Atec Megger-DDA-1600 - Manual (Page 2)

DDA-1600
Circuit Breaker Test Set
■ Zero dc offset: Use of digitally controlled SCRs instead
of a contactor to initiate the output of the test set
eliminates closing-time error and ensures precise
initiation at of the output current waveform every time.
Accurate, repeatable test results are ensured even with
currents of very short duration, as when conducting tests
of instantaneous or short-time delay trip elements.
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 elimination of a the dc offset caused by a
change in impedance of the varying loads.
Controller and Instrumentation
Module
Model DDA-1: 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
therefore 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 one cycle, Model
DDA-1 can calculate the true rms value of the output
current pulse. For any output less than one cycle, a true
rms measurement is invalid.
2. For any current pulse, Model DDA-1 can measure the
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: Because of the Model DDA-1 digital signal
processing technology, the system knows exactly when
current is present and when the breaker under test opens.
This provides a high-accuracy timing even when testing
the instantaneous trip function on fast-acting breakers. The
digital timer can display the breaker trip time in cycles or
seconds.
A completely digital, solid-state circuit automatically starts
the timer 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:
1. When testing a circuit breaker or a device which has no
auxiliary contact to monitor (each as a single-pole circuit
breaker), the timer starts when the output current starts
to flow and stops when the output current is
interrupted.
2. When testing a device and monitoring normally closed
contacts, the timer starts when the output current starts
to flow and stops when the contacts open.
3. When testing a device and monitoring normally open
contacts, the timer starts when the output current starts
to flow and stops when the contacts close.
Digital voltmeter: Model DDA-1 can be used to
measure the input voltage to the test set or the output
voltage from the test set. It also can be used as a diagnostic
tool to evaluate contact condition by measuring the voltage
drop across breaker contacts while subject to high current.
Panel indicators: Panel lamps incorporated for operator
safety and convenience, indicate:
1. Output of the set ENERGIZED
2. Thermal WARNING or SHUTDOWN
3. GROUND INTERLOCK open
4. OVER RANGE of ammeter
External initiate circuit: allows initiation of the test set
from a remote location when desired.
Model DDA-1600 uses the Model DDA-1 Digital Data Acquisition Instrumentation and Control System. This system offers the latest in digital signal
processing technology to control the test set and measure reactions of the breaker under test.