North American Standards - GE P642 Technical Manual

Chapter 9 - Current Protection Functions
2.1.3

NORTH AMERICAN STANDARDS

The IEEE IDMT Operate equation is:
β

t TD
=

op
α
M
−

and the IEEE IDMT Reset equation is:
β

t TD
=

r
α
1 M
−

where:
● t is the operating time
op
t is the reset time
●
r
● TD is the Time Dial setting
M is the ratio of the measured current divided by the threshold current (I/I
●
b is a constant, which can be chosen to satisfy the required curve characteristic
●
a is a constant, which can be chosen to satisfy the required curve characteristic
●
C is a constant for adding Definite Time (Definite Time adder)
●
L is a constant (usually only used for ANSI/IEEE curves)
●
The constant values for the IEEE curves are as follows:
Curve Description
IEEE Moderately Inverse Operate
IEEE Moderately Inverse Reset
IEEE Very Inverse Operate
IEEE Very Inverse Reset
IEEE Extremely Inverse Operate
IEEE Extremely Inverse Reset
CO8 US Inverse Operate
CO8 US Inverse Reset
CO2 US Short Time Inverse Operate
CO2 US Short Time Inverse Reset
ANSI Normally Inverse Operate
ANSI Normally Inverse Reset
ANSI Short Time Inverse Operate
ANSI Short Time Inverse Reset
ANSI Long Time Inverse Operate
ANSI Long Time Inverse Reset
Note:
* When using UK Long Time Inverse, BPN, UK Rectifier, or FR Short Time Inverse for the Operate characteristic, DT is always
used for the Reset characteristic.
198

L C
+  +
1




0.0515
4.85
19.61
21.6
28.2
29.1
5.95
5.95
0.16758
2.261
8.9341
9
0.03393
0.5
2.18592
15.75
b constant a constant
0.02
2
2
2
2
2
2
2
0.02
2
2.0938
2
1.2969
2
1
2
)
s
L constant
0.114
0
0.491
0
0.1217
0
0.18
0
0.11858
0
0.17966
0
0.2663
0
5.6143
0
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