ABB REG670 Applications Manual page 337

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
Current (A)
Operate current
Reset current
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
³ ×
Ipu 1.2
k
EQUATION1262 V2 EN
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
The IED does not reset
Section 9
Current protection
Line phase current
Time (s)
IEC05000203-en-2.vsd
(Equation 182)
331