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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 M.
Similar
equipment
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
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 HZ impedance
or
type
HZM
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
with
the
type
HZM relay.
•
Zl, is set for 80-90%
operates independently of carrier.
element, Z2, is set for about 150% of the line
section and so covers the entire line, but
particularly
associated
which
is
beyond
*
element;
that is, the last 20-10% of the line
(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
a time
delay contact T2, is used in
carrier,
with
the
contact
series
output during a
These are
is required at each line
Each
as a unit and
frequency to
sets are tuned to
frequency
so that
opposite end of the sec
its own transmitter,
element
contact
transmitting auxiliary
using the usual connec
For simplicity, the
when Z3
is offset
The first element
of the line section and
The second
is
with
that portion
the setting
of the first
is not possible to
of the second zone
CARR I ER
POS.
(
RECEIVER RELAY-COILS RRH
HOLOING
RRGt 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 bel<:· W .
The third element, Z3 of
Type HZ Relays , is given a distance sett
the
ing
to
provide complete
through
contact
T3,
transmission.
When the Z3 element of the Type HZM Relay is
offset to operate
for
element
has
directional
will
not
send
blocking carrier for external
Consequently, in the Type HZM carrier
faults.
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
internal
faults,
the
characteristics and
extending
out of
the
to
the
is started by
type
HZ and HZM relays
3
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