GE T35 Instruction Manual page 522

DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES
Due to the mathematical complexity involved in shaping the curve between Breakpoint 1 and Breakpoint 2, an
Excel-based simulation tool is available from the GE Grid Solutions website (look for the T35/T60 Percent Differential
Element Simulator in the support documents for the product). With this tool, you can see the preset I
ratios and the actual I
restraint current magnitudes and indicates whether the relay operates.
3. In this example, a ratio of I
differential current I
Winding 1
Phase Single current (I
A 0 A ∠0°
B 1.1 A ∠0°
C 1.1 A ∠–180°
4. Read the following differential and restraint current values from the T35 actual values menu.
Phase Differential current (I
A 0 ∠0°
B 1.471 pu ∠–180°
C 1.471 pu ∠0°
8.2.2.6 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
C 0.5 A ∠–180°
2. Read the following differential and restraint current values from the T35 actual values menu.
Phase Differential current (I
A 0 ∠0°
8.078 pu ∠–180°
B
8.078 pu ∠0°
C
8
Since I /I = 89.8% and lower than the required 95%, the Percent Differential element does not operate.
d r
3. Adjust the I current as follows (thereby increasing I
1
Winding 1
Phase Single current (I
0 A ∠0°
A
B 0.2 A ∠0°
C 0.2 A ∠–180°
8-8
/I ratio as per the entered test currents. The tool graphically indicates differential and
d r
/I > 38% causes the element to trip. Decreasing I
d r
, causing the element to operate.
d
Winding 2
) Phase Single current (I
1
A 0 A ∠0°
B 3.5 A ∠–180°
C 3.5 A ∠0°
) Phase
d
A
B
C
I > I (Break 2) = 8 pu
r r
Winding 2
) Phase Single current (I
1
0 A ∠0°
A
9 A ∠–180°
B
C 9 A ∠0°
) Phase
d
A
B
C
Winding 2
) Phase Single current (I
1
0 A ∠0°
A
B 9 A ∠–180°
C 9 A ∠0°
as shown in the table increases the
1
)
2
Restraint current (I )
r
0 ∠0°
3.5 pu ∠–180°
3.5 pu ∠0°
is larger than the restraint current at Breakpoint 2; that is,
r
)
2
Restraint current (I )
r
0 ∠0°
9 pu ∠–180°
9 pu ∠0°
) and verify that the relay operates.
d
)
2
T35 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 8: COMMISSIONING
/I curve point
d r
Eq. 8-11