Page one of 5 pages on selecting the right 3 phase conversion method.
Let them speak! Let’s look at what the manufacturers say about their products and their competition.
What is marketing hype and what isn’t.
I’ve gathered information from a small group of 3 phase conversion manufacturers. I give credit to the companies and links to their websites.
Italicized text is from the company, yellow highlight focuses on central themes, and I’ve parsed the information in blue text.
One more point;
When I was publishing my information in 2006 I felt that I was on to something good, so I filmed everything. Ran the motors and balanced them using voltage meters and amp meters.
I filmed live so all the voltages and amps could be seen. I rigged up switches so I could balance the converters in real time. I wanted to demonstrate the effect the capacitors had on the balance. Viewers could learn something from it.
Ever wonder why people selling 3 phase conversion products don’t do the same thing? How many years have they been selling rotary converters? How many videos do you see on You Tube? I have not seen one manufacturer put their machines up for live tests.
American Rotary has a You Tube channel. They have videos but they don’t show running volts and amps. There’s one of a 20 hp air compressor. The video does show starting it compared to another brand x converter. But it is disappointing, no amps, volts, idle amps, or single phase amps. Then, no restart after the pressure has built up. Parameters that I believe are essential to have in my videos.
Lets get on with what Larry Meiners from Phase Perfect has to say about phase conversion options:
He is one of the people behind the Phase Perfect all digital phase converter. This could be, a disruptive technology.
PHASE CONVERSION TECHNOLOGY OVERVIEW Dr. Larry Meiners, Ph.D.
Introduction A wide variety of commercial and industrial electrical equipment requires three-phase power. Electric utilities do not install three-phase power as a matter of course because it costs significantly more than single-phase installation. As an alternative to utility installed three-phase, rotary phase converters, static phase converters and phase converting variable frequency drives (VFD) have been used for decades to generate three-phase power from a single-phase source. However these technologies have serious limitations, which motivated Phase Technologies, LLC to develop a new digital phase converter, Phase Perfect®. This new patented technology overcomes the limitations of earlier phase converters, and is an affordable alternative to utility three-phase. Reduced motor life caused by voltage and current imbalance, harmonics that pollute the power grid and damage equipment, or the inability to operate sensitive equipment or multiple loads are just some of the problems that have limited the use of phase converters.
He first mentions the most common methods of 3 phase conversion used over the last 30 years.
He neglects to mention the transformer converter, probably because only one manufacturer makes it now.
He brings up the limitations and drawbacks of the typical methods. Rotary converters and vfd’s pretty much ruin everything.
Phase Perfect® is a new, patented technology that supplies three-phase power from a single phase source to power inductive, resistive and capacitive loads with distinct advantages over any existing converter technology. Rotary and Static Phase Converters Phase converters provide 3-f power from a 1-f source, and have been used for decades. The simplest type of old technology phase converter is generically called a static phase converter. This device typically consists of one or more capacitors and a relay to switch between the two capacitors once the motor has come up to speed. These units are comparatively inexpensive. They make use of the idea that a 3-f motor can be started using a capacitor in series with the third terminal of the motor. It is almost guaranteed that a static phase converter will do a poor job of balancing the voltages on the motor. Unless motors operated on static converters run only for short periods or deliver significantly less than half of their rated output, they will be damaged from overheating.
No argument here, we all know statics are no good.
Note that Ronk Electrical calls their transformer converter a ‘static converter’ which is true, no moving parts, but this is not what people today call a ‘static converter’.
Now continuing on, they start in on the rotary.
The second type of old-technology phase converter is generically called a rotary phase converter. This device consists of a 3-f motor (usually without external shafts) and a bank of capacitors wired together to act as a single large capacitor. . Typically the motor used in the phase converter is larger than the loads it is supplying. The electrical interaction between the capacitor bank and the free-running phase converter motor generates a voltage on the third motor terminal which approximates the voltage needed for a balanced 3-f system. However, it usually isn’t a very good approximation. For example, measurements on a 7.5 Hp rotary converter in an actual machine shop installation resulted in line-to-line voltages of 252 V, 244.2 V and 280.5 V, which is about a 12% imbalance in the voltages. Notice that while the voltages were only 12% out of balance, the currents differ by almost a factor of three. Since the negative sequence voltages feed into an inductance which is one sixth of the inductance seen by the positive-sequence voltages, a rather modest imbalance in the voltages produces a totally unacceptable imbalance in the currents. In this example, the lead to the motor carrying the smallest current could be totally disconnected and it would not significantly change the performance of the motor. If a single motor is always run at a constant load, and the rotary phase converter and its associated capacitor bank are carefully adjusted, then it is possible to achieve better than a 12% voltage imbalance as discussed in the example above and get acceptable operation of the motor. The procedure would involve setting up the system of phase converter, motor and load; then measuring the generated voltages and the currents in each motor phase. If the current balance were unacceptable, then capacitors would need to be either added to, or taken out of the capacitor bank until the currents were balanced. In some cases, it might be necessary to switch to a different size phase converter to get the system balanced. If the motor were required to operate over a wide range of load conditions, or if several motors were powered using the same phase converter, it would be nearly impossible to get good voltage balance over the whole range of operation.
