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Date Code 20150401 SEL Application Guide 2015-12
=>>TEST 87L
Entering 87L Test Mode
Select Test: Characteristic or Loopback (C,L) ? c
Test Mode: Single, Multi Terminal, or Disabled (S,M,D) ? m
87L Element: (A,B,C,Q,G) ? a
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 secure-
mode 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) ? c
Test Mode: Single, Multi Terminal, or Disabled (S,M,D) ? s
87L Element: (A,B,C,Q,G) ? a
Alpha Plane Security: Normal or Secure (N,S) ? n
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
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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