The required differential current for tripping at a certain stabilizing current level can be
calculated using the formulae:
For a stabilizing current lower than
End section 1
I
I
Low trip values
doperate
n
[%
]
=
Set
GUID-4FAC8F94-FBB0-47DB-A952-F995889969C6-ANSI V1 EN
(Equation 110)
For a stabilizing current higher than
End section 1
but lower than
End section 2
I
I
Low trip value
I
I
End section 1 Slop
doperate
n
b
n
[%
]
(
[%
]
)
=
+
−
⋅
e
e section
2
GUID-EB0A327A-4079-45A5-87E6-AA30A8D2220C-ANSI V1 EN
(Equation 111)
For higher stabilizing current values exceeding
End section 2
I
I
Low trip value
End section
End section
doperate
n
[%
]
(
=
+
−
2
1))
(
[%
]
)
⋅
+
−
Slope section
I
I
End section
b
n
2
2
GUID-E9DA330C-84A8-40C2-BCFB-1F7E517395D8-ANSI V1 EN
(Equation 112)
When the differential current exceeds the operating value determined by the operating
characteristics, the
OPR_LS
output is activated. The
TRIP
output is always activated
when the
OPR_LS
output activates.
The trip signal due to the biased stage can be blocked by the activation of the
BLK_OPR_LS
or
BLOCK
input. Also, when the operation of the biased low stage is
blocked by the waveform blocking functionality, the
INT_BLKD
output is activated
according to the phase information.
The phase angle difference between the two currents I_A1 and I_A2 is theoretically 180
electrical degrees for the external fault and 0 electrical degrees for the internal fault
conditions. If the phase angle difference is less than 50 electrical degrees or if the biasing
current drops below 30 percent of the differential current, a fault has most likely occurred
in the area protected by 87G, 87M. Then the internal blocking signals (CT saturation and
DC blocking) of the biased stage are inhibited.
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
573
Technical Manual
Summary of Contents for Relion 615 series
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