ABB Relion 670 Series Applications Manual page 146

Section 8
Current protection
Current I
Reset current
ANSI09000146 V1 EN-US
Figure 62: Pickup and reset current for an overcurrent protection
The lowest setting value can be written according to Equation 31.
³
Ipu 1.2
EQUATION1262 V2 EN-US
where:
1.2
k
Imax
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 protection must be calculated.
Taking this value as a base, the highest pickup current setting can be written according to
Equation 32.
140
Pickup current
The IED does not reset
Im ax
×
k
is a safety factor
is the reset ratio of the protection
is the maximum load current
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Line phase current
Time t
ANSI09000146-en-1.vsd
1MRK 511 401-UUS F
(Equation 31)
Bay control REC670
Application manual