this training. Last but not the least, I would like to thank all the other Pradeep Jangid whose timely help and support was needed for the successful completion of the training. RAHUL KUMAR 11EJEEC072
  4. 4. CONTENTS Chapter no Particulars Page no. 1. Introduction of PLCC 1 1.1 Communication System in PLCC 2 2. Equipment 4 2.1 Outdoor Equipment 4 2.1.1 Line Trap 4 2.1.2 Capacitor Voltage Transformer (CVT) 4 2.1.3 Line Matching Unit (LMU) 4 2.1.4 Balancing Transformer (BT) 5 2.1.5 HF Cable 5 2.2 Indoor Equipment 5 2.2.1 EPAX 5 2.2.2 Carrier Terminal 5 2.2.3 Battery Charger 6 2.2.4 Lighting Arrestor 6 2.2.5 PLCC Cabinet 7 3. Coupling Equipment 8 4. Modes of Coupling to Power Line 9 4.1 Phase to Ground Coupling 9 4.2 Two-Phase coupling 9 4.3 Phase to Phase Coupling 9 4.4 Inter Phase Coupling 9 5. Essential Units of a Power Line 10 5.1 Coupling Capacitor 10 5.2 Wave trap 10 5.2.1 Features of Wave Trap 13 5.2.2 Construction 13 5.3 Line Matching Unit (LMU) 14 5.3.1 Lighting Arrester 14 5.3.2 Tuning Capacitor 15 5.3.3 Drainage Coil 15 5.3.4 Earth Switch 15 5.4 Battery Charger 15
  5. 5. 5.4.1 General Description 15 5.5 Float Charger 16 5.5.1 Circuit Description 16 5.5.2 Control Circuit 17 5.5.3 Alarm Circuit Associated with Float Charger 18 5.6 Boost Charger Section 18 5.6.1 Circuit Description 18 5.6.2 Alarm Associated to the Boost Charger 18 5.6.3 Operation of Charger 18 6. Maintenance and Fault Tracing Procedure 20 7. EPAX 21 7.1 Power Supply Card 21 7.2 Central Processing Card 21 7.3 Digital Switch Card (DSWIC Card) 21 7.4 Line Interface Circuit (LIC) 22 7.4.1 Active DC Feed Circuit 22 7.4.2 Hook-State Sensor 22 7.4.3 Ringing 23 7.4.4 Regulator 23 7.4.5 Speech 23 7.4.6 Communication and Time Slot Generation 23 7.5 E & M Trunk and Interface Card (EMTIC) 23 7.6 Digital Optional Card (DOPT) 24 7.6.1 Party Conference Circuit 24 7.6.2 4DTMF Transmitters 24 7.6.3 3DTMF Receivers 24 7.6.4 Paging Amplifier circuit 24 8. ETI PANEL CARRIER SET POWER SUPPLY 25 8.1 TRANSMITTER 25 8.2 RECEIVER 25 8.3 AF – MULTIPLEXER 25 8.4 ETI 21 ADDITIONAL PARTS 26 9. Equipment Description 27 9.1 General Description of ETI Equipment 27 9.1.1 The Low Frequency Multiplex Section 27 9.1.2 Carrier Frequency Section 27
  6. 6. 10. TELEPHONE, TELEOPERATION AND 29 ALARM FACILITIES 10.1 Modes of Operation 29 10.2 Telephone Facilities 29 10.3 Compressor and Expander (Compander) 29 10.3.1 4-W ire Hand/Emergency Call 30 10.3.2 Service Telephone 30 11. Advantage and Disadvantage 31 11.1 Advantages 31 11.2 Disadvantages 31 CONCLCSION 32 APPENDIX 33 REFERENCE 34
  7. 7. 1 | P a g e Chapter-1 Introduction of PLCC As electronics play a vital role 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 large interconnected system where a control load dispatch station has to coordinate the working of various unit to see that the system is maintained in the optimum working condition. Power line carrier communication has been found to be the most economical & reliable method of communication for the medium and long distance in the power network. For short distance the ordinary telephone phone system is used. Open wire or underground cable and in some cases VHF wireless communication is found to be more economical as they do not involve the use of costly high voltage coupling equipment. In PLCC the higher mechanical strength and insulation level of high voltage power line result in increased reliability of communication & lower attenuation over long distance. PLCC is used for establishing speech/ data communication between two stations using a power line. PLCC is an approach to utilize the existing power lines for the transmission of information. In today’s world every house and building has properly installed electricity lines. By using the existing AC power lines as a medium to transfer the information, it becomes easy to connect the houses with a high speed network access point without installing new wirings. This technology has been in wide use since 1950 and was mainly used by the grid stations to transmit information at high speed. Now days this technology is finding wide use in building as it avoids the need of extra wiring. The data collected from different sensors is transmitted on these power lines thereby also reducing the maintenance cost of the additional wiring. In some countries this technology is also used to provide Internet connection.
