Transformer Coupled Output; Low Frequency Operating In Transformer Coupled Mode - Pacific Power Source LMX Series Operation Manual

5.12.5 Transformer Coupled Output

5.12.5.1 Neutral Grounding
NOTE: Importance of grounding the output neutral (N) when using Transformer coupled
output.
The output of the LMX-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 LMX-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 output, 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 however, neutral MUST BE connected to chassis
ground (either locally at the power sources' rear-panel or remotely at the load), because
line to neutral voltages can be greater than 150 Vac. If a phase voltage (Va, Vb, or Vc) 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.

5.12.6 Low Frequency Operating in Transformer Coupled Mode

LMX-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 primary
voltage) 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
T
30 Hz
Calculate the reduced output voltage value at 20Hz with maximum Volt Second Product
value
T
20 Hz
Therefore, to prevent output transformer saturation at 20Hz operation, the maximum
primary voltage of the transformer should be 82.5Vac.
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Entire Contents Copyright 2018 by Pacific Power Source, Inc. (PPS) • All Rights Reserved • No reproduction without written authorization from PPS.
LMX Series Power Source Operation Manual
1 1
= = =
. 0 033 sec
Freq 30 Hz
1 1
= = =
. 0 050 sec
Freq 20 Hz
LMX SERIES® OPERATION MANUAL
Unpacking and Installation
SECTION 5:
• = × =
Volt Sec T V
max 30 Hz rms
•
Volt Sec . 4 125
= =
max
Volts
T . 0 050
20 Hz
× = •
. 0 033 125 . 4 125 volt sec
•
volt sec
=
82 5 . volts
sec
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