Test Example 2 - GE T35 Instruction Manual

8 COMMISSIONING
e) INTERMEDIATE CURVE BETWEEN BREAKPOINT 1 AND BREAKPOINT 2
This procedure tests the intermediate section of the differential characteristic curve that lies between the Breakpoint 1 and
Breakpoint 2 points (points B
1
1. Inject currents so that the magnitude of I
2; that is:
<
For this example, 2 pu I
WINDING 1
PHASE SINGLE CURRENT (I
0 A ∠0°
A
1.2 A ∠0°
B
1.2 A ∠–180°
C
2. The following differential and restraint current should be read from the T35 actual values menu:
PHASE DIFFERENTIAL CURRENT (I
0 ∠0°
A
1.287 pu ∠–180°
B
1.287 pu ∠0°
C
⁄
The I I ratio is 36.77% and the Differential element does not operate because the actual
d r
low at I 3.5 pu .
=
r
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 Multilin website at http://www.GEindustrial.com/multilin.
NOTE With this tool, the user can see the preset
test currents. The tool graphically indicates differential and restraint current magnitudes and indicates whether
the relay should operate.
3. In this example, a ratio of
the differential current I , causing the element to operate.
d
WINDING 1
PHASE SINGLE CURRENT (I
0 A ∠0°
A
1.1 A ∠0°
B
1.1 A ∠–180°
C
4. The following differential and restraint current should be read from the T35 actual values menu:
PHASE DIFFERENTIAL CURRENT (I
0 ∠0°
A
1.471 pu ∠–180°
B
1.471 pu ∠0°
C
GE Multilin
and B on the Differential Restraint Characteristic diagram).
2
is between the restraint magnitudes defined by Breakpoint 1 and Breakpoint
r
( ) I < <
I at Breakpoint 1
r r
<
8 pu . Remember that the maximum current is the restraint current
r
WINDING 2
) PHASE SINGLE CURRENT (I
1
0 A ∠0°
A
3.5 A ∠–180°
B
3.5 A ∠0°
C
) PHASE RESTRAINT CURRENT (I
d
0 ∠0°
A
3.5 pu ∠–180°
B
3.5 pu ∠0°
C
⁄
I I
d r
⁄ >
I I 38% causes the element to trip. Decreasing I
d r
WINDING 2
) PHASE SINGLE CURRENT (I
1
0 A ∠0°
A
3.5 A ∠–180°
B
3.5 A ∠0°
C
) PHASE RESTRAINT CURRENT (I
d
0 ∠0°
A
3.5 pu ∠–180°
B
3.5 pu ∠0°
C
T35 Transformer Management Relay
8.2 DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES
( )
I at Breakpoint 2
r
)
2
)
r
curve point ratios and the actual
as shown in the table below increases
1
)
2
)
r
(EQ 8.10)
I 3.5 pu .
=
r
I 1.287 pu is still too
=
d
⁄
I I ratio as per the entered
d r
8-7
8