Siemens ISGS SG8158-00 - Manual (Page 61)

Appendix A: Trip Curves & Equations
Siemens Energy & Automation, Inc. 55
Figure A.7 Extremely Inverse Curve (SEA6)
Figure A.8 Slightly Inverse Curve (SEA7)
0.01
0.1
1
10
100
1000
1 10 50
9.9
7.0
5.0
3.0
1.5
0.5
0.1
Multiples of Pickup
T
ime to T
rip (Seconds)
T
ime Dial
0.01
0.1
1
10
100
1 10 50
9.9
7.0
5.0
3.0
1.5
0.5
0.1
Multiples of Pickup
T
ime to T
rip (Seconds)
T
ime Dial
A.3 Definite Inverse Equation
Equation A.2 The ISGS provides an emulation of the
popular CO-6 Definite Inverse characteristic. This curve is
defined by the equations shown in Equation A.3.
Equation A.3 Definite Inverse Equation
In Equation A.3, the time dial term 6.33D + 0.37 is neces-
sary to convert the time dial range defined by Westinghouse
and the range that Siemens is using.
Equation (1) is valid for values of I/Ip greater than 1.5 and
equation (2) is valid for values of I/Ip between 1.0 and 1.5
(note that the equation is undefined at I/Ip = 1.0).
Trip Characteristic
Reset Characteristic
T = time to trip, in seconds
= multiple of pickup setting
D = time dial setting, 0.1 to 9.9 in steps of 0.1
tr = reset constant = 1.0394
N = inverse constant = 2.54096
For
i
ip
----- 1.5
T 785
671
i
ip
---- 


 N
1.19 –
------------------------------- +
6.33D 0.37 +
24000
------------------------------- × =
>
For1.0
i
ip
----- 1.5:
T 785
671
i
ip
---- 


 N
1.19 –
------------------------------- +
6.33D 0.37
+
24000
---------------------------------- × =
< <
For
i
ip
----- 1: T
t
r
D
i
ip
---- 


 N
1 –
------------------------
= <
i
ip -----
 
 
 
A
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