The above statements are all true about the rotary converter and the transformer converter.
They need to be balanced and they don’t balance the same at all loads.
This is what annoyed me the most with the claims made by rotary converter manufacturers.
For years they never said anything about bad balance.
Now suddenly some of the manufacturers have come out with balance circuits as an option on their converters.
They never said we needed that years ago! Years ago their literature stated these things were like having ‘real three phase’ in your shop!
Below he gets into why VFDs are not the way to go.
Variable Frequency Drives Variable frequency drives (VFDs) are designed primarily to control the speed of AC motors, but can be adapted to function as phase converters. They also have some problems with power quality. While a phase converter will supply a 3-f output at the same frequency as the input voltage from the power line, a VFD has the ability to create voltages that vary in frequency. A VFD has an input rectifier (either 4 or 6 semiconductor diodes) which charge up a DC link capacitor. A VFD cannot produce a sinusoidal output voltage. It can only connect the output terminals to either the positive or negative terminal of the link capacitor. Problems can arise with VFDs if they are used to power loads other than motors, if there are multiple loads on the VFD, if the motor needs to provide braking action, if the distance between the motor and the VFD is appreciable, or if the current drawn by the VFD is large compared to the rating of the utility step-down transformer. VFDs were not originally designed to function as phase converters, in fact most VFDs are powered from a three phase source. When used in this manner, six input diodes rectify the 3-f input signal and are used to charge up the DC link capacitor. If a 1-f source is used instead, then 2 of the input diodes go unused and all of the current into the unit has to be carried by the remaining 4 diodes. Also, the ripple current in the DC link capacitor will be significantly larger, so the power handling capability of all these components has to be increased if the unit is to be powered from a 1-f source. This type of input rectifier typically produces large harmonic distortion in the input current. The harmonic component of the current will be a problem when the current flowing into the VFD is a significant portion of the total current load that the step-down transformer is capable of delivering. If a very large VFD is used or if multiple smaller VFDs are all attached to the same line then there may be problems. The relatively large current drawn by the input circuit of the VFD at the peak of the voltage sine wave can distort the voltage waveform and cause problems for other users on the power system. Input line reactors are often used between the VFD and the power system to help alleviate this problem.
Here he actually says something nice about the rotary converter.
Rotary and static phase converters intrinsically have the ability to absorb braking currents because two of the wires to the motor are connected directly to the supply system. A Phase Perfect unit is able to feed power from the generated phase back into the power system as well.
More on problems with the VFD method.
The output voltage from a VFD is not sinusoidal, but rather a series of pulses which have average values that are sine waves. If the distance between the VFD and the motor is short (less that 10 feet), there shouldn’t be any problem. As the distance approaches 50 feet or more, most VFD manufacturers recommend that output line filters be used on each of the output leads. In their simplest form these filters consist of an inductor in series with each output line with a capacitor connected to the second terminal of each inductor. The other terminal of each capacitor is connected to a common point. This filtering does not make the output voltages sinusoidal, and so even with filtering, residual harmonics may have some impact on the wire and motor in installations where the motor and drive are far apart. At distances of 200 feet or more, as would be typical for a deep-well submersible pump, output line filters are a necessity and will add to the cost of the drive installation. Phase Perfect® Digital Phase Converters Both rotary and static converters have difficulty adjusting voltage balance to accommodate changing load conditions. Voltage regulation schemes for rotary converters are available which switch in different amounts of capacitance as the load changes. However, it is still difficult to get good control, and the high current pulses created in the system as the capacitors are switched in and out can be a problem.
Here and below he restates the problem and tells how the Phase Perfect unit over comes that.
The system is controlled by a small microcontroller, specifically a digital signal processor (DSP) which can measure voltages and feed controlled pulses into the switches, in addition to performing high-speed calculations. The DSP is constantly monitoring the system voltages and current to insure that the input current is sinusoidal, and the output voltage is also sinusoidal. The output voltage can be made equal in magnitude to the input voltage to an accuracy that is primarily determined by the measurement accuracy of the DSP. Typically, the line-line output voltages of Phase Perfect® are balanced to within 1-2%. As the load on the system changes, the DSP senses any drop in the voltage and adjusts the pulses to the semiconductor switches to maintain this accuracy from no load up to full load. Any motor load, or any combination of motors up to the maximum rating of the digital phase converter can be connected without creating unbalanced voltages. This is the first product to apply modern technology to the problem of phase conversion. Because the voltages from a Phase Perfect® converter will be balanced as long as the total load on the converter is less than or equal to its load rating, there isn’t any engineering work required by the customer. If you examine the product literature provided by manufacturers of rotary phase converters, one thing conspicuously absent is any mention of the phase balance provided by the converter. Since a rotary converter has no control over the output voltage, each motor and each load represents a different situation and manufacturer is not able to predict how their converter will behave.
