This logic is useful in a situation where two transformers feed a single bus or two busses have a bus tie
between them. The feeder and bus relays must be coordinated for the situation where only one source is
in service (bus tie open or one transformer out of service). However, when both sources are in service,
such as when the bus tie is closed, each bus relay sees only half of the current for a fault. This results in
poor sensitivity and slow clearing time for the bus relays.
Example 2:
Adapting the logic in different setting groups.
The logic in most of the preprogrammed logic schemes can be varied in each of the different setting
groups. This is accomplished by disabling functions by setting their primary settings at zero. More
sophisticated modification of the logic in each of the different setting groups is possible by using the
active setting group logic variables SG0, SG1, SG2, and SG3 in the BESTlogic expressions.
Output Contact Seal-in
Trip contact seal-in circuits have historically been provided with electromechanical relays. These seal-in
circuits consisted of a dc coil in series with the relay trip contact and a seal-in contact in parallel with the
trip contact. The seal-in feature serves several purposes for the EM relays. One is to provide mechanical
energy to drop the target. Second is to carry the dc tripping current from the induction disk contact that
may not have significant closing torque for a low resistance connection. The third is to prevent the relay
contact from dropping out until the current has been interrupted by the 52a contacts in series with the trip
coil. If the tripping contact opens before the dc current is interrupted, the contact may be damaged. The
first two of these items are not an issue for solid-state relays, but the third item is an issue.
To prevent the output relay contacts from opening prematurely, a 200 millisecond hold timer can be
selected with the SG-HOLDn=1 command. (See Table 8-38.) Refer to Section 3,
Input and Output
Functions, Outputs, Programmable Hold Timer,
for more information on this feature. If the protection
engineer desires seal-in logic with feedback from the breaker position logic, he/she can provide this
feature by modifying the BESTlogic expression for the tripping output. To do this, use one of the general
purpose timers, 62, or 162 and set it for mode 1 (Pickup/Dropout Timer). Set the timer logic so that it is
initiated by the breaker position input, and set the timer for two cycles pickup and two cycles dropout.
Then AND the timer output with the tripping output (VO1) and OR it into the expression for the tripping
output. The same can be done for the closing output. See Figure 8-17 for the seal-in logic diagram and
Seal-in Logic Table 8-38 that follows. This table is based on the CDS240-BATX-A-BE preprogrammed
logic scheme.
OUTPUT
LOGIC
OPTO
OUTPUT
LOGIC
INI
62
BLK
IN1
52b
+
+
62
-
TRIPPING
LOGIC
52TC
CLOSING
LOGIC
52CC
OUT2
OUT1
+
-
52a
52b
52TC
52CC
D2590-10
03-23-98
VO1
VO2
VO7
VO6
Figure 8-17. Output Seal-in Logic Diagram
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BE1-CDS240 Application
8-55
Summary of Contents for BE1-CDS240
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