Core Power Concepts
Single-Phase Power
Electricity delivered as a voltage that rises and falls in a repeating wave (alternating current). Single-phase power carries just one such wave, on two wires, and is the standard service to homes and small businesses. It runs single-phase equipment — lighting, outlets, and small tools — but on its own it cannot start a three-phase motor of any size, which is the reason phase converters exist.
Three-Phase Power (3Ø)
Three separate voltage waves carried on three wires and timed so that each one peaks a third of a cycle after the last. Because the three waves take turns pushing, together they create a magnetic field that appears to rotate, and that rotating field is what starts and turns most industrial motors smoothly. It is the form of power that factories are built around.
Phase
One of the individual voltage waves in a supply. A single-phase supply has one wave; a three-phase supply has three, evenly spaced in time. The word refers to where a wave is in its rise-and-fall cycle compared with the others.
Leg
A common word for one of the individual power lines in a circuit. A three-phase system has three legs; a standard single-phase service has two. Those two legs are the hot lines of a split-phase service: the utility feeds the building through a transformer whose output winding is center-tapped, meaning a wire is attached to the middle of the winding. That center tap becomes the grounded neutral, and the two ends become the two hot legs — each measuring 120 volts to the neutral and 240 volts across the pair. In a phase converter, those two legs pass straight through to the output and the converter makes the third.
Transformer
A device that raises or lowers the voltage of alternating-current power. Two coils of wire share a magnetic core; power fed into the first coil is passed magnetically to the second, and the ratio of turns between the two coils sets how far the voltage steps up or down. Transformers work only with alternating current and do not change its frequency.
Phase Angle (120 Degrees)
A way of describing how far apart the three waves are in their cycle. One full cycle is 360 degrees, so spacing the three waves evenly places each one 120 degrees — one-third of a cycle — behind the next. This even spacing is what makes three-phase power balanced.
Generated Leg / Manufactured Leg / Manufactured Phase
The third power line that a converter produces on its own. The two incoming single-phase lines pass straight through to become two of the output legs, and the converter creates the missing third so the output carries all three.
Voltage Balance / Imbalance
How evenly voltage is spread across the three legs. A three-phase motor is built to run on equal voltage on all three legs and is sensitive to any imbalance: a voltage imbalance produces a current imbalance several times larger, and that extra current turns into heat in the windings that shortens the motor's life. Derating the motor — running it below its rated load — is the way to keep that heat in check as imbalance rises, so imbalance is generally held to a couple of percent. Because of this, how tightly a converter holds voltage balance is the main measure of its quality; a Phase Perfect stays within 2 percent under all load conditions.
Types of Converters
Static Phase Converter
In its simplest form, a static phase converter is really just a motor starter. Using capacitors to shift the timing of a leg tapped from the single-phase supply, it briefly energizes the motor's third winding to break the motor free of the locked-rotor condition and get it spinning. Once the motor is up to speed the capacitors switch out, and from then on the motor runs on only two of its three windings, which reduces its power and efficiency.
Rotary Phase Converter (RPC)
A rotary phase converter is a spare three-phase motor, called the idler, that is started by a static phase converter and then left to spin freely with nothing attached to its shaft. Once the idler is turning on two legs of the single-phase supply, its third winding acts like a generator and produces the third leg of power. That third leg combines with the two incoming legs to give a continuous three-phase output that can run several machines at once. Its balance is not steady, though: as the load rises and falls the idler changes speed, and the generated leg drifts with it, so an RPC has trouble holding tight voltage balance — where a solid-state Phase Perfect regulates the generated leg continuously.
Digital / Solid-State / Electronic Phase Converter
A digital phase converter builds the third leg with electronics instead of a spinning motor. Fast electronic switches called IGBTs pull power from the two incoming legs and convert it to direct current held on an internal DC bus; a second set of switches then rebuilds that direct current into a fresh AC wave to serve as the third leg. A microprocessor runs the switching continuously, trimming the output to keep all three legs balanced. The design is much like a variable frequency drive, except it puts out steady 60 Hz power and its current-carrying parts are sized four or more times larger, so it can absorb the heavy surge of starting a motor directly rather than only easing it up to speed.
Variable Frequency Drive (VFD)
A VFD controls how fast a motor spins by changing the frequency and voltage of the power it sends, and it can also make three-phase power from a single-phase supply. Its output is not steady 60 Hz but a rapidly switched (PWM) wave built for driving a motor, so it is not meant to serve as a general three-phase source for control circuits, contactors, or lighting the way a converter is. It can, however, power a transformer — output and step-up transformers are used with VFDs all the time — as long as the frequency and the volts-per-hertz ratio are kept in the range the transformer needs so its magnetic core does not saturate.
