GE 845 Instruction Manual page 206

SYSTEM
Windings
4–78
Path: Setpoints > System > Transformer > Winding 1
Path:
Setpoints > System > Transformer > Winding 2(3)
All transformer windings from 845 are associated with CT bank inputs. Depending on the
selected 845 order code, the following CT banks represent the winding currents:
1. 845 orders for two-winding transformers without voltage inputs:
– Winding 1-K1 CT bank
– Winding 2-K2 CT bank
2. 845 orders for two-winding transformers with voltage inputs:
– Winding 1-J1 CT bank
– Winding 2-K1 CT bank
Voltage inputs: J2 VT bank
3. 845 orders for three-winding transformers (voltage inputs are always included):
– Winding 1-J1 CT bank
– Winding 2-K1 CT bank
– Winding 3-K2 CT bank
Voltage inputs: J2 VT bank
Transformer differential protection uses calculated quantities (per phase): fundamental,
2nd harmonic and 5th harmonic differential current phasors, and restraint current
phasors. This information is extracted from the current transformers (CTs) connected to the
relay by correcting the magnitude and phase relationships of the currents for each
winding, so as to obtain zero (or near zero) differential currents under normal operating
conditions. Traditionally, these corrections were accomplished by interposing CTs and
tapped relay windings with some combination of CT connections.
The 845 simplifies these configuration issues. All CTs at the transformer can be connected
wye (polarity markings pointing away from the transformer). User-entered settings in the
relay characterizes the transformer being protected and allows the relay to automatically
perform all necessary magnitude, phase angle, and zero-sequence compensation.
The settings specific to each winding are shown as follows.
WINDING SETTINGS
RATED MVA
Range: 0.001 to 2000.000 MVA in steps of 0.001
Default: 5.000 MVA
Enter the self-cooled (100%) load rating for the power transformer.
NOMINAL PH-PH VOLTAGE
Range: 0.001 to 1000.000 KV in steps of 0.001
Default: 13.800 kV
Enter the nominal phase to phase voltage rating winding 1 of the transformer.
CONNECTION
Range: Wye, Delta, Zig-Zag
Default: Wye
Enter the winding connection.
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS