Idmt Curve Saturation Of Undervoltage Protection - ABB RELION REX640 Technical Manual

Section 11
General function block features
11.3.2.3
11.4
1702
k A
t s ⋅
 
=
   
U U
< −
 
B C
⋅ −
 
U
<
 
GUID-0C319E46-5B93-4C24-8002-4104FFA6DF58 V1 EN
t[s] Operate time in seconds
Curve parameter A
A Set value of
Curve parameter B
B Set value of
Curve parameter C
C Set value of
Curve parameter D
D Set value of
Curve parameter E
E Set value of
U Measured voltage
Start value
U< Set value of
Time multiplier
k Set value of

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.
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 0.2...1.5 × F
range always starts from 0.6 × F
regarded as out of range and a minimum or maximum value is held as the measured
D
+
E
. When the frequency exceeds these limits, it is
n
1MRS759142 C
(Equation 364)
. The df/dt measurement
n
REX640
Technical Manual