GE IAC57A - Page 10

GEH
-
1753
Time
Overcurrent
Relays
Type
IAC
A
-
C
TRIPPING
UNIT
INTRODUCTION
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
.
Ti
$
l
BR EAK E R
TRIP
CO I L
CURRENT
TRANS
AC
TRI P
UN IT
NORMALLY
CLOSED
CONTACTS
IOC
T
I
LQC
AC
TRIP
UNIjT
SHORTING
J
COIL
O
v
AC
TRIP
'
UN IT
MAI N
COIL
TOC
Fig
.
9
(
K
-
6154766
-
2
)
Diagram
Illustrating
Operation
of
Type
IAC
Relays
having
an
A
-
C
Tripping
Unit
.
0.030
OPERATING
TIME
RANGE
FOR
ANY
PICKUP
SETTING
0.025
o
Ul
<
r
>
0.020
i
UJ
t
-
0.015
a
.
<
-
>
0.010
Q
-
0.005
0
7
fa
y
io
3
5
6
0
4
MULTIPLES
OF
PICK
-
UP
(
6306872
[
5
]
)
Time
-
current
Characteristics
o f
Original
Instantaneous
U n i t
Fi g
.
10
8
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