Microelettrica Scientifica MC20-CEI, Руководство по эксплуатации

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MC20-CEI
Doc. N°
MO-0431-ING
Microelettrica Scientifica S.p.A. - Copyright 2009 FW 1080.36.03.X Date 18.11.2011 Rev. 3 Pag. 7 of 35
2.2.2.3 – Earth Fault Current Input (Ion)
Same as for the Phase Currents, the relay directly displays the r.m.s. value of the Zero Sequence Residual
Current flowing at the Primary of the Current Transformers.
If the input to the Earth Fault element is supplied by the residual connection of the 3 phase C.Ts., we shall
set for the variable “
Io1 ” the same value as “ I1 ”.
If the input to the Earth Fault element is supplied by a separated Core Balance C.T., or by another CT, “ Io1 ”
value will be the Rated Primary Current of this C.T., normally different from “ I1 ”.
2.2.2.4 - Algorithm of the time current curves
The Time Current Curves are generally calculated with the following equation :
(1)
r S
a
T T K B
1
Is
I
A
t(I)
+ ⋅ ⋅ ⋅














+
−






where
t(I) = Actual trip time delay when the input current equals “I”
Is
= Set minimum pick-up level
K =
T
s
= Set time delay: t(I) = T
s
when
tr = Operation time of the output relay on pick-up
The parameters “ A “ , “ B “ and “ a “, have different values for the different Time Current Curves.
Curve Name Curve Identifier A B a
IEC A Inverse A 0.14 0 0.02
IEC B Very Inverse B 13.5 0 1
IEC C Extremely Inverse C 80 0 2
IEEE Moderate Inverse MI 0.0104 0.0226 0.02
IEEE Short Inverse SI 0.00342 0.00262 0.02
IEEE Very Inverse VI 3.88 0.0963 2
IEEE Inverse I 5.95 0.18 2
IEEE Extremely Inverse EI 5.67 0.0352 2
The maximum measuring current is “ 40xIn ” for phase elements and “ 4xOn ” for the neutral elements.
1
a
B
1 10
A
−






+
−
10
I
I
s
=