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ence at
all
times over all other uses of the
carrier channel.
The
are
circuits
action
of
the
ground
perference
over
the
phase
done
by
connecting
the
type HRK or HRP relay
around CSP carrier stop
contacts
as shown.
This means that if IoS of
relay
starts carrier, it is than
the
ground
impossible
for
the CSP contact and the phase
relays
to
stop carrier.
ground
perference
is to prevent possible in
correct indieations of the phase relays due to
load
currents
and
the
negative
sequence
currents
ground faults.
The
carrier
controlled receiver relay is a
sensitive
polarized d-e relay
two
make contacts, RRP and RRG, and one break
contact, RRB.
These contacts are operated by
the
action
of
two
coils,
coil, RRT, energized
by the local battery and
controlled
as
explained above by CSP and CSG
contacts,
and
the
other
coil, RRH,
connected
the
carrier
receiving
coils are de-energized
RRP and RRG, are held open by a magnetic bias.
The relay is prevented from operating when the
carrier holding
coil,
though
the
operating
gized.
This
means that as long as carrier is
being
received
either
mitter or
from the opposite end, RRH is ener
gized and carrier tripping is prevented.
The
complete
sequence
briefly
summarized
as follows:
ternal
phase-to-phase
zone
of one of the Zl elements.
be
initiated
immediately at both ends of the
line by the closure of one of the Z3 contacts.
Meanwhile, the directional and second zone im
pedance contacts
close and energize the auxi
liary switch, CSP,
stopping carrier and ener
gizing the operating coil, RRT, of the carrier
receiver
relay.
Since
occurred
at
the
far
carrier
is
received and the contact, RRP, is
closed
at
both ends completing the trip cir-
arranged
so
that the
relay can be
given
relays.
This is
contacts CSO of the
The purpose of this
flow of positive and
during
external
provided
with
one an operating
a carrier
holding
in the plate circuit of
tube.
Normally, both
and the make contacts,
RRH, is energized even
coil, RRT,
is
ener
from the local trans
of
events
may
be
Assume an in
fault
just beyond the
Carrier will
the same
action has
end
of the
line, no
cuits
through
D and Z2.
coil
one
at
end
has already been energized
through Zl.
If the fault has been external to
the
section, then tripping could not have oc
curred
since
the
carrier holding coil, RRH,
would
have
been
energized by
the end nearest the fault where D would not be
closed to stop carrier.
If
an internal-two-phase-to-ground fault is
assumed,
the ground carrier start contact IoS,
and
one
of
the phase contacts will close to
start
carrier.
If the ground preference con
tact
is
connected, then the operation of IoS
will
energize
CSO and its contact will short
out
CSP
thus
making
phase relays
to
stop carrier.
ground
tripping
contacts
close
energizing
the
stop carrier.
It
will be noted that carrier is not start
ed at either end unless fault current operates
(
a
starting element
fault detector
significant in case a line becomes diSC')nnect
ed
from a source of power at one end in other
words,
becomes a stub end feeder.
occurs on such a line, the carrier transmitter
will
be
started
and stopped only at the end
which
is connected to the source of power and
no carrier will be received from the other end
to interTere with tripping.
On
parallel
lines,
the
fault
power
undergo a quick reversal as
the
breakers on the faulted line open.
this
condition, carrier transmission is main
tained
at one end until it has had time to be
started at the other.
It is
desirable
to
condition
of the carrier set to determine its
ability
to send and receive a carrier signal.
For
this
purpose
a test push button is con
nected
in
parallel
with
elements.
Pressing the test push button sends
a
carrier signal which is received by the re
ceiver tubes
at both ends of the line section
to
cperate
an
alarm
milliammeter.
.If the carrier set is not func
tioLing,
the
alarm is not heard and the mil
not
liammeter
does
deflect indicating trouble
However,
the trip
carrier from
it
impossible for the
However, the
Do and Io2,
will
CSG auxiliary relay to
)
.
This is
If a fault
it is possible to have
Under
check periodically the
the
carrier start
relay
and
energize
5
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