Application Guide
Volume I
AG2015-12
Testing a Two-Terminal Application
of the SEL-411L in Test Mode
Ashwin Vashist and George Alexander
INTRODUCTION
The SEL-411L Advanced Line Differential Protection, Automation, and Control System has a
built-in test mode with flexible single-terminal and multiterminal testing options. This mode
allows you to perform acceptance, commissioning, and maintenance testing on a line differential
application that uses SEL-411L Relays in an easy and efficient manner. The TEST 87L
command makes it possible to test the differential element on an in-service line from only one
terminal or from all terminals at the same time (the latter requires the test sets to be satellitesynchronized).
Figure 1 shows a typical line differential protection arrangement where the exchange of local and
remote operating data between the relays in the scheme takes place over two channels. Bay 1
(Channel 1) uses a dedicated fiber direct connection between the two relays and a channel-based
data synchronization method (ping pong). Bay 2 uses multiplexers to create a hot standby
channel. This has the potential for channel asymmetry, so a time-based synchronization is used
for Channel 2. When external time-based synchronization is used, both SEL-411L Relays must be
connected to an external, high-precision, IEEE C37.118-compliant time source.
This application guide is a test guide for the scenario presented in Figure 1. The goal of this guide
is to provide the ability to test the characteristics of the differential elements in an SEL-411L and
to provide the tools to calculate the currents to be injected into the relay to validate the
differential scheme.
SEL-411L
Dedicated Fiber
Bay 1
Bay 2
Digital
Multiplexer
Hot Standby
Channel
Bay 1
SEL-411L
Bay 2
Digital
Multiplexer
Figure 1 Typical two-terminal SEL-411L application
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SEL-411L TEST MODE FEATURES
With the default settings, the {RELAY TEST MODE} front-panel pushbutton (Pushbutton 4, as
shown in Figure 2) allows you to test the protection functions of the relay by disabling the output
contacts of the relay that are used for tripping, closing, and pilot-scheme keying of the breakers in
the scheme.
RELAY
TEST
MODE
Figure 2 The {RELAY TEST MODE} pushbutton supervises the 87L test mode
The function of this pushbutton in the default settings of the SEL-411L is to supervise the
Access Level 2 TEST 87L command. The TEST 87L command allows for the testing of the
Alpha Plane or the relay differential operating characteristic. The TEST 87L command is
supervised by the SELOGIC® control equation 87TMSUP, which must be asserted to a logical 1 to
allow the use of the TEST 87L command. In the default logic, 87TMSUP asserts when the
{RELAY TEST MODE} pushbutton is used to place the SEL-411L in relay test mode, which
turns on the pushbutton LED.
DEFAULT PROGRAMMING AND TEST 87L MODE
The SEL-411L ships from the factory programmed with the following default equations, which
correspond to the activation, supervision of test mode, and LED indications in the relay.
PLT04S := PB4_PUL AND NOT PLT04 # ACTIVATE OR LATCH IN RELAY TEST MODE
PLT04R := PB4_PUL AND PLT04
87TMSUP = PLT04
# TEST MODE SUPERVISION
PB4_LED = PLT04
# LED RESPONSE
Note that pressing the {RELAY TEST MODE} pushbutton does not automatically initiate the
TEST 87L command. The TEST 87L command must be entered at Access Level 2 via terminal
emulation software.
With the default settings, if the RELAY TEST MODE LED is not on, then typing the
TEST 87L command returns the error message: 87 Test Mode Supervision is not asserted, test
aborted.
The following is an example of entering the 87L test mode, as shown on the screen of a terminal
emulation program:
Level 2
=>>TEST 87L
Entering 87L Test Mode
Select Test: Characteristic or Loopback (C,L)
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Note that when not in test mode, the relay differential element is supervised by both local and
remote disturbance detectors. An operation of the differential element that occurs without
assertion of the disturbance detection logic (sometimes due to channel asymmetry or unaligned
ramping of local or remote currents during testing) can cause a watchdog error. Two counters are
started when these spurious assertions take place, and their outputs are represented by the
targetable Relay Word bits 87ERR1 and 87ERR2. If these Relay Word bits are asserted at any
time, the relay is disabled, 87L function is inhibited, the 87L ALM and 87L LOST LEDs
illuminate on the front panel (assuming default LED programming), and you can no longer
continue testing. The command to reset this watchdog error is COM 87L WD C, issued from
Access Level 2 on the terminal as follows:
Level 2
=>>COM 87L WD C
Clear 87L watchdog counters?
