# Questions tagged [three-phase]

AC power with three legs run 120 degrees out of phase

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### 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, ...
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 ...
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 ...
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) ...
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 ...
2k views

### SPWM vs 6-step PWM vs SVMPWM

While learning 3-Phase scalar control of ACIM using STM32F407 MCU I could not clearly understand the diffrence between the following terms: 1. SPWM 2. 6-step PWM 3. SVMPWM How do they differ from ...
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 ...
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 ...
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, ...
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 ...
453 views

### Making a three phase voltage source to drive a gyroscope

I'm trying to drive a gyroscope that needs a 3 phase 400Hz 32v 1A power supply. How can I provide that supply? It's one part of my university project and I'm a beginner in this field. I'd like to find ...
278 views

### Understanding this power supply design

I'm doing some kind of reverse engineering to this very old power supply design. I'm having hard time trying to understand it all. I'm asking for some hints that help me read this schematic. From this ...
3k views

### Instantaneous vector sum of three phases 120 apart is not zero?

Vector sum of equal 3 phases 120 degree apart is zero and serves as a neutral. However, while drawing instantaneous vectors of the three phases, they summed up all together to give a vector. I have ...
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 ...
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?
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 ...
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 ...
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 ...
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 ...
313 views

### Help with a full bridge three phase rectifier powered floor

I originally posed a question here asking about solutions to power a small rover 24/7 from a powered floor. It seems the best solution is a full bridge three phase rectifier circuit. I have a few ...
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 ...
2k views

### How can i measure voltages on each phases of a 3 phase system, Using a microcontoller?

How can i measure voltages on each phases of a 3 phase system. The measurement is to be processed by a microcontroller. Is there any special chips available, or do i need to use the ordinary ...
510 views

### Find impedence given per unit value-transformer

I really can't wrap my head around this. Three single phase transformers are connected to create a 3 phase transformer. They all have the same nominal values : voltage conversion : 1.2kV/120 V (...
1k views

### MOSFET H-Bridge Design - Capacitor/Diode/Resistor Selection

welcome to my first post! I am designing a small 3-phase Brushless DC Electronic Speed Controller (ESC). The design utilizes 3 half bridges and a FAN7388 driver IC. The FAN7388 datasheet has a ...
2k views

### DIY Rotary Phase Converter with starter motor, cutout relay in parallel with load?

I am working on a DIY Rotary Phase converter with pony motor. This will use single phase 240v and run capacitors to feed 2 legs of a 3 phase motor, which will generate the 3rd leg. It uses a 1/2 HP ...
112k views

### How to change rotation direction of 3-phase electrical machines?

I was taught that if you want to change the direction of a three phase rotating machine that is rotating in forward direction, you interchange the phases. Since the phases has the same features (...
36k views

### How to wire 3 phase motor to VFD

I am trying to wire a new motor to a variable frequency drive (VFD) and having some trouble figuring out how to wire the motor to the VFD. The motor is a 1 HP, 3-phase, 208-230/460 volts, and I'm ...
191 views

### Max Current through Neutral in wye-wye 3phase circuit

Assume that you have a wye-wye 3 phase circuit. Each of the 3 phase wires can take a max of X Amps. What is the max current the neutral of the circuit could have? Is it possible for the neutral ...
100 views

### Relation between phase angle and current direction

In a triphasic system (any), is there a way to tell if the current is entering or leaving a phase/line/load just by the angle of the phasor of the source ? In the following picture we can see the ...
400 views

### BLDC Current Driver Encountering Current Problems

The attached Schematic uses 6 N Channel Power Mosfets "IRL3303". I have wound my inrunner bldc motor with 180 windings per phase using a 26 Gauge Magnetic Wire. My motor is a 6 pole 2 magnets machine. ...
2k views

### A basic question about load balancing and power factor correction in three-phase systems

I know basically about phasor representation of line voltages and active reactive power concepts in three-phase systems. But what I'm wondering is the reasons of two things I hear a lot. 1-) What is ...
134 views

### Three phase system questions

I have been trying to solve homework questions on three phase systems but I am got stuck in two questions while solving solving them. Three similar impedances are connected in star across 2000V, ...
9k views

### when does the neutral wire in a 3 phase system carry voltage?

I am curious, and I've found a bit of information online, but maybe its not clicking in my head... when does the neutral line in a 3 phase system carry voltage. i do understand the answer is quite ...
1k views

### How do remaining two phases act as return path in three phase system

Since they are out of phase one against the other then there is a potential difference between them and the one that is on the higher potential is enclosed in the lower one. This is my assumption, ...
2k views

### What is a return line in AC power transmission? Why is it needed?

This diagram shows V vs. t for three-phase power transmission: What is the corresponding I vs. t diagram? Would that diagram help explain what a "return line" is and why it is necessary? (cf. the ...
481 views

### Three phase converter - capacitor switching

I've started building a single to three phase converter. My research started with the likes of this paper. I've set a bank of 40uf/440v capacitors up and a potential relay. The relay is a Supco SUPR. ...