ABB RELION 620 Series Technical Manual page 876

Section 12
General function block features
12.3.1.2
12.3.1.3
870
User programmable inverse-time characteristics for overvoltage
protection
The user can define the curves by entering the parameters using the standard formula:
k A ⋅
 
t s
=
   
− >
 V V 
B × − C
 
V >
 
GUID-6E9DC0FE-7457-4317-9480-8CCC6D63AB35-ANSI V1 EN
t[s] trip time in seconds
Curve parameter A
A the set value of
Curve parameter B
B the set value of
C the set value of Curve parameter C
Curve parameter D
D the set value of
Curve parameter E
E the set value of
V measured voltage
V> the set value of Pickup value
Time multiplier
k the set value of
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.
+
D
E
1MAC504801-IB E
(Equation 113)
620 series ANSI
Technical Manual