GE T60 Instruction Manual page 603
Transformer protection system
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CHAPTER 8: COMMISSIONING
The tests verify the operation and no-operation response for points from all regions of the percentage differential
characteristic. These tests are:
•
Test for zero differential current
•
Minimum pickup
•
Slope 1
•
The region between Slope 1 and Slope 2
•
Slope 2
Relay configuration
The AC Inputs and Source are configured as follows.
Table 8-1: AC Inputs and Source configuration
AC Inputs setting
CT F1
Phase CT Primary
200
Phase CT Secondary
1
Ground CT Primary
X
Ground CT Secondary
X
Two winding transformer configuration
Table 8-2: Winding configuration
Winding 1 settings
Value
Source
SRC 1
Rated MVA
20 MVA
Nom Ph-Ph Voltage
115 kV
Connection
Wye
Grounding
Not within zone
Angle WRT
0°
Resistance 3Ph
10.000 ohms
Application of excessive current (> 3 ´ In) for extended periods damages the relay.
8.2.2.2 Test for zero differential current
1.
Inject the following currents into the relay.
Winding 1
Phase
Single current (I
A
0 A ∠0°
B
0.434 A ∠0°
C
0.434 A ∠–180°
2.
These are determined as follows.
From the Current Distribution diagram earlier, there is a 0.866 pu x 100.4 A/200 = 0.434 A secondary current for HV
phases B and C, and a 0.866 pu x 925.98 A/1000 = 0.8 A secondary current for LV phases b and c.
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CT M1
Source setting
1000
Name
1
Phase CT
X
Ground CT
X
Phase VT
Aux VT
Winding 2 Settings
Source
Rated MVA
Nom Ph-Ph Voltage
Connection
Grounding
Angle WRT
Resistance 3Ph
Winding 2
)
Phase
Single current (I
1
A
0 A ∠0°
B
0.8 A ∠–180°
C
0.8 A ∠0°
DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES
Source 1
Source 2
SRC 1
SRC 2
F1
M1
X
X
X
X
X
X
Value
Percent Diff
SRC 2
Minimum PKP
20 MVA
Slope 1
12.47 kV
Breakpoint 1
Wye
Breakpoint 2
Within zone
Slope 2
0°
10.000 ohms
)
2
Value
0.1 pu
15%
2 pu
8 pu
95%
8
Eq. 8-7
8-5
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