Alstom MiCOM P546 - 1.25.1 Reset characteristics for overcurrent elements

Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546 (OP) 5-79
OP
The IEEE/US IDMT curves conform to the following formula:
t = TD x







(
/s)

–1
+ L
t = Operation time
 = Constant
 = Measured current
s = Current threshold setting
 = Constant
L = ANSI/IEEE constant (zero for IEC curves)
T = Time multiplier setting for IEC/UK curves
TD = Time multiplier setting for IEEE/US curves
IDMT curve description Standard
 Constant  Constant
L Constant
Standard Inverse IEC 0.14 0.02 0
Very Inverse IEC 13.5 1 0
Extremely Inverse IEC 80 2 0
Long Time Inverse UK 120 1 0
Moderately Inverse IEEE 0.0515 0.02 0.114
Very Inverse IEEE 19.61 2 0.491
Extremely Inverse IEEE 28.2 2 0.1217
Inverse US-C08 5.95 2 0.18
Short Time Inverse US 0.16758 0.02 0.11858
Note: The IEEE and US curves are set differently to the IEC/UK curves, with
regard to the time setting. A time multiplier setting (TMS) is used to
adjust the operating time of the IEC curves, whereas a time dial
setting is employed for the IEEE/US curves. The menu is arranged
such that if an IEC/UK curve is selected, the ‘> Time Dial’ cell is not
visible and vice versa for the TMS setting.
1.25.1 Reset characteristics for overcurrent elements
The IEC/UK
inverse characteristics can be used with a definite time reset characteristic,
however, the IEEE/US curves may have an inverse or definite time reset characteristic. The
following equation can used to calculate the inverse reset time for IEEE/US curves:
tRESET =
TD x S
(1 - M
2
)
in seconds
Where:
TD = Time dial setting for IEEE curves
S = Constant
M = /s