engineering

Phase converter

Phase converter is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Phase converter rather than just read about it. In short: A phase converter is a device that converts electric power provided as single phase to multiple phase or vice versa. The majority of phase converters are used to produce three-phase electric power from a single-phase source, thus allowing the operation of three-phase equipment at a site that only has single-phase electrical service.

Key takeaways

Phase converter belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Phase converter to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Phase converter from memory before moving on to harder problems.

Reference excerpt

A phase converter is a device that converts electric power provided as single phase to multiple phase or vice versa. The majority of phase converters are used to produce three-phase electric power from a single-phase source, thus allowing the operation of three-phase equipment at a site that only has single-phase electrical service. Phase converters are used where three-phase service is not available from the utility provider or is too costly to install. A utility provider will generally charge a higher fee for a three-phase service because of the extra equipment, including transformers, metering, and distribution wire required to complete a functional installation.

Types of Phase Converters Three-phase induction motors may operate adequately on an unbalanced supply if not heavily loaded. This allows various imperfect techniques to be used. A single-phase motor can drive a three-phase generator, which will produce a high-quality three-phase source but at a high cost to the longevity of the system. While there are multiple phase conversion systems in place, the most common types are:

Rotary phase converters constructed from a three-phase electric motor or generator "idler" and a simple on/off circuit. Rotary phase converters are known to drive up operations costs, due to the continued draw of power while idling that is not common in other phase converters. Rotary phase converters are considered a two-motor solution; one motor is not connected to a load and produces the three-phase power, the second motor driving the load runs on the power produced. A digital phase converter uses a rectifier and inverter to create a third leg of power, which is added to the two legs of the single-phase source to create three-phase power. Unlike a phase-converting VFD, it cannot vary the frequency and motor speed, since it generates only one leg. Digital phase Converters use a Digitial Signal Processor (DSP) to ensure the generated third leg matches the voltage and frequency of the original single-phase supply. It does have the advantage of a sine-wave output voltage and excellent voltage balance between the phases. More details about these methods are explained in the patents Medagam et al. “Active Single Phase to Three Phase Power Converter” US Patent 10,333,420 and Meiners et al. “Phase Converter” US 6,297,971. Static conversion techniques "jump start" a motor by temporarily providing the necessary power levels before transitioning back down to single phase power levels. These systems are unfit to run multiple machines or machines that require a maximum RPM due to their temporary nature. In these systems the motor must be derated and they are prone to overheating.

Rotary Phase Converters

A rotary phase converter is a common way to create three-phase power in an area where three-phase utility power is not available or cannot be brought in. A rotary phase converter uses a control panel with a start circuit and run circuit to create power without excessive voltage. A three-phase motor uses a rotating magnet surrounded by three sets of coils to produces the third leg of power within the idler motor. Some rotary phase converters are digitally controlled, enabling them to produce power that can run on voltage-sensitive loads such as a CNC machine, welder, or any other computer-controlled load. A rotary phase converter does not change the voltage, but it can be paired with a transformer to step the voltage up or down depending on what is needed.

Digital Phase Converters A Digital Phase Converter creates a three-phase power supply from a single-phase supply. A Digital Signal Processor (DSP) is used to control power electronic devices to generate a third leg of voltage, which along with the standard, single-phase voltage from the supply creates a balanced three-phase power supply. AC power from the utility is converted to DC, then back to AC using insulated-gate bipolar transistors (IGBTs). This conversion process allows for the generation of the third leg from the existing power supply. In one type of digital phase converter, the input rectifier consists of IGBTs being used alongside inductors to create the third leg of power. The IGBTs are controlled by software in the DSP to draw current from the single-phase line in a sinusoidal fashion, charging capacitors on a constant-voltage DC bus. Because the incoming current is sinusoidal, there are no significant harmonics generated back onto the line as there are with the rectifiers found in most VFDs. The controlled rectifier input allows power factor correction to take place. The second half of the digital phase converter consists of IGBTs that draw on the power previously stored in the DC bus to create an AC voltage that is not sinusoidal. It is a pulse-width modulated (PWM) waveform very high in harmonic distortion. This voltage is then passed through an inductor/capacitor filter system that produces a sine-wave voltage with less than 3% total harmonic distortion (standards for computer grade power allow up to 5% THD). By contrast, VFDs generate a PWM voltage that limits their versatility and makes them unsuitable for many applications. Software in the DSP continually monitors and adjusts this generated voltage to produce a balanced three-phase output at all times. It also provides protective functions by shutting down in case of utility over-voltage and under-voltage or a fault. With the ability to adjust to changing conditions and maintain voltage balance, a digital phase converter can safely and efficiently operate virtually any type of three-phase equipment or any number of multiple loads. Since Digital Phase Converters are solid-state designs, there are little to no moving parts except for cooling fans. In turn, this allows digital phase converters to be fit into small packages and operate between 95% and 98% efficiency. These converters also do not draw power when idling, reducing overall costs and increasing longevity.

Electric railways In Europe, electricity is normally generated as three-phase AC at 50 hertz. Five European countries: Germany, Austria, Switzerland, Norway and Sweden have standardized on single-phase AC at 15 kV 16+2⁄3 Hz for railway electrification. Phase converters are, therefore, used to change both the phase and the frequency.

See also Rotary phase converter Variable frequency drive Scott-T transformer

References

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Phase converter

Start with the simplest possible case. Write down what Phase converter claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Phase converter before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Phase converter ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Phase converter

In research: Phase converter appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Phase converter in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Phase converter is common in secondary-school and first-year university syllabi. It links to neighbouring topics AC power, Electric power conversion, Electrical engineering, so understanding it makes those chapters shorter.
In everyday life: Look for Phase converter outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Phase converter in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Phase converter means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Phase converter out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Phase converter in simple terms?

Why does Phase converter matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Phase converter?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Phase converter.