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2.4. THEORY OF OPERATION
CRA Series STABILINE®Power Conditioners maintain
a constant regulated output AC voltage by simulating an
infinite number of taps, between two real taps, on the
input of an isolation transformer. This is accomplished
automatically by adjusting a POWERSTAT®Variable
Transformers connected between a boost tap and a
buck tap of the isolation transformer. Using the brush of
the POWERSTAT as the input point, the “input tap” and
thus the output voltage can be controlled with great
accuracy.
A solid-state control unit detects the output voltage and
continually compares it with output and accuracy
settings selected by the user. If the voltage is out of
specifications, the control unit drives the POWERSTAT
variable transformer, by means of a synchronous motor,
to the required new position.
These units attenuate transverse-mode (line-to-line)
transients by 60 dB (1,000 to 1). This is accomplished
with a low-pass filter that attenuates regardless of
where on the sine wave or in which direction the
transient is applied, and does not rely on an absolute
amplitude before attenuation occurs. Peak clipping
devices are also included to assist in handling larger
transients.
Voltage transformation and common-mode (line and
neutral to ground) noise attenuation of 120 dB
(1,000,000 to 1) is provided by the double shielded
isolation transformer. Shield 1 in the isolation
transformer should be connected to the secondary
ground and increases the common mode noise
rejection. Shield 2 is between the primary and the
grounded shield, need not be connected, and is used to
reduce the conversion of common mode input noise to
normal mode output noise.
3.0. INSTALLATION
3.1. TRANSPORTING THE POWER CONDITIONER
Due to its weight and size, proper lifting procedures
must be followed when transporting the unit and moving
it into the location where it is to be installed.
The proper method for moving these units is to place a
forklift under the base. A heavy frame is provided in this
area to allow lifting the unit in this manner without
damage. The 26 inch (559 mm) wide enclosures can
also be lifted by removing the top cover and using the
lifting eyes provided in the sides of the cabinet.
3.2. MECHANICAL INSTALLATION
The power conditioner is designed for floor mounting.
When mounting the unit, allow a minimum clearance of
4 inches (100 mm) behind the unit for proper ventilation.
All internal components and wiring connections are
accessible through the front panels. A 3 foot (1000 mm)
area in front of the unit should be kept clear for
installation and service.
3.3. ELECTRICAL INSTALLATION
All CRA Series Power Conditioners are designed to be
hard-wired to the input power and the load using copper
wire. When these units increase low input voltage to
give nominal output voltage, the input current is
substantially higher than the nominal input current.
Maximum rated input and output currents for each unit
are given in the enclosed rating charts. Select a wire
size that is adequate to carry the maximum rated
current as specified by local and national code
requirements.
The front panel(s) of the power conditioner must be
removed to allow access to the input and load
terminals. To remove a panel, use a screwdriver to
release the ¼ turn fasteners, which hold the front panel
in place, and lift the panel off the base. A full range of
knockouts is provided in the base and the rear panel of
the unit for wire entry and exit.
The location of the power connections varies depending
on the options provided. On units with an input circuit
breaker, input connections are made directly to the
circuit breaker. The input connection for other options or
no options varies. Input connections are labeled L1
and L2. Load connections are made directly to the
isolation transformer on units without any options.
These output connections are labeled X1 and X2.
Units that have output options (ex. ammeters) will not
have the output connections on the isolation
transformer. These output connections are labeled
T1 and T2.
The outputs of the CRA Series Power Conditioners are
floating (not referenced grounded). If the unit’s output is
to be grounded the installer must make the ground
connection to the proper terminal.
For optimum common mode noise attenuation, it is
usually best to ground the shield 1 connection and allow
shield 2 to float. The unit is shipped with shield 1
connected to X1. If the installation’s ground is on X1
this is fine. If the installation requires the ground on X2,
the shield 1 connection should also be moved from X1
to X2.
The safety ground terminals are a ground stud on the
cabinet wall, or a lug on the base, and must be
connected to a suitable earth ground to reduce the
chance of electrical shock.
4.0. START UP
Set the Output Voltage Range toggle switch on each
control module to the 120 volt position to turn on the
control. The Output Voltage Adjustment and the
Sensitivity potentiometers are set at the factory for a
nominal output voltage and approximately 2% accuracy,
and should not be readjusted until the power
conditioner is initially energized.
