Application Guide
Volume III
AG2015-05
Using SELOGIC® Control Equations to Provide
a Trip Coil Monitor Alarm in SEL-351,
SEL-451, and SEL-751 Relays
Ariana Hargrave
INTRODUCTION
References [1] and [2] show how to create a trip coil monitor (TCM) alarm using
SELOGIC® control equations when both 52A and 52B breaker status contacts are available. This
TCM logic (as well as the SEL-2652 Trip Coil Monitor, a separate TCM device) monitors the trip
coil when the breaker is either open or closed. However, some breakers (including many industrial
breakers in metal-clad switchgear) only have a 52A contact available and, therefore, the solutions
in these documents cannot be implemented.
This application guide shows how a simple TCM alarm can be created using SELOGIC control
equations in the SEL-351 Protection System; the SEL 451 Protection, Automation, and
Bay Control System; and the SEL-751 Feeder Protection Relay when only a 52A breaker contact
is available. Unlike the TCM used in [1], [2], and the SEL-2652, this TCM only monitors the
health of the trip coil when the breaker is closed.
For information on how to provide TCM alarms for a two-breaker line terminal using the SEL-321
Phase and Ground Distance Relay, please see [3].
RELAY CONNECTIONS
To implement the TCM, two inputs must be connected to the relay. The first input (IN101) is the
status of the breaker 52A contact. The second input (IN102) monitors the integrity of the trip coil
circuit and is connected in parallel with the appropriate tripping contact.
Common DC Source
If the relay running the TCM logic is on the same dc source as the breaker circuit, wire the TCM as
shown in Figure 1.
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+DC
Trip
Contact
Relay
Power
Supply
IN102
52A
Trip
Coil
TC
IN101
52A
–DC
Figure 1
Wiring for Simple TCM Alarm With Common DC Source
When the breaker is closed and the trip coil is healthy, both IN101 and IN102 will be asserted. If
the trip coil has failed, IN101 will still be asserted, but IN102 will not. If there is a problem with
the 52A contact connected to IN101, but the trip coil is still good, IN101 will be deasserted and
IN102 will be asserted. When the breaker is open, IN102 will not be able to assert regardless of the
health of the trip coil, so IN101 and IN102 will both always be deasserted. This is summarized in
Table 1.
If a trip circuit fuse blows, neither IN101 nor IN102 will assert, and the scheme will not alarm.
Because the relay and the breaker circuit are on the same dc source, this is not a problem. When
the fuse blows, it will also cut power to the relay, causing the relay failure alarm to assert for a loss
of dc to the trip circuit.
Table 1
TCM Alarm State for Various Conditions With Common DC Source
Breaker Status
Trip Coil Status
IN101
IN102
TCM Alarm
Closed
Healthy
1
1
0
Closed
Failed
1
0
1
Closed with 52A failure
Healthy
0
1
1
Open
Healthy
0
0
0
Open
Failed
0
0
0
0
0
0
Loss of dc
Independent DC Sources
If the relay circuit is independent from the breaker trip circuit and they each have their own dc
source, wire the scheme as shown in Figure 2.
+DC2
+DC1
Trip
Contact
Relay
Power
Supply
52A
Trip
Coil
IN101
–DC1
Figure 2
IN102
TC
52A
–DC2
Wiring for Simple TCM Alarm With Independent DC Sources
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The behavior of the inputs for this scheme is exactly the same as in Table 1, with the exception of
what occurs when the independent dc sources are lost. A blown fuse in the relay circuit will cause
the relay failure alarm to assert, while a blown fuse in the breaker trip circuit will cause IN102 to
deassert, as shown in Table 2. Using independent sources will allow the scheme to act as a true trip
circuit monitor instead of just a trip coil monitor, and it will alarm for dc failures as well as failure
of the trip coil itself.
Table 2
TCM Alarm State for Various Conditions With Independent DC Sources
Breaker Status
Trip Coil Status
IN101
IN102
TCM Alarm
Closed
Healthy
1
1
0
Closed
Failed
1
0
1
Closed with 52A failure
Healthy
0
1
1
Open
Healthy
0
0
0
Open
Failed
0
0
0
Loss of DC1
N/A
N/A
N/A (relay failure alarm asserts)
Loss of DC2
1
0
1
SETTINGS
Because of the behavior of the inputs shown in Table 1 and Table 2, the TCM should only alarm
when the statuses of the two inputs disagree. This detects problems in the trip circuit when the
breaker is closed and does not alarm when the breaker is open. A delay of 60 cycles is added to
prevent erroneous pickups of the TCM alarm during breaker transitions. The TCM alarm can be
used to drive an output contact or a target LED.
