CHAPTER 8: COMMISSIONING DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES
T35 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL 8-5
8
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
Two winding transformer configuration
Table 8-2: Winding configuration
8.2.2.2 Test for zero differential current
1. Inject the following currents into the relay.
2. These are determined as follows.
Eq. 8-7
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.
AC Inputs setting CT F1 CT M1 Source setting Source 1 Source 2
Phase CT Primary 200 1000 Name SRC 1 SRC 2
Phase CT Secondary 1 1 Phase CT F1 M1
Ground CT Primary X X Ground CT X X
Ground CT Secondary X X Phase VT X X
Aux VT X X
Winding 1 settings Value Winding 2 Settings Value Percent Diff Value
Source SRC 1 Source SRC 2 Minimum PKP 0.1 pu
Rated MVA 20 MVA Rated MVA 20 MVA Slope 1 15%
Nom Ph-Ph Voltage 115 kV Nom Ph-Ph Voltage 12.47 kV Breakpoint 1 2 pu
Connection Wye Connection Wye Breakpoint 2 8 pu
Grounding Not within zone Grounding Within zone Slope 2 95%
Angle WRT 0° Angle WRT 0°
Resistance 3Ph 10.000 ohms Resistance 3Ph 10.000 ohms
Application of excessive current (> 3 ´ In) for extended periods damages the relay.
Winding 1 Winding 2
Phase Single current (I
1
) Phase Single current (I
2
)
A0 A ∠0° A 0 A ∠0°
B 0.434 A ∠0° B 0.8 A ∠–180°
C 0.434 A ∠–180° C 0.8 A ∠0°
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