Are you sure (Y/N) ?Y
87L watchdog counters cleared
=>>|
The test mode also allows you to bypass the watchdog timer logic in the SEL-411L and gives you
the ability to ramp local and remote currents into the relay in an independently adjustable manner.
This provides additional flexibility to find acceptable test points without needing to worry about
inhibiting 87L function.
Note: For applications that use SEL-411L Relays with firmware older than version R108, the
watchdog counters cannot be cleared from Access Level 2. You must log in to the
calibration level of the relay and clear the counters with the same command (i.e.,
COM 87L WD C).
For more information on the watchdog timer logic, please see the SEL-411L Instruction Manual
or contact SEL for further assistance.
PRELIMINARY CHECK
Changes may need to be made to the relay settings and test procedure, depending on the
application and protection scheme configuration.
Before entering test mode, ensure that the relays are communicating remote and local data with
each other by targeting the status of Relay Word bit 87CH1OK. This bit is a snapshot of the
channel health. To monitor this bit, use the command TAR 87CH1OK.
You should also use the Sequential Events Recorder (SER) in the SEL-411L to monitor Relay
Word bit 87CH1OK over a larger time frame to make sure the bit does not de-assert due to an
excess number of lost packets. Doing so verifies that the channel is healthy.
If the channel-addressing settings in the relay (87TADR, 87R1ADR, 87R2ADR) are configured
correctly, and the direct fiber and multiplexer arrangements are physically sound, the expected
result of the target command should be as follows:
=>>TAR 87CH10K
87MTR
1
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87SLV
0
87LST
0 |
87CH10K 87CH20K 87CH30K 87SYNH
1
1
0
1
87SYNL
0
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In addition, you can use the target command to monitor the status of Relay Word bits such as
87BLKL, 87BLK, and 87LST to troubleshoot issues, like the watchdog error, that inhibit 87L
function in the SEL-411L.
Note: Noticing whether the red and green transmit and receive lights are illuminated on the
back of the SEL-411L is one way to verify that the fiber connections on the channel ports
on the back of the SEL-411L are correct.
87L CHARACTERISTIC TEST METHODS
There are two methods to test the 87L characteristics, depending on the availability of personnel
and equipment and the choice of testing philosophy:
•
Single-terminal characteristic testing: Use a single test set to inject current at one
terminal. The channels do not have to be in use, and local and remote currents are
simulated locally by the test set.
•
Multiterminal characteristic testing: Use multiple test sets at multiple terminals. Test sets
are satellite-synchronized, channels are in use, and currents can be ramped at all
terminals.
SINGLE-TERMINAL AND MULTITERMINAL CHARACTERISTIC TESTS
In the single-terminal mode, you can apply both local and remote currents to one SEL-411L. This
allows for the simulation of independently adjustable local and remote currents without the need
to apply any current to the remote relay(s). Figure 3 depicts a single-terminal 87L characteristic
test.
Test Set
V, I
87L
87L
Figure 3 Single test set connection to a single relay
Figure 4 shows a multiterminal 87L characteristic test.
