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Appendix A Trip Curves
Use this section to observe the relationship between trip
time and threshold levels. Determine which rove closely fol-
lows the requirements of your system and select the appli-
calje curve when performing the settings n address !jocks
1 700
-
2000 (overcurrent),
and
2200
-
2300 (over/l.Xldervolt-
age).
A.1
Standard Inverse Time
Overcl.l'rent Equations
Seven of the nine time nverse tme overcurrent characteris-
tics supported by the ISGS relay are based on suggested
IEEE standards for approximation of electromechanical
relays. The folowing equations describe the curves listed in
Table A.1 below.
AD
T
= (
i
)N
+
BD
+
0.028
I
-1.00
p
Where:
T
=tme to trip, n seconds
i
..- =muttiple of pickup settng
lp
D=time dial setting, 0.1 to 9.9 n steps of 0. 1
A.
8, and N = constants as follows:.
Curve
Type
Designation
A
B
inverse
SEA1
8.9341
0.17966
S
hof
t inverse
SEA2
0.2663
0.03393
Long Inverse
SEA3
5.6143
2.18592
Moderately
SEA4
0.3022
0.12840
inverse
Very Inverse
SEAS
5.4678
0.10814
Extremely
SEA6
7.7624
0.02758
inverse
Sightly
SEA?
0.4797
0.21359
inverse
N
2.0938
1.2969
1.0000
0.5000
2.0469
2.0938
1.5625
Table A .1
T1me-Current Charactenstlc Ct.rve Constants
A.2
Definite Inverse Equations-SEAS
The ISGS relay provides an emulation of the popjar C0-6
Definite Inverse characteristic, as defined by the following
equations:
i
For
1
> 1.5
:
p
Siemens Energy & Automation, Inc.
Appendices
T=
[
8
671
l
6.33
0
+
0.37
7 5
+
(
j
)
X
24000
(
1
)
1
-
1.1
9
p
i
For
1.0
<
1
<
1.5 :
p
[
1475
]
6.330
+
0.37
T
=
(
I
)
X
24000
(
2
)
r - -
1
lp
Where:
T
= time to trip, in seconds
i
1
= mutiple of pickup setting
p
0
= tme dial setting, 0.1 to 9.9 in steps of 0.1
Equation
(1) is valid for values of ifrp greater than 1.5 and
equation (2) is valid for values of ilip between 1.0 and 1.5.
(Note that the equation is undefined at ifrp = 1.0).
A.3
1 2 t Equation
The ISGS relay provides an 12 t characteristic in addition to
standard nverse curves.
T
-
50.70
+
10.14
-
(~Y
Where:
T
= tme to trip, in seconds
i
1
= mutiple of pickup settng
p
0
=time dial setting, 0.1 to 9.9 n steps of 0.1
A.4
Custom Protective Curve
The custom curve consists of up to 60 current-time pairs
corresponding to points on the time-current characteristic
ct.rve. Current refers to muttiple-of-pickup value
{if~J)
on the
horizontal axis, and time refers to time-to-trip values on the
vertical axis. Each pont consists of two values
Wio
and
n.
loaded n order from lowest to highest value of ilip via the
SEAbus or local
ports.
Siemens ISGS Wisdom software is
37
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