Powerpoint Presentation
On
“POWER LINE CARRIER COMMUNICATION”
(PLC)
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| Sample of PPT Download link is below |
Introduction
The electric power generated at the power station located at far off place where the natural source of energy is available. This electric power of energy is conveyed to various substation through transmission line. In fact there is a network of transmission lines. Whenever, breakdown occurs or shutdown is required to taken for some maintenance, quick message are required to send to various substations. To convey this message some communication system is required. The ordinary telephone network cannot serve the purpose because of this busy schedule. Therefore, same transmission or power line are used for career communication. The communication signal is sent at higher frequency.
In this we shall focus attention on principle on Power Line Carrier Communication (PLC) and the various component used for this purpose.
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Purpose of Power Line Communication PLC
The main purpose of PLC is transmit speech or convey message from one substation to other substation through transmission line at higher frequencies. however, power line communication serve other purpose also like tele-meeting ,tele- printing, tele- controlling, tele indication and tele-protection. All the signals are been communicated in the carrier frequency range from 35 to 500 kHz. thus, by PLC system, the various electrical equipments (power, current and voltage) are measured; message conveyed can be printed on the paper like telex and protective device can operate very quickly in mini seconds.
Principle or operation of PLC
In power line carrier communication PLC, a speech signal is modulated with the carrier frequency ranging from 35k Hz to 500Hz. Before modulation the speech band is limited to 300 to 2400 Hz .Whenever 2.4 to 4K hertz frequency band is used for tele- entry, tele- printing, tele- control, tele- indicate and tele-protection. The modulated signal is filtered and amplified and then it translate to over the power (Transmission line 66kV,132kV, 220kV, 400kV etc) lines through line matching unit protective device and coupling capacitors.
At the receiving end the high frequency carrier signal is separated from high voltage power frequency with the help of line trap and coupling capacitor, through line matching unit, the carrier frequency signal send to the power line communication terminal. Where the speech signal is separated from the carrier frequency and send it to subscriber.
Detailed description of principle of operation of PLC: The principle of operation of PLC is described with the aid of the block diagram shown in figure. In the transmitter the speech signal reaches the a.f hybrid (27), The output of which is connected via the a.f amplifier to a limiter intend to prevent over modulation due to short peak in the speech input. if required, a compressor (2) you can be incorporated to improve signal to noise ratio in the speech channel.The subsequent a.f low pass filter (3) prevents cross-talk between the speech channel and the tele-operation and the pilot channels.Several low pass filter are available with cutoff frequency between 800 and 3400 Hertz. Speech tele-operation and the pilot dialing signal are combined in the a.f mixer amplifier.Several low pass filter are available with cutoff frequency between 800 and 3400 Hertz. Speech tele-operation and the pilot dialing signal are combined in the a.f mixer amplifier.Several low pass filter are available with cutoff frequency between 800 and 3400 Hertz. Speech tele-operation and the pilot dialing signal are combined in the a.f mixer amplifier.The two mixture models (5) close and (6) close have each five symmetrical 600 Ohm inputs which can be set individually and which are completely decoupled from one another. Depending on their importance, the output of a mixture module (5) can be connected to one of the point marked "channel can be disconnected". "Channel that cannot be disconnected" and "boost channels". This set therefore provides facilities for transmitting especially important information such as distance protection signals for a brief period at an information such a distance protection signal for a brief period and increase power if conditions for transmission along the line are unfavorable. During this time certain other channels example:- speech have to be disconnected channel that can be disconnected. The pilot signal is used for regulating the level of the channel as a whole and also for transmitting the dialing pulses. The mixed signal at the output of the mixer amplifier (4) is converted to the intermediate frequency by the first modulator (7). A • highly stable oscillator (8) serves as the carrier for the conversion. Of the two side bands thus created the lower one is normally filtered out by the i.f. filter and fed into the if.mixing amplifier/modulator (10). Through a second input the auxiliary carrier from the if.oscillator (8) is mixed in, as it is needed to Obtain a dependable fixed-frequency link. The desired signal pilot signal and auxiliary carrier are now transposed to the required carrier frequency, the subsequent ref. filter (12), once again removes the upper Side band. Here too an oscillator (II) acts as the carrier. The lower side band is amplified to the required output power in the h.f.. amplifier (13), reaching the r.f. output via the transmitter filter (14) and the r.f. lines hybrid. From there it passes through the line matching unit, protective device and coupling capacitor to the high voltage line.
1.Transmitter speech amplifier plus limiter
2.Compressor
3.A.F. low-pass filter
4.A.F, mixing amplifier plus pilot oscillator
5.Mixer.module 1
6.Mixer module 2
7.Transmitter a.f,/i.f modulator
8.IF. oscillator
9.I.F. filter
10.IF. mixing amplifier plus if./r.f,modulator
11.R.F. oscillator
12.Transmitter r.f. filter
13.R.F power amplifier
14.R.F transmitter filter
15.R.F hybrid
16.Receiver if. filter
17.R,F./a.f. demodulator plus carrier Amplifier
18.IF. amplifier plus AVC voltage amplifier
19.Carrier filter
20.Limiting amplifier
21.I.F./a.f demodulator
22.A.F. high-pass filter plus afe amplifier plus shift filter
23. Tele-operation amplifier
24. Dialing receiver
25.Receiver speech amplifier
26. Expander
27.A.F. Hybrid
28.Carrier monitor
At the receving end, the carrier signals pass through the coupling elements into the r.f. filter (16) which perform' a certain amount of preselection and rejection of the image frequency band. The h.f./i,f. demodular (17) converts the incoming coming signal back to the i.f., the i,f. filter (9) removes the upper sideband. The if. amplifier (18) is designed as a control amplifier to compensate for fluctuations in the 'level. The pilot signal is rectified in the same printed circuit module (18) and compared with a reference voltage so that a control voltage can be derived from it. The i.f;/a.f, demodulator (21) is either controlled by the local 17-KHz oscilator (8) (connection without rigidly fixed frequency link) or by the auxiliary carrier transmitted by the opposite station. The required carrier is extracted from the received frequency mixture by the extremely narrow-band.
