8.11
Date Code 20110408 Instruction Manual SEL-551 Relay
Testing and Troubleshooting
Acceptance Testing
Inverse-Time
Overcurrent Elements
Step 1. Purpose:
Determine the expected time delay for the overcurrent element.
Method:
a. Execute the SHO command via the relay front panel or
serial port and verify the time delay settings (i.e., SHO
51P1P <Enter>).
The delay settings will follow the pickup settings when
they are displayed.
b. Calculate the time delay to pickup (tp).
Inverse-time elements are calculated using three
element settings and the operating time equations
shown in Section 4: Setting the Relay. TD is the time-
dial setting (i.e., 51P1TD), and M is the applied
multiple of pickup current.
For example, if 51P1P = 2.2 A, 51P1C = U3, and
51P1TD = 4.0, we can use the equation below to
calculate the expected operating time for M = 3
(applied current equals M • 51P1P = 6.6 A):
Equation 8.1
Step 2. Purpose:
Set the Sequential Event Recorder to record the element timing.
Method:
a. Use SET R SER1 <Enter> to set SER1 equal to the
element pickup and time-out Relay Word bits (i.e.,
51P1, 51P1T).
b. When prompted, set SER2 and SER3 to NA.
c. Save settings.
Step 3. Purpose:
Connect and apply a single current test source at a level that is
M times greater than the pickup (i.e., 2.2 • M = 6.6 A; M = 3 for
this example).
Method:
a. Connect a single current test source (i.e., source 1 to
current input IA) as shown in Figure 8.3.
b. Turn on the single current test source for the phase
under test at the desired level.
Step 4. Purpose:
Verify the operation times.
Method:
a. Type SER <Enter> to view the sequential event
records.
The assertion and deassertion of each element listed in
the SER 1, 2, and 3 settings is recorded.
NOTE: This example tests the 51P1T
phase inverse-time overcurrent
element. Use the same procedure to
test all inverse-time overcurrent
elements for each phase.
tp TD 0.0963
3.88
M
2
1–
----------------+
⎝⎠
⎛⎞
• =
tp 2.33 seconds=
To Next Page
Loading...