  8. 8. 2 | P a g e Fig 1.1: Power Line Carrier Communication 1.1 Communication System in PLCC Power generation and transmission need a good &healthy communication system for proper functioning of the power system and to give uninterrupted supply to the consumers. Power line carrier communication (PLCC) is mainly used for telecommunication, tele-protection and tele-monitoring between electrical substations through power lines at high voltages, such as 110 kV, 220 kV, 400 kV. In a PLCC system the communication is established through the power line. PLCC integrates the transmission of communication
  9. 9. signal and 50/60 Hz power signal through the same electric power cable. The audio frequency is carried by a carrier frequency and the range of carrier frequency is from 50 kHz to 500 kHz. The voice signal is converted /compressed into the 300 Hz to 4000 Hz range, and this audio frequency is mixed with the carrier frequency. The modulation generally used in these systems is amplitude modulation. The carrier frequency range is allocated to include the audio signal, protection and the pilot frequency. The pilot frequency is a signal in the audio range that is transmitted continuously for failure detection. The carrier frequency is again filtered, amplified and transmitted. The transmission of these HF carrier frequencies will be in the range of 0 to +32db. This range is set according to the distance between substations. Different types of power line communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. PLCC can be used for interconnecting PBXs. The electricity board in India has an internal network PLCC between PBXs. 3 | P a g e Fig 1.2: Power Lines
  10. 10. 4 | P a g e Chapter -2 Equipment 2.1 Outdoor Equipment 2.1.1 Line Trap It is also called "Wave trap". It is connected in series with the power (transmission) line. It blocks the high frequency carrier waves (24 KHz to 500 KHz) and let power waves (50Hz - 60Hz) to pass through. It is basically an inductor of rating in millinery. Fig 2.1: Line Trap Fig 2.2: Circuit diagram of Line Trap 2.1.2 Capacitor Voltage Transformer (CVT) It allows to pass the frequency to line. It provides low impedance path for carrier energy to HV line and blocks the power frequency. Circuit by being a high impedance path easily. 2.1.3 Line Matching Unit (LMU) LMU is a composite unit consisting of Drain Coil, Isolation transformer with Lightning Arrester on its both the sides, a Tuning Device and an earth switch. Tuning Device is the combination of R-L-C circuits which act as filter circuit. LMU is also known as Coupling Device. Together with coupling capacitor, LMU serves the purpose of connecting effectively the Audio/Radio frequency signals to either transmission line or PLC terminal and protection of the PLCC unit from the over voltages caused due to transients on power system. It is also used for matching the impedance of the power line and HF cable.
  11. 11. 2.1.4 Balancing Transformer (BT) It is used when phase to phase communication system is used for balancing the two LMU. 5 | P a g e Fig: 2.3 Balancing Transformer (BT) 2.1.5 HF Cable It is used to carry the signal from PLCC cabinet to switch yard. 2.2 Indoor Equipment The equipments installed in the control room are called indoor equipments. 2.2.1 EPAX Fig 2.4: EPAX Consist of PLCC carrier equipment and related electromechanically switching equipments like EPAX to provide voice communication. 2.2.2 Carrier Terminal The 9505 PLC terminals are intended for transmission of speech, telemetering, teleidication
  12. 12. and teleprotection in the signal carrier frequency. 2.2.3 Battery Charger It is used for 48 volts DC supply. 2.2.4 Lighting Arrestor The lighting arrestor against high voltage surges caused by atmospheric effects or switching operations protects the wave traps .The nominal discharge current of this lighting arrester is selected to suit that of the substation lighting arrester behind the wave trap. The tuning elements however have been rated at 20to30%. The lighting arrester used may be vacuum type arrester whose are over voltage lies below the rated voltage of the tuning capacitor, but about the voltage produced across the coil during a short circuit current surge. Therefore it protects the tuning capacitors against momentary over voltages caused by traveling waves. Sustained over voltages resulting from short circuit currents are not high enough to cause the lighting arrester to be over. Hence, sustained and consequent destruction of the arrester are avoided. High voltages high