17
4
to> = K x
b
I
Io>
a
– 1
to> = K x b
1 2 3
4
Parameters a and b can take on the following
values according to the curve selected.
• Normal inverse time curve (NI):
a = 0.02 b = 0.14.
• Very inverse time curve (VI):
a = 1 b = 13.5.
• Extremely inverse time curve (EI):
a = 2 b = 80.
Selection of to> trip time
The trip time of the protection is adjusted by using
the Dip Switches as shown in the figure.
By means of the Dip Switches, the value of K is set
which, when replaced in the previous relation-
ships, determines trip time to>.
The following settings are possible:
• 16 trip times (to>),
(K = 0.1...1.6 with steps of 0.1)
0.1 0.2 0.3 0.4 0.5
0.6 0.7 0.8 0.9 1.0
1.1 1.2 1.3 1.4 1.5 1.6
Definite time curve
For protection with definite time, the relationship
between trip time and overcurrent is given by the
following formula.
The following settings are possible:
• 16 threshold current values (Io>)
(1)
0.100 0.150 0.200 0.250
0.350 0.400 0.450 0.500
0.600 0.650 0.700 0.750
0.850 0.900 0.950 1 x In
OFF
(1) The unit guarantees no entry in the threshold for
currents under 1.05 x Io> set and guarantees entry in
the threshold for currents higher than 1.30 x Io> set.
Selection of type of Io> curve
Four different time-current relationships can be
selected.
Fixed time curve (b = 2)
For protection with fixed time (DT), the trip time is
given by the following relationship.
Caption
1 Dip Switch for setting
the trip threshold of
protection Io>
2 Dip Switch for setting
timing K of protection
Io>
3 Dip Switch for selecting
the type of curve for
protection Io>:
•DT curve with
definite time
•NI curve with normal
inverse time
•VI curve with very
inverse time
• EI curve with
extremely inverse
time.
4 Dip Switch for selection
of type of toroid for
earth fault (internal/
external)
Caption
to> trip time
k parameter set by the user to select the trip curve
a, bpair of parameters, depending on the type of
protection selectable
I earth fault current
Io> trip threshold selectable by the user.
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