BOOSTERS
(Single Phase to Three Phase Converters) :
Selecting a Single to Three-phase Booster
- Introduction
- Electricity
- Why Three phase is better.
- 3 Phase utility.
- Producing the Three phases.
- Capacitors.
- Applying the Eco.
- Boosters.
- Booster - E.
- Some Booster Constructional Details.
- What to expect from Eco's & Boosters.
- Balanced voltages.
- Three phase voltages.
- Welders & Boosters.
- Irrigation pumps & Boosters.
- Technical Information.
This publication is written to help you make some intelligent choices about Boosters. Specifically, what type might work best for your machines, and some things to look for as you might compare with single to three-phase converters. We will try to make you as well informed as possible in a short time. But, please, always talk to an application engineer before you make your final selection.
Electricity is used to produce a magnetic field that turns a motor. Electricity is measured in terms of voltage and current. Think of voltage as the pressure, and current as a measure of the flow. Voltage is measured in Volts. Current is measured in Amps. The product of volt and amps results in power, measured in watts or thousands of watts: kilowatts kW. One kW is equivalent to about 1.36 horsepower.
Electricity
is distributed as Alternating Current (AC). Where a battery has two
terminals, one that is always positive (+), and one that is always
negative (-), AC voltage changes, or alternates, from positive (+) to
negative (-) at a set frequency, usually 50 times a second (50 cycles or
Hertz or Hz).
In a pole or street distribution transformer, voltage is reduced from
11,000V to either 1x 230V and Neutral (Ground) or to 3x 230V. If
voltages are measured between the three phases, three times 400V will be
found.
There are still some variations found in different countries: 220V,
which will result in 380V between phases, and 240V, which is equivalent
to three times 415V. Around the USA and Canada and in some South
American countries you will find single phase 110-127V which means
190-220V between the three phases.
An electric motor operates on the principle of one magnetic field chasing another. As the electrical polarity on the AC line changes (from + to -), the magnetic poles in the motor change from north to south in relation to the rotor poles, causing the motor to turn.
With each change in polarity the voltage rises and falls as a wave, with a brief period of no voltage, called a zero crossing. Each time the voltage rises, either above or below zero crossing, the motor receives power, much as a car is propelled by the engine firing.
Think of the spark plug on a running engine. If you took hold of that spark plug, you'd swear the electricity was a continuous flow rather than an intermittent spark. Single-phase AC power is a lot like that, and the flow of power--in mechanical terms--is more like a pulsating shower head than a garden hose running freely. This zero crossing shows up as a subtle but persistent power interruption in single-phase and is the reason that single-phase motors above 5 hp are rare and expensive.
Power every 1/50th second sounds fairly often. But consider that a motor turning 1500 revolutions per minute gets only 2 power strokes per turn. This is the same as the crank in a 4-cylinder car engine.
With three phase power the power flow of each phase overlaps the dead space in the others. Very much like in a six and eight cylinder motor. This overlap in power is the key to the smooth, continuous and universally adaptable power of three-phase.
Many readers have already learned that 3-phase is not easily obtained from their local utility supplier. An installation reaching only one mile often costs 15 to 30 thousand dollars. There is a good reason for this.
Since the utility provides three-phase from the primary, or transmission side, three hot wires and three transformers are required--along with three times the maintenance and installation expenses. Single-phase, however, requires only one hot wire and one transformer. So, unless you are in an urban area where a service may be shared with several customers, installation costs may be prohibitive.
Customers have also been surprised to learn that even if the power company drops in 3-phase for free, many extra costs, in the form of daily or monthly line charges, "demand" billing based on peak usage and higher kilowatt per hour rates, serve to drive up the price of utility-supplied three-phase far higher than the investment required for a Booster.
Since Boosters work from the secondary side of the power grid (after the utility-supplier's street or pole transformer), a simple installation is involved. Three-phase loads only are applied to the Booster. All existing lighting and other wiring to single-phase loads remains the same.
As for Boosters costs, a 4 hp Eco may cost less than NZ$1,400 Gst included. It will operate one motor only and install in a few minutes. Its operating cost is virtually zero.
A
Booster, or a superior Booster E, can be connected to your three-phase
loads in about 30 minutes. It can operate any combination of motors,
heaters, welders, or 3-phase rectifiers (AC to DC). The purchase price
is usually about NZ$295- $540 per operated horsepower, depending on size
and type.
This you buy once, and may expect it to last 30 years and more with
virtually no repairs! And, with an operating cost of only about 5% of
the operated load it is easy to see that phase conversion is one of the
best industrial bargains available.
The next step is to determine the type of Booster that is best suited to your needs.