stability mica capacitors with low losses are used .For low voltages class of tuning units (up to 40kv) polystyrene capacitor are used .For high voltage class of tuning units (up to 150kv) .Capacitors with mineral oil impregnated paper dielectric are used which are similar in construction to the coupling capacitor . All types are molded in epoxy resin .Single frequency traps have double tuned parallel resonant circuit. All elements belonging to the tuning circuit are usually mounted in a common housing which can be resolved and substituted with another similar tuning device to resonate the trap to a different frequency. The drainage coil has a pondered iron core serves to ground the power frequency charging to appear in the output of the unit .The coarse voltage arrester consist of air gap, which spark over at about 2kv and protect the matching unit against line surges . 6 | P a g e Fig 2.5: Lighting Arrestor 2.2.5 PLCC Cabinet
  13. 13. It is installed in control room. It has two sections:  Transmitter: In this, voice frequency (VF) is amplified and then modulated to intermediate frequency (IF) and amplified, modulated into HF and then transmitted.  Receiver: In this section HF signal is received and then demodulated from HF to IF and connected to the tale phone. 7 | P a g e
  14. 14. 8 | P a g e Chapter -3 Coupling Equipment The most important technical problem in a power line carrier is to devise methods and equipment to couple the low voltage and high frequency carrier set to the high voltage and low frequency power line. During the annual stages of carrier operation on power lines, and aerial wire of more than 300 feet length, supported on power line structure, was used. On one end of it was connected the output from carrier equipment. While the aerial coupled the signals to power lines mainly due to the capacitance between them. The modern practice is to achieve the coupling by connecting a capacitor between the carrier terminal and high voltage line. The particular value of the capacitor is a compromise between two conflicting requirements.
  15. 15. 9 | P a g e Chapter - 4 Modes of Coupling to Power Line Power transmission lines have usually three conductors, one for each phases running between points to point. This presents many different configurations for coupling to carrier equipment. 4.1 Phase to Ground Coupling Carrier terminals are connected between one phase conductor and ground. The wage traps and coupling capacitors are all connected to one conductor of the power line. The remaining two conductor do not have wave traps a portion of carrier energy is lost and also radiated losses are high as the connection at the receiving end cannot be made to match the line perfectly. 4.2 Two-Phase coupling It provides reliability of operation in case a coupled conductor. It needs twice the coupling equipment and wave trap. For this reason this mentioned is not used in practice. 4.3 Phase to Phase Coupling It provides metallic go and return paths to the carrier currents. In this case the uncoupled conductor does not have any appreciable influence on the transmission. 4.4 Inter Phase Coupling When two power transmission lines run on the same poles, one terminal of the carrier set is coupled to one phase conductor of one of the lines, and the other to the similar phase conductor of the other line. 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 is sparsely populated areas.
  16. 16. 10 | P a g e Chapter-5 Essential Units of a Power Line 5.1 Coupling Capacitor The important role of coupling capacitor in carrier operation over power lines has already been mentioned. Their special features are that they are rated to withstand the high voltages and are insulated to same degree as the line or the other high voltage equipment. Now they are made up of oilpaper and due to their large size are preferably installed outdoors. Necessary devices for protection against high voltages like spark gap; drain coil and grounding switch are contained in a box at the base of the coupling capacitor. 5.2 Wave trap Wave traps or line traps are used between the transmission line and power station to avoid carrier power dislocation in the power plant and cross talk with other power line carrier circuits connected to the same power station. They offer high impedance to carrier frequencies but pass 50 cycles power currents easily. They can be resonated at a single carrier frequency with a parallel capacitor. The tuning capacitors are protected against the surge voltages by a spark gap arranged in parallel.
