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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
AC
SEL
ERATOR
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
.
You will see the
Negative Sequence Instantaneous
Overcurrent
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
Содержание SEL-421-4
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