By using the properties of only these three quantities, a new patented differential
algorithm has been formed in the IED. This differential algorithm is completely stable
for all external faults. All problems caused by the non-linearity of the CTs are solved in
an innovative numerical way. Meanwhile, very fast tripping time, typically 11 ms, can
be commonly obtained for heavy internal faults.
SEMOD127483-4 v4
Discriminating zones in the IED includes a sensitive operational level. This sensitive
operational level is designed to be able to detect busbar ground faults in low impedance
edgrounded power systems (that is, power systems where the ground-fault current is
limited to a certain level, typically between 300 A and 2000 A by neutral point reactor
or resistor) or for some other special applications where increased sensitivity is
required. Operation and operating characteristic of the sensitive differential protection
can be set independently from the operating characteristic of the main differential
protection. The sensitive differential level is blocked as soon as the total incoming
current exceeds the pre-set level. By appropriate setting then it can be insured that this
sensitive level is blocked for external phase-to-phase or three-phase faults, which can
cause CT saturation. Comparison between these two characteristics is shown in
Figure
.
Differential protection
operation characteristic
Operate
region
DiffOperLevel
I
d
[P
ri
m
a
ry
A
m
p
s
]
I
in
[Primary Amps]
s=0.53
Sensitive
differential
protection
IEC06000142-2-en.vsdx
SensOperLevel
SensIinBlock
IEC06000142 V2 EN-US
Figure 41:
Differential protection operation characteristic
where
I
in
RMS value of the incoming current into the differential protection zone
I
d
RMS value of the differential current from the differential protection zone
s = 0.53
operating slope for the differential function (fixed in the algorithm).
1MRK 505 370-UUS A
Section 6
Differential protection
Busbar protection REB670 2.2 ANSI
113
Application manual
Summary of Contents for RELION REB670
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