Hitachi Relion 670 Series Applications Manual page 82

Section 6
Differential protection
Operate current [%]
(differential current)
IEC15000390 V2 EN-US
Figure 32:
The operate-restrained characteristic is determined by five parameter settings:
• IdMin
• EndSection1
• EndSection2
• SlopeSection2
• SlopeSection3
slope
IECEQUATION15054 V1 EN-US
6.2.4.2 Elimination of zero sequence currents
To avoid unwanted trips for external earth faults, zero sequence currents should be subtracted on the
side of the protected railway power transformer where they can flow during external earth faults.
Eliminating the zero sequence component is necessary when:
76
Unrestrained Limit IdUnre
Section 1
IdMin
EndSection 1
Operate-restrain characteristic
The slope is relative to the characteristic breakpoint.

I
 
DIFF
100 %

I
BIAS
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Operate
unconditionally
Operate
conditionally
Section 2
SlopeSection 2
EndSection 2
1MRK506375-UEN Rev. N
SlopeSection 3
Section 3
Restrain
Restrain current [%]
(bias current)
IEC15000390-2-en.vsdx
GUID-80FC0155-321C-4E60-B5F7-25628F9CD4E6 v3
Railway application RER670
Application manual
(Equation 3)