Sel 751A - Current Imbalance Metering Accuracy; Table 10.2 Phase Current Measuring Accuracy; Table 10.3 Current Unbalance Measuring Accuracy; Figure 10.3 Current Source Connections

10.6
SEL-751A Relay Instruction Manual Date Code 20100129
Testing and Troubleshooting
Commissioning Tests
Figure 10.3 Current Source Connections
Current Imbalance Metering Accuracy
Step 1. Connect the current source to the relay, as shown in
Figure 10.3.
Step 2. Using the front-panel
SET/SHOW function or the serial port SHO
command, record the CTR and PHROT setting values.
Step 3. Set the phase current angles to apply balanced three-phase
currents in accordance with the PHROT setting. Refer to
Figure 10.1.
Step 4. Apply the appropriate magnitude for each phase current, as
shown in Column 1 of Table 10.3.
Table 10.2 Phase Current Measuring Accuracy
|I| Applied
(A secondary)
a
a
I
NOM
= rated secondary amps (1 or 5).
Expected
Reading
CTR x |I|
A–Phase
Reading
(A primary)
B–Phase
Reading
(A primary)
C–Phase
Reading
(A primary)
0.2 x I
NOM
0.9 x I
NOM
1.6 x I
NOM
SEL-751A
Current
Test
Source
IA
IB
IC
IC
IB
IA
IN
Z01
Z02
Z03
Z04
Z05
Z06
Table 10.3 Current Unbalance Measuring Accuracy (Sheet 1 of 2)
|I| Applied (A secondary) Expected Reading (%) Actual Reading (%)
|IA| = 0.9 • I
NOM
7%
|IB| =
I
NOM
|IC| = I
NOM
|IA| = 0.75 • I
NOM
17%
|IB| =
I
NOM
|IC| = I
NOM
|IA| = I
NOM
12%
|IB| = 1.2 •
I
NOM
|IC| = 1.2 • I
NOM