GE T35 Instruction Manual page 216

8.1 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 ) into Winding 2 Phase A as follows:
y
2. At Breakpoint 1, the injected current I
and the differential current should be equal to:
3. Preset the I current to
x
ratio will become less than the Slope 1 setting. Switch off the current.
4. Preset the I current to
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 current to a magnitude that results in the restraint current being equal to Breakpoint 2. Use the following
y
calculation to define the magnitude of the injected current:
2. At the above current (restraint), the I
3. Preset the I current to
x
ratio will become less than the Slope 2 setting. Switch off the current.
4. Preset the I current to
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.
8
The above two tests can be repeated for Phases B and C.
8-2
I Breakpoint 1
=
YB1
is determined by:
XOP1
I Breakpoint 1
=
XOP1
×
I Slope 1 (in %) Breakpoint 1 (in pu)
=
d
×
1.05 I . Switch on the test set. The relay should restraint, as the differential to restraint
XOP1
×
0.95 I . Switch on the test set. The relay should operate. Switch off the current.
XOP1
I Breakpoint 2
=
YB2
current required to operate the element is calculated as:
XOP2
I Breakpoint 2
=
XOP2
×
1.05 I and switch on the test set. The relay should restrain, as the differential to restraint
XOP1
×
0.95 I . Switch on the test set and verify relay operation. Switch off the current.
XOP1
I (pu)
d
S
1
PKP
Figure 8–1: DIFFERENTIAL RESTRAINT CHARACTERISTIC
T35 Transformer Management Relay
CT
× ---------- -
M[2]
CT
× ( ) ×
---------- -
1 Slope 1
–
M[1]
CT
×
---------- -
M[2]
CT
× ( ) × ---------- -
1 Slope 2
–
M[1]
S
2
B B
I (pu)
1 2
r
8 COMMISSIONING
(EQ 8.2)
(EQ 8.3)
(EQ 8.4)
(EQ 8.5)
(EQ 8.6)
GE Multilin