# Questions tagged [three-phase]

AC power with three legs run 120 degrees out of phase

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21k views

### Why three-phase power? Why not a higher number of phases?

Is there a reason, beyond historical reasons, that three phases has become the dominant number of phases? I am aware of the advantages against one phase and two phase, namely the reduced amount of ...
10k views

### Why 3 phase and not 1 phase power transmission?

Why does power transmission use three lines with three different phases? Why not three lines all in the same phase? Does it have to do with the alternators used for generating the power, or is there ...
72k views

### Why is three-phase offset by 120 degrees?

For three phase electricity the wave is offset by 120 degrees(2$\pi/3$ Rad). Why aren't the phases closer together? Is it because it will affect the frequency of the phases? How was this 120 degrees ...
5k views

### Why don't three-phase transformers use toroidal cores?

When looking at different transformer core designs, three phased, I never see any core designed as a circle or torus. Why is that so? Will it not work as well as the common B-shaped core?
37k views

### Why are there only 3 wires on this power line?

When I was in Alaska, I saw a high voltage line, but I didn't see the Neutral. Is this because the water is conductive enough next to it to use as neutral? Or is it just two Phases. Where I live, ...
96k views

### Why are the letters U, V and W used in AC motors to represent the windings?

I am connecting up an AC motor and was wondering if this labeling system was representative of something? Or just another set of letter like X,Y,Z? I could not find any information regarding this in ...
86k views

I have been studying three-phase systems for the whole course of a subject (on the first year of the university degree). I have finished now, and I know both "Y" (star) or "Delta" (triangle) ...
56k views

### Why does a delta/wye transformer make 30 degrees phase shift ?

I'v heard that a delta/delta or Wye/Wye transformers do not make any phase shift. In delta/wye or wye/delta transformers, There is a 30 degrees phase shift between the primary and secondary coils. So, ...
13k views

### How is transition from three-phase distribution without neutral to three-phase consumption with neutral achieved?

A typical distribution grid supplies 6 or 10 kilovolts AC to a substation near the consumers. This is typically done with a three-phase line without neutral - just three wires going in parallel. Then ...
15k views

### Single-phase to 3-phase conversion

I have seen some boxes (with some capacitor circuits inside) which do single-phase power supply to 3-phase power supply conversion. The problem with them is that they cause the load motor to heat up, ...
2k views

### Is there a convention for the ordering of phases in three-phase power in the US?

I recently moved my small machine shop to a new location. Both locations had 3-phase power, and I wired up a 3-phase air compressor in both locations. In both locations, I used the convention of ...
2k views

### Why does current flow from the most positive to the most negative in three phase system?

I put the following circuit in a simulator to see how it works. I understood it but I have a question: At the time of the vertical green line, The simulator shows me that the current flows from the ...
11k views

### 3-phase Motor Speed Controller

Background If you look at my profile description, you'll see that I'm involved in building and wiring up Carnival floats that are powered by an 800KVA, 415v, 3 phase Generator. Electrically, they ...
4k views

### How does a three-phase transformer work with phases sharing a common core?

Google search reveals a lot of pictures of three-phase transformers. Looks like a common setup is to have three pairs of winding and a shared core. The core typically consists of three "bars" in ...
73k views

### 3-phase explanation

I have been reading about single phase and three phase power. I'm completely confused now. Can someone please give me a working example of when I would use three phase power instead of single phase (...
40k views

### Why does a 240 volt outlet save money in electrical cost than a 120 volt outlet?

I live in the US and we have many outlets that run at 120 Volts. I heard that for devices that support the 240 volt standard may not cost as much in electricity prices. Can someone explain how by ...
125k views

### Three phase power supply - what is line to line voltage

Well this seems like a basic principle, yet I can't seem to get it. (We're expect to "know" this already). In a three phase situation I'm given a source voltage of 230V. - So the waveform of each of ...
5k views

### Why aren't there any 3-phase domestic power-outlets, or any interest in 3-phase for household (mains) power or anything relatively low-power?

Since I discovered what 3-phase electrical power is on Wikipedia, I have noticed that it's associated with very high-power applications. I have not been able to find anything on the subject of 3-...
885 views

### Do I have pseudo three-phase power at home?

I get three live wires and one neutral from the mains. Different rooms in the house are connected to different circuits which terminate at a changeover panel. The changeover switches allow each ...
2k views

### Why the triangle reference wave is used in PWM for sine modulation?

I'm implementing PWM for a three-phase inverter. The documentation on the subject, especially the technical implementations, is very good but as far as I am able to understand none of the one I read ...
1k views

### Three phase systems - are there any single phase devices that are connected between two phases instead of between one phase and neutral?

In star system, single phase consumers are connected between a line and neutral but are there any single phase devices connected between two phases (would that even be considered a single phase device?...
2k views

### Does the neutral wire have any voltage?

In this article, the author talks about 3 phase and the magic of a missing neutral wire. And there's the following paragraph: In a 3-phase system the voltage between any two phases is 3 times ...
57k views

### Unbalanced three phase system - Neutral fails/opens/disconnects - consequence?

I have a very basic question about three phase system. I am not an electrical engineer hence I might not have a good understanding of the subject. So, please be bit lenient in answering and asking ...
398 views

### An overseas company is making a machine for me and they need to know whether I want 1,2 or 3 phase and what voltage

I'm in Quebec and the company making the machine is in China. The machine is an industrial sized T-Shirt sublimation machine that does two sided printing. So there's a large heated plate that is ...
2k views

