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CHAPTER 4: SETPOINTS
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
RCA
Range: 0 to 359° in steps of 1°
Default: 180°
This setting specifies the Relay Characteristic Angle (RCA) for the Directional Power
function. Application of this setting is threefold:
1.
It allows the element to respond to active or reactive power in any direction (active
overpower/underpower, etc.).
2.
Together with a precise calibration angle, it allows compensation for any CT and VT
angular errors to permit more sensitive settings.
3.
It allows for required direction in situations when the voltage signal is taken from
behind a delta-wye connected power transformer and phase angle compensation is
required.
For example, the active overpower characteristic is achieved by setting DIR POWER 1
RCA to "0°," reactive overpower by setting DIR POWER 1 RCA to "90°," active underpower
by setting DIR POWER 1 RCA to "180°," and reactive underpower by setting DIR POWER 1
RCA to "270°".
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.
x VT
Ratio
x VT
Secondary (phase-phase)
Ratio
PROTECTION
x CT
(Wye-connected VT), or
Primary
x CT
(Delta-connected VT)
Primary
4–243
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