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G EH-1753
Time Overcurrent Relays Type lAC
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.
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.
sary to prevent the right-hand stationary contact
be
from getting out of adjustment. Screws should not
in both taps at the same time.
INDUCTION UNIT
CURRENT SETTING
The tap plug must not be removed without first
withdrawing the connecting plug.
be
The current at which the contacts operate may
changed by changing the position of the tap plug
in the tap block at the top of the relay. Screw th
tap plug
firmly into the tap marked for the desired
current (below which the unit is not
When changing the current setting
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.
the operating current
into agreement with the tap setting employed,
some reason, this adjustment has been disturbed.
This adjustment also permits any desired setting
intermediate
between the various tap settings
obtained.
The unit is adjusted at the factory to close
its
contacts from
any
time-dial
mum
current within five percent of the tap-plug
setting.
The
unit resets at 90
mum closing value.
T IME SETTING
The setting
of the time
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 thi.s setting gives the maximum
12
ADJUSTMENTS
This procedure is neces
to
operate).
of
the unit,
be
By
turning the ring,
if
of
the unit may
brought
to be
position at a mini
per
cent
of
the mini
dial determines the
t
im
e setting.
The primary
adjustment
tion of the unit is made
However, further
adjustment
the permanent
magnet along its
moving the magnet toward the disk shaft
the time, while moving it away increases
H
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 operatio'll of the
To
several circuit breakers. Allowance must
for the time involved in opening each break � r after
the relay contacts close.
the circuit time of operation is known with accuracy,
there should be
a
the maximum current) between relays whose opera
tion is to be selective.
EXAMPLE OF SETTING
The time and current settings of
unit can be made easily and quickly.
shown in
Fig.
2 indicates
contacts to close with a particular time-dial
when the current is
the current-tap setting.
the particular time-current settings shown in Fig. 2,
insert the removable plug in the
ceptacle and adjust the time-dial
position.
The
following example
e
procedure in making a relay setting.
Assume a Type lAC relay
where the circuit breaker should trip on a sustained
current of approximately 450 amperes;
breaker should trip in 1.9 seconsts on a short-circuit
current of 3750 amperes.
current
transformers
The current tap sett
minimum
primary tripping current
transformer ratio.
equals 7.5 amps. Since there is no 7.5-amp tap,
8-amp. tap is used.
for
setting to give 1.9 seconds time dela y at 3750 am
peres, divide 3750 by the transformer ratio. This
62.5
gives
amperes secondary current which
times the
8-ampere
time current curves (Fig. 2), i
times the minimum
seconds time
delay when the
above the No. 6 time-dial setting.
The above results should be checked by p1eans
of an accurate t
im
of the dial can be made until the de�ired time
obtained.
Aid in making the
settings may
be
obtained on
Sales Office of the General Electric Company.
for the
time
of opera
b
y
means of the time
is obtained by moving
supporting
decreases
the time.
For this reason, unless
difference of about 0.5 second (at
the overcurrent
Each time value
the time required
In
a
prescribed number
order to secure
to the
proper
illustrates the
is
used
in a cir
Assume further that
of
60/1
ratio
ar
ing is
found
by d
i
vi
In
by the current
this case, 450
divided
To find the proper time-dial
setting.
By r
e
ferr
i
n
t will
be seen that 7.8
operating
current gives 1.9
relay is set slightly
in
g
device.
Slight readjustment
proper
selection of relay
application
to the nearest
dial.
shelf;
�e made
for the
setting
of times
any of
tap r
e
proper
cu
it
also, the
e
us
ed.
din
g
the
by 60
the
is 7.8
g to the
is
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