Power Line Carrier Communication Plcc 72k40

POWER LINE CARRIER COMMUNICATION (PLCC) Introduction Use of PLCC in modern electrical power system is mainly for telemetry and telecontrol. Tele means remote. Telemetry refers to science of measurement from remote location. Different types of data transmission system can be used depending upon the network requirement and conditions. Main data transmission system for telemetry and telecontrol are: 1. Use of telephone lines 2. Use of separate cables 3. Power Line carrier communication 4. Radio wave micro wave channel

Fig: PLCC Block Diagram Application:  For large power system power line carrier communication is used for data transmission as well as protection of transmission lines. Carrier current has a frequency range of 30 to 200 kHz in USA and 80 to 500 kHz in UK.  Each end of transmission line is provided with identical PLCC equipment. PLCC equipment consisting of equipment: 1. Transmitters and Receivers 4. Line Traps 2. Hybrids and Filters 5. Power amplifier 3. Line Tuners 6. Coupling capacitors PLCC Scheme: Distance protection relay in relay at one end of the transmission line gets the input from CT (CapacitiveTransformer) and CVT (Capacitive Voltage Transformer) in line. The output of relay goes to modem of PLCC.

Fig: PLCC scheme Prepared By: Parthiban. S., Assistant Professor, VRS College of Engineering and Technology, Arasur.

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The output of PLCC goes to coupling capacitor and then to transmission line and travels to another end where it is received through coupling capacitor and inputted to relay and control at that end. Major goal/Application of PLCC PLCC in modern electrical power system substation is mainly used for following purpose: 1. Carrier protection relaying of transmission line so that: o Inter trip command can be issued by relay due to tripping of circuit breaker at any one end. o To trip the line circuit breaker nearest to the fault, this is done by: a) Distance protection relay (V/I characteristics) b) Differential comparison method c) Phase comparison method 2. Station to station communication between operating personnel 3. Carrier telemetring, electrical quantities that are telemetered are kW, kVA, kVAR, Voltage and Power factor etc. Following methods are used for telemetring as well as telecontrol: o Simplex o Duplex o Multiplex o Time division Multiplex Many factors will affect the reliability of a power line carrier (PLC) channel. If both of these requirements are met then the PLC channel will be reliable. The factors affecting reliability are: 1. The amount of power out of the transmitter. 2. The type and number of hybrids required to parallel transmitters and receivers. 3. The type of line tuner applied. 4. The size of the coupling capacitor in of capacitance. 5. The type and size, in of inductance, of the line trap used. 6. The power line voltage and the physical configuration of the power line. 7. The phase(s) to which the PLC signal is coupled. 8. The length of the circuit and transpositions in the circuit. 9. The decoupling equipment at the receiving terminal (usually the same as the transmitting end). 10. The type of modulation used to transmit the information, and the type of demodulation circuits in the receiver. 11. The received signal-to-noise ratio (SNR). Main Components of PLCC 1. Coupling Capacitor

Fig: PLCC component - Coupling Capacitor  Coupling capacitor connects the carrier equipment to the transmission line.  The coupling capacitor’s capacitance is of such a value that it offers low impedance to carrier frequency (1/ωC) but high impedance to power frequency (50 Hz).

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2. Line trap Unit  The carrier energy on the transmission line must be directed toward the remote line terminal and not toward the station bus and it must be isolated from bus impedance variations. This task is performed by the line trap.  The line trap is usually a form of a parallel resonant circuit which is tuned to the carrier energy frequency.  A parallel resonant circuit has high impedance at its tuned frequency, and it then causes most of the carrier energy to flow toward the remote line terminal. The coil of the line trap provides a low impedance path for the flow of the power frequency energy.  This unit prevents the high frequency carrier signal from entering the neighboring line. 3. Transmitters and Receivers The carrier transmitters and receivers are usually mounted in a rack or cabinet in the control house, and the line tuner is out in the switchyard. This then means there is a large distance between the equipment and the tuner, and the connection between the two is made using a coaxial cable.

From Line Coupler

Attenuator

Matching Element

Band Filter

Amplifier Detector

Carrier Receiver

Protective Relay Fig: PLCC component - Transmitters and receivers The coaxial cable provides shielding so that noise cannot get into the cable and cause interference. The coaxial cable is connected to the line tuner which must be mounted at the base of the coupling capacitor. If there is more than one transmitter involved per terminal the signal must go through isolation circuits, typically hybrids, before connection to the line tuner. 4. Hybrids and Filters  The purpose of the hybrid circuits is to enable the connection of two or more transmitters together on one coaxial cable without causing intermodulation distortion due to the signal from one transmitter affecting the output stages of the other transmitter.  Hybrids may also be required between transmitters and receivers, depending on the application.  The hybrid circuits can, of course, cause large losses in the carrier path and must be used appropriately. High/low- and band- networks may also be used, in some applications, to isolate carrier equipment from each other. 5. Line Tuners  The purpose of the line tuner in conjunction with the coupling capacitor is to provide low impedance path for the carrier energy to the transmission line and a high impedance path to the power frequency energy. .

