Meggerm
DDA-3000
and
DDA-6000
Universal Circuit Breaker Test
Sets
The
Model
DDA-1 control
panel
digitally
s.amples
the
output
current
and
mathematically
calculates
the
current supplied
to
the
breaker
under
test.
The digital control
of
the
SCRs
also allows the unit
to
initiate at
any
point
within 90 degrees
of
the zero
crossover
point
of
the
output-current waveform. This
will allow
the
intentional insertion
of
a dc offset into
the
waveform for a complete investigation
of
a breaker's
operation.
•
Compact
enclosure:
Improvements
in
transformer
and
circuit design have resulted in a very high-capacity test
set
in
a single, relatively small enclosure. For safety
and
mobility,
the
test
set
is
housed
in a single, rugged,
sheet
metal enclosure with a
low
center
of
gravity,
tow
ring,
lifting eyes
and
large, locking swivel casters with brakes.
To increase maneuverability, all four casters swivel;
however,
they
also
can
be
locked into a fixed pOSition
easily. The
compact
size
of
test sets permits easy
movement
through
narrow doors. Controls
and
instrumentation are positioned so that the operator
can
Simultaneously observe
the
circuit breaker
under
test.
•
Construction:
Built for years
of
trouble-free, reliable
operation,
the
test sets include rugged instrumentation
and controls designed to withstand
the
vibration
and
shock
of
frequent transportation. They
need
never
be
removed from
the
enclosure .
• Protection: Fuse, circuit breaker
and
overload
protective devices are incorporated. The output-initiating
SCRs
are forced-air cooled,
and
temperature sensors
provide protection from overheating. Emergency
stop
pushbutton is
provided
to de-energize all
input
power
to
the test set.
•
Ground
safety
interlock:
An
interlock circuit ensures
that
the
test
set
chassis
is
connected to system
ground
before
the
output
of
the
test
set
can
be
energized.
•
Accessory
outlet: A ground-fault-protected, 120 volt
outlet with a capacity
of
1.2
kVA
is
proVided for
convenient
connection
of
accessory equipment.
Other
voltages are available internally for customer-installed
outlets.
INSTRUMENTATION
AND
CONTROLS
Model
DDA-l:
The
Digital Data Acquisition
instrumentation
and
control system was deSigned
specifically
to
provide precise control
of
the
output
current
and
accurate metering
of
the
breaker
under
test.
Model DDA-1 uses the latest in digital signal processing
(DSP) technology. This technology provides complete
digital control
of
the
SCRs
and
digitally samples
the
output
current for high-accuracy measurements.
Digital
ammeter:
Model DDA-1 samples
the
output
current digitally
and
mathematically calculates
the
current
that is supplied to
the
breaker
under
test. This process
increases
the
accuracy
of
the
ammeter systems
and
provides extreme flexibility in
what
current value is
displayed. For example,
when
the
test
set
is
delivering a
continuous current, the digital
ammeter
is continuously
sampling
the
output
waveform
and
can
display a true rms
value
of
the
current.
For measuring short-duration currents, Model DDA-1 can
calculate
the
output
current in
the
following ways via
selection from the soft control buttons
on
the
panel:
1.
For any
output
current greater
than
half a cycle, Model
DDA-1
can
calculate the true rms value
of
the
output
current pulse. For any
output
less
than
half a cycle, a true
rms measurement
is
invalid.
2.
For
any
current pulse, Model DDA-1
can
measure
th~
peak
current
and
calculate
an
anticipated rms value
of
the
current from
the
peak
current.
This multiple-current calculation feature is also useful
when
testing different styles
of
solid-state trip devices. This
feature allows the test set to simulate a similar type
of
current calculation that is being
used
by
the
various solid-
state trip devices.
Digital
timer: Thanks to digital signal processing
technology, Model DDA-1's system
knows
exactly
when
current is
present
and
when
the
breaker
under
test opens.
This provides high-accuracy timing
even
when
testing the
instantaneous trip function
on
fast-acting breakers.
In
addition,
the
digital timer
can
display
the
breaker
trip time
in
cycles
or
seconds.
A completely digital, solid-state circuit starts
the
timer
automatically
when
the
output
current starts to flow
and
stops it
when
the
device
under
test operates. This circuit
will accommodate a variety
of
test conditions including:
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