GE P642, Technical Manual

Page: 222 / 592

2.1.3 NORTH AMERICAN STANDARDS
The IEEE IDMT Operate equation is:
t TD
M
L C
op
=
−
+





 +
β
α
1
and the IEEE IDMT Reset equation is:
t TD
M
r
=
−






β
α
1
where:
●
t
op
is the operating time
●
t
r
is the reset time
●
TD is the Time Dial setting
●
M is the ratio of the measured current divided by the threshold current (I/I
s
)
●
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
b
constant
a
constant L constant
IEEE Moderately Inverse Operate 0.0515 0.02 0.114
IEEE Moderately Inverse Reset 4.85 2 0
IEEE Very Inverse Operate 19.61 2 0.491
IEEE Very Inverse Reset 21.6 2 0
IEEE Extremely Inverse Operate 28.2 2 0.1217
IEEE Extremely Inverse Reset 29.1 2 0
CO8 US Inverse Operate 5.95 2 0.18
CO8 US Inverse Reset 5.95 2 0
CO2 US Short Time Inverse Operate 0.16758 0.02 0.11858
CO2 US Short Time Inverse Reset 2.261 2 0
ANSI Normally Inverse Operate 8.9341 2.0938 0.17966
ANSI Normally Inverse Reset 9 2 0
ANSI Short Time Inverse Operate 0.03393 1.2969 0.2663
ANSI Short Time Inverse Reset 0.5 2 0
ANSI Long Time Inverse Operate 2.18592 1 5.6143
ANSI Long Time Inverse Reset 15.75 2 0
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.
Chapter 9 - Current Protection Functions P64x
198 P64x-TM-EN-1.3