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Testing
One
other major difficulty with primary current testing
is
related
to the duty cycle
limitation
of the circuit breaker and current
sensor.
A
properly operating tripping
system
will be
self-
protecting
from
thermal damage
up
to
the
circuit
breaker short
time
and
interruption
rating, providing that
the
duty
cycle
applicable
for each rating
is
not
exceeded.
The
standard
duty
cycle
for the
short
time rating
as
demonstrated
per
ANSI
C37
50
is
0.5
Seconds On,
15
Seconds
Off
followed
by
another
On
period
of
0.5
Second.
The On
intervals
are too short to
read
the
ammeter
on the
current
source,
For
the
instantaneous
interruption rating
each of the On
intervals
are reduced
to
approximately 50
Milliseconds.
Because
of
this,
calibration
of
the
trip device
high range settings cannot be
accurately
done
with primary current.
The
calibration can
be
verified safely
at
the lower settings and
"operation only"
verified
at
the higher
set points.
CAUTION:
lf
the duty cycle limits are
exceeded during
testing,
the
circuit
breaker or
current
sensor
as
well
as
the
trip
device may
be
damaged. Between tests, the
unit must
r'emain OFF
long enough
to allow
the
current
sensor to
cool.
ln
addition,
if
there
is
a
fault
in
the
system,
the
breaker
may
not
operate
within
its
rated
time,
and
the
system
will
not
be
self protecting.
Therefore
to
properly protect the tripping system
from
potential damage
and still
assure proper operation,
the
following procedure is
recommended.
lf
the breaker
has a
ground
fault sensing
trip device connect
a
jumper
between terminals
4
and 5 of the
trip
device,
1
Apply
to one pole
of
the
circuit
breaker an input current of
one
half
the
current sensor rating
and
measure the
trip
device
power supply voltage,
This
voltage
can
be
mea-
sured with
the negative
lead of the voltmeter on
Pin
I
or
2
of
the
15
pin connector. The positive lead
is
terminal
block
number
7, the red
lead
of the
actuator.
lf
this
voltage
exceeds
I
I
Volts
with
half
rated current
supplied,
it
can be
assured
that the
wave shape distortion can
be
disregarded
except
for
its possible effect on the ammeter
indication,
Test
all
three poles
of
the
breaker
in a
similar manner, this
establishes that
the
device
power supply circuits
are
work-
ing
2.
Set
the
long
time current setting
to
the
.5
position.
Slowly
increase
the
current from
zero
while watching the
long
time
pickup
LED.
Pickup should
occur
at one-half the current
sensor rating
with a
tolerance
of
minus
zeto
lo
plus
20
percent, not including any ammeter error. Pickup is
the
lowest
current
at
which
the
LED
remains illuminated, Repeat
for
all three poles of the
circuit
breaker. This proves
the
input circuits
are all
working,
When
the
pickup
indication
is
present,
the long tlme
circuittiming
element
is
released and
the device
will time out on LONG
TIME.
Repeat calibration check on the other long
time
current
settings
as desired.
3.
Set long time
current
setting on .5, long time delay on
3.5,
short
time pickup and
jnstantaneous
on
12
Set
the
inpul
current equal
to the
current sensor rating.
Remove and
reapply the power, allow the device
to
time out and trip the
breaker.
The
time delay should meet the
published
curves
for the
device
being tested. Repeat
for all
long time bands.
Note
that
the
Static
Trip lll
long time
circuits
respond
to
the
RMS
value
of
the input current, and
depending
on the
type
of
ammeter
being
used the
times
may
all
appear
to
be
longer than
expected.
lf
the test set
has
an
RMS
responding
ammeter the time values
should check
properly.
4.
Set instantaneous at 2, short
time pickup at
12, long time
delay
on its
maximum
of 30.
The breaker should
trip
instantaneous
at
twice
the
current sensor rated current with
a
tolerance
of
minus zero
lo
plus 20
percent.
Repeat for
all
three
poles of
the
breaker.
5
Set short
time pickup
at
2,
instantaneous
at
12, long time
delay on
its
maximum, and short time delay
on
minimum of
08. Set long time current setting
.5.
Slowly increase
the
current.
The
breaker should trip
at
the
current sensor rated
current
with a
tolerance
of mlnus zero
to plus
20 percent,
The
time delay circuit can
allow the
current
to
increase after
tripping
has been initiated,
so
the
rate at
which the
current
is
increased must be
limited
to prevent
"overshoot."
6
With
the
same settings
as
in step
5,
adjust the
supply
current
to 3
times the current
sensor rating,
Apply
the
current
and
observe
the
tripping
time, Test allf
ive
shorttime
delay bands. Note
if
the
device contains Zone lnterlocking,
a
Zl
input signal must be supplied or the Zone
lnterlock
switch moved
to
the "out" position
in
order
to
test other
than
the
minimum time
delay
band.
7.
lncrease both
instantaneous
and
short
time pickup
to
12,
set
the long time delay
on
3.5, long time current setting
on
.5
Adjust
the
supply
to
twice current
sensor rating.
Apply
this current and observe
tripping
time. Test at the
same
current for all long time
delay
bands. Verify that they meet
the
published values.
Other
values
of
current can
be
tested
if
overheating
is prevented.
8.
The
operation of the
Short
Time
l,t
ramp, and time delay
bands can
also be
checked
as desired.
9.
lf
the
device
has ground fault
tripping,
remove the
jumper
from terminals
4
and 5. Set Ground Fault pickup on
60,
increase
the supply
current from zero, verify that
the
ground circuit trips the
breaker
aI60%
with
a
tolerance
of
plus
or
minus 10%
of the
Ground Sensor rating.
Lower
settings
can be
tested. Depending
on the
amount
of
waveshape distortion there may not be enough power
to
trip the breaker
at
the lowest available ground fault
pickup
value
with
no
other
phase currents.
l0.To
demonstrate operation at normal control settings, reset
all
controls
to the
desired values,
set
current
to a
high
enough value to definitely cause
tripping, apply
current,
and
verify that
tripping does occur
as
expected.
34
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