GE IAC55A Instructions Manual page 12

GEH
-
1753 Time Overcurrent
Relays Type IAC
A
-
C TRIPPING UNIT
I N T R O D U C T I O N
The a
-
c
tripping unit is
a Type REA
relay unit
designed
to
energize
a
circuit breaker trip coil from
its associated
current transformer upon the
operation
of the main unit of the IAC relay
.
It transfers
the
current
from the
secondary of the
current trans
-
former into the
trip coil
and
removes
the
current
from the trip coil when the breaker trips
.
The tripping unit is mounted
on
the
rear
of the
frame opposite the tapped operating coil of the
induction unit ( see
Fig
.
8 )
.
The operation
of this
unit is illustrated in Fig
.
9
.
The
secondary
current
circulates through the induction unit
current coil
and the main coil of the REA auxiliary tripping
unit
,
returning through
the REA contacts to
the
current
transformer
.
Normally
,
most
of the flux generated
by the main
REA coil passes through the upper limb
of
the magnetic
structure
and holds the
armature
firmly against this limb
.
When the
contacts
of the
induction unit close
,
the shorting coil of the REA
is
short
-
circuited
and
current flows
in this coil by
transformer action
,
causing
a
redistribution of flux
which
actuates
the
armature
and the
REA
contacts
.
The opening of the REA
contacts causes
the secondary
current to
flow
through the trip coil which trips the
breaker
.
TdSI
BREAKER
TRIP COIL
CURRENT
TRANS
AC TRIP UNIT
NORMALLY
CLOSED
CONTACTS
IOC
j
::
icc
f
LQC
AC
TRIP
UNIT
SHORTING
J
con
o
v
AC
TRIP
UNIT
MAIN COIL
TOC
Fig
.
9 (
K
-
6154766
-
2 )
Diagram Illustrating
Operation
of Type IAC Relays having an
A
-
C Tripping Unit
.
0.030
K
T T
OPERATING TIME
RANGE FOR ANY
PICKUP SETTING
0.025
<
J
>
Ul
<
/
>
0.020
i
UJ
*
-
0.015
a
.
Jc
<
-
>
0.010
Q
-
0.005
0
2
0 3 10 5 6 7 b
4
y
MULTIPLES OF PICK - UP
( 6306872 [ 5 ]
) Time
-
current
Characteristics
of Original Instantaneous Unit
Fig
.
10
8