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2.2
OVERCURRENT UNITS
A Phase Time Overcurrent unit is provided in the MIF. The relay offers the following 4 current/time operation
characteristics: Definite Time, Inverse Curve, Very Inverse Curve and Extremely Inverse Curve. One group of curves
complies with the criteria specified in the IEC255-4 Standard and in British Standard BS142, while another group
(defined in the same unit) complies with ANSI C37.90 standards. A time dial can be applied to any of these curves to
optimize co-ordination with other devices in the net. Additionally, there is a possibility to define a User's Curve, which
can be used for both three-phase overcurrent and ground units.
2.2.1.1.
IEC CURVES
Response times for IEC curves are as follows:
<
<
For
1
V
1.05,
the
unit
≤
<
For
1.05
V
20.00,
tripping
≤
For
20.00
V,
the
tripping
T
Where:
CURVE NAME
Inverse (IEC Curve C)
Very Inverse (IEC Curve B)
Extremely Inverse (IEC Curve A)
D =Time Dial setting (set in the relay by user).
V = I / I
> 1.05
pickup setting
GEK-106273L
PRODUCT DESCRIPTION
will
produce
a
pickup
signal,
time
will
be
:
A
*
D
=
T
−
P
V
Q
time
will
be
the
same
A
*
D
=
−
P
20
Q
A
0.14
13.5
80
MIF Digital Feeder Protection
2.2.1.
but
not
a
trip.
+
+
B
*
D
as
for
20.00
times
the
setting
+
+
B
*
D
P
0.02
1
2
PHASE TIME OVERCURRENT UNIT (51P)
K
:
K
Q
B
1
0
1
0
1
0
K
0
0
0
2-3
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