The settings that are required to implement the TCM for an SEL-351 or SEL-751 are shown in
Table 3.
Table 3
Settings to Implement a TCM in SEL-351 or SEL-751 Relays
Setting
SEL-351
SEL-751a
Breaker status
52A = IN101
52A = IN301
Timer logic
Map the input connected to the
52A breaker status.
SV1 =
SV01 = (NOT 52A
Start a timer when the monitoring input and 52A
(!52A*IN102) + AND IN302) OR (52A
breaker status input do not agree.
(52A*!IN102)
AND NOT IN302)
Timer pickup
SV1PU = 60
SV01PU = 1
Set the pickup time to 60 cycles.
Timer dropout
SV1DO = 60
SV01DO = 1
Set the dropout time to 60 cycles.
Output contact alarm OUT107 = SV1T
a
Description
OUT301 = SV01T
Map an output contact or a target LED to show the
TCM status.
IN101 and IN102 on the SEL-751 share a common neutral connection. Because of this, the inputs cannot be wired as shown in
Figure 1 or Figure 2. For the SEL-751, we must use the inputs on a 4 Digital Input/4 Digital Output card in one of the
expansion slots. Here we are using IN301 and IN302 in place of IN101 and IN102, respectively.
The settings required to implement the TCM alarm in the SEL-451 are different for single-breaker
and dual-breaker applications, as shown in Table 4. The single-breaker application has one alarm,
while the dual-breaker application has two alarms (one for each breaker).
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Table 4
Settings to Implement a TCM in an SEL-451 Relay
SEL-451 With a
Single Breaker
SEL-451 With Dual
Breakers
Breaker
status
52AA1 = IN101
52AA1 = IN101
52AA2 = IN201
Timer
logic
PCT01PU := 60
PCT01DO := 60
PCT01IN := (NOT
52AA1 AND IN102)
OR (52AA1 AND
NOT IN102)
PCT01PU := 60
PCT01DO := 60
PCT01IN := (NOT 52AA1
AND IN102) OR (52AA1
AND NOT IN102)
PCT02PU := 60
PCT02DO := 60
PCT02IN := (NOT 52AA2
AND IN202) OR (52AA2
AND NOT IN202)
Start a timer when the monitoring input and 52A
breaker status input do not agree. Set the pickup and
dropout times to 60 cycles. This is done in the protection
freeform logic.
For the dual-breaker application, this logic assumes that
IN202 is the monitoring input for Breaker 2.
OUT104 = PCT01Q
OUT105 = PCT01Q
OUT106 = PCT02Q
Map an output contact or a target LED to show the TCM
status for each breaker.
Setting
Output
contact
alarm
Description
Map the input(s) connected to the
52A breaker status(es).
CONCLUSION
The logic in this application guide can be used to create a simple TCM in an SEL-351, SEL-451,
or SEL-751.
REFERENCES
[1]
J. Roberts, A. Guzmán, and L. Gross, “Making Trip Circuit Monitor Logic With SELOGIC™
Control Equations,” 1996. Available: selinc.com.
[2]
M. Thompson, “The Power of Modern Relays Enables Fundamental Changes in Protection
and Control System Design,” proceedings of the 60th Annual Conference for Protective
Relay Engineers, College Station, TX, March 2007.
[3]
W. Fleming, “Using SELOGIC® Control Equations to Provide Separate Trip Coil Monitor
(TCM) Alarm Outputs in the SEL-321 Relay When Applied to Two-Breaker Line Terminals,” 1997. Available: selinc.com.
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FACTORY ASSISTANCE
We appreciate your interest in SEL products and services. If you have questions or comments,
please contact us at:
Schweitzer Engineering Laboratories, Inc.
2350 NE Hopkins Court
Pullman, WA 99163-5603 U.S.A.
Tel: +1.509.338.3838
Fax: +1.509.332.7990
Internet: selinc.com/support
Email: info@selinc.com
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SEL Application Guide 2015-05
Date Code 20180921