  17. 17. 11 | P a g e Fig 5.1: Wave Trap
  18. 18. 12 | P a g e Fig 5.2: Wave Trap (Line trap)
  19. 19. 5.2.1 Features of Wave Trap  Epoxy resins compatible with the glass fiber under thermal hock condition.  Aluminum constructions throughout with current carrying connections yielded.  No maintenance required.  It can withstand extreme temperature fluctuations and weather condition. Finish given by sand blasting and treating with specially modified epoxy resin paints. Tuning element design using sophisticated programs run on advanced computers and the components carefully selected to give the optimum performance under all condition of service. Atmospheric pollution and climatic changes do not affect the performance. No creep age path dues to the encapsulation of mains coil. Some conductors are used to minimize loss due to eddy currents. The terminal supporting spider reinforced to withstand the short circuit forces during fault conditions .Insulation material used much higher than class f requirements of temperature. Corona ring provided to maintain the RIV voltage levels low and within specified limits. 5.2.2 CONSTRUCTION  Main coil The main coil windings are encapsulated by roving continuous filament fiber glass that has been impregnated with a specially selected epoxy resin hardener system. The epoxy resin fiberglass composite is then cured according to a programmed temperature schedule. This process results in high mechanical strength and heat distortion temperature above 160degree Celsius. The inherent bonding properties of the fiberglass resin composite system convert coil into compact solid package. The mechanical strength required to withstand specified short circuit current is achieved by winding sufficient filament fiberglass around the conductor. The two ends of the coils are reinforced with additional fiberglass roving to take up the severe stresses on the end turns of the coil caused by high voltage surges or external short circuit. The main coil windings are terminated at each end on aluminum flat called spider arm. The spider arm bearing the termination is further reinforced to carry the high short time current.  Tuning Pack 13 | P a g e
  20. 20. The tuning pack is connected in parallel with the main coil to provide high impedance to the desired carrier frequency .The type of tuning pack used will depend on whether a single frequency, two frequencies and band of frequencies is to be blocked. Wideband tuning is most suitable for multichannel application as relatively constant impedance is obtained over broad frequency band .The tuning pack is designed to have a minimum specified resistive component over the entire blocking range so that these wave trap will not be detuned by the widely variable value of the station reactance’s. Tuning packs can be supplied with fixed bandwidths to suit customer requirements. The minimum blocking impedance in the range 400ohms to 1000ohms can be given as required. Tuning pack is constructed using high quality and closed tolerance capacitors, carefully designed non-securable inductors and non inductive high watt resistors .The components are individually tested and assembled inside a fiberglass tube .This is then completely filled with a special grade resin mixture and sealed. This encapsulation protects them from the environment and mechanical shocks ensuring stability over long period of service.  Lighting Arrestor The lighting arrestor against high voltage surges caused by atmospheric effects or switching operations protects the wave traps .The nominal discharge current of this lighting arrester is selected to suit that of the substation lighting arrester behind the wave trap. The tuning elements however have been rated at 20to30% more than the maximum residual voltage of the lighting arrestor at the maximum discharge currents. 5.3 Line Matching Unit (LMU) LMU is also called the coupling filter. It consists of the matching transformer and tuning capacitor to suit the individual requirement of the coupling equipment and is generally tuned too wide band of carrier frequencies (100-450 kHz typical). 5.3.1 Lighting Arrester In addition to tuning devices which usually consists of a capacitor. It is invariable connected across the choke coil of wave trap. The lighting arrester used may be vacuum type arrester whose are over voltage lies below the rated voltage of the tuning capacitor, but about the voltage produced across the coil during a 14 | P a g e
  21. 21. short circuit current surge. Therefore it protects the tuning capacitors against momentary over voltages caused by traveling waves. Sustained over voltages resulting from short circuit currents are not high enough to cause the lighting arrester to be over. Hence, sustained and consequent destruction of the arrester are avoided. 5.3.2 Tuning Capacitor High voltages high stability mica capacitors with low losses are used .For low voltages class of tuning units (up to 40kv) polystyrene capacitor are used .For high voltage class of tuning units (up to 150kv) .Capacitors with mineral oil impregnated paper dielectric are used which are similar in construction to the coupling capacitor . All types are molded in epoxy resin .Single frequency traps have double tuned parallel resonant circuit. All elements belonging to the tuning circuit are usually mounted in a common housing which can be resolved and substituted with another similar tuning device to resonate the trap to a different frequency. 5.3.3 Drainage Coil The drainage coil has a pondered iron core serves to ground the power frequency charging to appear in the output of the unit .The coarse voltage arrester consist of air gap, which spark over at about 2kv and protect the matching unit against line surges . 5.3.4 Earth Switch As the coupling device is inserted between the low voltages terminal of the coupling capacitor and earth, the earth switch is provided to ensure a temporary direct earthing of the coupling capacitor during maintenance or commissioning. 15 | P a g e Fig 5.3 Earth Switch 5.4 Battery Charger 5.4.1. General Description
