Frequency Time Accumulation Protection Function Ftaqfvr - ABB REG670 Applications Manual

1MRK 502 071-UEN -
11.4
11.4.1
11.4.2
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
take place very quickly, and there might not be enough time to wait until the frequency
signal has reached an abnormal value. Actions are therefore taken at a frequency level
closer to the primary nominal level, if the rate-of-change frequency is large (with
respect to sign).
The start value for SAPFRC is set in Hz/s. All voltage magnitude related settings are
made as a percentage of a settable base voltage, which normally is set to the primary
nominal voltage level (phase-phase) of the power system or the high voltage
equipment under consideration.
SAPFRC is not instantaneous, since the function needs some time to supply a stable
value. It is recommended to have a time delay long enough to take care of signal noise.
However, the time, rate-of-change frequency and frequency steps between different
actions might be critical, and sometimes a rather short operation time is required, for
example, down to 70 ms.
Smaller industrial systems might experience rate-of-change frequency as large as 5
Hz/s, due to a single event. Even large power systems may form small islands with a
large imbalance between load and generation, when severe faults (or combinations of
faults) are cleared - up to 3 Hz/s has been experienced when a small island was isolated
from a large system. For more "normal" severe disturbances in large power systems,
rate-of-change of frequency is much less, most often just a fraction of 1.0 Hz/s.
Frequency time accumulation protection function
FTAQFVR
Identification
Function description
Frequency time accumulation protection
Application
Generator prime movers are affected by abnormal frequency disturbances. Significant
frequency deviations from rated frequency occur in case of major disturbances in the
system. A rise of frequency occurs in case of generation surplus, while a lack of
generation results in a drop of frequency.
The turbine blade is designed with its natural frequency adequately far from the rated
speed or multiples of the rated speed of the turbine. This design avoids the mechanical
resonant condition, which can lead to an increased mechanical stress on turbine blade.
If the ratio between the turbine resonant frequencies to the system operating frequency
is nearly equal to 1, mechanical stress on the blades is approximately 300 times the
nonresonant operating condition stress values. The stress magnification factor is
shown in the typical resonance curve in Figure 217.
Frequency protection
IEC 61850 IEC 60617
identification identification
FTAQFVR f<>
Section 11
ANSI/
IEEEidentification
81A
441