EuroTech is not the only company producing single to three-phase converters. There are about 15 companies in the US and Canada producing so-called static and rotary phase converters for the 115V to 208V 60 Hz market. To our knowledge, most manufacturers still use timers and mechanical contactors inside. Since this method is not free of maintenance and cannot provide hard-start capabilities, we have developed the solid state Booster based on modern capacitor-switching technologies. Today we supply Boosters to New Zealand customers, and Booster components to other manufacturers producing Boosters under license.
A capacitor may be viewed as an electrical trampoline. AC power pauses as it bounces through, producing a distinct delay. Capacitors have been used to operate three-phase motors on single-phase power for decades. In this method, the two single-phase wires are connected to two of the inputs on a three-phase motor. A capacitor is then connected to one of the single-phase inputs and the third leg of the motor.
A
motor requires about 6 times as much current to start as it does to run,
so a capacitor-type single to three-phase converter must have some means
of switching a large group of capacitors in and out during motor
starting.
This solid-state switch is a high-voltage high-current German made
semiconductor, tested at 2200V and, in the smallest Booster,
withstanding short circuit currents of 2,300A. Switching is precisely
triggered at zero voltage and zero current transitions in order to
minimise stress to components, to the motor and to the supply line.
The trigger and switch circuitry, a state-of-the-art CMOS logic, is
protected against any kind of moisture, dust, electric noise, magnetic
and electrostatic fields, over- and undervoltage.
Some
limitations of static Boosters: The Eco is an inexpensive solution to
powering simple machines with one electric motor only. The static method
alone is not as good as generated three-phase power produced by a
Booster or Booster E. With the simple capacitor-start, capacitor-run
operation, you can run a three-phase motor at 70% maximum torque all day
long; or make short bursts of around 90% torque for up to 5 minutes at a
time. Also, Ecos will not operate three-phase welders, transformers or
rectifiers. The electricity provided by an Eco is only of good quality
when connected to an induction motor of the right size.
Ecos can be installed in minutes with no modifications to your machine.
The smallest one may even be operated on a household socket. They
incorporate the new solid-state controller-switch, which is
maintenance-free for lifetime. This is superior to motor starting
switches or timers used by other manufacturers.
Here is a good rule of thumb to follow: Motor-driven tools are generally
OK for the Eco. Most mills, drills, saws, grinders, etc. will work well.
Even mechanical shears and punch presses work well if they have a
flywheel.
Back
to machine tools. Lathes with a clutch are an easy load. metal lathes
with no clutch and a high speed spindle (over 750 rpm) are a different
story. High-speed lathes that can start under full load require more
starting torque then a Eco ore a Booster can produce. In this case, only
a Booster E will do the job.
You can run most of the modern belt-drive air compressors on the Eco.
Air compressors produce a heavy motor load, but it doesn't last long,
and the motor gets to cool off between cycles. But continuous full-time
loads should not exceed 70% of the motor's power rating.
Many motors in water pumps are loaded with less than 70% of their
capacity, but check with an engineer first.
Here
are some machines that generally won't work on a static Eco:
Refrigeration pumps are out. Hydraulic machines push the motor too hard
for an Eco to keep up. Printing presses, wide-belt sanders, and heavily
loaded water pumps are out. Dust collectors and other high-speed,
high-volume fans are out. Vacuum pumps -- no. Any load that is not a
three-phase induction motor is out. Transformers, CNC machine tools and
variable speed drives will not run on an Eco.
The Eco is useful in operating moderately loaded motors. All motors can
be wired in either star or delta configuration. This is done by changing
a few connections in the motors connector box.
Connected to an Eco, a motor running in delta configuration produces
more torque compared to a motor in star. Smaller motors need 3x 230V in
delta and 3x 400V in star. Larger motors, usually above 3kW, are wired
for 3x 400V in delta or 3x 690V in star.
Change your motor to delta configuration, should it not already be
connected in delta. Should the new motor voltage be different from the
output voltage of the matching Eco in our product list, please specify
the required voltage in your order.
A
more versatile converter, the Booster, actually generates all three
phases internally. Such a device distributes three-phase power to
multiple motors and to many machines.
Electric power is injected into a running motor-generator, resulting in
three useful sinewave phases separated by 120 degrees as with utility
power. The equipment may then be started and stopped in any combination
up to the Booster's total load capacity. Any type of three-phase load
may be operated with a Booster.
A Booster is capable of producing burst currents of up to 200% of the
maximum continuous output power to start motors starting under no load
or under moderate load.
If an electric motor is connected to three phase utility supply, the current during start-up is about 6 times higher than under full load at nominal speed. A Booster therefore will accelerate motors not as fast as utility supply. Should fast starts be required, or should a motor have to start under load, choose a Booster E.
