ABB REB670 Applications Manual page 185

1MRK 505 337-UUS -
Application manual
Current I
Operate current
Reset current
IEC05000203 V3 EN
Figure 82: Pick up and reset current for an overcurrent protection
The lowest setting value can be written according to equation 34.
Im ax
³ ×
Ipu 1.2
k
EQUATION1262 V2 EN
where:
1.2 is a safety factor,
k is the resetting ratio of the protection, and
I is the maximum load current.
max
The maximum load current on the line has to be estimated. From operation statistics the
load current up to the present situation can be found. The current setting must be valid also
for some years ahead. It is, in most cases, realistic that the setting values are updated not
more often than once every five years. In many cases this time interval is still longer.
Investigate the maximum load current that different equipment on the line can withstand.
Study components such as line conductors, current transformers, circuit breakers, and
The IED does not reset
Section 7
Current protection
Line phase current
Time t
IEC05000203-en-2.vsd
(Equation 34)
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