Explanation by Phase Perfect below
pretty neat and gives expected measures amp draws and explains why they will appear high but are not! thank you all for your input on this topic and have a great day
Capacitive Current and Standby Loss for the Phase Perfect®
240V Digital Phase Converter
Introduction
The Phase Perfect utilizes filter capacitors to reduce electronic switching noise that is created by the
active switching technology employed in its architecture. These filter capacitors cause the system to
circulate reactive power. The purpose of this white paper is to explain what capacitive current or
power is, how it affects stand-by losses, and why measured stand-by current does not equate to
consumed power and is not billed for by the utility.
Capacitive Power Fundamentals
Our Phase Perfect systems utilize LC filtering (inductors and capacitors) to reduce noise from the
switching technology. Capacitors and inductors do not dissipate or consume power. Capacitors
store energy in the form of electrical charge, and inductors store energy in the form of a magnetic
field. These components both have a net effect of zero, as they alternate between supplying and
consuming energy.
In an AC circuit, capacitors and inductors continually charge and discharge at even rates. This means
that the average power through these components is 0. Half of the period of the power waveform is
spent absorbing power, and the other half of the period is spent supplying power. Averaging these
two parts together yields no net power loss because the charging and discharging curves are
symmetrical.
Example
Below is an example of how AC power functions in a simple circuit with a reactive load. This circuit,
illustrated in Figure 1, is composed of a resistor representing line resistance (10 ohms is a very small
resistance) and a capacitor.
Figure 1. Simple RC Circuit
Design
Assume this circuit is supplied with a 240V 60Hz source. Figure 2 below shows one complete cycle
of the voltage and current waveforms through the capacitor, as measured by probes “V” and “I” in
Figure 1 above. Note that the current waveform has been scaled up to match the range of the
Published: May 18, 2018
Phase Technologies, LLC
231 East Main Street North
Rapid City, SD 57701
605-343-7934 - Main
866-290-7934 – Toll Free
605-343-7943 - Fax
P a g e | 3
voltage curve. Using a large capacitance value like 2.65F gives a very clean current waveform to
compare to the voltage.
Figure 2. Voltage and Current Waveforms through the Capacitor
Figure 3 illustrates the instantaneous power through this simple circuit as measured at “V1” in Figure
1. The instantaneous power is the product of the current at voltage at any point in time. The cyclical
nature of this waveform oscillates between power consumption and power supply as previously
discussed.
Figure 3. Instantaneous Power in the Simple RC Circuit
The formula for average power in an ideal AC system is:
P = Vm · Im · cos(θ)
where m = magnitude
P = power
V= voltage
I = current
θ = phase angle (between voltage and current curves)
In this example circuit, there is always a phase angle of 90° because a purely reactive load (a load
composed entirely of capacitors and/or inductors) causes a phase shift of 90°. If θ is always 90°, then
cos(θ) will always be 0. Regardless of the voltage or current, the average power of an AC circuit in
-400
0
400
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Time (ms)
I
-40
0
40
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Time (ms)
Power
Consumption
V
Power
Consumption
Power
Supply
Power
Supply
Published: May 18, 2018
Phase Technologies, LLC
231 East Main Street North
Rapid City, SD 57701
605-343-7934 - Main
866-290-7934 – Toll Free
605-343-7943 - Fax
P a g e | 4
this configuration will always be 0W. However, as Figure 3 illustrates, even though the average
power is 0, the instantaneous power does vary.
Phase Perfect Stand-By Power
The Phase Perfect systems are much more complex than the simple RC circuit explored up to this
point. However, the same general concepts do apply. Due to the LC filtering in the Phase Perfect
systems, the filter capacitors are alternately charging and discharging.
Table 1 calculates the expected currents when measuring a system in stand-by. The formula for
calculating the current in a Phase Perfect system in stand-by is:
I = 2π · V · f · C
where f = frequency
C = capacitance
Table 1 calculates this expected circulating current in stand-by mode for the various Phase Perfect
models. These currents are not consumed, but reflected back to the source.
Table 1. Expected Circulating Current in Phase Perfect Systems
Model PT330 PT355 PT380 PT3110 PT3160
Capacitance [C] (μF) 40 80 60 160 240
Voltage [V] (V) 240 240 240 240 240
Frequency [f] (Hz) 60 60 60 60 60
Current
(A) 3.62 7.24 10.85 14.48 21.71
Unlike the ideal circuit explored in the example, the Phase Perfect has losses, which means that the
system is not 100% efficient. The system is consuming a nominal amount of energy, even in standby
mode.
Utility meters only measure power consumed (i.e. currents that are greater than 0). In a Phase
Perfect system, the utility meter will not register the circulating current (which averages to no net
power consumption). The utility is measuring an average of the current flowing to the capacitors and
being reflected back to the source. For a PT330 system, the current measured at the PT330 is
approximately 4.06A in stand-by mode. Per Table 1, the circulating current is approximately 3.62A.
Approximately 0.44A (the net difference) is consumed by the Phase Perfect. Thus, the stand-by
power consumption for a Phase Perfect system is:
P = V · (Iconverter – Ireflected)
where V = utility voltage
Iconverter = current measured at the Phase Perfect system
Ireflected = circulating current reflected back to the source
For the PT330 system, the stand-by power consumption is:
P = 240V · (4.06A – 3.62A) = 105.6W
Published: May 18, 2018
Phase Technologies, LLC
231 East Main Street North
Rapid City, SD 57701
605-343-7934 - Main
866-290-7934 – Toll Free
605-343-7943 - Fax
P a g e | 5
SUMMARY
Filter capacitors in Phase Perfect systems alternate between charging and discharging, creating a
reactive load which consumes no power. The actual peak currents that may be measured at the
source to a Phase Perfect unit will be much higher than what is actually being consumed. The actual
power consumption is the difference between this current and the current that is reflected back to the
source due to circulation.
Utility meters only measure current consumption, NOT circulation. Thus, though the amount of
current passing through the Phase Perfect system may be significant, the utilities are only charging
for the net power consumed, NOT the reactive current.
About Phase Technologies
Founded in 1999, Phase Technologies developed Phase Perfect® digital phase converters, the first
major advance of phase conversion technology in decades. Recognized as the world’s leading
manufacturer of phase converter technologies, the company expanded its product offerings to include
variable frequency drives (VFD’s).
Specializing in VFD with Active Front End technology, Phase Technologies produces the only low
harmonic, fully regenerative, phase-converting VFD that complies with IEEE 519, the international
standard for allowable harmonic levels on utility mains. The company has an extensive product lineup
of low harmonic, fully regenerative drives in both three-phase and phase-converting models.
Phase Technologies relies on a team of in-house power electronics and mechanical design engineers
to develop innovative products, encompassing all aspects of hardware and firmware design. All
products are manufactured at our facilities in the USA under exacting quality standards. In-house
processes include printed circuit board population and custom magnetics fabrication.
The company operates a certified UL 508A panel shop to integrate our drives into rugged outdoor
panels with custom options for applications including irrigation, oil and gas production and general
industrial control.
Integrity and honesty are the cornerstones of customer interaction at Phase Technologies.
Knowledgeable sales experts are available to help customers select the right product to fit their
needs, and we partner with the best distributors and dealers to make our products available with rapid
delivery times and local service. Experts in our customer service department are standing by to
answer technical questions and provide the support to keep your application up and running.
