GE T60, Instruction Manual

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GE Multilin T60 Transformer Protection System 9-1
9 COMMISSIONING 9.1 DIFFERENTIAL CHARACTERISTIC TEST
9
9 COMMISSIONING 9.1DIFFERENTIAL CHARACTERISTIC TEST 9.1.1 DESCRIPTION
a) OVERVIEW
The following commissioning tests are organized in two parts: general procedures for testing points of the differential-
restraint characteristics, and examples of the percent differential element response, based on different transformer configu-
rations and fault current distribution. The following tests can be performed by using either 2 or 3 individually adjustable cur-
rents, and do not require additional specialized equipment.
PREPARATION:
1. Select a 0° or 180° transformer phase shift and identical winding connection type into the relay.
2. Select the “Not Within Zone” setting value for each winding grounding setting.
3. Select and set the CT ratios for each winding.
4. Calculate the magnitude compensation factors M[1] and M[2] for each winding.
5. Enable the Transformer Percent Differential element, and enter the required test settings to shape the differential
restraint characteristic.
6. Connect the relay test set to inject x current ( I
x
) into the Winding 1 Phase A CT input, and y current ( I
Y
) into the Wind-
ing 2 Phase A CT input.
TESTING:
The tests of the differential restraint characteristic verify the minimum pickup point, the intersection point of Breakpoint 1
and Slope 1, and the intersection point of Breakpoint 2 and Slope 2.
For simplicity, enter the following settings for each winding:
SYSTEM SETUP

TRANSFORMER

WINDING 1(4)

WINDING 1(4) CONNECTION:
“Wye”
SYSTEM SETUP

TRANSFORMER

WINDING 1(4)

WINDING 1(4) GROUNDING:
“Not Within Zone”
SYSTEM SETUP

TRANSFORMER

WINDING 2(4)

WINDING 2(4) ANGLE WRT WINDING 1:
“0°”
If the power transformer phase shift is 0°, the two currents to be injected to the relay should be 180° apart. The 180° phase
shift results from the inversion of the field CT, as their positive marks are away from the protected transformer terminals and
are connected to the positively marked terminals on the relay.
b) MINIMUM PICKUP
Inject current ( I
x
) into Winding 1 Phase A and monitor the per-unit Phase A differential current until it exceeds the minimum
pickup setting. The theoretical injected current for minimum pickup verification can be computed as follows:
(EQ 9.1)
where CT is the 1 A or 5 A tap, and M[1] is the calculated magnitude compensation factor (see the Transformer section in
Chapter 5 for details on calculating the M[1] and M[2] factors).
I
x
minimum pickup
CT
M[1]
----------- ×
=