Frequency Measurement And Protection - ABB 615 series Technical Manual

1MAC059074-MB A
11.4
11.5
615 series ANSI
Technical Manual

Frequency measurement and protection

All the function blocks that use frequency quantity as their input signal share the common
features related to the frequency measurement algorithm. The frequency estimation is
done from one phase (phase-to-phase or phase voltage) or from the positive phase
sequence (PPS). The voltage groups with three-phase inputs use PPS as the source. The
frequency measurement range is 0.6...1.5 × F
when Frequency adaptivity is enabled.) The df/dt measurement range always starts from
0.6 × F . When the frequency exceeds these limits, it is regarded as out of range and a
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minimum or maximum value is held as the measured value respectively with appropriate
quality information. The frequency estimation requires 160 ms to stabilize after a bad
quality signal. Therefore, a delay 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 × Vn at f
• 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 TRIP outputs are blocked until the frequency restores to a valid
range.
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, available
only in REG615, can be enabled by setting Frequency adaptivity. When selected, the
operation range of the relay measurements is extended to 0.2...1.5 xFn (10...75 Hz when
Rated frequency = 50 Hz or 12...90 Hz when Rated frequency = 60 Hz).
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.
General function block features
. (For REG615 the range is 0.2...1.4 × F
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