I.L. 40-386.3
2-20
(10/94)
function
(FDOG)
works in conjunction with the pilot ground distance unit. The FDOG
directional unit is determined by the setting of
Dir Type (DIRU) (Zero Sequence /Nega-
tive Sequ / Dual Polariz)
.
Refer to Section 3.4.11 for the setting of Dir Type (DIRU)
. FDOG
is supervised by the Iom setting. A coordination timer FDOG Timer (T/0) is provided
to allow preference for pilot ground distance (mho) unit operation. The delay time (T)
can be set from 0 to 15 cycles in 1 cycle steps. It is recommended to set the FDOG
Timer to 3 cycles or longer for security reasons.
2.5.4
Instantaneous Reverse Directional Overcurrent Ground
Similar to FDOG, the instantaneous reverse directional overcurrent ground function
(RDOG)
supplements the pilot Zone logic.
2.5.4.1
Supplement to Reverse Zone3 Ground Trip
In the blocking system, RDOG, supervised by IOS, provides additional ground fault de-
tection (high resistance) beyond what is available by Z3G (reverse looking) for carrier
start.
2.5.4.2
Carrier Ground Start, Blocking Scheme
In the POTT/UNBLOCK systems, RDOG supervises PLTG and prevents keying or trip-
ping on reverse faults.
2.5.4.3
Weakfeed System Application
For weakfeed applications, an inherent part of the logic requires reverse fault detec-
tion; Zone3Ø/Z3G and RDOG supply this requirement.
2.5.5
3-terminal Line Application
For a 3-terminal
(OUT)
application, since the frequency of the 3 transmitters are the
same, any one transmitter starting will block the pilot system from tripping, therefore,
logic for the 3-terminal
(OUT)
pilot system would be the same as that used for the 2-
terminal
(OUT)
system. However, for POTT/PUTT/UNBLK systems, since the transmit-
ter frequency is different at each terminal, logic for the second receiver
(RCVR-2)
should be added to the system when the application involves 3-terminals. Functional
display “3Term” should be set at “YES” position when the 3-terminal line is applied.
a. Additional Logic For POTT and Simplified Unblocking
(Figure 2-28)
This logic includes contact converters
(CC)
for RCVR-2, AND-55, and logic for
the second receive indication. The second receiver output operates the contact
converter (or voltage). Output of AND-55 provides carrier trip signal
(CR)
to
satisfy AND-30 via AND-64 and allows pilot tripping.
b. Additional Logic for PUTT
(Figure 2-29)
The additional logic for this scheme would be similar to that as described for
POTT scheme, except logic includes AND-56, AND-57 and 50/ms timer. This
is because only the Zone1 reach relay keys the transmitter on internal faults.
For a close-in Zone1 fault, only the local terminal can key its transmitter and
the other two cannot. This logic provides a CR pilot trip signal for 50 ms for
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