Operate current
Current (A)
The IED does not reset
Line phase current
Time (s)
Reset current
IEC05000203-en-2.vsd
IEC05000203 V4 EN-US
Figure 75: Operate and reset current for an overcurrent protection
The lowest setting value can be written according to Equation 102.
EQUATION1262 V2 EN-US (Equation 102)
where:
1.2 is a safety factor
k is the reset ratio of the protection
Imax is the maximum load current
The load current up to the present situation can be found from operation statistics.
The current setting must remain valid for several years. In most cases, the setting
values are updated once every five years or less often. Investigate the maximum
load current that the equipment on the line can withstand. Study components, such
as line conductors, current transformers, circuit breakers, and disconnectors. The
manufacturer of the equipment normally gives the maximum thermal load current
of the equipment.
The maximum load current on the line has to be estimated. There is also a demand
that all faults within the zone that the protection shall cover must be detected by the
phase overcurrent protection. The minimum fault current Iscmin to be detected by
1MRK 505 393-UEN B Section 8
Current protection
Line differential protection RED650 2.2 IEC 159
Application manual
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