2 SEC. OHM
M IN.
184A529
Fig.
3.
Out- of-S tep Blocking O perations.
separately fused supply, along with the phase back
up relays.
Transmitter Control
Break contacts, Z S (ZS·¢¢
&
'ZB-3¢)
&
los•
85
CO contact
7-8,
and the- test pushbutton break con
tact, PB, in fig. 2, connect the transmitter "start"
lead to minus. When any one of these contacts opens,
the "start" lead is connected to positive through
resistor, R2. This positive potential will key the
transmitter on (or shift the frequency, when a fre
quency shift channel is utilized), to block remote
breaker tripping, provided that the "stop " lead is not
tied to minus, through contact CSP or CSG. CSP
&
CSG coils are energized by ZP
&
D0 contacts, re
spectively, so that any time a fault is detected in the
trip direction the "stop" lead is tied to minus to
prevent transmission of a blocking signal. Thus, the
stop lead has precedence over the start lead. If, for
example, the channel is being used for voice com
munication at the instant of an internal fault, the
stop circuit will interrupt transmission to permit
tripping, provided that either ZP or D0 operates.
A blocking signal is required from breaker B,
fig.
1 ,
during an external fault because the phase or
ground tripping units would otherwise trip at breaker
A.
At breaker B either the 10s or the
ZS
contact
opens to put positive voltage on the start lead; since
neither the CSP nor the CSG contacts close at B
the stop lead is not energized, and, therefore, a
blocking signal is transmitted.
4
Receiver Relay Comparison Circuits
Receiver relay, RR, has an RRH holding coil and
an RRT tripping coil as shown in Fig. 2. RRH is
energized by the receiver output when a blocking
signal is transmitted; RRT coil is energized when
ever the local tripping relay contacts close in an
attempt to tri p the breaker. RRH coil current holds
the RRP and RRG contacts open; RRT coil current
closes the RRP and RRG contacts in the absence of
RRH coil current.
Tliis is the key point, which
produces the comparison function - the force pro
duced by RRH current is stronger than the opposing
force produced by RRT current, so that the RRP and
RRG contacts will be closed by RRT current only
when no blocking signal is received.
In Fig. 1, ZP or D0
+
I0 contacts close at breaker
A whether the fault is internal, or external to the
right of breaker B; in either case, CSP or CSG is
energized and RRT, in turn, is energized. For the
external fault only, the transmitter at B sends a
blocking signal, which produces a receiver output at
A, which energizes the RRH coil to prevent RRP and
RRG contacts from closing; thus, tripping is pre
vented.
Conversely, for an ihternal fault, tripping
units operate at both stations to energize CSP or
CSG contacts to prevent transmission of a blocking
signal; another set of CSP /CSG contacts energize t he
RRT coil. Since neither station receives a blocking
signal, both RRH coils are deenergized; both RR
relays operate to close their RRP and RRG contacts
to permit either ZP or D0
+
I0 contacts to energize
the trip coil.
A reactor is shown in series with the RRT coil
in fig. 2. This reactor is used only with audio tone
or frequency shift carrier channels, where the channel
delay time is abnormally large. This reactor delays
RRT coil current buildup long enough to compensate
for the RRH coil current buildup time occasioned by
the channel delay.
Otherwise undesired tripping
might occur before a blocking signal can be received.
Operation will now be summarized.
External Phase Fault Operation
Refer to Table I, which tabulates external phase
fault functioning at the top. The external fault is to
the right of breaker B as shown in the upper left of
Table I.
At breaker B,
Z'S
contact opens and the ZP con
tact remains open, so that CSP is not energized; the
start lead is at positive and the stop lead is open,
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