Power line carrier communication,ETL41/42

Power Line Carrier
Communication
ABB Make ETL Terminal
by
Sreenivas Gundu

PLCC – Brief Overview
• Power line carrier is used to transfer information
via HV transmission lines and has become an
important instrument for the management and
safety of electrical power systems.
• Transmission of Speech, Data and Protection
Signals.
• Single Sideband Modulation with a 4 kHz
spacing to make the best use of the available
frequency bands.

Line Matching Unit (LMU)
• LMU = Impedance Matching Transformer
+ Protection form High Voltage
• Purpose of LMU :
 To Isolate PLCC Equipment from
High Voltage on the Transmission Line
 To match PLCC Impedance to
Transmission Line Impedancae

Coupling Methods – Phase to Ground

Coupling Methods – Phase to Phase

Coaxial Cable
• Center Conductor: Copper
• Outer Shied: Mixture of Copper &
Aluminium
• Dielectric:Polytetrafluoroethylene
(PTFE)
• Typical Impedance :
75Ω, 125Ω & 150Ω(Balanced)
• Impedance used in TSTransco:
125Ω

Audio frequency Range
for Speech Transmission

Frequency Range Required for
Speech
• Language comes from the spoken word.
• When transmitting the speech, you should
always consider speech intelligibility.
• The spectrum of speech covers quite a wide
portion of the complete audible frequency
spectrum. (20Hz to 20KHz)
• Two factors determine the frequency range
required for satisfatory speech transmission.
Intelligibility/Frequency Distribution
Energy/Frequency Distribution

Speech
• In one form of articulation test, a group of
listeners was asked to record syllables as they
hear them from a loud speaker.
• The frequency range is reduced in steps.
• The number of correctly recorded syllables as a
percentage of number of syllables transmitted is
termed as articulation efficiency.
• In practice, it is found that 80% articulation
efficiency is about 100% intelligibility of normal
speech.

Speech
• In figure, red color shows the effect of
suppressing the High Frequencies in the
speech.
• It is seen that to maintain high Intelligibility,
frequencies up to 2.5KHz must not be
suppressed.
• Blue Color shows the effect of suppressing
the Low Frequencies.
• As much as 80% is transmitted, even
though all frequencies above 1KHz are
suppressed.

Speech
• The conclusion is therefore, that the energy
in speech sounds is contained in low
frequencies.
• The frequency limits for telephone speech
adopted internationally based on such tests
are from 300Hz to 3400Hz.

Typical PLCC Terminal
Block Diagram

Types of ETL Terminals
• ETL Series units vary in number of
channels and transmitting power.
 ETL-41 Single Channel 40 W PEP
 ETL-42 Twin Channel 40 W PEP
 ETL-43 Three Channels 40 W PEP
 ETL-44 Four Channels 40 W PEP

ETL – Technical Features
• PILOT:
 SELECTABLE FROM 3780 HZ / 2160HZ
/2640HZ / 3360HZ / 3600HZ
• RF PROGRAMABILITY:
 EASY TO TUNE THE SET IN EITHER 40 TO
100KHZ OR 100 TO500KHZ IN A RASTER OF
4KHZ
• RF TERMINATION:
 75Ω, 125Ω

ETL – Modulation Scheme
• Single Side Band Suppressed Carrier (SSBSC)
• Transmitter has Three Stages of Modulation
• Receiver has Four Stages of Demodulation

ETL-43/44-Modulation Scheme(Tx)

ETL-43/44-Modulation Scheme(Rx)

O4LA – Tele-control Interface

O4LC – 2/4Wire PAX Interface

O4LD - Remote Subscriber Interface

E5LA-TX Filter & P3LB-RF Hybrid

Power Supply
• B5LA – Connected to 48V DC Supply
• B5LC – Connected to 220/110V AC Supply*
• B4LA – DC/DC Converter per Rack

Frequency Shift Keying (FSK)
• Digital modulation technique in which the
frequency of the carrier signal varies
according to change in the input digital
signal.
• The data are transmitted by shifting the
frequency of a continuous carrier in a
binary manner to one or the other of two
discrete frequencies.

• One frequency is designated as the
“MARK” frequency and the other as the
“SPACE” frequency. The mark and
space correspond to binary one and
zero, respectively.
• By convention, MARK corresponds to
the higher frequency and SPACE
corresponds to the lower frequency.

Binary Data (a) Frequency Modulates
Carrier to produce FSK Signal (b)

• With FSK, the carrier frequency(fc) is shifted in
up and down in the frequency domain by binary
input signal.
As the binary input signal changes from a logic 0
to a logic 1 and vice versa, the output frequency
shifts between two frequencies: a mark, or logic
1 frequency (fm), and a space, or logic 0
frequency (fs). The mark and space frequencies
are separated from the carrier frequency by the
peak frequency deviation (∆f) and from each
other by 2 ∆f.

