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5.
Setting the Relal
5.1
OvercurrentElement
Remove front cover by releasing captive screws top and buttom.
Removal of the cover automatically short circuits the input from
the associated current transformer and disconnects it from the
internal circuits. Thus the accessible components on the relay
front are entirely volt-free. When used for phase overcurrent
protection, one or two further
7SK88
relays are installed in the
remaining phases. These remain operative.
The overcurrent element (I
) has two settings:
Current setting
(Ip) (Plug setting)
10 - 40
~,
20 - 80
~,
50 - 200
~
or
100 - 400
~
in 7 equal steps
selected by rotary link on the front plate. This setting values
on the front plate are given in amps secondary. The two screws
must be re-tightened carefully. The link must not be left in an
open position. This setting allows the overcurrent pick-up
v~lue
to be selected with respect to circuit rated load and current
transformer ratio
e.g.
C.T.
ratio
circuit full load current
required pick-up value
(for example)
relay range
120
Ip
=
200 x 5 x 1.25
=
3.75 A.
Nearest setting
=
3.75 A (75
~)
•
200/5
A
120 A
1.25
x
full load current
50 - 200
J
(i.e.
2.5
to 10 A)
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