About Ac Sources - GE D90 Plus Instruction Manual

POWER SYSTEM

About AC sources

144
Nominal Frequency
Range: 50 Hz, 60 Hz
Default: 60 Hz
The power system
Nominal Frequency
sampling rate if the system frequency cannot be measured from available signals. This
may happen if the signals are not present or are heavily distorted. Before reverting to the
nominal frequency, the frequency tracking algorithm holds the last valid frequency
measurement for a safe period of time while waiting for the signals to reappear or for
the distortions to decay.
Phase Rotation
Range: ABC, ACB
Default: ABC
The phase sequence of the power system is required to properly calculate sequence
components and power parameters. This setting matches the power system phase
sequence and informs the relay of the actual system phase sequence, either ABC or ACB.
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The D90 AC inputs (labeled as A, B, and C) must be connected to system phases A, B,
and C for correct operation.
Frequency and Phase Reference
Range: LINE (SRC 1), BKR 1 (SRC 2), BKR 2 (SRC 3)
Default: LINE (SRC 1)
This setting determines which signal source is used (and hence which AC signal) for
phase angle reference. The AC signal used is prioritized based on the inputs configured
for the signal source. Phase voltages takes precedence, followed by auxiliary voltage,
then phase currents, and finally ground current. For three-phase selection, phase A is
used for angle referencing (V
phase signals is used for frequency metering and tracking (V
better performance during fault, open pole, and VT and CT fail conditions.
The phase reference and frequency tracking AC signals are selected based upon the
source configuration, regardless of whether or not a particular signal is actually applied
to the relay.
The reference signal phase angle will always display zero degrees and all other phase
angles are relative to this signal. If the pre-selected reference signal is not measurable at
a given time, the phase angles are not referenced.
The phase angle referencing is done via a phase locked loop, which can synchronize
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independent UR -series devices if they have the same AC signal reference. These
results in very precise correlation of time tagging in the event recorder between different
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UR -series devices provided the relays have an IRIG-B connection.
Frequency Tracking
Range: Disabled, Enabled
Default: Enabled
This setting should only be programmed to "Disabled" in very unusual circumstances;
consult GE Grid Solutions for special variable-frequency applications.
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The D90 may be used on systems with breaker-and-a-half or ring bus configurations. In
these applications, each of the two three-phase sets of individual phase currents (one
associated with each breaker) can be used as an input to a breaker failure element. The
sum of both breaker phase currents and 3I_0 residual currents may be required for the
circuit relaying and metering functions. For a three-winding transformer application, it
may be necessary to calculate watts and vars for each of the three windings, using voltage
from different sets of VTs. These requirements can be satisfied with a single D90
value is used as a default to set the digital
= V ), while the Clarke transformation of the
ANGLE_REF A
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D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: PROTECTION
= (2V – V –V ) / 3) for
FREQ A B C
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