10.21
Date Code 20170601
Instruction Manual
SEL-387-0, -5, -6 Relay
Testing and Troubleshooting
Acceptance Testing
U87P Unrestrained Differential Element
Step 1. Purpose: Verify the expected unrestrained differential element
pickup setting.
Method: Execute the
SHO
command via the relay front panel
or serial port and verify the setting (i.e.,
SHO U87P <Enter>
).
This value is in per unit of tap.
Step 2. Purpose: Calculate the required current to pick up the
unrestrained differential element.
Method:
a. Calculate the expected pickup for the 87U element by
multiplying the U87P setting by the TAP1, TAP2,
TAP3, or TAP4 setting and the compensation constant
A shown in
. The CT connection
compensation settings W1CTC, W2CTC, W3CTC, and
W4CTC determine the A constant for the calculations.
b. Use the corresponding TAP
n
and W
n
CTC settings for
the winding under test.
Step 3. Purpose: Display the appropriate Relay Word bit on the front-
panel LEDs.
Method: Execute the
TARGET
command (i.e.,
TAR F 87U
<Enter>
). The SEL-387 now displays the state of several
differential elements in the second row of the front-panel
LEDs. The 87U bit is the fourth from the left.
Step 4. Purpose: Connect and ramp a single current test source until the
appropriate LED illuminates.
Method:
a. Connect a single current test source as shown in
b. Turn on the current test source for the winding under
test, and slowly increase the magnitude of current
applied until the 87U element asserts. Note the
magnitude of the current applied. It should equal the
value calculated in
, ±5% ±0.02 I
NOM
.
Step 5. Purpose: Repeat the test for each phase for each winding if
desired.
Method:
a. Repeat
through
b. Remember to view the appropriate TARget and apply
current to the appropriate winding. The computer
terminal will display the LED labels from left to right
when the
TAR F
command is issued.
Table 10.4
Connection Compensation Factor
WnCTC Setting
A and B Constants
0
1
Odd: 1, 3, 5, 7, 9, 11
3
Even: 6, 12
1.5
Even: 2, 4, 8, 10
3.0
!
CAUTION
The continuous rating of the current
inputs is 3 • I
NOM
. For this test, you
may want to choose low values of
U87P and TAPn, in order to limit the
required test current to a safe value.
Summary of Contents for SEL-387-0
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