  22. 22. The battery charging system is intended to:  Keep the 50v-200AH, 350AH & 600AH Battery on trickle or boost charge as required.  Supply DC power to the Sub-Station. The Battery charge mainly consists of 4 sections which are:-  Float charge section.  Boost charge section.  Control section.  Alarm circuit. All the four section are housed in a floor mounted sheet steel enclosures with a rigid angle framework for mounting of components. The sides and top of the frame are provided with removable panels. The rear portion consists of 2 nos. of hinged panels. A suitable recess has been provided in the front panel to prevent the components from projecting out. All meter, indicating lamp, push buttons have been mounted on the front panel. The completed panel rests on two 75-mm channels on two sides. The float charge essentially consists of a three phase transformer rectifier set for automatic regulation of DC output. The float charge is means to supply regulated DC voltage to the load and keep the battery on trickle charge. The boost charge section is initial or refresher charging of the 50 V-200AH, 350 AH & 600 AH battery as per manufacturer’s specifications. This section essentially consists of a manually controlled (by rotary switches) three phase transformer rectifier set. In case of float charge failure the boost charge can be put in emergency use to supply DC voltage to the load by reducing the boost charging voltage and using voltage dropping diodes. 5.5 Float Charger 5.5.1 Circuit Description The float charger is basically static type 3phase charge with stabilized output DC voltage. Here the Charge’s output DC-Voltage is constantly compared with standard DC reference voltage and error voltage is again amplified. This amplified voltage controls the triggering signal of all the three thyristors of three phase Bridge controlled rectifier. As the output voltage tends to decrease than its selected value, it makes the triggering signals of each thyristors of the all three phase to advance for firing them, so that the output voltage remains within the specified accuracy. If the output voltage tends to increase more than the selected value, then triggering pulses of these thyristors of all the three phase are delayed in firing 16 | P a g e
  23. 23. operation in such a way, so that Dc Output voltage is again brought back to its stabilized voltage. Through current limiter of the DC voltage signal are compared in the over current circuit. For load current more than 110% it sends the signal to trigger controller in such a way so that switching signal are delayed in operation, which makes the fall of output voltage sharply. 5.5.2 Control Circuit The output of the charger is controller through the electronic controller. Using phage control of the SCR and feedback controls the output. The control circuit consists of following function circuits.  Power Supply This card provides regulated power of+12V stabilized output and 24 V unregulated DC output.  UJT Card These are 3phase identical firing cards each for triggering one SCR in the main bridge. Refer circuit diagram Sheet 2zener diode DZ1 to DZ6 and resistor R15,R16 and R17 connected to the secondary of TX2, TX3 and TX4 clamp the positive half of the input sine wave to the zener voltage giving a trapezoidal waveform. RV1 and RV2 are adjusted the conduction angle of the SCR’s resulting in low ripple. Initialize RV2 is set such that without amplifier card at +10% input and output adjusted to 5 Volts, all SCR’s have the same conduction angle RV2 again adjusted in full load to keep conduction angle of the SCR’s equal. C1 being charging at the start of the cycle, through current supplies by R2, RV2 TR1.When voltage across C1 reaches the threshold value (intrinsic standoff ratio times VBB) UJT fires & C1 discharge through the pulse transform. Output voltage control is obtained by varying the current of C1 by varying the base-emitter 17 | P a g e bias of TR1.An increasedecrease in charging current leads to a decreaseincrease in firing angle and a corresponding increasedecrease in the output voltage. Zener DZ1 limits the gate volts of the main SCR to the Zener Voltage.  Amplifie r Card This card consists of 2 operational amplifiers IC1 & IC2 reference zener diode DZ1,
  24. 24. emitter follower TR1 and buffer amplifier TR3 & TR4 is the error detector amplifier.  DC Under Voltage & Over Voltage Sensing Card This circuit senses the charge output voltage in normal condition and gives audiovisual indication in case of deviation of the charge’s output from the set limits. 5.5.3 Alarm Circuit Associated with Float Charger An alarm circuit is also associated with the float charger which works on 50 V from the 50V DC Output Battery terminals. 5.6 Boost Charger Section 5.6.1 Circuit Description Boost charge is used to charge the battery after power resumption i.e. charging process. The input supply is switched ON means of Rotary switch RS1, three Nos. HRC Fuses F21 to F23have been provided for over current protection. Ac Contactor CON-2 have also been provided.TX6 steps down the input AC voltage to suitable level. Necessary taps are provided in the primary of the transformer to cater for varying input that may prevail at the sub-station. The necessary voltage of TX6 is applied to a bridge rectifier, which consists of six silicon diodes D6 to D11 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 diode are protected by capacitors and resistances against whole storage effects and transient over voltage and also by HRC fuse. 5.6.2 Alarm Associated to the Boost Charger The Boost charge has audio visual alarms similar to float charger used for indication of faults. 5.6.3 Operation of Charger The float boost charger can be switches ‘ON’ means of selector switch RS1 thus at a time only one charge 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 by passed through the contacts of DC contactor. This enable complete voltage appearing on the load. In case of mains fail also the entire battery voltage is available on load though 18 | P a g e
  25. 25. contacts of DC contacts. When the charger is operated on boost mode the contacts of DC contactor is open. Load voltage can be adjusted by VDD switch RS8 as per the requirement main switch RS9 have been provided to isolate the charger from load & battery. When the selector switch RS9 have is in charger mode then it will supplying load as well as trickle charge the battery in float mode & boost charge the batteries mode when the switch RS9 is in Maint Mode then load will be supplies by the battery. 19 | P a g e
  26. 26. 20 | P a g e Chapter -6 Maintenance and Fault Tracing Procedure This section helps the operator to maintain the equipment and attend top common faults, which may occurs in practice the following points must be borne by the operator.  All connection should be thoroughly checked. The control circuit boards should be inserted firmly in their respective sockets before energizing the battery charger  All mounting Boltsscrews should be checked before energizing as loose mounting cause vibrations.  The charger should be switching off once in every month and the connections and mountings should be checked.  The battery terminal should be connected first and the AC input after that.  The instruction manual and the drawings should be referred initially to avoid any wrong operation.
