ABB REC670 Applications Manual page 159

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
Current (A)
Operate current
Reset current
IEC05000203 V4 EN-US
Figure 61: Operate and reset current for an overcurrent protection
The lowest setting value can be written according to Equation 28.
Im ax
³ ×
Ipu 1.2
k
EQUATION1262 V2 EN-US
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
The IED does not reset
Section 8
Current protection
Line phase current
Time (s)
IEC05000203-en-2.vsd
(Equation 28)
153