of 160 ms is added to the transition from the bad quality. The bad quality of the
signal can be due to restrictions like:
• The source voltage is below 0.02 × U
n
at F
n
.
• The source voltage waveform is discontinuous.
• The source voltage frequency rate of change exceeds 15 Hz/s (including stepwise
frequency changes).
When the bad signal quality is obtained, the nominal or zero (depending on the
Def frequency Sel
setting) frequency value is shown with appropriate quality
information in the measurement view. The frequency protection functions are
blocked when the quality is bad, thus the timers and the function outputs are
reset. When the frequency is out of the function block’s setting range but within
the measurement range, the protection blocks are running. However, the OPERATE
outputs are blocked until the frequency restores to a valid range.
11.5 Frequency adaptivity and generator start-up
protection
Frequency adaptivity enables sensitive and selective protection during the start-
up and shutdown phase of the generator when low frequency and low voltage
amplitude exist at the same time. Sensitive protection is necessary because,
for example, the fault current level in generator internal fault during start-up or
shutdown (when field excitation is not present) may not exceed even the nominal
current level.
Frequency adaptivity can be enabled by setting
Frequency adaptivity
and setting
one UTVTR
Frequency adaptivity
to "Main frequency source". One additional UTVTR
or ILTCTR can be set to "Backup frequency source". For main or backup frequency
source, all three-phases must be connected. Each TxTR block that is set to
Frequency adaptivity mode enable outputs measurements adapted to either main
or backup source frequency depending on their availability.
See the Preprocessing blocks chapter for more information.
Harmonics calculation is limited to 2
nd
, 3
rd
and 5
th
harmonic when
frequency adaptivity is enabled.
The frequency adaptivity uses the positive-sequence voltage in the frequency
tracking and adapts the DFT, RMS, peak-to-peak and peak measurement accuracies
of the current and voltage inputs by using the tracked frequency in the operation
range of 0.2...1.5 xFn. Frequency adaptation starts when the generator terminal
positive-sequence voltage level exceeds 0.04 xUn (minimum level). If frequency
adaptivity backup source is currents their positive sequence must exceed 0.07 xIn
to be usable as backup source. Backup source threshold limit is valid at nominal
frequency and threshold increases when frequency deviates from nominal (up to
0.35 xIn or 0.2 xUn at 0.2 xFn or 0.11 xIn or 0.06 xUn at 1.5 xFn). As the Synchronism
and energizing check (SECRSYN) bus voltage U12b voltage input always expects
Rated frequency
, the frequency adaptivity does not apply for this input.
If the generator terminal positive-sequence voltage is below the minimum level, the
relay is not able to maintain frequency adaptation. The non-adaptive situation is
1MRS759142 F
General function block features
REX640
Technical Manual
1907
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