Siemens ISGS User Manual

Appendix A: Trip Curves & Equations
Siemens Energy & Automation, Inc. 53
Equation A.1 Standard Inverse Curves Equation
Figure A.2 Inverse Curve (SEA1)
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
A, B, N, t
r
= constants
For
i
ip
-----
1 : T
AD
i
i
p
----




N
1–
------------------------BD0.028++=>
For
i
ip
-----
1 : T
t
r
D
i
i
p
----




N
1–
------------------------
=
<
i
i
p
-----



0.01
0.1
1
10
100
1000
11050
Multiples of Pickup
9.9
7.0
5.0
3.0
1.5
0.5
0.1
Time to Trip (Seconds)
Time Dial
A Trip Curves & Equations
This section provides equations and curve characteristics for
current and voltage to show the relationship between trip
time and threshold levels. Determine which curve closely fol-
lows the requirements of your system and select this curve in
the applicable protective functions.
A.1 Instantaneous Curve
The Instantaneous response characteristics can be used
with protection functions 50, 50N, 50HS, and 50HSN.
Figure A.1 Instantaneous Curve
A.2 Standard Time Overcurrent Equation
The ISGS comes with nine standard overcurrent characteris-
tic curves that can be adjusted with a time dial parameter.
Seven of the nine curves are based on suggested IEEE stan-
dards for approximation of electromechanical relays.
Table A.1 describes the first seven curves (SEA1 to SEA7)
listed below.
Standard Overcurrent Coefficients
Curve Type Des.
A
1
B
1
N
1
t
r
Inverse SEA 1 8.9341 0.17966 2.0938 8.8
Short Inverse SEA 2 0.2663 0.03393 1.2969 0.831
Long Inverse SEA 3 5.6143 2.18592 1.0000 12.9
Moderately
Inverse
SEA 4 0.3022 0.12840 0.5000 1.07
Very Inverse SEA 5 5.4678 0.10814 2.0469 5.741
Extremely
Inverse
SEA 6 7.7624 0.02758 2.0938 7.432
Slightly
Inverse
SEA 7 0.4797 0.21359 1.5625 1.5625
1
The A, B, and N coefficients are for the standard relay formula
Table A.1 Standard Overcurrent Coefficients
0.01
0.1
1
11050
Multiples of Pickup
Time to Trip (Seconds)
A
isv3o_1.bk : isv3ocrv.frm Page 53 Wednesday, August 7, 1996 10:51 AM

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