11.3.1.2
User programmable inverse-time characteristics for overvoltage
protection
The user can define the curves by entering the parameters using the standard formula:
t s
k A
B
V
V
V
C
D
E
=
⋅
×
−
>
>
−
+
GUID-6E9DC0FE-7457-4317-9480-8CCC6D63AB35-ANSI V1 EN
(Equation 180)
t[s] trip 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
V
measured voltage
V> the set value of
Pickup value
k
the 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 trip time does not start
until the voltage exceeds the value of
Pickup 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
Pickup 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
Pickup value
to
Curve Sat Relative
in percent over
Pickup value
, the
equation uses
Pickup value
* (1.0 +
Curve Sat Relative
/ 100 ) for the measured voltage.
Although, the curve A has no discontinuities when the ratio V/V> 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 trip
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.
Section 11
1MAC059074-MB A
General function block features
1118
615 series ANSI
Technical Manual
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