Pacific Power Source 308-AMX - Transformer Outputs - Special Considerations

SECTION 3 INSTALLATION
72
3.4.4 TRANSFORMER OUTPUTS - SPECIAL CONSIDERATIONS
OUTPUT GROUNDING
The output of the AMX-Series Power Source is electrically isolated from the input power and
earth ground. This allows the user to establish a local ground for the output of the Power
Source. The AMX-Series Power Source is designed to withstand voltage potentials of 150
VAC between the Neutral output terminal and chassis ground.
When using the direct-coupled outputs, any output or neutral may be connected to chassis.
Since the line to neutral voltage cannot exceed 150 VAC, the voltage stress from neutral to
chassis never exceeds designed limits.
In the case of transformer-coupled outputs, neutral must be connected to chassis ground
(either locally or remotely), because line to neutral voltages can be greater than 150 VAC. If
a phase voltage (V
a
, V
b
, or V
c
) were connected to chassis, the voltage could exceed the 150
VAC limit specified for the neutral to chassis voltage. Neutral must remain within 150 VAC of
chassis (earth ground) at all times.
LOW FREQUENCY OPERATION
AMX-Series output transformers are designed to operate from 45 to 5,000 Hz. In the case of
steady-state sine wave output, operation at frequencies as low as 30 Hz (125 VAC V
pri
) is
possible. Operation at lower frequencies ( below 30Hz ) may cause saturation of the output
transformers, but at reduced output voltages, lower frequency operation is possible. The
VoltSecond Product of the output MUST NOT exceed the maximum VoltSecond rating of the
transformer to prevent saturation of the transformers when operating at lower frequencies.
For example, to determine the value of reduced voltage at 20Hz operation of the transformer
described above,
1. Calculate the VoltSecond Product maximum value of the transformer at 30Hz and 125 Vac
2. Calculate the reduced output voltage value at 20Hz with maximum Volt Second Product
value
Therefore, to prevent output transformer saturation at 20Hz operation, the maximum primary
voltage of the transformer should be 82.5Vac.
Systems with transformers connected to the output require special attention when designing
transient profiles (applicable to systems w/UPC). It is possible to design transients in which
the DC Component of the periodic waveform is not zero. Attempting to push DC voltage
through the transformer will cause saturation of the device. However, the output
transformers are designed to support a single event, half-cycle dropout at 125 VAC
pri
, 50 Hz
without saturating. Continuous operation with an asymmetrical waveform (DC component 
0) will cause saturation.
sec050.0
20
11
20

HzFreq
T
Hz
sec033.0
30
11
30

HzFreq
T
Hz
sec125.4125033.0
30max






voltVTSecVolt
rmsHz
volts
volt
T
SecVolt
Volts
Hz
5.82
sec050.0
sec125.4
20
max




