GE 845 Instruction Manual page 336

PROTECTION
4–232
CALIBRATION
Range: 0 to 0.95° in steps of 0.05°
Default: 0°
This setting allows the Relay Characteristic Angle to change in steps of 0.05°. This may
be useful when a small difference in VT and CT angular errors is to be compensated to
permit more sensitive settings.
The setting virtually enables calibration of the Directional Power function in terms of the
angular error of applied VTs and CTs. The element responds to the sum of the DIR
POWER 1 RCA and DIR POWER 1 CALIBRATION settings.
STAGE 1 SMIN
Range: -1.200 to 1.200 x Rated Power in steps of 0.001 x Rated Power
Default: 0.100 x Rated Power
The setting specifies the minimum power as defined along the relay characteristic angle
(RCA) for the stage 1 of the element. The positive values imply a shift towards the
operate region along the RCA line; the negative values imply a shift towards the restrain
region along the RCA line. Refer to the Directional power sample applications figure for
details. Together with the RCA, this setting enables a wide range of operating
characteristics.
The setting applies to three-phase power and the rated power is as follows:
Rated Power = 3 x VT
Secondary (phase-neutral)
1/2
Rated Power = (3) x VT
For example:
A setting of 2% for a 200 MW machine is 0.02 × 200 MW = 4 MW. If 7.967 kV is a primary
VT phase-neutral voltage and 10 kA is a primary CT current, the source rated power is
239 MVA, and, SMIN must be set at 4 MW/239 MVA =0.0167 x Rated ≈ 0.017 x Rated. If
the reverse power application is considered, RCA = 180° and SMIN = 0.017 x Rated.
The element drops out if the magnitude of the positive-sequence current becomes
virtually zero, that is, it drops below the cutoff level.
STAGE 1 DELAY
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 0.500 s
The setting specifies a time delay for stage 1. For reverse power or low forward power
applications for a synchronous machine, stage 1 is typically applied for alarming and
stage 2 for tripping.
STAGE 2 SMIN
Range: -1.200 to 1.200 x Rated Power in steps of 0.001 x Rated Power
Default: 0.100 x Rated Power
The setting specifies the minimum power as defined along the relay characteristic angle
(RCA) for stage 2 of the element. The setting needs to be coordinated with the setting of
stage 1.
STAGE 2 DELAY
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 20.000 s
The setting specifies a time delay for stage 2. For reverse power or low forward power
applications for a synchronous machine, stage 1 is typically applied for alarming and
stage 2 for tripping.
BLOCK
Range: Off, Any operand from the list of FlexLogic operands
Default: Off
x VT
Ratio
x VT
Secondary (phase-phase) Ratio
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS
x CT (Wye-connected VT), or
Primary
x CT (Delta-connected VT)
Primary