  27. 27. 21 | P a g e Chapter -7 EPAX As on today PLCC carrier equipment and related digital switching in which we use microprocessor, provides non- blocking switching on line diagnostic, integrated voice and data communication, redundancy. The system employs stored program control (SPC) using pulse code modulation (PCM) and time division multiplexing (TDM) confirming to latest CCITT standards. The system has networking capability as well. An 8*24 Line MELTEL EPAX consist of 14 slot cabinet system that consists of following cards:- 7.1 Power Supply Card It gives input signal of -48 and output of +5volt,-12volt ,+12volt & Ring 75VRMS. The input -48 volt also serves as feed voltage to the extensions. It makes use of air cooling using a fan operating on -12 volt DC. 7.2 Central Processing Card It carries out all the control function in EPAX. These functions include the following:  Call processing  Line supervision  Digit out pulsing over trunk link etc….. A DISPLAY circuit is provided on the CPU board. This circuit contains two seven segment LED displays and two switches. Display indicated the error code of the fault occurred in the system. This will also indicate the type of fault occurred in the system on the pressing the ‘ACV’ (advance) switches. The second switch, ‘ALM CLR’, is used for the stopping the alarm from the ‘BUZZER’ mounted on the CPU board, which gives audible alarm on any fault occurrence in the system. 7.3 Digital Switch Card (DSWIC Card)
  28. 28. This card consists of a PCM switch which does the VOICE SWITCHING. In this module the following circuits are present.  Tone generator.  Music-on-hold circuit.  Two DTMF receiver circuits.  PCM clock generating circuit. A basic tone oscillator generates a 440 Hz single tone, which is fed to a CODEC. Dual tone also can be generated. The codec injects the digitized tone samples into the PCM stream at time slot 1 of highway zero. PCM clock, 2.048 MHz, and frame sync signal are generated and distributed to other module through a buffer. When a P&T subscriber is kept waiting instead of HOLD TONE, pleasant music can be sent with this music circuit. The music is generated internally. There is also an option for connecting external music of customer’s choice. To identify the digits dialled from telephones DTMF receivers are used. There are 2 DTMF present in the card. 7.4 Line Interface Circuit (LIC) The LIC is the analogue LINE INTERFACE CIRCUIT module. It provides interface for 4 analogue extension lines. The following are the functions of LIC. Feeding DC voltages to the telephone instrument.  Detection of telephone hook-status and dialing.  Connection / disconnection of ringing to the telephone.  Transmitting, receiving and processing of speech signals.  Generation of time slots for the equipments. 7.4.1 Active DC Feed Circuit This circuit feed -48V DC to the telephone while blocking the speech signals from passing through the DC feed circuit itself, to avoid any loss of speech signals. 7.4.2 Hook-State Sensor It becomes active whenever an extension handset is lifted. The digits dialled from the 22 | P a g e
  29. 29. telephones are identified through this HOOK-STATE SENSOR only. 7.4.3 Ringing Ring is given to the telephone connected to the system by command from the CPU module. These ringing signals are generated in the power supply unit. Ringing is disconnected either by a command from CPU card or when the telephone handset is lifted off the hook. 7.4.4 Regulator The power supply is regulated before supplying to the speech IC’s since regulated supply is generated in each LIC; it helps to reduce the power supply noise in speech signals. 7.4.5 Speech The speech signal coming from the telephone instruments is sampled, filtered PCM coded and sent to the DSWIC module. This sample will be switched to another extension which is listening .On the listening side, the PCM word is converted into an analogue sample amplified and sent to the telephone instrument. The CODEC (Coder Decoder IC) does most of the above function. To reduce power consumption, the CODEC is enabled only when the hook state signal is active. The hybrid transformer does the ‘2 wire to 4 wire conversion’ of speech and vice versa. 7.4.6 Communication and Time Slot Generation The transmission of information like Hook state and Ring control data between LIC and CPU is done by buffers which are enabled only when necessary. Transmission of digitized voice signals is done only when any subscriber connected to that card goes off hook. A TIME SLOT GENERATOR is used to generate the time slot signal for each line. The CPU card identifies the presence if a LIC module in the exchange by reading the card presence information from LIC. 7.5 E & M Trunk and Interface Card (EMTIC) When a subscriber of one exchange wants to call a subscriber of another exchange in the 23 | P a g e
  30. 30. network, the module sends the seizing signal and followed by the digits to the far exchange. When the required subscriber of the far exchange picks up the handset the module connects the speech path between both the subscribers. Alternatively, when the module receives the seizing signal & the digits from the far exchange, it sends RING to the local subscriber and connects the speech path when the subscriber lifts the handset. The module also provides the TIE LINE STATUS/FAULT indications. Apart from these functions, EMTIC does the Generation of necessary time slots and processing of speech signals. 7.6 Digital Optional Card (DOPT) The DOPT is optional module, which contains the Following circuit. 7.6.1 Party Conference Circuit A maximum of local subscribers can have a conferencing the conference circuit. The speech signals of all 4 subscribers are sent to this module from DSWIC module. Care is taken not to send his/her own speech to subscribers. So, a subscriber. listens to the voices of all other subscribers and not his/her own voice. 7.6.2 4 DTMF Transmitters It is used for transmitting the signal. 7.6.3 3 DTMF Receivers It is used for receiving the signal. 7.6.4 Paging Amplifier circuit Paging announcement can be done using this circuit the preamplifier output is available for the customer to connect power amplifier and loud speakers. Other circuits like Regulator, Speech, Communication and Time slot generation circuits are similar to the LIC. A potential free contact of the alarm relay is provided to which an external alarm circuit cab be connected. This will be activated when a faith of serious nature occurs. 24 | P a g e
  31. 31. 25 | P a g e Chapter- 8 E T I PANEL CARRIER SET POWER SUPPLY Power supply unit 48/60 V DC B5EC Regulator B3EA 24 V Stabilizer & B3EB 8.1 TRANSMITTER Transmit IF modulator P3EA Transmit IF Filter E3EA Transmit RF Modulator P3EB Transmit Prefilter E3EB Power Amplifier 25 W P5EA Power Amplifier 50 W N5EA Transmit Filter E5EA RF Hybrid 100 W P3EO 8.2 RECEIVER Receive RF Filter E3EC Receive RF modulator P3EC Receive Filter E3ED IF & AGC Amplifier P3EDa Receive IF Demodulator P3EFa Receive IF Demodulator P3EFb Signal output O3EHa Signal output O3ES Supervision I O3EIa 8.3 AF - MULTIPLEXER Signal Input O3EAa Signal Adapter O3EC Pilot /Dial Module O3ED
  32. 32. Pilot/Dial Module O3EDa Pilot/Dial Module O3PEQ Telephone Adapter O3EEa Voice Amplifier O3EGa Voice Amplifier O3EGb Voice Filter 2000 Hz E3EF Voice Filter 2400 Hz E3EH Voice Filter 3400 Hz E3EL Compander O3EB 8.4 ETI 21 ADDITIONAL PARTS Dummy Load 20 W P3EG Test Meter N3FL 26 | P a g e
  33. 33. 27 | P a g e Chapter- 9 Equipment Description 9.1 General Description of ETI Equipment The multipurpose equipment type ETI21 and ETI22 transmits simultaneously Speech and multiplexed Teleoperation signals in SSB technique over high voltage lines or cables. The transmitted intelligence is suitable for Telephony Teleoperation; for example  Telemetry  Remote control  Remote analog metering  Teleprinter Teleprotection signaling, for example  High voltage power equipment  High voltage power lines While the telephone and teleoperation facilities are typically used for economic control and supervision of energy networks, the teleprotection channels are kept continuously on hot standby and are used only in rare cases of power fault. The equipment is built from three main parts:- 9.1.1 The Low Frequency Multiplex Section With speech and upto five teleoperation channels, together with an optional speech compander. 9.1.2 Carrier Frequency Section Designed for a single channel duplex (ETI21) or double channel duplex (ETI22) working in a 4 kHz or 2.5 kHz raster. The carrier frequency ranges from 24 kHz to 500 kHz and with a transmitted power of 20 watts or as a variant, 100 watts (ETI101 and 1020.  Power Supply Unit This can be operated from 110/220 volts, 50/60 Hz or a separate battery/charger unit of 24 volts, 48 volts or 60 volts. The technique of single side band modulation with double conversion provides frequency equalization, automatic gain control and
  34. 34. frequency synchronization and ensures perfect reproduction of the transmitted intelligence. 28 | P a g e