Motors starting under heavy load should only be connected to a Booster E. This unique single to three-phase transformer will produce up to 600% the maximum continuous power. For how many minutes? Donīt worry, if the start-up time of a motor is too long, the motor rated fuse in your fuse box will blow or the overload protection in your machine will trip. A Booster E is a very tough device, not easily to be overloaded.
The
output of a Booster E is nearly as good as utility power, providing the
single phase supply is stable enough to provide short high power bursts
required by the Booster E. Especially when starting motors or when
motors are under excessive load. When output currents are rising to
600%, the input current will momentarily go up to 600% of the maximum
input current as well.
In case your supply cable is not really heavy, severe voltage drop may
occur at the input side. The same relative voltage drop will be found at
the converters output: Motors will finally not accelerate as fast as
they should, motors will not cope with excessive loads as well as they
would with stable voltages. When connecting a Booster E, always use a
heavier single-phase supply cable than actually needed. In case of
extreme hard-starts found with applications like refrigeration systems,
metal lathes, hydraulic systems or wheel balancers, have very good wires
and cables installed. Or compensate for input wire losses by selecting a
Booster E with about 30% more power.
Some Booster Construction Details
The internal motor-generator has a lot of shared characteristics with the three-phase motors it operates. There is a set of stationary field coils, or stator, that determines the magnetic poles in the electrical steel of the rotary. These coils and their poles have 120° spacing to produce a uniform three-phase wave form. A squirrel-cage type rotor produces the poles of the rotating magnetic field. Very much like a rotating transformer. The rotor has a good bearing support in aluminium end-bells. The rotor-to-stator air gap is smaller than in many motors, since a magnetic "flux" that produces three-phase voltages must pass this air gap.
The phase-shifted current from the capacitors is absorbed by the electrical steel of the rotary motor-generator, then distributed in a three-phase waveform that is usable by any type of equipment. The type of motor-generator used in a Booster and Booster E has the highest efficiency found on the market. It is free of maintenance and it is of the type being used as generators in wind turbines.
Capacitors
in the internal capacitor bank are switched when needed. Switching is
performed at zero crossing transitions of each sine wave. Using this
method, there is no stress to any part. Polypropylene capacitors are the
guarantee for extremely long life expectation.
Due to the zero crossing switching, EMC, or electromagnetic radiation,
is kept low and always within limits in all countries. Ecos and Boosters
comply with EMC regulations in Australia, New Zealand and all European
countries.
The
compact and smart switch-controller is German made. Inputs and outputs
are filtered against incoming spikes, noises and other disturbances. The
controller measures output conditions and senses the need for high
currents to accelerate external motors. It also contains the German made
high voltage and high current power switches activating capacitors in
the Boosterīs capacitor bank. They are designed to withstand at least
2,300 A (Booster 4) and 2.200 Volt (all versions), well above the
highest peaks found in rural areas.
The CMOS logic is completely embedded in Epoxy raisin giving protection
against dust and moisture for lifetime.
Life expectancy is practically unlimited.
What to expect from Ecos and Boosters
Compared
to an Eco, a Booster is more versatile and powerful. Compared to your
local power company, a Booster is still a compromise -- but a viable
option. A Booster is certainly better than an Eco, and a Booster E as
the top unit can cope with motor hard-starts. But if you want to operate
machines and motors not starting with load attached, a Booster is what
you need.
This is stated to prevent unwarranted expectations of the equipment.
Converters have weaknesses and strengths which should be considered
before a purchase is made.
As mentioned earlier, Boosters also have a low purchase cost -- about
$500 per hp on multi-motor installations, far lower than the dollar cost
to bring three-phase even one mile via power lines. Operating cost is
very low on rotary STTs -- about five percent of the electrical cost of
the operated load, that is, five dollars for every $100 worth of energy
purchased.
A Booster in a standard, multi--motor installation will not quite balance each line's power as well as a utility-supplied, three-wire, three-phase system. The quality of the Boosterīs three-phase output depends a lot on the quality and stability of the single phase input line. Since output currents (Booster E) sometimes increase to 600% of the maximum continuous currents, the input lines are loaded with higher currents as well.
A Booster E4 draws about 18A max. continuous input current. But with a motor starting, it can increase to about 110A peak current for a fraction of a second. This could be a longer period of time if the starting motor has to accelerate a heavy mass. Motor rated fuses accept high currents during the start-up time of a motor.
High
input currents may result in input voltage drops. When motors are
starting under load, we have seen voltage drops from 230V down to 170V.
Because the nature of a Booster is a transformer, this will result in a
voltage drop at the three phase output from 3x 400V to about 3x 280V.
Under these conditions, starting motor will not accelerate as fast as
they should.
The time period of excessive input currents is extended. Either the
input fuse will blow, or the protective overload switch in your
equipment will trip.
