GE T60 User Manual

8-2 T60 Transformer Protection System GE Multilin
8.1 DIFFERENTIAL CHARACTERISTIC TEST 8 COMMISSIONING
8
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
y
) into Winding 2 Phase A as follows:
(EQ 8.2)
2. At Breakpoint 1, the injected current I
XOP1
is determined by:
(EQ 8.3)
and the differential current should be equal to:
(EQ 8.4)
3. Preset the I
x
current to . Switch on the test set. The relay should restraint, as the differential to restraint
ratio will become less than the Slope 1 setting. Switch off the current.
4. Preset the I
x
current to . Switch on the test set. The relay should operate. Switch off the current.
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
current to a magnitude that results in the restraint current being equal to Breakpoint 2. Use the following
calculation to define the magnitude of the injected current:
(EQ 8.5)
2. At the above current (restraint), the I
XOP2
current required to operate the element is calculated as:
(EQ 8.6)
3. Preset the I
x
current to and switch on the test set. The relay should restrain, as the differential to restraint
ratio will become less than the Slope 2 setting. Switch off the current.
4. Preset the I
x
current to . Switch on the test set and verify relay operation. Switch off the current.
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.
Figure 8–1: DIFFERENTIAL RESTRAINT CHARACTERISTIC
I
YB1
Breakpoint 1
CT
M[2]
-----------
=
I
XOP1
Breakpoint 1 1 Slope 1–
CT
M[1]
-----------
=
I
d
Slope 1 (in %) Breakpoint 1 (in pu)=
1.05 I
XOP1

0.95 I
XOP1

I
YB2
Breakpoint 2
CT
M[2]
-----------
=
I
XOP2
Breakpoint 2 1 Slope 2–
CT
M[1]
-----------
=
1.05 I
XOP1

0.95 I
XOP1

I
d
(pu)
I
r
(pu)
PKP
B
1
S
2
S
1
B
2

GE T60 Specifications

General

Brand	GE
Model	T60
Category	Relays
Language	English