GE T35 Instruction Manual page 342

Transformer protection system ur series
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9.1 DIFFERENTIAL CHARACTERISTIC TEST
c) SLOPE 1 / BREAKPOINT 1
The point of Slope 1 and Breakpoint 1 is tested as follows. Refer to the Differential Restraint Characteristic diagram below
for details.
1.
Inject current (I
2.
At Breakpoint 1, the injected current I
and the differential current should be equal to:
3.
Preset the I
x
ratio will become less than the Slope 1 setting. Switch off the current.
4.
Preset the I
x
To test any other point from the Slope 1 section of the curve, inject a per-unit restraint current smaller than the Breakpoint 1
current and repeat the steps above by substituting the Breakpoint 1 value with the new per-unit restraint current value into
the equations above.
d) SLOPE 2 / BREAKPOINT 2
The point of Slope 2 and Breakpoint 2 is tested as follows. Refer to the diagram below for details.
1.
Preset the I
y
calculation to define the magnitude of the injected current:
2.
At the above current (restraint), the I
3.
Preset the I
x
ratio will become less than the Slope 2 setting. Switch off the current.
4.
Preset the I
x
To test any point from the Slope 2 portion of the characteristic, inject a per-unit restraint current greater than the Breakpoint
2 current as restraint and repeat the steps above by substituting the Breakpoint 2 value in the equations above with the new
per-unit restraint current value.
The above two tests can be repeated for Phases B and C.
9
9-2
) into Winding 2 Phase A as follows:
y
I
YB1
XOP1
I
Breakpoint 1
=
XOP1
I
Slope 1 (in %) Breakpoint 1 (in pu)
=
d
current to
1.05 I
. Switch on the test set. The relay should restraint, as the differential to restraint
XOP1
current to
0.95 I
. Switch on the test set. The relay should operate. Switch off the current.
XOP1
current to a magnitude that results in the restraint current being equal to Breakpoint 2. Use the following
I
YB2
current required to operate the element is calculated as:
XOP2
I
Breakpoint 2
=
XOP2
current to
1.05 I
and switch on the test set. The relay should restrain, as the differential to restraint
XOP1
current to
0.95 I
. Switch on the test set and verify relay operation. Switch off the current.
XOP1
I
(pu)
d
PKP
Figure 9–1: DIFFERENTIAL RESTRAINT CHARACTERISTIC
T35 Transformer Protection System
CT
---------- -
Breakpoint 1
=
M[2]
is determined by:
CT
---------- -
1 Slope 1
M[1]
CT
---------- -
Breakpoint 2
=
M[2]
CT
---------- -
1 Slope 2
M[1]
S
2
S
1
B
B
1
2
9 COMMISSIONING
I
(pu)
r
(EQ 9.2)
(EQ 9.3)
(EQ 9.4)
(EQ 9.5)
(EQ 9.6)
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