GE T60 Instruction Manual page 604
Transformer protection system
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DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES
3.
When test setup is correct, the relay displays the following differential and restraint currents, and the element does
not operate.
Phase
Differential current (I
0 ∠0°
A
B
0 ∠0°
C
0 ∠0°
8.2.2.3 Minimum pickup test
Reduce the restraint current I
the pickup). This is obtained from I
the setting of Slope 1. Note that
where I
is an intersection of Minimum PKP and Slope 1 calculated as PKP/Slope 1 value.
ri
1.
Change the current magnitude as follows.
Winding 1
Phase
Single current (I
A
0 A ∠0°
B
0.15 A ∠0°
C
0.15 A ∠–180°
2.
Read the following differential and restraint current values from the T60 actual values menu.
Phase
Differential current (I
A
0 ∠0°
B
0.044 pu ∠0°
C
0.044 pu ∠0°
The relay does not operate since I
3.
Increase I
to 0.2 A. The differential current increases to I
1
4.
Verify that the Percent Differential element operates and the following are displayed in the actual values menu.
Phase
Differential current (I
A
0 ∠0°
B
0.136 ∠0°
C
0.136 ∠0°
8.2.2.4 Slope 1 test
8
Inject current in such a manner that the magnitude of I
intersection of the minimum PKP and Slope 1 and smaller than the Breakpoint 1 setting; that is,
1.
Change the current magnitudes as follows.
Winding 1
Phase
Single current (I
0 A ∠0°
A
0.48 A ∠0°
B
0.48 A ∠–180°
C
8-6
)
Phase
Restraint current (I
d
0 ∠0°
A
B
0.801 pu ∠–180°
C
0.801 pu ∠0°
to a value lower than 0.67 pu (the restraint corresponding to the intersection of Slope 1 and
r
= 0.1/0.15 = 0.67 pu, where 0.1 is the differential setting of minimum pickup, and 0.15 is
r
0 < I
r
Winding 2
)
Phase
Single current (I
1
A
0 A ∠0°
B
0.23 A ∠–180°
C
0.23 A ∠0°
)
Phase
Restraint current (I
d
A
0 ∠0°
B
0.275 pu ∠–180°
C
0.275 pu ∠0°
is still lower that the 0.1 pu
d
)
Phase
Restraint current (I
d
A
0 ∠0°
B
0.367 pu ∠–180°
C
0.367 pu ∠0°
is larger than the restraint current of 0.67 pu, corresponding to the
r
I
(intersection of Min PKP and Slope 1) < I
r
Winding 2
)
Phase
Single current (I
1
0 A ∠0°
A
1 A ∠–180°
B
1 A ∠0°
C
)
r
<I
ri
)
2
)
r
setting.
MINIMUM PICKUP
= 0.136 pu > Min PKP and I
d
)
r
(actual) < I
(Break 1)
r
r
)
2
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 8: COMMISSIONING
Eq. 8-8
< 0.67 pu.
r
Eq. 8-9
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