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CARRIER RELAYING -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --�'�-L� .4� �-� ��o.3
5.
A Line Trap
to prevent short circuiting
the carrier
transmitter
a
nearby
external ground
same phase wire
coupled.
These are usually
such as types P-400, P-800, PDF-400
PDF-800.
Similar equipment
is required
terminal of the protected
line section
is
considered
should be assigned
a different
minimize the possibility
other lines.
The transmitter-receiver
respond
to the
assigned
either receiver
may receive a signal from the
transmitter
at
the
section.
It is not
necessary
ceiver to receive a signal from its own trans-
mitter, since the
carrier
terminal serves only to
opposite
terminal
for
Therefore, it is
possible
lines to use two frequencies in
scheme
and obtain
two
channels for transmitting auxiliary
in two directions simultaneously.
OPERATION OF SCHEME
Figure l shows
a complete basic diagram
one
terminal
of
the
three-phase
line
currents
quence filter.
The single-phase output of the
sequence
filter is
con��cted
detectors
(FDl and FD2)
two thyratrons Vl and V2 through a transformer
Tl.
These thyratrons and associated resistors
and
capacitors
comprise
which
is
operated
by the filter output vol
tage.
The fault detectors are used to
an intermittent carrier scheme, and are usual
ly set above load current so that
channel
is
available
function such as communication or telemetering
except during the time of a fault.
Fault
detector FDl
relay
tap
value,
and
output
during
fault on the
to which the carrier is
the type P,
and
at each line
line section.
Each
as
a
unit
and
frequency
to
of interference with
sets are tuned
to
frequency
so
that
opposite
end
of
the
for
the
re
signal from
each
block tripping at the
an
external
fault.
on
two
terminal
this carrier
independent
carrier
functions
of
relaying system.
The
energize
the se
to
two
fault
and
to the grids of
a
trigger
circuit
obtain
the carrier
for
any
auxiliary
is set
to trip at
the
allows
the
trigger
circuit
to
operate sending
blocks
of
carrier
and
voltage.
Fault detector• FD2 is set to trip 25
�ercent above tap value, and
operation
of
the
tripping
through the relay tube.
line breaker cannot occur until FDl and
have both
picked up.
between them
is to insure
start fault detectors (FDl)
of a line
will pick up
fault
before the
relay
through FD2 to insure correct bloc1cing.
a condition of temporary overload on the line,
the fault detectors
may pick
the relaying system continuously.
a time, the carrier channel
for any auxiliary function.
Upon
the occurrence of a fault, the contact
of the
fault detector
positive direct voltage to the plate
of
Vl
and
V2.
When the grid
positive,
as a
result of
voltage, it fires
and its plate or anode cur
rent
very
rapidly
rises
value as determined by the supply voltage
the plate and cathode resistors (Rp and Rc) of
the tube.
On the next half cycle, the grid of
V2 becomes
positive,
When this occurs, the
connected between the plates Vl and V2 make
C,
the plate potential of Vl momentarily negative
which extinguishes Vl.
plate
current
on
either
square half-cycles
of fixed magnitude for any
value or wave
form of grid voltage providing,
sufficient grid voltage is present
of course,
to fire the thyratrons Vl and V2.
drop across the Vl cathode resistor Rc is used
as the plate-supply voltage for the oscillator
tube
in
the
carrier
this
voltage to the
plate of the
causes the
transmission
nate half-cycles of the power frequency.
The voltage (Eo)
across
resistor Rc
of thyratron V2
the
grid
circuit of the relay tube
series with the rectified
carrier receiver as shown.
voltage drop across R'c makes the grid of
out
half
cycle
operating
providing
supervises
the
relay element
R
This
tripping of the
FD2
The
25 percent
maq;:in
that
the
carrier
at both terminals
on
a remote external
tube
is
energized,
Under
up and
operate
During such
is not
available
FDl
opens and applies
circuits
of Vl becomes
the
filter output
to
a steady-state
and
and thyratron V2 fires.
charge on the capacitor
Thus, the wave form of
thyratron
will be
The voltage
transmitter.
Applying
oscillator
of carrier on alter
the
other cathode
is
connected in
V4
in
(ER) of the
output
When V2 fires, the
the
3
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