Test Set
V, I
87L
87L
V, I
Test Set
Satellite
Time
Figure 4 Test set connections to the relays at multiple terminals
The following are examples of entering the test mode for single-terminal and multiterminal tests,
respectively:
=>>TEST 87L
Entering 87L Test Mode
Select Test: Characteristic or Loopback (C,L)
Test Mode: Single, Multi Terminal, or Disabled (S,M,D)
87L Element: (A,B,C,Q,G)
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=>>TEST 87L
Entering 87L Test Mode
Select Test: Characteristic or Loopback (C,L)
Test Mode: Single, Multi Terminal, or Disabled (S,M,D)
87L Element: (A,B,C,Q,G)
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Select one of the 87L differential elements for testing. In the 87L test mode, the normal 87L
elements (i.e., 87LA, 87LB, 87LC, 87LQ, and 87LG) are blocked from operating. Their bits are
replaced with 87TOUT. Only the differential element selected is active. If 87LA is selected,
87LQ and 87LG will not cause 87TOUT to assert, even though their pickups may be more
sensitive.
Note that once one of the 87L elements has been selected, it cannot be changed until you exit and
re-enter the 87L test mode. The 87L test mode permits testing of both the normal and securemode 87L elements.
The following shows the application of the TEST 87L command in a terminal emulation
program:
=>>TEST 87L
Entering 87L Test Mode
Select Test: Characteristic or Loopback (C,L)
Test Mode: Single, Multi Terminal, or Disabled (S,M,D)
87L Element: (A,B,C,Q,G)
Alpha Plane Security: Normal or Secure (N,S)
Ensure that relay outputs are isolated or supervised.
Are you sure (Y/N)? y
Testing is enabled
Warning!
Ctrl X does not exit test mode
Type “TEST 87L OFF” to exit
?
?
?
?
c
s
a
n
When testing is complete, exit the 87L test mode by using the command TEST 87L OFF, as
follows:
=>>TEST 87L OFF
Exiting 87L Test Mode
=>>|
Note: When exiting the 87L test mode, there is no warning message requiring a second user
input as there is when entering 87L test mode.
Be sure to restore line currents to the relay prior to terminating the 87L test mode.
As soon as you exit the 87L test mode, the differential protection is enabled. If the correct
line currents are not present at all terminals, the differential protection may operate. This
could trip the line when the relay is taken out of test mode.
Note also that it is also necessary to restore the line currents and terminate the 87L test
mode when switching between characteristic tests of the various elements (87LA, 87LB,
87LC, 87LQ, and 87LG). You must re-enter the 87L test mode, disconnect the line
currents, and reconnect the test set currents before testing the next 87L element.
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SINGLE-TERMINAL 87L TEST CURRENT SOURCES
When using the single-terminal test mode, the local and remote currents are injected into different
phase current inputs of the SEL-411L being tested. The currents used are determined by the
element under test. Table 1 shows the analog substitutions to test the phase, ground, and negativesequence fault quantities. A pictorial representation of Table 1 is shown in Figure 5.
Table 1 Single-terminal test analog substitutions
87LA
87LB
87LC
87LQ
87LG
IA
IA
IB
IB
IA
Local IA
IB
Local IB
IC
Local IC
IB
Remote IA
IC
Remote IB
IA
Remote IC
Single-Terminal
87LA Element Test
Single-Terminal
87LB Element Test
87TOUT
Local
Current
IA
Remote
Current
IB
87L
A
87TOUT
Local
Current
IB
Remote
Current
IC
Single-Terminal
87LQ Element Test
87L
B
IA
Remote
Current
IB
87L
Q
87TOUT
Local
Current
IC
Remote
Current
IA
87L
C
Single-Terminal
87LG Element Test
87TOUT
Local
Current
Single-Terminal
87LC Element Test
87TOUT
Local
Current
IA
Remote
Current
IB
87L
G
Figure 5 Diagrams of single-terminal test analog substitutions
87LA, 87LQ, and 87LG Testing
The local current is injected into the IA current input. The remote current is injected into the
IB current input.
87LB Testing
The local current is injected into the IB current input. The remote current is injected into the
IC current input.
87LC Testing
The local current is injected into the IC current input. The remote current is injected into the
IA current input.
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SINGLE-TERMINAL AND MULTITERMINAL TEST PROCEDURE
Current injection for these tests is based on the differential element selected in the 87L test mode,
as described in the previous section. This procedure checks the pickup, radius, and angle settings.
