Power Line Carrier Communication

COLLEGE OF ENGINEERING AND TECHNOLOGY

Submitted to: submitted by:Dr. Abhimanyu Mohapatra, Soumya Mishra & Dr. Ranjan Ku. Jena Regd no-0901106013 Lecturers , Dept ofElectrical Engineering,CET.

Seminar on, Power Line Career Communication DEPARTMENT OF ELECTRICAL ENGINEERING

Fast and efficient communication is a prerequisite for the management of modern power systems.

To maintain a large power grid in optimum working condition,the central load despatcher has to have at his command a large battery of communication systems.

For this the load dispatcher may use the commercial P&T telephone system using underground cables or open wires or VHF wireless communication.

Introduction

But for communication over medium and long distances in a power network,Power Line Carrier Communication is the most economical and reliable method of communication. This is because of :

a. The higher mechanical strength and insulation level of HV powerlines.

b. Lower attenuation over longer distances.c. Absence of additional communication lines.

Like any other communication system in PLCC the three basic blocks of communication are: 1) transmitter 2) Channel and 3) Receiver

What exactly PLCC is?

In PLCC we use wired channel of communication.

The idea of Power line communication came into picture in 20th century and practically this idea came into operation in several countries after 1920.

In early time antennae similar to those used in radio work were being used to couple telephone systems into powerline systems.

History of PLCC

But due to their inefficiency owing to their length and interference with nearby long wave radio transmitters they were replaced by oil and paper capacitors by about 1930.

These coupling capacitors could withstand high voltages and serve as effective coupling devices for power line carrier communication.

History of PLCC

These early PLC communication systems today handle not only speech communication but also:

Telemetry Tele-signaling Tele-control Tele-printer Tele-protection signals.

The various components of PLC communication includes:

1. Carrier Signals2. Modulation3. Coupling arrangements Wave traps Coupling capacitors Drainage coil The line matching unit

Components of PLCC System

The carrier signals used in modern PLC systems are audio frequency currents of frequencies between 24khz to 500khz.

The use of audio frequency carrier currents enables several channels of communication to be held over a single physical circuit.

Carrier signal

The frequency limits are decided basing on the following points:

Ease of separation between power frequency and radio frequency

Cost of coupling equipments Radiation losses Signal to noise ratio in the communication

circuit Interference to and from other services

We use the word modulation to mean the systematic alteration of one waveform, called the carrier, according to the characteristic of another waveform, the modulating signal or the message.

In Continuous Wave (CW) modulation schemes, the carrier is a sinusoid.

Modulation

The various advantages of modulation are:Ease of radiationEfficient transmissionMultiplexing Frequency assignment Improvement of signal to noise ratio

The four important types of linear modulation schemes are:

1) Double Sideband, Suppressed Carrier (DSB-SC)

2) Double Sideband, Large Carrier (DSB-LC) (also called conventional AM or simply AM)

3) Single Sideband (SSB) 4) Vestigial Sideband (VSB)

DSB-SC Modulation:This modulator basically is a multiplier

Let gm denotes the amplitude sensitivity (or gain constant) of the modulator, with the units per volt (we assume that m(t ) and Ac are in volts). Then the modulator output s (t ) is,

s (t ) = gm m(t ) (Ac cos(ωc t ))For convenience, let gm = 1. Then, s (t ) = Ac m(t )cos(ωc t )

There are two popular methods for generation of single side band sinals:

i. Frequency discrimination methodii. Phase discrimination method

Generation of SSB signals

Frequency discrimination method Conceptually, it is a very simple

scheme. First generate a DSB signal an then filter out the unwanted sideband.

Two stage generation of SSB signal

A typical BPF characteristic

This scheme requires: two product modulators two π/2 phase shifters and an adder. One of the phase shifter is actually a

Hilbert transformer (HT); it should provide a π/2 phase shift for all the components in M(f ) .

Phase discrimination method

SSB generation: Phase discrimination method

Demodulation of SSB

The received SSB signal is multiplied by the local carrier which is of the same frequency and phase as the carrier used at the transmitter.

In the output we get the spectrum centered at ± 2fc which will be eliminated by the LPF following v (t ).

Wave traps: Wave traps prevent the carrier currents

from entering into the power equipments in the stations removing the chances of:

High attenuation Complete loss of signals

Coupling arrangements

These wave traps consist of choke coils connected in series with the power lines and offer:

o Negligible impedance to power frequency currents

o But a suitably high impedance to the radio frequency carrier currents.

Wave trap mounting

Vertical Pedestal Suspension

Wave trap assembly

Corona ringLifting lugTerminalMain coilTuning devicePedestalProtective deviceTie rod

Modern coupling capacitors are designed to obtain,

Highest possible surge withstand capacity Highest cutoff frequency Lowest series resistance at carrier

frequencies.

Coupling capacitors:

The drainage coil serves to ground the power frequency charging current of the capacitor and allows the carrier frequency current to appear in the output of the unit.

The line matching unit: It consists of the matching transformer

and tuning capacitors and is generally tuned to a wide band of carrier frequencies(100-450khz).

Drainage coils

Phase to ground coupling Phase to phase coupling Inter line or inter circuit coupling CVT coupling

Types of coupling

Phase to ground :

Advantages: More economical than all others. Disadvantages: Loss of carrier current. Carrier energy & radiation losses are more. Noise pick ups are correspondingly higher. Applications: Short or unimportant lines where carrier

protection is not essential.

Phase to ground coupling

Phase to phase:

Advantages: The third conductor has no appreciable

effect on carrier current transmission. Switching conditions have little effect on

transmission. Signal attenuation is less. More reliable over longer distances. Application: Used in load dispatch work.

Phase to phase coupling:

Inter line or inter circuit:

Advantages: It is more reliable than phase to phase coupling

on the same circuit as it permits operation with one of the two circuits opened out & grounded for maintenance.

More reliable under broken conductor conditions. Applications: In 220kv and 400kv lines where interference

levels are high. In long110kv lines where attenuation is a

problem.

Inter line coupling

Use of CVT as coupling capacitors

PLCC Panel ( type: ABB ETL 41/42)

Cabinet Module

Digital PLCC – latest version

Now a day PLC communication is finding application in domestic and many corporate sectors also.

Spread spectrum is the main field of research these days.

Very soon this system will have a wide range of applications due to its reliability, fastness and more economic features.

Conclusion

Thank You