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9.2 DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES
f) SLOPE 2 TEST
Inject currents in such a manner that the magnitude of I
1.
Change the current magnitudes as follows:
WINDING 1
PHASE
SINGLE CURRENT (I
0 A ∠0°
A
0.5 A ∠0°
B
0.5 A ∠–180°
C
2.
The following differential and restraint current should be read from the T60 actual values menu:
PHASE
DIFFERENTIAL CURRENT (I
0 ∠0°
A
B
8.078 pu ∠–180°
C
8.078 pu ∠0°
⁄
Since
I
I
=
d
r
3.
Adjust the I
1
WINDING 1
PHASE
SINGLE CURRENT (I
0 A ∠0°
A
0.2 A ∠0°
B
0.2 A ∠–180°
C
4.
The following differential and restraint current should appear in the T60 actual values menu:
PHASE
DIFFERENTIAL CURRENT (I
A
0 ∠0°
B
8.631 pu ∠–180°
8.631 pu ∠0°
C
5.
The actual
I
d
g) SUMMARY
The above tests describe the principles of testing the differential element for all regions from the operating characteristic.
For verification of more points, one should consider adjusting the magnitude of the restraint current I
of the characteristic and change the other current to vary I
actual and expected operating values.
A blank result table is provided at the end of this chapter for convenience.
9
9-8
I
r
WINDING 2
)
PHASE
1
A
B
C
)
d
89.8%
and lower than the required 95%, the Percent Differential element will not operate.
current as shown below (thereby increasing I
WINDING 2
)
PHASE
1
A
B
C
)
d
⁄
I
ratio is now 95.9%. Verify that the element operates correctly.
r
T60 Transformer Protection System
is larger than the restraint current at Breakpoint 2; that is,
r
>
I
(
Break 2
)
8 pu
=
r
SINGLE CURRENT (I
)
2
0 A ∠0°
9 A ∠–180°
9 A ∠0°
PHASE
RESTRAINT CURRENT (I
0 ∠0°
A
B
9 pu ∠–180°
C
9 pu ∠0°
) and verify that the relay operates.
d
SINGLE CURRENT (I
)
2
0 A ∠0°
9 A ∠–180°
9 A ∠0°
PHASE
RESTRAINT CURRENT (I
A
0 ∠0°
B
9 pu ∠–180°
9 pu ∠0°
C
until the relay operates. Use the Excel tool to compare the
d
9 COMMISSIONING
)
r
)
r
to the desired portion
r
(EQ 9.11)
GE Multilin
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