t s
k A
B
U U
U
C
D
E
=
⋅
×
− >
>
−
+
(Equation 400)
t[s] Operate time in seconds
A Set value of
Curve parameter A
B Set value of
Curve parameter B
C Set value of
Curve parameter C
D Set value of
Curve parameter D
E Set value of
Curve parameter E
U Measured voltage
U> Set value of
Start value
k Set value of
Time multiplier
11.3.1.3 IDMT curve saturation of overvoltage protection
For the overvoltage IDMT mode of operation, the integration of the operate time
does not start until the voltage exceeds the value of
Start value
. To cope with
discontinuity characteristics of the curve, a specific parameter for saturating the
equation to a fixed value is created. The
Curve Sat Relative
setting is the parameter
and it is given in percents compared to
Start value
. For example, due to the curve
equation B and C, the characteristics equation output is saturated in such a way
that when the input voltages are in the range of
Start value
to
Curve Sat Relative
in
percent over
Start value
, the equation uses
Start value
* (1.0 +
Curve Sat Relative
/
100 ) for the measured voltage. Although, the curve A has no discontinuities when
the ratio U/U> exceeds the unity,
Curve Sat Relative
is also set for it. The
Curve
Sat Relative
setting for curves A, B and C is 2.0 percent. However, it should be
noted that the user must carefully calculate the curve characteristics concerning
the discontinuities in the curve when the programmable curve equation is used.
Thus, the
Curve Sat Relative
parameter gives another degree of freedom to move
the inverse curve on the voltage ratio axis and it effectively sets the maximum
operate time for the IDMT curve because for the voltage ratio values affecting by
this setting, the operation time is fixed, that is, the definite time, depending on the
parameters but no longer the voltage.
11.3.2 IDMT curves for undervoltage protection
In the inverse-time modes, the operate time depends on the momentary value of
the voltage, the lower the voltage, the faster the operate time. The operate time
calculation or integration starts immediately when the voltage goes below the set
value of the
Start value
setting and the START output is activated.
The OPERATE output of the component is activated when the cumulative sum of
the integrator calculating the undervoltage situation exceeds the value set by the
inverse-time mode. The set value depends on the selected curve type and the
setting values used. The user determines the curve scaling with the
Time multiplier
setting.
General function block features
1MRS759142 F
1902 REX640
Technical Manual
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