ABB Relion 670 Series Technical Reference Manual page 560

Section 9
Frequency protection
9.1.2.4
9.1.2.5
554
1
Exponenent
0.5
0
90
ANSI05000075 V1 EN
Figure 281: Voltage dependent inverse time characteristics for underfrequency
protection SAPTUF (81). The time delay to operate is plotted as a
function of the measured voltage, for the Exponent = 0, 1, 2, 3, 4
respectively.
Blocking
It is possible to block underfrequency protection SAPTUF (81) partially or completely,
by binary input signals or by parameter settings, where:
BLOCK: blocks all outputs
BLKTRIP: blocks the TRIP output
BLKREST: blocks the RESTORE output
If the measured voltage level decreases below the setting of IntBlockLevel, both the
PICKUP and the TRIP outputs, are blocked.
Design
The frequency measuring element continuously measures the frequency of the positive
sequence voltage and compares it to the setting PUFrequency. The frequency signal is
filtered to avoid transients due to switchings and faults. The time integrator can operate
either due to a definite delay time or to the special voltage dependent delay time. When
the frequency has returned back to the setting of RestoreFreq, the RESTORE output is
issued after the time delay TimeDlyRestore. The design of underfrequency protection
SAPTUF (81) is schematically described in figure 282.
0
1
2
3
4
95
V [% of VBase]
en05000075_ansi.vsd
1MRK505222-UUS C
100
Technical reference manual