Minimum Operating Current - ABB REL650 series Technical Manual

Section 6
Impedance protection
6.1.6.5
6.1.6.6
120
X
f
VA
ZRev
ANSI09000123 V2 EN
Figure 48: Simplified characteristic for offset mho in reverse direction for A-to-
ground fault

Minimum operating current

The operation of Five zone distance protection, quadrilateral and mho characteristic
(ZQMPDIS, 21) is blocked if the magnitude of input currents fall below certain threshold
values.
The phase-to-ground loop AG (BG or CG) is blocked if IA (IB or IC) < IMinOpPG.
IA (IB or IC) is the RMS value of the current in phase IA (IB or IC). .
The phase-to-phase loop AB (BC or CA) is blocked if I
The current limits IMinOpPG and IMInOpPP are automatically reduced
to 75% of regular set values if the zone is set to operate in reverse
direction, that is, DirModeZx = Reverse (where x is 1-5 depending on
selected zone).
Measuring principles
Fault loop equations use the complex values of voltage, current, and changes in the
current. Apparent impedances are calculated and compared with the set limits. The
Z
ArgNegRes
IA
R
ArgDir
ANSI09000123-2-en.vsd
1MRK 506 335-UUS A
< IMinOpPP.
AB (BC or CA)
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