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CAR RIER REL AYIN G-- ----- - -- -- - -- -- - ' - l_ .
by
the
carrier
transmitter
nearby
external
fault on the same phase wire
to
which
the
carrler is coupled.
usually the Type P or the Type
Similar
equipment
is required at each line
terminal
of the protected line section.
line
section
is
considered
should
be
assigned a different
minimize
the possibility of interference with
other lines.
The
transmitter-receiver
respond
to
the
assigned
either receiver
may receive a signal from the
transmitter
at
the
opposite end of the sec
tion.
It is not necessary for the receiver to
receive
a
signal
from
since
under
this condition, the fault is ex
ternal
and
the directional
blocks tripping.
Therefore, it is possible on
two
terminal
lines to use two frequencies in
this carrier scheme and obtain two independent
carrier
channels
for
functions in two directions simultaneously.
OPERATION OF SCHEME
The
ground
relay and the type
HZM
or
type
distance relays are operated by
current
and
voltage
tions
for
these relays.
current
and voltage circuits are not shown in
the d-e simplified schematic diagram of Figure
1.
The
three impedance elements of these re
lays are set in the usual manner for step-type
distance
relaying
except
HZM
with
the
type
relay.
Zl,
80-90%
is set for
operates independently of carrier.
Z2,
element,
is set for about
section and so covers the entire line, but
particularly
associated
which
is
beyond
the setting
element;
that is, the last
(
)
end zone
adjacent to the next sectionalizing
point.
In this
zone, it
determine
by
distance indication whether the
fault is just within or just beyond the end of
the
section.
For distance relaying, without
carrier,
a time
delay contact T2, is used in
series
with
the
contact
output during a
These ar8
M .
Each
as a unit and
frequency to
sets are tuned to
frequency
so that
its own transmitter,
element
contact
transmitting auxiliary
HZ
impedance
using the usual connec
For simplicity, the
Z3
when
is offset
The first element
of the line section and
The second
150%
of the line
is
with
that portion
of the first
20-10%
of the line
is not possible to
of the second zone
CARRIER
POS.
RECEIVER RELAY-COILS RRH(HOLDING)
RRG, RRP., RRB.
Fig. 2-Simplified D-C Schematic Of The Carrier Control
Circuits Using The Type
Make-One Break Third Impedance Element
Contacts.
impedance element to allow time for the break
er in the next section to clear.
carrier relaying, this T2 contact is parallel
ed by
a
contact, RRP, controlled by carrier,
as
explained bel0w.
The third element, Z3 of
Relays , is given a distance sett
HZ
the
Type
ing
to
provide complete
through
contact
T3,
transmission.
When the Z3 element of the Type
offset to operate
for
element
has
directional
will
not
send
blocking carrier for external
faults.
Consequently, in the Type
scheme, it is necessary to reverse the Z3 ele
ment.
This
means that the third zone back-up
protects
the
lines
station instead of the lines adjacent
remote terminal breaker.
The
synchronous
timer motor
the
directional and third element contacts in
series
in
both
the
CONTROL
NEG.
6
RRT (TRIPPING). CONTACTS
HZ
Relay With Two
When used in
back-up
protection
and
to
start
carrier
HZM
Relay is
internal
faults,
the
characteristics and
HZM
Carrier
extending
out of
the
to
the
is started by
HZ
HZM
type
and
relays
3
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