  35. 35. 29 | P a g e Chapter-10 TELEPHONE, TELEOPERATION AND ALARM FACILITIES 10.1 Modes of Operation The PLCC equipment is suitable for connecting to a telephone exchange and furthermore, a 4- wire remote/ emergency call stations can be created by operating it in parallel with the built-in service telephone equipment. The transmission facilities for teleoperation working use separate input and separate output circuits according to their classification. When 4 KHz equipment carries simultaneous speech and teleoperation 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 teleoperation signals. 10.2 Telephone Facilities The associated automatic telephone exchange (PAX) is suitable for a network with a limited no. of subscribers. Between PAX and the PLCC channel, control circuits give out signals for the setting- up, dialling and later releasing a telephone connection and the switching criteria between PAX and PLC. The PAX sending contact will, via the PLCC signalling channel, close an output contact in the PLCC receiver at the distant end of the link. The dialing impulses are transmitted over the combined pilot and signaling channel which has a maximum transmitting speed 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 type 10.3 Compressor and Expander (Compander) The inclusion of the compander improves the carrier signal quality of the speech and is normally reserved for use over lines with high noise. The improvement over Signal to Noise Ratio (SNR) is approximately 12dB. When the speech is carried over several PLCC links in series, it is recommended that only one compander is used, the compressor being installed at the sending end of the line and the expander in the farthest receiving station.
  36. 36. 10.3.1 4-Wire Hand/Emergency Call The equipments, especially in the extension phases can, without additional units in the HF equipment, are equipped throughout with hand/emergency call telephone. These telephones with the DC Bell can connected directly via a 6-wire extension cable. The calling of the opposite station is accomplished by 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 set. By lifting the handset in 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. 10.3.2 Service Telephone With the help of the built-in speech facilities, service calls can be carried out in 4-wire from the front panel. 30 | P a g e
  37. 37. 31 | P a g e Chapter -11 Advantage and Disadvantage 11.1 Advantages  No separated wires are needed for communication purposes, as the power lines themselves carry power as well as communication signal. Hence the cost of constructing separate telephone lines is saved.  When compared with ordinary lines the power lines have appreciabry higher mechanical strength. They would normally remain unaffected under the condition which might seriously damage telephone lines.  Power lines usually provided the shortest route between the power stations.  Power line has large cross-section area resulting in very low resistance per unit length. Consequently the carrier signals suffer much less attenuation then when does they travel on usual telephone lines of equal lengths.  Power lines are well insulated to provide only negligible leakage between conductors and ground even in adverse weather conditions. 11.2 Disadvantages  Proper care has to be taken to guard carrier equipment and persons using them against high voltages and currents on the lines.  Reflection is used on spur lines connected to high voltage lines. This increases attenuation and creates other problems.  High voltage lines have transformer connections which attenuates carrier currents.  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 process.  It is obvious that an effective power line carrier system must overcome these and many other difficulties. So we should use this system very carefully. So precautions must be taken before using the system.
  38. 38. 32 | P a g e CONCLUSION I have gained a wonderful experience and practical knowledge in this training period. Although the time period provided was very short for allotted task. Yet I wanted to do many things in detail. After doing this training I got sufficient confidence for doing such type works for industrial applications. I also learnt the importance of PLCC in power system, without PLCC a large power system cannot be assumed. For communication purpose between the power systems, PLCC plays a vital role. For better reliability between interconnected systems PLCC is must. I am also thankful to those who had been helpful during my training period.
  39. 39. 33 | P a g e Appendix Float charger (a)Technical specification Normal Input : 415 V AC 3 Phase. Input Variation : +10% of Normal Voltage. (b) Float section DC Output : 50 V +1% Output Current : 202540Amps. Line regulation : Better than +1% Load regulation : Better than +1% Ripple : 0.6Vpp. Efficiency : More than 75% (c) Boost section DC Output : 43.2 to 67.2 V DC Output Current : 254070Amps. Over Load : 10% Efficiency : More than 75%
  40. 40. 34 | P a g e REFERENCES 1. www.google.com 2. www.slideshare.net 3. www.seminarprojects.com

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