The following is a list of the settings that are used and tested in this application guide:
•
87LPP, 87LQP, and 87LGP are the differential pickups for phase, negative-sequence, and
ground elements.
•
87LPR, 87LQR, and 87LGR are the Alpha Plane radius settings for phase, negativesequence, and ground elements.
•
87LPA, 87LQA, and 87LGA are the Alpha Plane blocking angle settings for phase,
negative-sequence, and ground elements.
As mentioned previously, 87TOUT is the Relay Word bit that is targeted to look for differential
element operation in test mode. Use the TAR 87TOUT 1000 command to see the differential
element assert (Relay Word bit changes from 0 to 1) or drop out (Relay Word bit changes from
1 to 0) as the test currents are applied.
Use the MET DIF command while injecting currents to look at measured quantities, the validity
of the test set injected quantities, and the position of the operating point on the Alpha Plane. The
following shows an example MET DIF command output capture for a sample single-terminal
characteristic test:
=>>MET DIF
Relay 1
Station R
Date: 05/11/2012 Time: 10:42:35.698
Serial Number: 1111240304
87L Communication: Master
87L Function: Available
Stub Bus:
Disabled
MAG (pu)
ANG (DEG)
THROUGH (pu)
IA
1.634
0.00
1.634
IB
0.000
37.44
0.000
Local Terminal
IC
0.000
37.44
0.000
I1
0.545
0.00
3I2
1.634
0.00
0.000
3I0
1.634
0.00
0.000
MAG (pu)
ANG (DEG)
THROUGH (pu)
IA
6.535
79.97
6.534
IB
0.000
37.44
0.000
Remote Terminal 1
IC
0.000
37.44
0.000
I1
2.178
79.97
3I2
6.535
79.97
0.000
3I0
6.535
79.97
0.000
MAG (pu)
ANG (DEG)
IA
7.007
66.70
IB
0.000
37.44
Differential
IC
0.000
37.44
3I2
7.007
66.70
3I0
7.007
66.70
k
alpha (DEG)
87LA
0.250
79.94
87LB
1.000
180.00
Alpha Plane
87LC
1.000
180.00
87LQ
0.000
0.00
87LG
0.000
0.00
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SINGLE-TERMINAL TESTS
Pickup Setting Check
Step 1.
Connect the proper local current source. Start with no current applied.
Step 2.
Slowly increase the applied local current until Relay Word bit 87TOUT asserts.
The pickup value should be within ±5 percent of the value calculated by (1):
I PICKUP = 87LTAPn • 87LkP
(1)
where:
87LTAPn is 87LTAPW or 87LTAPX, depending on which input is under test.
87LkP is 87LPP for an 87LA, 87LB, or 87LC test; 87LQP for an 87LQ test;
and 87LGP for an 87LG test.
Radius Setting Check
Step 1.
Connect the proper local and remote current sources suggested in Table 1.
Step 2.
Set the magnitudes of the local and remote currents equal to each other and greater
than the pickup value calculated in (1). Set the local current angle at 0 degrees and
the remote current angle at 180 degrees.
Step 3.
Confirm that 87TOUT is deasserted.
Step 4.
Slowly increase the local current until 87TOUT asserts. The pickup value should
be within ±5 percent of the value calculated by (2):
I PICKUP = [magnitude of the remote current] • 87LkR
(2)
where:
87LkR is 87LPR for an 87LA, 87LB, or 87LC test; 87LQR for an 87LQ test;
and 87LGR for an 87LG test.
Block Angle Setting Check
Step 1.
Connect the proper local and remote current sources suggested in Table 1.
Step 2.
Set the magnitudes of local and remote currents equal to each other and greater
than the pickup value calculated in (1). Set the local current angle at 0 degrees and
the remote current angle at 180 degrees.
Step 3.
Confirm that 87TOUT is deasserted.
Step 4.
Rotate the angle of the local current in the counter-clockwise direction until
87TOUT asserts. Record this angle as ANG1.
Step 5.
Reset the angle of the local current to 0 degrees.
Step 6.
