ABB Relion REG670, Applications Manual

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Operate current
Current (A)
The IED does not reset
Line phase current
Time (s)
Reset current
IEC05000203-en-2.vsd
IEC05000203 V4 EN
Figure 174: Operate and reset current for an overcurrent protection
The lowest setting value can be written according to Equation 182 .
Im ax
Ipu 1.2
k
³ ×
EQUATION1262 V2 EN
(Equation 182)
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
1MRK 502 071-UEN -
Section 9
Current protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 331
Application manual