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Time Overcurrent Relays
t NTR ODUCTION
The instantaneous element is a small instan
taneous hinge -type element which may be mounted
on the right front side of the induction unit (See Fig.
7). Its contacts are normally connected in parallel
with the contacts of the main unit . Its coil is con
nected in series with the operating coil of the main
unit .
When the current reaches a predetermined val
ue, the instantaneous element operates, closing the
contact circuit and raising its target into view. The
target latches in the exposed position until released
by pressing the button beneath the lower left -hand
corner of the relay cover.
A P P LICATION
The instantaneous element is used on certain
lAC relay models to provide instantaneous tripping
for current exceeding a predetermined value.
OPER ATING
The instantaneous element operates over a 4 to
1 range and has its calibration stamped on a scale
i
F i g. 7 Typ e l AC R e l ay W i th An I ns tantaneous U n i t
8
Type lAC
INSTANTANEOUS
CHAR ACTER ISTI-CS
OPERATING
COIL.
TARGET
CONTACTS
CONTACT
ASS£MIIL.Y
ELEM ENT
mounted beside the adjustable pole piece. Time
current characteristics are showJl in Fig. 10.
RATIN GS
The instantaneous element is designed to use
either of two coils having pickup ranges
and 20 to 80 amperes respectively . The current
closing rating of the c o n t a c t s is 30 amperes for
voltages not exceeding 250 volts.
BURDENS
Burden data on the instantaneous element coils
are given in the following table :
Volt
Coil
Freq
Amp
10-40
60
5
0 .83
50
5
0.80
25
5
0.65
20 -80
60
5
0.21
50
5
0 . 20
5
25
0
�
F i g . 8
Type l AC
e l ay W i th An A-C T r i p p i n g Un i t
of
10 to 40,
Imp .
Amp
Ohms
PF
0.033
0.95
0 .032
0.95
0 . 98
0.027
0.008
0 .95
0 .95
0.008
15
0 .98
0 .007
.
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