 The line tuner/coupling capacitor combination provides a low impedance path to the power line by forming a series resonant circuit tuned to the carrier frequency. 6. Master Oscillator and Amplifiers  High frequency carrier signal is generated in oscillator.  Oscillator can be crystal oscillator with which operation for a particular bandwidth can be achieved. The output voltage of an oscillator is held constant by voltage stabilizer.  The output of oscillator is fed to amplifier so that loses in transmission can be compensated.  Losses occurring in carrier current is termed as attenuation of carrier signal.  They are mainly: Losses in coupling equipment which are constant losses for a given carrier frequency bandwidth.

Fig: PLCC component - Master oscillator and amplifiers  Line losses vary with length line, size of line, weather condition etc…These losses for underground line is more than overhead line.  Frequency spacing is a process using different carrier frequency in two adjacent transmission lines. Wave trap/Line trap help in accomplishing this. 7. Protection and earthing of coupling equipment  Over voltage can be caused due to lightning, switching and sudden loss of load etc.  They produce stress on coupling equipment and line trap units. Non linier resistor in series with protective gap is connected across the line trap unit and inductor of coupling unit.  The gap is adjusted to spark at a set value of over voltage.

Fig: Protection and earthing of coupling equipment Coupling unit and PLCC equipment are earthed through a separate and dedicated system, so that ground potential rise of station earthing system does not affect the reference voltage level/Power supply common ground of the PLCC equipment. In this regard that is earthing of PLCC and other communication/Instrumentation/Electronic equipment please refer to NEC Article 645 for data centers (IT equipment.) Advantages of Digital PLCC over Analog ones 1. Immune to noise in processing and storage stages, as it is completely digital. 2. Digital: Require less no. of circuits (hardware), since Digital Processor is a single chip. 3. Processing is accurate and reliable. .

4. Frequency conversion is done in a single step (Digital Conversion). 5. Digital processing allows the application of a wide range of mathematics. (Analog processing is limited by the availability of devices to perform desired functions, while) 6. Equalization is perfect: High-resolution digital filtering gives very flat filter response as desired. 7. In addition, in digital circuits there is little need for component matching. 8. Simplified Production: Lower Parts count and improved testability.

OPTICAL FIBER SYSTEMS Advantages of using Optical Fiber Systems  Long transmission distance  Large information capacity  Small size and low weight  Immunity to electrical interference  Enhanced safety  Increased signal security Elements of an Optical Link

Fig: Fiber optic communication link From a simplistic point of view, the function of an optical fiber link is to transport a signal from some piece of electronic equipment (e.g., a computer, telephone, or video device) at one location to corresponding equipment at another location with a high degree of reliability and accuracy. Figure 2.5 shows the key sections of an optical fiber communications link, which are as follows: Transmitter:  The transmitter consists of a light source and associated electronic circuitry.  The source can be a light-emitting diode or a laser diode. .

 The electronics are used for setting the source operating point, controlling the light output stability, and varying the optical output in proportion to an electrically formatted information input signal. Optical fiber:  The optical fiber is placed inside a cable that offers mechanical and environmental protection.  A variety of fiber types exist, and there are many different cable configurations depending on whether the cable is to be installed inside a building, in underground pipes, outside on poles, or underwater. Receiver:  Inside the receiver is a photodiode that detects the weakened and distorted optical signal emerging from the end of an optical fiber and converts it to an electric signal.  The receiver also contains amplification devices and circuitry to restore signal fidelity. ive devices:  The ive devices are optical components that require no electronic control for their operation.  Among these are optical connectors for connecting cables, splices for attaching one bare fiber to another, optical isolators that prevent unwanted light from flowing in a backward direction, optical filters that select only a narrow spectrum of desired light, and couplers used to tap off a certain percentage of light, usually for performance monitoring purposes. Optical amplifiers:  After an optical signal has traveled a certain distance along a fiber, it becomes weakened due to power loss along the fiber.  At that point the optical signal needs to get a power boost.  Traditionally the optical signal was converted to an electric signal, amplified electrically, and then converted back to an optical signal.  The invention of an optical amplifier that boosts the power level completely in the optical domain circumvented these transmission bottlenecks. Active components:  Lasers and optical amplifiers fall into the category of active devices, which require an electronic control for their operation.  These include light signal modulators, tunable (wavelength-selectable) optical filters, variable optical attenuators, and optical switches. Chapter 10 gives the details of these devices. BENEFITS OF OPTICAL FIBER COMMUNICATION SYSTEM : Some of the innumerable benefits of optical fiber communication system are:  Immense bandwidth to utilize  Total electrical isolation in the transmission medium  Very low transmission loss,  Immunity to interference and crosstalk,  Small size and light weight,  Very low power consumption and  High signal security, wide scope of system expansion etc. These are the main advantages that have made optical fiber communication system such an indispensable part of modern life. Field of Application: Due to its variety of advantages optical fiber communication system has a wide range of application in different fields namely : a. Public network field which includes trunk networks, junction networks, local access networks, submerged systems, synchronous systems etc. b. Field of military applications , c. Civil, consumer and industrial applications, d. Field of computers which is the center of research right now.

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