• Baud = (fb/N)
 fb = bit rate in bits per second
 N is the number of bits encoded into each
signaling element.
• For FSK, N= 1, Hence, Baud = fb
• The minimum bandwidth for FSK is given as
B = |(fs – fb) – (fm – fb)| = |(fs– fm)| + 2fb
and since |(fs– fm)| equals 2∆f,
The minimum bandwidth can be approximated as
B = 2(∆f + fb) (2.15) 14
where B= minimum Nyquist bandwidth (Hz)
∆f= frequency deviation |(fm– fs)| (Hz)
fb = input bit rate (bps)

Bit Rate Vs Baud Rate
• Bit rate can be defined as the number of bit
intervals per second. And bit interval is
referred to as the time needed to transfer one
single bit. In simpler words, the bit rate is the
number of bits sent in one second, usually
expressed in bits per second (bps).
• Baud rate is expressed in the number of times
a signal can change on transmission line per
second.

Key Differences between Bit rate
and Baud Rate
• Bit rate is the number bits (0’s and 1’s) transmitted
per second.
On the other hand Baud rate is the number of times
a signal is traveling comprised of bits.
• Baud rate can determine the bandwidth of the
channel or its required amount to send the signal
while through Bit rate it is not possible.
• Bit Rate can be expressed by the given equation:
Bit rate = baud rate x the number of bits per
signal unit
In contrary Baud rate is expressed in the given
equation:
Baud rate = bit rate / the number of bits per
signal unit

Bit Rate Vs Baud rate
Basis for
Comparison
Bit Rate Baud Rate
Basic Bit rate is the count of
bits per second.
Baud rate is the count of
signal units per second.
Meaning It determines the
number of bits traveled
per second.
It determines how many
times the state of a
signal is changing.
Term usually
used
While the emphasis is
on computer efficiency.
While data transmission
over the channel is more
concerned.
Bandwidth
determination
Can not determine the
bandwidth.
It can determine how
much bandwidth is
required to send the
signal.
Equation Bit rate = baud rate x
the count of bits per
signal unit
Baud rate = bit rate / the
number of bits per signal
unit

NSK 5 Modem to ETL Interconnection

Main Features of G4AE(NSK-5)
• The G4AE is a fully programmable VFT channel
with DIL switch settings for baud rate transmitter
and receiver frequencies and gain.
• Operating Modes:
 max. three 600 Baud channels.
 - a 1200 Baud channel above the 2000 Hz speech
channel or combined with other data channels
 at lower frequencies.
 - a 1200 Baud channel according to CCITT V.23
 - a 2400 Baud channel

Carrier Protection
• A secure and uninterrupted supply of
electricity is only possible with the help
of comprehensive protection and control
functions, which ensure the reliable
operation of the power system.
• Protection equipment in conjunction with
communication links provide the best
possible means of selectively isolating
faults on high voltage transmission lines.

Carrier Protection
• In addition to the Communication,
Supervisory Control and Tele-metering,
Carrier Signals are also used for
Transmission Line Protection.
• The circuit breakers at both the ends of
the line trip simultaneously when a fault
occurs at one of the ends of the
protected line sections.

Carrier Protection
• Carrier Protection helps in improving the
stability of the system
• The carrier signals can be used either to
initiate or to prevent the tripping of a
protective relay according to which they
are classified.

Carrier Protection
• When a carrier signal is used to initiate
tripping of relay, the scheme is known as
carrier inter-tripping, or transfer tripping
or permissive tripping scheme.
• The scheme is known as carrier-blocking
scheme when the carrier signals are
used to prevent the operation of a relay

Tele-Protection Device (NSD50)

NSD50 - Features
• The smallest NSD 50 has two plug-in units and
can transmit two independent tripping signals,
which are sufficient in most cases to protect a
transmission line.
• Expandable to handle four tripping signals by
simply inserting an additional relay interface.
• Totally, there are then two permissive and two
direct transfer tripping signals available, the
latter having priority.
• Equipped with the maximum of four tripping
signals per PLC link, two PLC links, for
example, are able to accommodate first and
second mainprotections for a double circuit line.

NSD50-Principle of Operation
• The guard/Pilot signal monitored by the
NSD50 is the carrier pilot.
• In the event of operation of protection
due to fault, the NSD50 interrupts the
guard/Pilot signal and transmits the
protection signal.
• When an NSD 50 receiver detects that
the pilot has disappeared and a correct
tripping signal of sufficient quality is
being received instead, the tripping
signal is relayed to the corresponding
O/P.

• By using the ETL pilot signal as the
guard signal for the NSD 50 and
transmitting tripping signals via the
speech channel, the NSD 50 does not
need any additional PLC bandwidth.

• Transmitter :
Start signal from distance relay to NSD-50
Speech cut off
Trip signal applied by distance relay to
NSD50
Pilot switch signal applied by NSD to ETL.
DSP of NSD50 will generate trip frequency
which will be fed to ETL at point TxAF (TxA
LED ON & Tx counter increments).

• Receiver :
Continuously monitor Guard signal (GRD
LED ON).
In absence of guard signal,NSD receiver
monitors RxAF (GRD OFF).
DSP of NSD analysis RxAF and when found
matching with any command frequency Rx
speech is interrupted.(RxA LED ON & Rx
counter increments).
At the same time Rx command on the
protection relay is activated.

Power line carrier communication,ETL41/42

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