Schweitzer Engineering Laboratories SEL-421-4 - Figure 3.7 Negative-Sequence Instantaneous Overcurrent Element Settings: Quickset

3.10
SEL-421 Relay Instruction Manual Date Code 20171021
Testing
Checking Relay Operation
The relay asserts ground overcurrent elements when the 3I
0
calculation exceeds
the ground current element pickup setting. If balanced currents are applied to the
relay, the relay reads 3I
0
= 0 (load conditions) because the currents cancel in the
calculation; the relay does not pick up the ground overcurrent elements.
For testing, apply current to a single phase of the relay, causing the residual over-
current elements to operate. For example, assume 1 A of current on A-Phase and
zero current input on B-Phase and C-Phase:
3I
0
= 1 A + 0 + 0 = 1 A (a simulated ground fault condition)
Checking the Negative-Sequence Instantaneous Overcurrent Element, 50Q1
The procedure in the following steps tests the 50Q1 negative-sequence overcur-
rent element. Use a similar procedure to test other overcurrent elements.
Step 1. Configure the relay.
a. Start
ACSELERATOR QuickSet SEL-5030 Software, and read the
present configuration in the SEL-421.
b. Click Settings > Read.
The relay sends all settings and configuration data to QuickSet.
c. Expand the Group 1 settings and click the Negative-Seq Inst
O/C button of the Settings tree view as shown in Figure 3.7.
You will see the Negative Sequence Instantaneous
Overcurrent dialog box similar to Figure 3.7.
d. Click the arrow in the Instantaneous and Definite Time
Overcurrent Element Levels E50Q dialog box and select 1.
e. For this test, set the 50Q1P level to 1.00 and 67Q1TC to 1.
NOTE: As you perform this test,
other protection elements can assert.
This causes the relay to assert other
targets and possibly close control
outputs. Be sure to isolate the relay
from the power system to avoid
unexpected system effects.
Figure 3.7 Negative-Sequence Instantaneous Overcurrent Element Settings: QuickSet