Phase Perfect® Phase Converter
The Phase Perfect® uses digitally controlled switches (IGBT’s) to take power as needed from two legs of a single-phase supply and rectifies it to charge a DC bus. A Phase Perfect then uses additional switches to convert the DC back into an AC waveform to generate the third leg. This digital phase conversion is actively controlled by a microprocessor. Because the system is microprocessor-controlled, the generated leg is continually optimized to provide balanced power and protect any attached equipment.
Parts Inside the Converter
Idler / Idler Motor / Idler Generator / Induction Generator
The three-phase motor inside a rotary converter. It runs with nothing connected to its shaft; its only job is to spin so that its third winding can generate the third leg of power.
Capacitor
An electrical part that stores energy in an electric field and resists sudden changes in voltage. Capacitors are the building blocks of the line-filter and film capacitors described below.
LC Filter
A filter made from an inductor (L) and a capacitor (C) that smooths a converter's electronic output into a clean, wave-shaped signal.
Digital Signal Processor (DSP)
The specialized processor that measures and regulates the output of a digital converter many times a second.
IGBT (Insulated-Gate Bipolar Transistor)
A high-power electronic switch that turns on and off very quickly. A digital converter uses IGBTs to convert incoming power to DC and then rebuild it into the AC wave of the third leg.
DC Bus
The internal direct-current rail inside a digital converter. Incoming power is first converted to DC and held on this bus before being converted back into AC.
Line Filter Capacitor
A capacitor placed on the power line to smooth it and drain off high-frequency electrical noise. The name describes the job the capacitor does, not how it is built.
Film Capacitor (Film-Type)
A capacitor named for how it is built: it uses a thin sheet of plastic film, such as polypropylene, as its insulating layer. Film capacitors are tougher and longer-lived than cheaper electrolytic types. A line filter capacitor may or may not be a film type, and a film capacitor may be used for many jobs besides line filtering — the two terms describe different things.
Inductor / Magnetics
An electrical part, usually a coil of wire, that stores energy in a magnetic field and resists sudden changes in current. It is the mirror image of a capacitor, and converters use inductors to smooth and filter their output.
Power Quality
Sine Wave / Sinusoidal
The smooth, rounded wave shape of clean alternating-current power. A “true sine wave” output is smooth enough to run sensitive electronic equipment safely.
Harmonics / Harmonic Distortion
Extra, unwanted waves at higher frequencies that ride on top of the main power wave and distort its shape. Too much harmonic distortion can overheat equipment and push disturbances back onto the utility's lines.
Power Factor
A measure of how much of the electricity a device draws is actually turned into useful work. A power factor near 1.0, called “unity,” means almost none of the supplied current is wasted.
Power Factor Correction
Adding electronics or capacitors to raise a system's power factor toward unity and cut wasted current. A Phase Perfect corrects power factor at its input, so it draws power efficiently and maximizes how much of an electrical service can go to useful work rather than being lost as waste.
Regenerative Power / Regeneration (Regen)
Power that flows backward, out of a load and toward the supply — for example when a motor is spun by its own load or is slowing down. “Regen” is the everyday shorthand. A Phase Perfect passes this energy back onto the single-phase line, where it does useful work. A rotary converter has no way to send it back, so the returned energy instead drives extra flux, and therefore heat, into the idler motor and degrades its run capacitors.
Active Front End (AFE)
The input stage of a drive or converter that draws current cleanly, with little harmonic distortion, and can also send regenerated power back to the line while staying within legal harmonic limits. The front end of a Phase Perfect is an AFE, which is what lets it draw near-unity power factor and pass regenerated power back to the supply.
Utility-Grade / Utility-Quality Power
Output that is as clean and evenly balanced as the power the electric company itself supplies.
Ratings, Units, and Measures
Horsepower (HP)
A rating of how much mechanical power a motor produces. Horsepower is used to rate many products, converters included, but it is only a rough figure; for an accurate match you have to look at the actual current (amp) ratings, since current is what determines whether a converter can truly start and run a given load.
kVA (Kilovolt-Amperes)
A measure of the total electrical power a device handles, called “apparent power.” It differs from real working power, measured in watts, because not all of the current a device draws does useful work.
Inrush / Starting Current
The large, brief surge of current a motor pulls in the first instant it starts, far above what it draws once running.
Standby / No-Load / Idle Draw
The amount of power a converter uses while switched on but with no equipment running from it. This varies enormously by technology: a rotary converter must keep its idler motor spinning, which draws significant power around the clock, whereas a Phase Perfect is solid state with no idler to spin and so draws very little at standby.
