ABB REG670 - Principle of Operation

25.2 Principle of operation
25.2.1 Mode of operation
The function can operate in a definite time-lag mode or in a current definite inverse
time mode. For the inverse time characteristic both ANSI and IEC based standard
curves are available. Also programmable curve types are supported via the component
inputs: p, A, B, C pr, tr, and cr.
Different characteristics for reset delay can also be chosen.
If current in any phase exceeds the set start current value (here internal signal
startValue), a timer, according to the selected operating mode, is started. The
component always uses the maximum of the three phase current values as the current
level used in timing calculations.
In case of definite time-lag mode the timer will run constantly until the time is reached
or until the current drops below the reset value (start value minus the hysteresis) and
the reset time has elapsed.
For definite time delay curve ANSI/IEEE Definite time or IEC Definite time are
chosen.
The general expression for inverse time curves is according to equation
158.
[ ]
= + ×
-
>
æ ö
ç ÷
ç ÷
ç ÷
æ ö
ç ÷
ç ÷
è ø
è ø
p
A
t s B k
i
C
in
EQUATION1189 V1 EN (Equation 158)
where:
p, A, B, C are constants defined for each curve type,
in> is the set start current for step n,
k is set time multiplier for step n and
i is the measured current.
For inverse time characteristics a time will be initiated when the current reaches the set
start level. From the general expression of the characteristic the following can be seen:
Section 25 1MRK502052-UEN B
Inverse time characteristics
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