This method ensures that the a.f. signal at the output of that modulator has exactly tne same frequency as the original signal at the transmitting end.
The signals reach the a.f amplifier (22) via a high-pass filter, the pilot signal being separated from the remaining signals by a band-pass and then fed to the dialing receiver (24). From the output of this a.f. amplifier the signals arrive at the tele-operation amplifier (23), whose low-independence output provides excellent decoupling between the various tele-operation channels. Finally the speech signal is separated from the tele-operation signals by low-pass filter (3) and reaches the
if necessary an expander (26) is fitted at this speech amplifier (25) ; point. From the amplifier (25) the speech signals continue through the a.f hybrid (27) to the automatic exchange and then eventually to the subscriber.
The following are the main equipment used in power line carrier
communication :
(i) Wave trap
(ii) Coupling capacitor
(iii) Line matching unit or line tuning unit
(iv) PLC Terminal
(v) Switching equipment.
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| Sample of PPT Download link is below |
The pictorial view of these equipment actually connected in the power system (switch yard) is
shown
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| Sample of PPT Download link is below |
The brief description of the various power line carrier communication equipment is given below :
(i) Wave trap : Wave trap contains a main coil, lightning arrestor and a tuning device, All are connected in parallel as shown in fig. 10.4. The main coil has an inductance of 0.2mH to 200mH. This inductance offers a high impedance to the high frequency (50KHz to 500KHz) carrier
signals and blocks them here. It does not allow them to enter the power system equipment. However, it offers a very low (negligibly small) impedance to the power frequency signal or wave. Hence, it acts as an insulator for high frequency carrier signals and a conductor for the power frequency (50 Hz) signal or wave. Since the main coil is connected in series with the line, it has to carry the line current even under fault conditions. Therefore, it is designed from the current rating point of view. The current rating of the main coil may be as high as 4000 A.The lightning arrestor is used to protect the main coil from high voltage surges whereas the tuning device is used to block the signals of narrow band carrier frequency. All the three components of wave trap are immersed in oil and are enclosed in a drum type porcelain container as shown in fig 10.3. having sufficient mechanical strength. The wave traps may be of hanging type or foundation mounted type. Most of them are hanging type.
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| Wave Trap |
(ii) Coupling Capacitor : The coupling capacitors, used for power line carrier communication have capacitance ranging from 2200 p.F. to 10000 pF. It offers a low impedance path to high frequency (50 KHz to 500KHz) carrier signals and allows them to enter the line matching unit (L.M.U.). However, it offers a high impedance path to low frequency (power frequency) signal or wave and blocks it.
Hence, it acts as a conductor for high frequency carrier signal insulator for the power frequency signals.
The coupling capacitor (CC) consists mainly of a porcelain insulator shell which contains the capacitor's stack, the oil impregnation and a gas cushion. Normally nitrogen under slight over pressure is used. The stacks of capacitors each consisting. of numerous flat-wound elements of purest cellulose paper and aluminium foil piled up between insulation rods forms a complete part.
These coupling capacitors are mounted on the foundation. These are designed for the voltages 33K V to 400 K V. In place of coupling capacitors (CC), some times capacitive voltage transformers (CVT) are used. With the help of CVTs we can measure voltage and power of the system accurately.
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| Coupling Capacitor |
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| Sample of PPT Download link is below |
(iii) . Line matching unit (L.M.U) or I.ine tuning unit (L.T.U) : The carrier signal received from the high voltage transmission line through coupling capacitor is given to the line matching unit 2. From here the signal is transferred to power line communication (PLC) terminal as shown
On the other hand, the carrier signal generated in a high frequency cubicle (terminal) is transmitted via terminals 6 through a line matching unit 2 and a coupling capacitor to the high voltage line.
In order to pass the line frequency displacement current of the coupling capacitor to ground, a train coil 4 is connected between the low voltage terminal of the capacitor and ground. A lightning arrestor 5 is provided for protecting this coil. The grounding switch 3 enables the coupling capacitor to be grounded directly. when the carrier connection is not working, or is not in use.
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| Line matching unit |
(iv) Power line carrier communication terminal : It is just a cabinate as shown in fig. which contains number of electronic cir- Its working is described circuits. under the heading 'Principle of Operation of PLC with the help of block diagram shown in This is the place where the speech signal in modulated with carrier frequency or vice versa.
(v) Switching equipment : The signal is fed to the switching system wherc it is used for any one
operation i.e. telemetering, tele-control, tele-printing, Indication, tele-protection- or tele-voice. 300Hz to 2.4KHz band is used for tele-voice, whereas 2.4KHz to 4KHz band is used for the remaining operations.
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| Sample of PPT Download link is below |
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