Nameplate Rating
The operating specifications the manufacturer stamps on a motor or unit, such as its voltage, current, and horsepower.
Motors and Loads
3-Phase Motor Loads
A three-phase induction motor has 3 sets of windings. When supplied with three-phase AC voltage, the uniform alternating (120 degree) separation between the wave forms will create a balanced rotating magnetic field that spins the motor. A three-phase motor can spin driven by only two of the three windings but cannot start spinning without all 3 or mechanical assistance to break it free of the initial locked rotor condition.
Winding
A coil of wire inside a motor. A three-phase induction motor has three sets of windings, and each set is fed by one of the three phases.
Rotating Magnetic Field
The magnetic field that forms when the three phases, arriving 120 degrees apart, energize the motor's three windings in turn. The field sweeps around the inside of the motor and drags the rotor along with it, making the motor spin.
Locked-Rotor Condition
The state of a motor sitting still, before it has broken free to turn. A three-phase motor can keep running on just two of its three windings, but it cannot start from a standstill unless all three windings are energized or something turns the shaft to get it going — which is the very problem phase converters solve.
Across-the-Line Start
Starting a motor by connecting it straight to full line voltage all at once, rather than easing it up to speed.
Soft Start
Bringing a motor up to speed gradually to limit the size of the starting-current surge.
High-Inertia / High-Torque / Hard-Starting Load
Equipment that is hard to get moving from a stop, such as compressors, pumps, dust collectors, geared-head lathes, and flywheels. These loads demand a large surge of power at startup. A Phase Perfect is engineered to start them directly at its rated size; loads like these are the reason a rotary converter often has to be rated at two or even three times the size of the load just to break it loose.
Inductive / Resistive / Capacitive Load
The three broad kinds of electrical load. Motors are inductive, heating elements are resistive, and some electronic devices are capacitive; each draws and returns power a little differently.
Single-Phasing
A fault in which a three-phase motor loses one of its three legs and is left running on only two. It causes the motor to lose power, run hot, and can destroy it.
Motor Starter (Magnetic or Manual)
A device built and rated to safely switch a motor on and off. An ordinary circuit breaker is not rated for the repeated surge of motor starting and should not be used in its place.
Enclosures and Environment
TEFC (Totally Enclosed Fan-Cooled)
A motor sealed against dust and moisture and cooled by an external fan, suited to dirty, damp, or outdoor locations. This is the point that matters when comparing technologies: a rotary converter's idler is an exposed motor, so to run outdoors it must be TEFC — that is how a rotary reaches the equivalent of a NEMA 3R rating. A Phase Perfect has no idler motor to protect, and reaches a NEMA 3R outdoor rating with an available rain hat.
ODP (Open Drip-Proof)
A motor with vents that let air flow through to cool it, shaped so dripping water cannot easily get in. It is meant for clean, dry indoor use and runs cooler than a sealed TEFC motor.
NEMA 3R
A rating for an enclosure built to keep out rain, making the equipment inside safe to use outdoors.
Rain Hat
An add-on cover that upgrades an enclosure so the unit can be installed outdoors. It is available for many Phase Perfect models, giving them an outdoor (NEMA 3R) rating at low extra cost.
Wiring Configuration
Delta
A three-phase wiring arrangement in which the three windings are joined in a triangle. It provides three power lines and no neutral. The output of a phase converter is wired this way.
Wye (Star)
A three-phase wiring arrangement in which the three windings share a common center point. That center point provides a neutral wire, which some equipment requires.
Neutral
The grounded wire that serves as the return and reference point in a wye system. Delta systems do not have one.
Delta-to-Wye (Isolation) Transformer
A transformer that takes delta power (three lines, no neutral) and provides a neutral on its output, so delta power from a converter can feed equipment that needs a wye supply.
High-Leg Delta / Center-Tapped Delta / Ungrounded Delta
A delta wiring arrangement, common in rural areas, in which one of the three legs reads a higher voltage to ground than the others. That higher leg is the “wild leg” and is kept off single-phase loads.
3-Wire vs. 4-Wire
Delta three-phase runs on three power wires. Wye three-phase adds a fourth wire, the neutral, for a total of four.
Standards and Regulatory
NEC (National Electrical Code), Article 455
The U.S. rulebook for safe electrical installation. Article 455 is the section written specifically for phase converters.
UL / UL 508A
A safety certification from Underwriters Laboratories. UL 508A is its standard for building industrial control panels.
NEMA (National Electrical Manufacturers Association)
The industry group that sets common standards for motors and enclosures, including the enclosure ratings used elsewhere in this list.
IEEE 519
An engineering standard that limits how much harmonic distortion equipment is allowed to put onto the utility's power lines.