GE 845 Instruction Manual page 220

SYSTEM
NOTE:
4–116
automatically compensate winding currents forming the differential current in the
transformer differential protection, or in cases where the differential protection is not
used at all.
All transformer windings from 845 are associated with CT bank inputs. Depending on
845 ordering, the following CT banks represent the winding currents:
1. 845 orders for two-winding transformers without voltage inputs:
– K1 CT bank is used for Winding 1
– K2 CT bank is used for Winding 2
2. 845 orders for two-winding transformers with voltage inputs:
– J1 CT bank is used for Winding 1
– K1 CT bank is used for Winding 2
3. 845 orders for three-winding transformers (voltage inputs always included):
– J1 CT bank is used for Winding 1
– K1 CT bank is used for Winding 2
– K2 CT bank is used for Winding 3
If the Tap Changer setpoint TC Winding Currents is set to J1, K1, or K2, the computed tap
position voltage will be used for automatic magnitude mismatch compensation for the
winding represented by the same CT bank currents. Otherwise, if the setpoint TC Winding
Currents is set to "None", the mismatch magnitude computation is not automatically
updated to include the new transformation ratio. In such cases, the relay may display
differential current, where this current will be higher for taps far away from the tap
representing the nominal winding voltage, and it will be lower for taps closer to the
nominal voltage tap. It is recommended to increase the minimum PKP setting of the
Percent Differential characteristic to be above the maximum differential current that can
be seen at either Maximum tap, or Minimum tap.
TAP DETECTION INPUT
Range: BCD
Default: BCD
MIN TAP
Range: -19 to +35 in steps of 1
Default: -16
This setting defines the minimum tap from the tap changer. The 845 uses the setting to
signal when the minimum tap is reached.
NEUTRAL TAP
Range: -17 to +37 in steps of 1
Default: 0
This setting defines the neutral tap position. The 845 uses the setting to signal when the
neutral tap is reached.
MAX TAP
Range: 0 to +39 in steps of 1
Default: +16
This setting defines the maximum tap from the tap changer. The 845 uses this setting to
signal when the maximum tap is reached.
MIN TAP VOLTAGE
Range: 0.01 to 20000.00 kV in steps of 0.01 kV
Default: 61.00 kV
Enter the voltage at the minimum position
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS