CARRIER RELAYING
PtiASE
A
PtiASE
B
PtiASE
c
GRD.
CS
P
)
(cs0
a
GROUND
ACK-UP
RELAY
OUT-OF-STEP ELEMENTS
,..---------_______..!'....._ ___ �
RRB
Jc
r:
T
c�)
TIMER DIRECTIONALLY CONTROLLED BY D AND Z3
31-D-52u7
*Fig. 2-Sirnplified D-C Schematic of the Trip Circuits.
for the breaker in the next section to clear.
When used in carrier relaying, this T2 contact
is para lleled by a
contact.
RRP ,
controlled by
ca rrier,
a s explained below.
The third ele-
ment, Z3 of the Ty�e HZ Relays,
is
given
a
distance
setting
to provide complete back-up
protection through contact T3,
and to start
carrier transmission.
When the Z3 element of the Type HZ-4 or HZM
Relay is offset to operate for internal faults,
the element has directional characteristics
and
will not
send blocking carrier for ex
ternal faults.
Consequently, in the Type HZ-4
or HZM Carrier scheme,
it is necessary to re-
verse the Z3 element.
This means that the
third zone back-up protects the lines extend
in� out of the station instead
of the lines
adjacent to the remote terminal breaker.
The
synchronous timer motor is started by
tJ,e directional
and
third element contacts in
4
series in the type HZ. HZ-4 and HZM relays ex
cept directional control is omitt�d
�hen
Z3 is
reversed for Ca rrier when
u
s
i
n
s
the
Type
HZ-4
or
HZM
relays.
The Ty[JeS
HRK or HR? ground relays have a
directional
element and two
instantaneous
over-current elements.
The operation
of
these
elements is
explained
below.
The
schematic
carrier
control
and trip cir
cuits are shown simplified
in Figs.
1
and 2 .
The Type HZM, HZ-4
or HZ relay shown here has
a single third impedance element contact and
directional control of
the timer.
The same
scheme also can be used with the older type HZ
relays with two make and one break third im-
pedance element contacts.
With this latter
type
HZ relay the carrier control circuit is
slightly different from that shown in Fig.
l.
The trip circuits using
either type HZ relay
are basically the
same
a shown in Fig. 2 as
(
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t
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