GE IAC57A - Page 14

GEH
-
1753
Time
Overcurrent
Relays
Type
IAC
ADJUSTMENTS
The
primary
adjustment
for
the
time
of
opera
-
tion
of
the
unit
is
made
by
means
of
the
time
dial
.
However
,
further
adjustment
is
obtained
by
moving
the
permanent
magnet
along
its
supporting
shelf
;
moving
the
magnet
toward
the
disk
shaft
decreases
the
time
,
while
moving
it
away
increases
the
time
.
TARGET
AND
SEAL
-
IN
UNIT
For
trip
coils
operating
on
currents
ranging
from
0.2
up
to
2.0
amperes
at
the
minimum
control
voltage
,
set
the
target
and
seal
-
in
tap
screw
in
the
0.2
-
ampere
tap
.
For
trip
coils
operating
on
currents
ranging
from
2
to
30
amperes
at
the
minimum
control
volt
-
age
,
place
the
tap
plug
in
the
2
-
ampere
tap
.
The
tap
screw
is
the
screw
holding
the
right
-
hand
stationary
contact
of
the
seal
-
in
unit
.
To
change
the
tap
setting
,
first
remove
the
connecting
plug
.
Then
,
take
a
screw
from
the
left
-
hand
station
-
ary
contact
and
place
it
in
the
desired
tap
.
Next
,
remove
the
screw
from
the
other
tap
,
and
place
it
in
the
left
-
hand
contact
.
This
procedure
is
neces
-
sary
to
prevent
the
right
-
hand
stationary
contact
from
getting
out
of
adjustment
.
Screws
should
not
be
in
both
taps
at
the
same
time
.
If
selective
action
of
two
or
more
relays
is
required
,
determine
the
maximum
possible
short
-
circuit
current
of
the
line
and
then
choose
a
time
value
for
each
relay
that
differs
sufficiently
to
in
-
sure
the
proper
sequence
in
the
operation
of
the
several
circuit
breakers
.
Allowance
must
be
made
for
the
time
involved
in
opening
each
breaker
after
the
relay
contacts
close
.
For
this
reason
,
unless
the
circuit
time
of
operation
is
known
with
accuracy
,
there
should
be
a
difference
of
about
0.5
second
(
at
the
maximum
current
)
between
relays
whose
opera
-
tion
is
to
be
selective
.
EXAMPLE
OF
SETTING
The
time
and
current
settings
of
the
overcurrent
unit
can
be
made
easily
and
quickly
.
Each
time
value
shown
in
Fig
.
2
indicates
the
time
required
for
the
contacts
to
close
with
a
particular
time
-
dial
setting
when
the
current
is
a
prescribed
number
of
times
the
current
-
tap
setting
.
In
order
to
secure
any
of
the
particular
time
-
current
settings
shown
in
Fig
.
2
,
insert
the
removable
plug
in
the
proper
tap
re
-
ceptacle
and
adjust
the
time
-
dial
to
the
proper
position
.
procedure
in
making
a
relay
setting
.
INDUCTION
UNIT
CURRENT
SETTING
The
tap
plug
must
not
be
removed
without
first
withdrawing
the
connecting
plug
.
The
current
at
which
the
contacts
operate
may
be
changed
by
changing
the
position
of
the
tap
plug
in
the
tap
block
at
the
top
of
the
relay
.
Screw
the
tap
plug
firmly
into
the
tap
marked
for
the
desired
current
(
below
which
the
unit
is
not
to
operate
)
.
When
changing
the
current
setting
of
the
unit
,
remove
the
connecting
plug
to
short
circuit
the
cur
-
rent
transformer
secondary
circuit
.
Next
,
screw
the
tap
plug
into
tap
marked
for
the
desired
current
and
then
replace
the
connecting
plug
.
The
pickup
of
the
unit
for
any
current
tap
is
adjusted
by
means
of
a
spring
-
adjusting
ring
.
The
ring
may
be
turned
by
inserting
a
screw
driver
in
the
notches
around
the
edge
.
By
turning
the
ring
,
the
operating
current
of
the
unit
may
be
brought
into
agreement
with
the
tap
setting
employed
,
if
for
some
reason
,
this
adjustment
has
been
disturbed
.
This
adjustment
also
permits
any
desired
setting
intermediate
between
the
various
tap
settings
to
be
obtained
.
The
unit
is
adjusted
at
the
factory
to
close
its
contacts
from
any
time
-
dial
position
at
a
mini
-
mum
current
within
five
percent
of
the
tap
-
plug
setting
.
The
unit
resets
at
90
per
cent
of
the
mini
-
mum
closing
value
.
The
following
example
illustrates
the
Assume
a
Type
IAC
relay
is
used
in
a
circuit
where
the
circuit
breaker
should
trip
on
a
sustained
current
of
approximately
450
amperes
;
also
,
the
breaker
should
trip
in
1.9
seconds
on
a
short
-
circuit
current
of
3750
amperes
,
current
transformers
of
60
/
1
ratio
are
used
.
Assume
further
that
The
current
tap
setting
is
found
by
dividing
the
minimum
primary
tripping
current
by
the
current
transformer
ratio
.
In
this
case
,
450
divided
by
60
equals
7.5
amps
.
Since
there
is
no
7.5
-
amp
tap
,
the
8
-
amp
.
tap
is
used
.
To
find
the
proper
time
-
dial
setting
to
give
1.9
seconds
time
delay
at
3750
am
-
peres
,
divide
3750
by
the
transformer
ratio
.
This
gives
62.5
amperes
secondary
current
which
is
7.8
times
the
8
-
ampere
setting
.
By
referring
to
the
time
current
curves
(
Fig
.
2
)
,
it
will
be
seen
that
7.8
times
the
minimum
operating
current
gives
1.9
seconds
time
delay
when
the
relay
is
set
slightly
above
the
No
.
6
time
-
dial
setting
.
TIME
SETTING
The
setting
of
the
time
dial
determines
the
length
of
time
the
unit
requires
to
close
its
contacts
when
the
current
reaches
a
predetermined
value
.
The
contacts
are
just
closed
when
the
dial
is
set
on
0
.
When
the
dial
is
set
on
10
,
the
disk
must
travel
the
maximum
amount
to
close
the
contacts
and
there
-
fore
this
setting
gives
the
maximum
time
setting
.
The
above
results
should
be
checked
by
jneans
of
an
accurate
timing
device
.
Slight
readjustment
of
the
dial
can
be
made
until
the
desired
time
is
obtained
.
Aid
in
making
the
proper
selection
of
relay
settings
may
be
obtained
on
application
to
the
nearest
Sales
Office
of
the
General
Electric
Company
.
12
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