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6.8.7 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.

BLOCK

TRIP

STUB PROTECTION FUNCTION

PU_A

PU_B

PU_C

AND

ENABLE

en05000731_ansi.vsd

ANSI05000731 V1 EN

Figure 58: Simplified logic diagram for Stub protection (50STB)

6.8.8 Technical data

Table 78: STBPTOC (50STB) technical data

Function

Range or value Accuracy

Operating current (1-2500)% of

IBase

± 1.0% of I

at I £ I

± 1.0% of I at I > I

Reset ratio > 95% -

Operate time 20 ms typically at 0 to 2 x I

set

Reset time 30 ms typically at 2 to 0 x I

set

Critical impulse time 10 ms typically at 0 to 2 x I

set

Impulse margin time 15 ms typically -

Section 6 1MRK 511 287-UUS A

Current protection

144

Technical manual

ABB REC650 ANSI User Manual

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