Operation Principle - ABB REL650 series Technical Manual

Section 7
Current protection
7.12.7
7.12.8
270

Operation principle

The sampled analog phase currents are pre-processed in a discrete Fourier filter (DFT)
block. From the fundamental frequency components of each phase current the RMS value
of each phase current is derived. These phase current values are fed to a comparator in the
stub protection function STBPTOC (50STB). In a comparator the RMS values are
compared to the set operating current value of the function IPickup.
If a phase current is larger than the set operating current the signal from the comparator for
this phase is activated. If the fault current remains during the timer delay t, the TRIP output
signal is activated. The function can be blocked by activation of the BLOCK input.
STUB PROTECTION FUNCTION
BLOCK
PU_A
PU_B
PU_C
ENABLE
ANSI05000731 V1 EN
Figure 126: Simplified logic diagram for Stub protection (50STB)
Technical data
Table 150: STBPTOC (50STB) technical data
Function
Operating current
Reset ratio
Operate time
Reset time
Critical impulse time
Impulse margin time
OR
Range or value
IBase
(1-2500)% of
> 95%
20 ms typically at 0 to 2 x I
set
30 ms typically at 2 to 0 x I
set
10 ms typically at 0 to 2 x I
set
15 ms typically
1MRK 506 335-UUS A
TRIP
AND
en05000731_ansi.vsd
Accuracy
± 1.0% of I at I £ I
n n
± 1.0% of I at I > I
n
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Technical manual