Samlexpower PST-15S-12E Owner's manual - Section 2 |
10 | SAMLEX AMERICA INC.
2.2 oUtPUt VoLtAGe WAVeFoRMS
TIME
360
320
280
240
200
160
120
80
40
0
40
80
120
160
200
240
280
320
360
Modified Sine
Wave sits at
ZERO for some
time and then
rises or falls
V
PEAK
= 325.22V
Modified Sine Wave
Sine Wave
Pure Sine Wave
crosses Zero Volt
instantaneously
V
PEAK
= 280 to 320V
V
RMS
= 230 VAC
VOL
TS (+)
VOL
TS (
–)
20.00 ms for 50 Hz
16.66 ms for 60 Hz
Fig. 2.1: Pure and Modified Sine Waveforms for 230 VAC, 50/60 Hz
The output waveform of the Samlex PST series inverters is a Pure Sine Wave like the
waveform of Utility / Grid Power. Please see Sine Wave represented in the fig. 2.1 that
also shows Modified Sine Waveform for comparison.
In a Sine Wave, the voltage rises and falls smoothly with a smoothly changing phase
angle and also changes its polarity instantly when it crosses 0 Volts. In a Modified Sine
Wave, the voltage rises and falls abruptly, the phase angle also changes abruptly and
it sits at zero V for some time before changing its polarity. Thus, any device that uses a
control circuitry that senses the phase (for voltage / speed control) or instantaneous zero
voltage crossing (for timing control) will not work properly from a voltage that has a
Modified Sine Waveform.
Also, as the Modified Sine Wave is a form of Square Wave, it is comprised of multiple
Sine Waves of odd harmonics (multiples) of the fundamental frequency of the Modified
Sine Wave. for example, a 50 Hz Modified Sine Wave will consist of Sine Waves with
odd harmonic frequencies of 3rd (150 Hz), 5th (250 Hz), 7th (350 Hz) and so on. The high
frequency harmonic content in a Modified Sine Wave produces enhanced radio interfer-
ence, higher heating effect in inductive loads like microwaves and motor driven devices
like hand tools, refrigeration / air-conditioning compressors, pumps etc. The higher
frequency harmonics also produce overloading effect in low frequency capacitors due to
lowering of their capacitive reactance by the higher harmonic frequencies. These capaci-
tors are used in ballasts for fluorescent lighting for Power factor improvement and in
single-phase induction motors as Start and run Capacitors. Thus, Modified and Square
Wave inverters may shut down due to overload when powering these devices.