GE T60

GE Multilin T60 Transformer Protection System 8-7
8 COMMISSIONING 8.2 DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES
8
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
and B
2
on the Differential Restraint Characteristic diagram).
1. Inject currents so that the magnitude of I
r
is between the restraint magnitudes defined by Breakpoint 1 and Breakpoint
2; that is:
(EQ 8.10)
For this example, . Remember that the maximum current is the restraint current .
2. The following differential and restraint current should be read from the T60 actual values menu:
The ratio is 36.77% and the Differential element does not operate because the actual is still too
low at .
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 (look in the support documents for the
product). With this tool, the user can see the preset curve point ratios and the actual ratio as per
the entered test currents. The tool graphically indicates differential and restraint current magnitudes and indi-
cates whether the relay should operate.
3. In this example, a ratio of causes the element to trip. Decreasing I
1
as shown in the table below increases
the differential current I
d
, causing the element to operate.
4. The following differential and restraint current should be read from the T60 actual values menu:
WINDING 1 WINDING 2
PHASE SINGLE CURRENT (I
1
) PHASE SINGLE CURRENT (I
2
)
A0 A 0° A 0 A 0°
B 1.2 A 0° B 3.5 A –180°
C 1.2 A –180° C 3.5 A 0°
PHASE DIFFERENTIAL CURRENT (I
d
) PHASE RESTRAINT CURRENT (I
r
)
A0 0° A 0 0°
B 1.287 pu –180° B 3.5 pu –180°
C 1.287 pu 0° C 3.5 pu 0°
WINDING 1 WINDING 2
PHASE SINGLE CURRENT (I
1
) PHASE SINGLE CURRENT (I
2
)
A0 A 0° A 0 A 0°
B 1.1 A 0° B 3.5 A –180°
C 1.1 A –180° C 3.5 A 0°
PHASE DIFFERENTIAL CURRENT (I
d
) PHASE RESTRAINT CURRENT (I
r
)
A0 0° A 0 0°
B 1.471 pu –180° B 3.5 pu –180°
C 1.471 pu 0° C 3.5 pu 0°
I
r
at Breakpoint 1I
r
I
r
at Breakpoint 2
2 pu I
r
8 pu
I
r
3.5 pu=
I
d
I
r

I
d
1.287 pu=
I
r
3.5 pu=
NOTE
I
d
I
r

I
d
I
r

I
d
I
r
 38%