To overcome these problems, it pays to install oversized cables between
your fuse box and the Boosterīs input. If voltage drop of the supply
side is reduced, motors on the transformers output will accelerate
faster.
Low input or output voltages will not do any harm to the ST transformer.
They only reduce the overall efficiency.
Compared to the utility grid, Boosters may not maintain close voltage balance over a wide range of operation. Line-to-line three-phase voltages may vary somewhat with changing loads. If you have voltage-sensitive equipment such as some computerised machine tools (CNC), best results can be obtained by using a separate Booster for the CNC, and another one for general workshop machines.
By
analysing the strengths and weaknesses of each option -- utility
three-phase or a Booster -- you minimise your disappointments with
either. Utility supplied three-phase power often brings higher
electrical costs than single to three-phase transformer power -- after
all, someone has to pay the purchase and maintenance cost of the extra
lines and extra street-transformers sitting out on a pole in the
weather.
A Booster is owned by you: when you don't need three-phase, you turn it
off and you're not paying any line charges. It is 100 percent tax
deductible for your business, and you can take it to a new location.
Interpreting Current Balance (Amp Readings) on Boosters
Balancing a three-phase load can be likened to 3 circus tight-wire walkers carrying a grand piano. If one of the three walk-wires is not drawn up as tightly as the other two, two guys are going to carry most of the piano -- the load. Voltage is the "tension" on the circuit, while the current, or amps is the portion of the piano each line carries. Consequently, unbalanced power will harm a motor if the imbalance is so great that part of the motor "pulls a muscle" electrically.
Motors
operated on an Eco will only achieve ideal current balance if the motor
is operated at about 50- 70% of its actual power rating. Rotary Boosters
operated on a multi-motor system are considerably better -- but not
perfect. As a motor in a car, it has a typical load at which it operates
at highest efficiency.
Concerning efficiency, the ideal load for a Booster or Booster E is
about 20-90% of itīs maximum load. Since most machines are designed to
utilise less than 100% of the motors power, a Booster will probably run
most efficiently when power range of a Booster matches the input power
range of a machine or motor.
In case of hard-start conditions, some manufacturers suggest to use a single to three-phase converter about 2-3 times the size of the operated motor. This is different with a Booster E.
Boosters produce a "delta voltage". The voltages between the three output connectors will be about 1.73 times (square root of 3) higher than the 230 V input: about 400 volts. If voltages are measured between one of the phases and ground, different values are found. This is because of the step-up input transformer configuration.
All modern motors and machines use the voltage between the three phases. Therefore do not connect any load to the Boosters output, which takes load between one of the phases and Neutral.
Should output voltage be needed between one of the phases and Neutral, use L3 only. L3 is directly connected to the hot input line and may be used for any kind of external control circuitry or general purpose.
When
someone explains his welder, he talks about Amp. This is always the
secondary current of an internal transformer. If the voltage is around
40V, this will be a power consumption of 200x 40= 8000W or 8kW.
To find out the input power of a welder, when only input currents are
mentioned on the welders nameplate:
Input current x 700 will give you the three-phase welders power
consumption in kW.
For a welder always choose a Booster, not a Booster E. try to oversize
by at least 50%.
A 8kW Booster would probably do the job, but if you choose a 12 kW
Booster, the output voltages will be more stable.
Welding is easier with stable voltages.
Operating
400V 3-Phase Irrigation Pumps on Single Phase Electric Power.
Some rural line companies do not supply three-phase electricity to
farms. The cost-efficient and dependable way to operate the irrigation
system is with a large Booster. 400V two-phase or 460V split-phase is
normally available from your local power company, and is easily
processed into 400V three-phase power through the Booster.
To size your Booster, add the total horsepower of pivot, pump, and end gun motors you wish to operate. Then subtract by 1,36 and you find a model in kW that fits your requirement. When windshield-wiper type (reversing) pivots are operated, install a heavier supply cable and a Booster E.
If your pivot operation is a "windshield wiper" configuration, that is, a pivot that runs a partial circle and then reverses direction, then you should choose a Booster E. Under normal pivot operation, only one-half the motors will start at once. However, when a pivot is reversed, all the motors that were "off" when stopped will now start. Thus, a 10 tower pivot may reverse, restarting 7 or 8 motors, and exceed a normal Boosters capacity.
The Booster should be mounted as close to the single phase service as possible to minimise the heavier single-phase wiring required. 32 and 48 and 64 kW Farm Boosters are equipped with a soft-starting feature that reduces the starting inrush of the Booster to approximately half of normal on start-up to prevent line disturbance.
All Boosters are high-efficiency models. Power consumed by a Booster itself will amount to approximately 5% of the operated load.