Rotate the angle of the local current in the clockwise direction until 87TOUT
asserts. Record this angle as ANG2.
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Step 7.
Assuming that the angles are measured as 0 to +180 degrees and 0 to –180 degrees,
respectively, check that the block angle is set within ±5 percent of the angle
determined by (3):
87LkA
= ANG1 + ANG2
(3)
where:
87LkA is 87LPA for an 87LA, 87LB, or 87LC test; 87LQA for an 87LQ test;
and 87LGA for an 87LG test.
Repeat the preceding steps for each of the differential elements.
Note: You can also test the extended security differential settings of the relay by choosing the
87TESTS = S option in test mode, which switches the normal radius and angle settings
to secure mode settings.
MULTITERMINAL TESTS
Pickup Setting Check
Step 1.
Connect the proper local current source. Do not apply current at any remote
terminal. Start with no current applied.
Step 2.
Slowly increase the applied local current until Relay Word bit 87TOUT asserts.
The pickup value should be within ±5 percent of the value calculated by (4):
I PICKUP = 87LTAPn • 87LkP
(4)
where:
87LTAPn is 87LTAPW or 87LTAPX, depending on which input is under test.
87LkP is 87LPP for an 87LA, 87LB, or 87LC test; 87LQP for an 87LQ test;
and 87LGP for an 87LG test.
Radius Setting Check
Step 1.
Connect the proper local and remote current sources.
Step 2.
Set the magnitude of the local current greater than the pickup value calculated
in (4). Set the local current angle at 0 degrees.
Step 3.
Set the magnitude of the remote current, as determined by (5), at 180 degrees.
I REMOTE = [magnitude of the local current] •
87LTAPn REMOTE
87LTAPn LOCAL
(5)
where:
87LTAPn is 87LTAPW or 87LTAPX, depending on which input is under test.
Step 4.
Date Code 20150401
Confirm that 87TOUT is deasserted.
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Step 5.
Slowly increase the local current until 87TOUT asserts. The pickup value should
be within ±5 percent of the value calculated by (6):
I PICKUP = [magnitude of the local current] • 87LkR
(6)
where:
87LkR is 87LPR for an 87LA, 87LB, or 87LC test; 87LQR for an 87LQ test;
and 87LGR for an 87LG test.
Block Angle Setting Check
Step 1.
Connect the proper local and remote current sources.
Step 2.
Set the magnitudes and angles of local and remote currents as determined in Step 2
and Step 3 in the previous subsection (Radius Setting Check).
Step 3.
Confirm that 87TOUT is deasserted.
Step 4.
Rotate the angle of the local current in the counter-clockwise direction until
87TOUT asserts. Record this angle as ANG1.
Step 5.
Reset the angle of the local current to 0 degrees.
Step 6.
Rotate the angle of the local current in the clockwise direction until 87TOUT
asserts. Record this angle as ANG2.
Step 7.
Assuming that the angles are measured as 0 to +180 degrees and 0 to –180 degrees,
respectively, check that the block angle is set within ±5 percent of the angle
determined by (7):
= ANG1 + ANG2
87LkA
(7)
where:
87LkA is 87LPA for an 87LA, 87LB, or 87LC test; 87LQA for an 87LQ test;
and 87LGA for an 87LG test.
Repeat the preceding steps for each of the differential elements.
Note: You can also test the extended security differential settings of the relay by choosing the
87TESTS = S option in test mode, which switches the normal radius and angle settings
to secure mode settings.
CONCLUSION
This application guide provides the tools to test the characteristics of the differential elements of
the SEL-411L relay in test mode.
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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 USA
Telephone: +1.509.332.1890
Fax: +1.509.332.7990
www.selinc.com • info@selinc.com
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© 2015 by Schweitzer Engineering Laboratories, Inc.
All rights reserved.
All brand or product names appearing in this document are
the trademark or registered trademark of their respective
holders. No SEL trademarks may be used without written
permission.
SEL products appearing in this document may be covered by
U.S. and Foreign patents.
SEL Application Guide 2015-12
*AG2015-12*
Date Code 20150401