t s
k A
B
U U
U
C
D
E






=
â‹…
×
< −
<
−

ï£

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GUID-4A433D56-D7FB-412E-B1AB-7FD43051EE79 V2 EN (Equation 108)
t[s] operate time in seconds
A the set value of
Curve parameter A
B the set value of
Curve parameter B
C the set value of
Curve parameter C
D the set value of
Curve parameter D
E the set value of
Curve parameter E
U measured voltage
U< the set value of
Start value
k the set value of
Time multiplier
11.3.2.3 IDMT curve saturation of undervoltage protection
For the undervoltage IDMT mode of operation, the integration of the operate time
does not start until the voltage falls below 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 with Start value. For example, due to the
curve equation B, the characteristics equation output is saturated in such a way that
when input voltages are in the range from Start value to Curve Sat Relative in
percents under 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 set for
it as well. 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 also 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.
11.4 Frequency measurement and protection
All the function blocks that use frequency quantity as their input signal share the
common features related to the frequency measurement algorithm. The frequency
estimation is done from one phase (phase-to-phase or phase voltage) or from the
positive phase sequence (PPS). The voltage groups with three-phase inputs use PPS
as the source. The frequency measurement range is 0.6 xFn to 1.5 xFn. When the
frequency exceeds these limits, it is regarded as out of range and a minimum or
Section 11 1YHT530004D05 D
General function block features
838 615 series
Technical Manual
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