# What is 3 phase: Definition and 133 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. ### A little help understanding 3 phase waveforms and summation

Hello all, I'm in the process of learning about 3 phase power and how to wire loads to a generator. I've searched high and low with as many sentence structures as I could think of in the google search bar and I can't seem to find the answers I'm looking for. I'm really hoping you guys can...
2. ### Exploring 3 Phase Wire Amperage: Understanding Ampere Rules and Calculations

If you have 3 phase power and let's say line A & B = 10 amperes line B & C = 10 amperes line C & A = 10 amperes For the single line B. Since it's in both in the first and second lines, then B can experience 10 + 10 = 20 Amperes? Or is it 15 A or still 10 Ampere? Thank you.
3. ### What does the 'power' vs 'time' graph look like for a 3 phase AC supply?

Hi, For years I wanted to understand why we have a 3 phase supply and not a 2 phase supply in AC. In Quora I found an interesting answer and was convinced about the purpose mentioned: Answer to Why there is no two phase electrical inputs instead of three phase and single phase? by Paul...
4. ### Convert 1 phase to 3 phase by using an old washing machine

We were in the process of going off grid when a tree fell over our power line. Hence we got off grid before we were ready as we didn't want to repair the power line. Now everything in the house runs on solar power, except for the well pump. The problem with the well pump is that it is a 3 phase...
5. ### How to wire a house using 3 phase

We are getting 3 phase power delivered to our property via our own dedicated transformer. We want to rewire the house and other buildings so that we can use different appliances on different phases. We have 4 air conditioners, 3 hot water units and the usual assortment of things you would find...
6. ### 3 Phase Harmonics and Solid State Relay Issues

I have a 3 phase problem that I think might be applicable to this forum. The setup is equipment which contains 5 resistive heaters (A through E). The unit is powered by 208V 3 phase and each of the heaters are hooked up line to line in an unbalanced configuration as follows: L1-L2: Heater D...
7. ### Exploring Phase Potential Difference in 3-Phase Power

I understand phase voltage (phase to neutral) well, but I'm still confused by what exactly the potential difference is between any 2 phases in 3 phase power. If you were to try to find the potential difference where 2 sine wave phases cross, then at that instantaneous point, the potential...
8. ### Using complex numbers to model 3 phase AC

Assume a transformer as above, with 230V L-N, and I want to work out the L-L voltage. A phasor diagram will show me that the voltages are 120° out of phase. (230∠0°) + (230∠120°) = (230cos0 + j230sin0) + (230cos120 + j230sin120) = 230 + (-115 + j199.2) 115 + j199.2 = 230∠60 What I’m looking...
9. ### What Could Be Causing My 3 Phase Motor to Lack Power and Torque?

I have a small 1hp 3 phase that really lacks torque, it was on a big lathe (12hp) and the entire rest of the machine was wired for 240V delta.. but this motor only has 3 wires coming into the connector box, so there are no options for changing the voltage, yet the nameplate says 220V Delta or...
10. ### 3 phase alternator is generating a voltage, but no current

I made a permanent magnet alternator out of a 3hp 3 phase induction motor. I am getting voltage, but no current at all. The alternator is wired delta and feeds a capacitor bank wired in a wye, to create a neutral. I have even tied the neutral into the alternator and still no current. I connected...
11. ### 400 volt 3 phase 16 amp machine -- can it be used in the US?

Maybe you can please give advice. I have a coffee roaster here in New Zealand I would like to bring to the US. It is 400 volt 3 phase 16 amp. It has a blower, a heater and computer components to run it. It is like a very large popcorn machine. Can this work in the US?
12. ### 50Hz 3 Phase Circuit - Twisting to reduce EMI?

I have done the maths to work out the Induced Voltage on a communication cable, from a bunch of 3 phase circuits in a panel - with the minimum distance between them I calculated it to be about 1.5nV; but for a larger system where there could be larger loads on the cables I was thinking about...
13. ### Electrical Help with making a heating element with a 3 phase power supply

hi everyone. my uncle currently has a big "cylindrical rolling cooking pot" (imagine a cement mixer with burners at the bottom) that he uses to cook his stuff, ie sesame seeds. this cooking pot currently runs on gas. as he has been facing some issues with the gas supplier, he intends to...
14. ### Line voltage in 3 phase as single sine wave

Howdy all. The typical image of a three phase electrical system involves 3 sine waves, phase shifted 120 degrees. These sine waves each, individually, represent the 'phase voltage,' which is to a common neutral in a wye configuration. In this wye configuration the line to line voltage is...
15. ### Unbalanced 3 phase power - what happens without a neutral wire?