### High power three phase ac motor controller

I have come across this question a lot in the design of a special 3 phase motor controller I plan to build this summer and I think I need to ask it directly to solve it. I need to be able to ...
5k views

### Controlling three phase heating element

I am building a small brewery and would like to heat a barrel of aprox. 280 liters of water with an three phase heating element. Its power would be 15 kW. That means that connected to 400V the full ...
782 views

### Simulate isolation transformer in LTspice

Hi, I am new to simulating transformers with LTspice, and I struggle getting the circuit to function as expected. The source is a three phase TN-S (wye) connected. Then I wanted to add a 1:1 ...
1k views

### Unknown motor, specifications interpretation and use

I got a motor on the picture. Does anyone know what it was used for? My main question is if is it feasible to use it as a barbecue motor or is it too strong? Can I connect it to one or three phases ...
31k views

### 3 phase induction motors with poles not equal to 3x

I am having trouble finding diagrams to show induction motors with poles not equal to 3x. Everything I find is 2 poles per phase. Can anyone explain and help me visualize, for example, a 4 pole 3 ...
5k views

### Switching a 3 phase pump using a solid state relay

I made a remote (GSM) controlled module for a 3 phase pump close to my friends house. The pump should run at night, and walking the 1km to the switch while they are sleeping is the problem. The ...
2k views

### Determining phase sequence in software

We have 3-phase electric network. How to determine phase sequence (L123 or L132) from 2 line-to-line voltages U12 and U32? I prefer computationally simple solutions. Is it possible to determine phase ...
60k views

### Why do we need 3 phase power supply?

Why do we need 3 phase? For the reason that voltage will never be zero in 3 phase? OR we need high voltage?
56k views

### Australian 3-Phase Colour Code Standard

We're ordering some machinery from China and need it manufactured to Australian electrical standards including the wiring colour code. Unfortunately we don't have any electricians or engineers that ...
992 views

### Choosing proper wire gauge

I have a machine (a machine with seven three-phase motors) with this information on its nameplate: 3 Phases 400 V, 50 Hz 100 A, 40 kW I am wondering: Is 100 A for all three phases ...
5k views

### Can we remove the neutral wire?

If we have the connection shown below (star connection of the secondary part of a TX), the load per each phase is equivalent (balanced load), then the vector sum of ...
7k views

### Will a RCBO 4P trip in case of neutral fault/failure/interrupt/float?

We have 3 phase power supply in my home which is used to power single phase 240V 50 hz appliances with common neutral. (Diagram in the link at the bottom) The only protection we have as of now are ...
221 views

### Obtaining DC from a tri-phase generator

I have a tri-phase generator which outputs AC voltage waveforms ($R$, $S$ and $T$) with 120o phase shift between them. I want to rectify these voltages and obtain a single DC voltage. I ...
3k views

### Control torque of 3-phase AC motors

Actually, we have 1x30HP, 2x10HP motors working at our workplace. When we start the motors there is a lot of torque generated due to which our grid supply charges us penalty every month. We need ...
1k views

### Shortcircuited motorcycle alternator leads to RPM proportional losses?

I've had this puzzle for a couple of years but never been able to figure it out. Regulator manufacturers for typical 3-phase alternators provide the 14.4V by 'shorting' the phases. Obviously this ...
66 views

### 3 Phase motor changing rotation on startup intermittently

I have a total of three 3-phase floating fountain aerators. Last year they functioned properly. This year when I connected them, two of them were running in reverse and 1 was running forward. All ...
1k views

### What is proper polyphase AC terminology?

I'm not entirely clear on the proper terminology for polyphase AC systems. I hear it used informally, but I'm not sure what the proper formal names are, if there are any. How I've got it in my head is ...
114 views

### “Black box” transformer: Y-Y, Y-Ī, or Ī-Ī connected?

As a preface, this is purely hypothetical. I know better than to use a transformer without knowing anything about it. I'm just trying to get an idea of whether this is possible, not whether it's a ...
928 views

### Park/Clarke Transform and Power

I'm looking to determine the electrical power input to a 3-phase BLDC motor, driven by TI's DRV8305 motor controller. I can't use the DC power flowing into the system because I'm trying to capture the ...
5k views

### Three phase rms voltage calculation

I am new in instrumentation and control. I am developing a hardware for a project and the following is my application. I have three phase stepped down voltages and stepped down currents entering my ...
1k views

### How calculate three phase kilowatt hour from time sampled data of voltage and current of each phase

My problem is I want to calculate three phase kilo watt hour from time sampled data of current and voltages. My doubts 1) How can I calculate the kilowatt hour from time sampled data? Is it any ...
754 views

### 3 phase computer chip

I have just had a conversation with a friend who studied quantum computing. Sadly I have forgotten most of the conversation as it was far beyond my knowledge threshold. Essentially he was saying was ...
2k views

### Three phase 230V input to single phase 5V/5W power supply [closed]

How can I design a 5V/5W DC power supply derived from 3 phase 230V AC input supply? My application need to work, even if, only one phase is available.
4k views

### Are normally open contactors virtually safe from failing closed?

Quick question: are normally-open contactors (which I assume are simply high breaking capacity relays) virtually safe from failing closed? I want to cut off a 400V 3-phase supply using an emergency ...
2k views

### drive 3 phase induction motor with only DC (not pwm) thru each phase

I've been researching making a driver for a 3 phase induction motor powered by DC source using PWM to approximate sine waves in each phase. However, the switching speeds of the PWM signal for the ...