# What is Three-phase: Definition and 35 Discussions

In electrical engineering, three-phase electric power systems have at least three conductors carrying alternating voltages that are offset in time by one-third of the period. A three-phase system may be arranged in delta (∆) or star (Y) (also denoted as wye in some areas). A wye system allows the use of two different voltages from all three phases, such as a 230/400 V system which provides 230 V between the neutral (centre hub) and any one of the phases, and 400 V across any two phases. A delta system arrangement only provides one voltage, but it has a greater redundancy as it may continue to operate normally with one of the three supply windings offline, albeit at 57.7% of total capacity. Harmonic current in the neutral may become very large if nonlinear loads are connected.

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1. ### Three-phase voltage inverter (some questions)

I have no idea how to answer to these questions. Our teacher has given it to solve, but i don't know where I sholud to search informations. Could somebody recommend me valuable sources of knowledge?
2. ### Conductor Temperature Rise, Three-Phase Vs. Single-Phase

Good Morning, I am not coming up with an answer in my search, could anyone confirm or deny whether a circuit conductor would experience more temperature rise with three-phase current than if the same R.M.S. current was single-phase. Alternating Current, 60 Hertz. If you want to know why I want...
3. ### Engineering Three-phase circuit: Why Z_Ye is parallel with Z_Δ?

Homework Statement This problem is taken from Fundamentals of Electric Circuits (chapter 12, problem 15). Homework Equations As shown in the first blue box, I have trouble seeing why after the conversion, Z_Ye will be parallel with Z_Y. I think it's because the voltages 'emitting' from the...
4. ### Fundamental confusion about THREE-PHASE electric power setup

Homework Statement Hello to everyone who's reading. :) I hope I posted this in the right place; while this is not exactly a homework problem, I am trying to improve my understanding of the background information before proceeding with course-style problems. This post is because I'm trying to...
5. ### Understand AC Transformer Polarity for Three-Phase Connections

my transformer book does not cover an area i am interested in and was wondering if someone would direct me to literature that would help me understand something and if you wouldn't mind trying to explain it to me yourself that would also be appreciated. you have three single phase transformers...
6. ### Ampere's law to calculate the B field from a balanced three-phase system

I am a little confused when I try to use Ampere's law to calculate the B field from a balanced three-phase system. Consider the following, shown in the picture below: Lets say I want to calculate the value of B at a distance r (radius of my Amperian loop), the value of r is big enough so that...
7. ### Neutral current in three-phase systems

Hello, In three-phase systems, star coupling for example, and in the case where single-phase sources are supplied using the three phases L1, L2 and L3 with a common neutral return, My first question is: when one is balanced il1 = il2 = Il3 is what the current flowing in the neutral is...
8. ### Three-phase electric power: Household distribution

Hi. How is three-phase electric power distributed in a household with mainly single-phase power plugs? Do they just connect a phase at random to every plug? As far as I understood, it's best if all three phases deliver the same current, since then neutral cancels. Do electricians take into...
9. ### Three phase star connection with different offset

Homework Statement For a balanced star connection i have given angles for V1=90 V2=0 V3=-90 i have to find the voltage required to produce the same phase currents as in standard three phase voltage source e.g V1=120 V2=0 V3 =-120 Homework EquationsThe Attempt at a Solution Im not even sure...
10. ### How to Determine Capacitance for Active Power in a Three-Phase System?

Homework Statement In the given AC circuit, electromotive forces form a symmetric and direct three-phase system. Angular frequency \omega, magnitudes U_{AB},U_{BC},U_{CA}=U, resistance R, inductance L and coefficient of inductive coupling k\neq 1 are given. Find capacitance C such that the...
11. ### Active power of three-phase system

Homework Statement Find active power of the given three-phase system. U_{RS}=U_{ST}=U_{TR}=220\sqrt 3 V R=\omega L=\frac{1}{\omega C}=10\Omega 2. The attempt at a solution After reducing the circuit to one phase (see attachments), equivalent impedance is...
12. ### Three-Phase Delta Network: Not all Voltage Sources are 120V?

Using the Delta Netowrk from this image: http://www.belden.com/images/B23_WyevsDelta.jpg Between Y-X, there should be 120V. Between Y-Z, there should be 120V. Between X-Z, there should be 120V. But wait! If we assign values to make the above statements true... Call X = 0V, and Y = 120V, so...
13. ### How Do You Calculate Current in a Three-Phase System's Middle Capacitor?

Homework Statement In the following three phase system, calculate the current in the middle capacitor: Homework Equations I = V/Z ZY = ZΔ / 3 The Attempt at a Solution Hello! I'm trying to figure out a method for solving any generic three phase system. In particular, I found very...
14. ### Three-phase power factor correction

Hello. I have a doubt regarding the following problem: 1. Homework Statement Calculate capacitors' capacity to rephase (cos(φF) = 1) the load ZL Homework Equations The formula to calculate capacity in this case is: CY = P(tan(φi) - tan(φF))/ωVrms2 or CΔ = P(tan(φi) - tan(φF))/3ωVrms2...
15. ### Three-phase to single phase for home

I live in a rural area in a third world country. Power problems are very common here. My house has three-phase power. It's quite big so maybe that's why my father used three-phase. It is currently distributed around the house. A phase is assigned to every section. Anyways, I have a problem...
16. ### Calculate Currents & Power in 3-Phase Systems w/ Star-Connected Load