Hi I've recently started learning about electrical three phase theory, and therefore got some questions. Imagine the following: Countries like Albania, Norway ++, have IT earthing configuration in their distribution grids, i.e. the neutral point is not solidly grounded, however "grounded"...
16. ### Is My Pramac GSL30 Generator Dead? Testing and Identifying Coil Connections

A mate of mine has bought a Pramac GSL30 generator (30kVA) ‘as seen’, and of course there is no output. Inside the connection box of the Stamford alternator unit, someone has been fiddling - the output wires have been disconnected and taped, and the AVR has also been unplugged. Now, it’s a...
17. ### Method for testing discharge resistors in 3 phase capacitors

A couple of months ago I was troubleshooting a blown fuse on a power factor correction capacitor in a 4160v motor starter. While I was working through it I noticed that my DMM (fluke 289) would charge the capacitor to a certain degree while on the Ω function. The current from the meter would...
18. ### Engineering Calculate the effective values in this 3-Phase Circuit

Homework Statement Given the known quantities ##R, C, L##, ##k##, and the effective values of the voltages ##E_1=E_2=E_3=E## , ##w = \frac{1}{\sqrt{LC}}## of the direct-symmetrical 3-Phase system find the expressions for the effective values of ##U_{12}##, ##U## and ##I## and calculate the...
19. ### Instantaneous current in stator of 3 phase IM

I am studying induction motors and i have equation for instantaneous value of current flowing in each phases.(please check to image below).I can see that its it the form Im.cosωt But isn't it supposed to be Im.sinωt ?because that's how we find all instantaneous parameters like voltage and...
20. ### Solve 3 Phase Total Power Problems

Homework Statement I have included the problems attached below. I have looked at a recent post and the equations made sense to me but I am very new to 3 phase systems basically know only what I have learned from trying to answer my questions. i feel my attempt is wrong from what I have seen...
21. ### Phase and Line current in 3 phase circuits

Homework Statement I need to first find phase current in the load and line current from the supply Homework EquationsThe Attempt at a Solution I thought it would be easier to work with a star because then the Ztl would be in series with it... I am not sure how to find the current but my best...
22. ### 3 phase Delta / Star : Line or Phase?

Homework Statement I am studying for an exam and I never know if I am finding line current / voltage or phase current / voltage. How can I tell? I guess I am confused on what "phase" and "line" represent. For example: If I do the voltage divided by the impedance, then this gives me phase...
23. ### Rotor and stator flux in 3 phase Induction motor

The rotor and stator flux speed are stationary with respect to each other in 3 phase induction motor. What will happen if there is relative speed between them? How these two fluxes interact with each other to develop a torque?
24. ### 3 phase motor net magnetic field

I am trying to understand the basics of bldc motor. My question is if i am driving the 3 phase motor with sinusoidal waveform. The magnetic field is produced for each phase or it will add together to generate net magnetic field? How to get the net magnetic field.
25. ### How grounding resistor and reactor have no effect in 3 phase fault?

How would you justify the above question? Please elaborate in detail with diagrams (if applicable). It will be really helpful. Thank you.
26. ### 3 Phase Systems in a Wye Configuration

Hello, I have been going over the above topic and have a question about the neutral point of a balanced wye configuration. Would the line to line voltage remain constant? I am trying to picture two sine waves 120° apart and it's making me think the Va would be reducing as Vb was increasing at...
27. ### 3 Phase Systems Theory and Procedure -- Determining Average Power

Homework Statement Consider the 3 following Scenarios: 1. 2. rms value of line voltage is 208 V Three equal impedances, 60 +j30 W each, are delta-connected to a 230-V rms, three-phase circuit. Another three equal impedances, 40 +j10 W are wye-connected across the same circuit at the same...
28. ### Where can I find a controller for a 3 Phase AC motor?

I'm working on a project with a team in building a motor. My task is to find a controller for the motor, but I haven't had much luck. Here are the specs for it : Permanent magnet synchronous motor, 3 phase 8 pole 2 layer winding 100 kw power 400V The motor is AC. If somebody can even point me...
29. ### Space vector analysis of 3 phase -- stuck on a concept

I am trying to understand space vectors in 3 phase machines. If you have a balanced 3 phase system, the 3 phasors of voltage, current or whatever... should sum to 0. i<0 + i<-120 + i<-240 = 0. But in this image of a rotating space vector ...
30. ### Using 400V 50Hz 3 phase motors with 240V single phase 60Hz

Hi, We have a machine from Europe with three 400V 50Hz 3 phase motors. Assume we only have 240V single phase available. There may be 480V single phase available. I don't currently know how many poles the motors have. Assume they are not made for both 50Hz and 60Hz as some are. Power consumption...
31. ### Question with 3 Phase Transformers Wye-Delta problem

Homework Statement Homework Equations Wye: V_Line = sqrt(3) x V_Phase Delta: V_Line = V_Phase The Attempt at a Solution My answer doesn't quite match up with the solutions in the book, and was wondering what I went wrong here? Any help is greatly appreciated!
32. ### 3 phase sewage scraper bridge with 24VAC control issues

Guys, I'm having a lot of issues where I work with a sewage scraper bridge chattering it's drive contactors when being called to run, the coils for the contactors are switched on their neutrals from an Allen Bradley logix processor. The control circuit is 24v AC. I've spent a few hours on this...
33. ### Open circuit test of 3 phase transformer in Ansys Maxwell

