GE G30 Instruction Manual page 242

5.4 SYSTEM SETUP
The power system
NOMINAL 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.
The phase sequence of the power system is required to properly calculate sequence components and power parameters.
The
PHASE ROTATION
actual system phase sequence, either ABC or ACB. CT and VT inputs on the relay, labeled as A, B, and C, must be con-
nected to system phases A, B, and C for correct operation.
The
REVERSE PH ROTATION
This allows the Product to follow the current phase rotation of the protected generator. For example, if the
setting is "ABC" but the condition defined for opposite phase rotation is true, then the phase rotation used for phasor calcu-
lation switches to "ACB." This feature is only intended for use in special applications, such as pumped storage schemes.
Typical application of using Reverse Phase Rotation is the pumped-storage hydroelectricity application. Water is pumped
from a lower elevation reservoir to a higher elevation (pumping or motor mode) during the off-peak period when low-cost
surplus electricity is available, and during periods of high electrical demand, the stored water is released through turbines
to produce electricity (generator mode), where pump operation is realized through phase rotation reversal operation
because the hydraulic units are designed to operate as turbines when rotating in one direction and as pumps when rotating
in the opposite direction.
When the operand assigned to the
defined by the
PHASE ROTATION
the opposite, ACB for the same example. Note that after successful rotation switching, the next switching is allowed only
after nine power cycles.
Typically, different relay setting groups are used to protect pumping operation mode and generating operation mode of the
5
hydraulic units respectively, therefore the logic for switching setting groups can be directly used to control the
.
ROTATION
Every time rotation change is performed, protection is blocked for three power cycles.
The
FREQUENCY AND PHASE REFERENCE
phase angle reference. The AC signal used is prioritized based on the AC inputs that are 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 (
phase signals is used for frequency metering and tracking (
ing 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.
Phase angle of the reference signal always displays 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 independent UR-series relays if they
have the same AC signal reference. This results in very precise correlation of phase angle indications between different
UR-series relays.
FREQUENCY TRACKING
frequency applications.
NOTE
The frequency tracking feature functions only when the G30 is in the "Programmed" mode. If the G30 is "Not Pro-
grammed", then metering values are available but can exhibit significant errors.
NOTE
Systems with an ACB phase sequence require special consideration. Refer to the Phase relationships of three-
phase transformers sub-section of chapter 5.
NOTE
5-102
value is used as a default to set the digital sampling rate if the system frequency
setting matches the power system phase sequence. Note that this setting informs the relay of the
setting allows the user to dynamically change the phase rotation used for phasor calculations.
REVERSE PH ROTATION
setting, ABC for example. When this operand is logical "1," the phase rotation changes to
setting determines which signal source is used (and hence which AC signal) for
is set to "Disabled" only in unusual circumstances; consult the factory for special variable-
G30 Generator Protection System
setting is logical "0," the phase rotation is matching the one
V V ), while Clarke transformation of the
=
ANGLE REF A
V ( 2V V V
= – –
FREQUENCY A B
5 SETTINGS
PHASE ROTATION
REVERSE PH
) 3 ⁄ ) for better performance dur-
C
GE Multilin