Homework Statement Hello, I am given the following problem. A balanced three phase 4 wire supply has r.m.s. line voltage of 415V and supplies a star-connected load made of 3 impedances: Za = 10 - j10; Zb = 10 + j10; Zc = 0 + j8; Calculate the current phase and neutral currents, also the total...
17. ### Evaluating indication of the wattmeter in three-phase system

Hi all, I am new to this forum and I hope you can help me. I have the following three-phase system where I have to evaluate the indication of the wattmeter W. Available data is: V = 380 V, R = 12 Ohm, R' = 120 Ohm. Can you make me understand the process for obtaining W?
18. ### Single-Phase to Three-Phase Cycloconverter

When my classmate report about cycloconverters. He discussed about different classifications and types of cycloconverters. He also discussed how Single-phase to Single-Phase Cycloconverters operate. But when he approached Three-Phase to Single-Phase and Three-Phase to Three-Phase...
19. ### Calculating Neutral Current in Three-Phase Unbalanced Systems

How to culculate neutral current in three phase system with unbalance load?
20. ### Engineering Characteristics in three-phase induction motor

Homework Statement I can not understand this question: "Describe the characteristics of a three-phase induction motor?" Does it mean speed,torque,etc? Thanks Homework Equations The Attempt at a Solution
21. ### Phase converters and their three-phase voltages/currens

Let’s assume I use an ideal rotary phase converter to power a three-phase 10HP motor (100% efficient, PF = 1). Thus, I need S = 10 VA. On a 120V single-phase line, I would get three-phase line-line voltages of 240V. Here’s my question. I was under the assumption that when you analyze motors...
22. ### [Electrical Engineering] Three-phase transmission line problem

Homework Statement A three-phase line delivers 3600 kW at its receiving end at a lagging power factor of 0.85. The line resistance and reactance are 5 Ohms and 8 Ohms per phase respectively. Given that the sending end line voltage is 33kV, you are asked to determine the receiving end line...
23. ### Unbalanced three-phase w. neutral. Finding currents

Homework Statement I have to find the currents in the three phases and the neutral. I understand that it has got something to do with Kirchoffs law, but how on earth? I can simulate it in multisim, and i get the right results for I_rms but i cannot figure out how to calculate. N->L...
24. ### Three-phase symmetrical components SPICE attempt

Hello I am trying to model in LTspice a matrix for symmetrical components. Keeping to the theory, the 120° delays were built with tlines, which means that whatever signal there is at the input, after the delay it becomes x(t-2*π/3), meaning multiplying with a2(=e-j*2*π/3). (to avoid such a long...
25. ### Engineering A question about a three-phase circuit

Attached. I'll be happy for some help here. Thanks. :redface:
26. ### Three-phase balanced wye-wye system problem

Homework Statement In a balanced three-phase wye-wye system, the source is an abc-sequence set of voltages and V_an = 120e^(i30°) V rms. The power absorbed by the load is 3435 W and the load impedance is 10 + j2 Ω. Find the two possible line impedance if the power generated by the source is...
27. ### How to memorize three-phase reaction terms.

So I'm always having troubles with memorizing the three-phase reaction terms, such as eutectic, eutectoid, peritectic and peritectoid. Are there any meanings of the prefix and suffix? Are there any tricks to memorizing the names and meanings (reactions) of these terms? Thanks a lot!
28. ### Converting three-phase into single/split phase

I recently acquired a 12kw three-phase Onan propane generator, like new, given to me basically. Is there a way to convert three-phase into single phase for use in a normal residential home, without swapping-out the gen head? My instincts tell me the answer is going to be, "step down...
29. ### Three-phase transformer DC-resistances

Homework Statement Three-phase transformer, 20/0.5 kV, dyn11. Not connected to the grid. DC-resistance between two primary windings is measured to be 80 ohm. What is the DC-resistance of ONE primary coil Homework Equations The Attempt at a Solution I thought I could just...
30. ### Three-phase power explained using water/electricity-analogy?

Basic electricity is often explained using the so called water/electricity analogy. This works, but I've never understood three-phase power. Can this also be explained using somewhat the same analogy?
31. ### Engineering Unbalanced Three-phase circuit.

[SOLVED] Unbalanced Three-phase circuit. Homework Statement This comes from "practice problem" 12.10 from Alexander's and Sadiku's Fundamentals of Electric circuits 3rd edition, chapter 12. The problem statement is: "Find the line currents in the unbalanced three-phase circuit of Fig...
32. ### How Do You Calculate Power and Current in a Three-Phase Wye-Delta System?

1. This is a problem in a 3-phase Wye to Delta/Wye system. 2. The question is how to find the TOTAL average, reactive and apparent power and the power factor of the load in the figure attached? All the information needed is labeled 3. I don't know how to find the phase voltages and...
33. ### How Does a Three-Phase AC Generator Create Voltages?

Although I am comfortable with three-phase circuits in general, visualizing the three-phase AC generator is giving me some problems. I understand that windings are placed 120 degrees apart, but that's about it. Would anyone happen to have a good animation/picture of a three-phase AC generator...
34. ### Understanding One-Phase vs Three-Phase Electricity in Europe: Explained

I have a question about electricity. In Europe, an electrical power plug has two "sticks" or whatever you call them. I understand here that power comes in through one of them - goes through the apparatus - and out the other stick. This makes sense. This is a so called "one-phase" system. What...
35. ### Calculating Result Vector for Unsymmetrical Three-Phase Current

Hi all, first I have to say, that my mother tongue is not English. So I'm not very used to special English words that belong to physics. But I try to translate as well as you can understand what I mean. Therefore it would be helpful to me, if you wouldn't use any special acronyms in your...