Questions tagged [three-phase]

AC power with three legs run 120 degrees out of phase

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44
votes
11answers
18k 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 ...
30
votes
3answers
9k 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 ...
21
votes
6answers
64k 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 ...
17
votes
6answers
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?
13
votes
10answers
32k 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, ...
12
votes
2answers
70k 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 ...
10
votes
3answers
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 ...
10
votes
3answers
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, ...
10
votes
8answers
79k views

Y or Delta connections advantages / disadvantages

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) ...
10
votes
2answers
1k 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 ...
8
votes
4answers
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 ...
7
votes
3answers
70k 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 (...
7
votes
1answer
39k 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 ...
7
votes
2answers
48k 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, ...
7
votes
3answers
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 ...
7
votes
3answers
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 ...
6
votes
5answers
117k 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 ...
6
votes
6answers
4k 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-...
6
votes
2answers
821 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 ...
5
votes
5answers
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?...
5
votes
4answers
676 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 ...
5
votes
6answers
54k 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 ...
5
votes
1answer
391 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 ...
5
votes
2answers
3k 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 ...
5
votes
2answers
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 ...
5
votes
1answer
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 ...
5
votes
6answers
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 ...
4
votes
5answers
55k 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?
4
votes
4answers
949 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 ...
4
votes
4answers
34k 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 ...
4
votes
2answers
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 ...
4
votes
4answers
6k 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 ...
4
votes
1answer
212 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 ...
4
votes
3answers
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 ...
4
votes
4answers
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 ...
4
votes
2answers
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 ...
4
votes
3answers
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 ...
4
votes
1answer
776 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 ...
4
votes
2answers
3k 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 ...
3
votes
4answers
661 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 ...
3
votes
4answers
1k 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.
3
votes
3answers
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 ...
3
votes
3answers
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 ...
3
votes
2answers
4k views

Three-phase Y and Delta Configurations Polarities

Please take a moment to look at the three-phase Y and Delta configurations pictures below (The pictures are screenshots taken from the “All About Circuits” online book). The first picture (Y ...
3
votes
3answers
2k views

Power Losses in a 3 phase rectifier

I'm trying to speck out a heat sink for a 3 phase rectifier. The rectifier consists of 3 individual rectifier blocks. I need a heat sink for each block. The rectifier is for a generator and all the ...
3
votes
2answers
5k views

General 3 Phase Motor Inductance Question

I know that motors are inductive loads. Does the inductance of a 3 phase motor depend on the load on the motor?
3
votes
1answer
526 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 ...
3
votes
3answers
753 views

IC for converting single phase to three phase

I want to design a device to control a 0.5 HP to 3.0 HP three phase AC motor with single AC power. I need to able converting single phase to three phase. Also an three phase ac motor controller ...
3
votes
1answer
274 views

Difference between a 3 phase VFD inverter and UPS inverter

this might seem like an odd question, but i consider myself still a newbie in Power electronics. This has been circling in my head for a few days. Intro : From a Hardware Standpoint i am assuming ...
3
votes
1answer
2k views

How to know if questions in an exam mean line, phase, or RMS voltage?

What is the difference between line, phase and RMS voltage? We get many questions where it is not mentioned whether the question is specifying line, phase or RMS voltage. I will attach some example ...