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

Section 11
General function block features
11.3.1.3
11.3.2
1698
k A
t s ⋅
 
=
   
U U
− >

B C
⋅ −

U
>

GUID-E6AA2249-97B9-410A-A2CC-BE990F393A58 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 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.
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-
D
+
E



1MRS759142 C
(Equation 362)
REX640
Technical Manual