Again same thing.
Sensitive CNC equipment may not even turn on if it is powered by a rotary converter. In the example of the 7.5 HP rotary converter used in a machine shop where one of the line-line voltages from the rotary converter was at 280 V, the electronics unit of a CNC would probably be damaged if it were operated at such a high voltage. A typical utility standard for voltage balance is nominal voltage +/-10%, so a Phase Perfect converter is achieving voltage balance about 5-10 times better than what the utility can guarantee.
Phase Perfect® CASE STUDY; A 10 HP model DPC-10 Phase Perfect® digital phase converter was connected to two legs of a 208V grounded wye three-phase service. The converter generated the third leg voltage. Two loads were connected to the output of the phase converter. One was a centrifugal pump powered by a 7.5 HP three-phase motor, the other a squirrel cage fan powered by a 3 HP three-phase motor. A load distribution panel allowed the loads to be switched in or out of the circuit independently. Measurements The input voltage to the phase converter was measured on terminals 1 and 2, and is referred to below as V12. The generated voltage occurs on terminal 3. The voltages on the phase converter output under various load conditions are given in table 1 below. Table 1 Load Condition V12 V13 V23 No load 201.0 V 204.3 V 200.3 V 3 Hp load 199.4 V 201.1 V 199.2 V 10.5 Hp load 193.4 V 194.1 V 196.4 V The single-phase input current supplied to the phase converter is expressed as Iin. The currents measured on the output are I1, I2 and I3, with I3 being the generated phase. The phase currents and the total input current to the system under the two loading conditions are given in table 2 below. Table 2 Load Condition I1 I2 I3 Iin 3Hp 4.7 A 4.6 A 4.8 A 7.6 A 10.5 Hp 22.6 A 23.6 A 25.1 A 39.0 A Results The NEMA definition for voltage imbalance is that the percentage voltage imbalance is given by (max. voltage on any line) – (average voltage) % imbalance = average voltage A similar equation gives the current imbalance. If this definition is applied to the above results, the voltage imbalance is 1.2% at no-load, 0.6% with a 3 Hp load, and 0.9% with a 10.5 Hp load. The current imbalance is 2.1% with the 3 Hp load, and 5.6 % with the 10.5 Hp load.
Here is something I should note: I always balanced my motors according to the amps.
Here he seems to put more emphasis on the voltages. I don’t know why.
But the amp and volt reading he shows above is very achievable with the transformer converter at full motor power.
Anything less then full power results in a widening of the imbalance.
But and this is a big but, the input power always goes down as the load goes down, and the amps are always below the max amps for any one leg.
So bottom line motor doesn’t over heat or have any problems.
The voltage imbalance at the output of the phase converter under all load conditions from zero to full load did not exceed 1.2% which is significantly better than the +/- 10% value that utility power is expected to maintain. The above result was obtained with no adjustments to the phase converter, that is, the unit self corrected to maintain the above voltage balance with no operator intervention. The current imbalance to the motors never exceeded 5.6%. This amount of current imbalance would have no perceptible impact on the life or proper functioning of the motor. The overall power factor of the system when it was operating at full load was 0.99. The near unity power factor reduces the input current to the system and under some utility billing programs will significantly reduce the power costs to the user.
A couple of things to mention here:
He states that utility power is only expected to maintain a +/- 10% voltage balance. Something to think about.
He mentions his unit provided 1.2% voltage imbalance and never exceeded 5.6% current imbalance. I can, at times, get either perfect amp balance or perfect voltage balance by making adjustments. I typically favored the amp balance side.
Volts times amps equals power so it is really six of one, half dozen of the other. (old fashion expression)
Okay, so what does Larry really say about other 3 phase conversion methods?
A recap would be that rotary converters are terrible things that generate harmonics, reeking havoc with the power lines, and they can not be balanced properly for different or varied sized loads.
He also points out that the balancing schemes employed today by rotary converter manufacturers are not very effective.
He did leave out one of my gripes, that they’re noisy.
So there you have it.
An entire group of manufactures should be out of business in a year or so.
That is what I thought when I first saw the Phase Perfect.
I figured all the other ways were obsolete.
Kind of like when they came out with inverter welders, same principal.
And of course VFD’s are out.
Now oddly enough Mr. Meiners views are also backed up by two other companies that sell 3 phase conversion products;
Ronk Electrical Industries and Smith Electric Motor Works.
My take on these two outfits is they don’t spend a lot of money advertising to the small retail market, but rather specialize in industrial sales.
Smith seems to have companies that sell three phase machines. When a customer buys one a Smith converter can be included in the sale, if needed.
I have noticed that American Rotary is instituting a similar program.