Hi all, I am designing a three phase 11000/433 Volts Delta/Star 50 Hertz transformer in Ansys Maxwell. It has 792 turns in 6 layers on HV side (132 turns per layer) and 18 turns in 2 layers (9 turns per layer). The resistance as I have calculated is 0.1325 ohms per phase of HV winding and 5.57...
34. ### 3 phase power systems: per unit with transformers

Hey, I'm currently working a problem that looks like this: There's more to this problem, but I'm sure I can solve the rest of it, there are just things I'm uncertain about. Actually, it's only one thing I'm uncertain about. I'm looking through my notes, and when converting the voltage...
35. ### Clean way to run 3 phase induction motor

Say you wanted to run an induction motor from a battery without putting dirty harmonics into it. Would a really clean way to do it, to be by using a higher phase number inverter, then transformer, then into the motor? For instance, a 6 phase inverter, into a 6 phase to 3 phase transformer, then...
36. ### Understanding the Benefits of a 3-Phase System: Explained with Diagrams

They say 3 phase system requires less conductor then single phase why that is so if we consider diagram below? Also why here current going out when neutral is there in form of earthing
37. ### 3 phase bridge uncontrolled rectifier, resultant waveform

Hi all, Having difficulty understanding the above resultant wave form, been looking at power electronics (C.W.Lander) but don't quite get the addition of the wave forms (positive and negative cycles)can anyone point me to some reading of theory I am missing for this, thanks.
38. ### What is the step for designing a 3 Phase Inverter?

I have troubles for designing a 3 phase inverter, and I cannot find the formula everywhere...
39. ### Exploring the Benefits of 6 Phase Inverters: A Scientist's Perspective

Simple question, What's the advantage of having more phases in an inverter? Like why have 6 or twelve phases? Is it something to do with harmonics? I know that the higher the switching frequency the further off in the freequency spectrum you can push the harmonics, but I can't see that being...
40. ### Commercial transformers for variable frequency & voltage

I am looking to step up the voltage of a 3 phase PM generator which has variable AC output of 200 - 400 Vl-l, and 15 - 30Hz. I am looking for a step up ratio between 1:1.5 and 1:2, and need this transformer to be a commercial device. What i have been finding is that most commercial...
41. ### Which capacitor shall i use for 3 phase 5 HP pump? how?

I'm using a 3 phase 5HP motor pump n want to use capacitor. Which capacitor should I use and how to connect it to all the three phases? Please do needful
42. ### Delta-Delta 3 phase transformer HNC help

<< Thread moved from the technical engineering forums to HH >> I'm currently studying for a HNC in electrical engineering and am currently stuck on a question on one of my assignments. The question is: A Delta-delta, 3 phase transformer steps down the system line voltage of 132kV to a local...
43. ### Harmonics on 3 phase 3 wire system

Lets say I have a switchboard that requires ONLY 3 Phase loads, transformer, UPS, Motors, ETC. ( no neutral is required at all) Now let's say I am feeding this from a generator where I have 4 wires from the alternator ABCN connected to the aforementioned switchboard. the N of the generator...
44. ### Designing a 3 Phase AC Generator

I intend designing a 3 phase AC generator. Thereafter I need to build it. Believing in "a picture tells a 1000 words", I am very much a "pictures" person, and as my studies in the electrical field were completed many moons ago, the formulas are now "forgotten" - so thus I want to approach this...
45. ### 3 Phase Induction Motor Full Load Power Factor

Hi, If the voltage, full load current and full load output power (kW) of a 3 phase induction motor are known, and the efficiency is assumed to be 90% (is this realistic), am I correct in thinking that the full load power factor can be approximated (due to assumed and not actual efficiency) as...
46. ### 3 phase transmission line mutual coupling

Hi, if I simulate a three phase transmission line operating with a fault across two of the phases, would the mutual coupling have any effect on the current through each of the lines, as I have calculated the fault current values using symmetrical component analysis and the values are...
47. ### 3 phase switch relactance motor

Hi Im doing a project to control a 3 phase switch relactance motor using power electronics. I have choosen 3 mosfets, 2 auto couplers and 2 resistors. 1. Would there be any other devices I need ( to solder to pcb board). 2. What would the circuit digaram look like so I can solder this and...
48. ### Elec Eng AC 3 Phase Symmetrical Components Q - Phase to Fault question

Hello again, I've got another question that involves symmetrical components, this time I've attempted it. The Question follows: 1. In a 3 phase circuit with resistance earthed and neutral and Earth fault in phase “A” which produces a fault current of 800 amps. Load currents may be taken as...
49. ### 3 phase system electrical question

Homework Statement https://www.physicsforums.com/attachments/question-jpg.73386/ the current go from a A N and n the 2nd current go from b B N and n the first thing, i make the matrix 27-4j -3 i1 230 <0 -3 27-4j x i2 = 230<0 x means the matrix multiplied to the next < means the degree then...
50. ### Balance an unbalanced 3 phase connection of appliances?

Hi there, I want to know what is the best way to connect these devices to a 3 phase power supply outlet and minimise the unbalanced load as much as possible safely? I am only worried about the single phase appliances. What type of connection would you recommend? 3x Power Supply units Single...