CARRIER RELAYING
RESTRAINING VOLTAGE
FROM CARRIER
.INTERNAL FAULT
A
8
T
I�
WAVE DIAGRAMS
EXTERNAL FAULT
LOCAL
FILTER OUTPUT
LOCAL
OPERATIN&
VOLTA&£
c
--------- LOCAL
CARRIER
__.__.._.
D
-------DISTANT CARRIER _________._
E
RECTIFIED CARRIER
AT
RECEIVER
(RESTRAINING VOLTA&£>
F
VOLTA&£
ON &RID OF
RELAY TUBE•(a>+<f)
G
PLATE CURRENT
OF R
E
L
A
Y TUBE
H
SEC. VOLTAGE
,.:
e'
c'
b'
E'
F'
e:
H'
I
RELAY TRIP5
RELAY
CURRENT
RELAY DOES NOT TRIP I'
Fig. 2-The Relay Tube Circuit and Typical Wave Dia·
grams Of The Type HKB System.
relay tube positive.
The rectified output
the carrier receiver is connected
with
of
the
opposite polarity and i.s sufficient to cancel
the effect of the voltage across R'c if carri
er is received at the same time that V2
is
conducting.
The voltage drop across resistor
RB
provides negative grid bias for the thrya
trons.
The carrier transmitter and receiver
are conventional carrier relaying units whose
construction
and principle of operation are
well known.
Response To Faults
Figure 2 shows in detail how the circuits
just described determine· whether an internal
or external fault exists.
The
relay-tube
circuit is shown at the top of Figure 2
for
convenience.
The
"operating voltage
from
trigger circuit" is the voltage drop Eo across
4
"R'' RELAY
CURRENT
20
180
Fig. 3-Typical Overall Characteristics of the Type HKB
System.
R'c of Figure
1.
It is called operating volt
age, as it makes the
grid of the relay tube
positive, causing the flow of relay-tube plate
current.
The "restraining voltage from carri
er"
is the d-e output ER of the carrier re-
ceiver and is so named as it
operating voltage and prevents
plate
current in the relay tube
negative potential to its grid.
opposes the
the flow of
by applying
To see how the quantities
shown in Figure 2
are utilized, consider first an internal fault.
The polarities of the sequence-filter-output
voltages at the two ends of the line are such
that, when the fault detectors operate, carri
er is transmitted
from both line terminals on
the same half-cycles (Figure 2, C and D) .
The
received and rectified c�rrier
restraining
voltage (Figure 2, E) is applied to the
grid
of the
relay tube in series with the opera
ting voltage (Figure 2,
B).
The
net voltage
on the grid of the relay tube is the
sum of
these two voltages, and has the wave form in
dicated at F on Figure 2.
The reference axis at F is the voltage
Ec
required to cut off the plate current of the
relay tube.
Consequently,
when the net grid
voltage is above this axis,
plate current
flows.
For an internal fault,
there is no
rect�fied carrier voltage during the half
cycles that the grid of the relay tube is made
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