GE P645

3 IMPLEMENTATION
To enable or disable Differential Protection, set Diff Pr
otection in the CONFIGURATION column and Trans Diff in the
DIFF PROTECTION column of the of the relevant settings group.
3.1 DEFINING THE POWER TRANSFORMER
To set up the transformer differential protection you need to define what type of transformer is being protected.
Y
ou do this with settings in the SYSTEM CONFIG column.
The P642 only supports two-winding transformers. For the P643 and P645, the Winding Config setting determines
whether the power transformer being protected is a two-winding (HV+LV), or a three-winding (HV+LV+TV)
transformer.
The Winding Type setting determines whether the protected transformer is a conventional transformer or an
autotransformer.
The Ref Power S setting sets the reference power of the protected transformer. This is used as a reference by the
differential function to calculate the ratio correction factors (which incidentally are displayed in the Match Factor
CT cells. The reference power is the maximum MVA rating specified in the transformer nameplate.
You can define each winding as Y (or Star, or Wye), D (delta), or Z (zigzag) in the settings HV connection, LV
Connection and TV connection.
You also need to set the nominal voltage of each winding. You do this with the settings HV Nominal, LV Nominal
and TV Nominal.
To ensure the device can perform vector group correction, you need to enter the vector groups for the LV and TV
windings. You do this by entering the relevant vector group reference (available on the nameplate) using the
settings LV Vector Group and TV Vector Group.
In addition to the LV Vector Group and TV Vector Group settings, there is a setting called Ref Vector Group. This
setting allows you to apply a phase shift to the HV current inputs. In the majority of cases, this would be set to 0,
but there are some specialist applications where you may wish to set the reference vector group to something
other than 0. An application note at the end of this chapter explains why you would want do to this.
Finally, you need to set the phase sequence with the Phase Sequence setting. This will be either standard ABC
or Reverse ACB.
If the phase rotation is changed from ABC to ACB, then the vector group settings need to reflect this change
accordingly. This can be achieved by setting them to be equal to 12 minus the original value. For example a Yd11
transformer has a vector group setting of 11 when the phase sequence is ABC. However if the phase sequence
changes to ACB, then the vector group setting should be set to 1.
Note:
To minimise imbalances due to tap changer operation, current inputs to the differential element should be set according to
the mid-tap position and not the nominal voltage. The Ref Vector Group setting provides a reference vector group to which
all other vector groups are referenced. Typically, this is set to 0°.
3.2 SELECTING THE CURRENT INPUTS
The P642 has two current terminal inputs (T1 and T2), the P643 has up to three terminal current inputs (T1 to T3),
and the P645 has up to fiv
e current terminal inputs (T1 to T5).
For the P642, you associate one terminal current input with the HV (High Voltage) winding and the other with the
LV (Low Voltage) winding.
For the P643 and P645 you can choose to associate more than one terminal current input with particular windings.
In cases where more than one terminal CT is associated with a winding, the input to the differential protection
P64x Chapter 6 - Transformer Differential Protection
P64x-TM-EN-1.3 107