Three Phase Power Simplified 

By on

A single phase system is perhaps the most common type of system most people are familiar with. This is what people have in their homes and what appliances are plugged in to. For larger amounts of power, three phase systems are used.

Electricity is generated by a coil of wire moving through a magnetic field. The illustration shows three such coils in an electrical generator , spaced evenly apart. Each coil is called a phase and as there are three coils, this is called a three phase system.

ThreePhasePower

From a such a system, power can be supplied as single phase (load connected between a line and neutral) or three phase (load connected between all three lines).   In the illustration, the motor is connected as a three phase load and the socket outlets and lamp as single phase loads.

Terminology

The three winding end connected together at the centre are is called the neutral (denoted as 'N'). The other ends are called the line end (denoted as 'L1', 'L2' and 'L3').

The voltage between two lines (for example 'L1' and 'L2') is called the line to line (or phase to phase) voltage. The voltage across each winding (for example between 'L1' and 'N' is called the line to neutral (or phase voltage).

Voltage Relationship

The line to line voltage is the vector sum of the phase to phase voltage across each winding. This is not the same as the arithmetic sum and is given by the following equation:

 

myElectrical Equation  

Example:

Line to Line Voltage (VLL)

 myElectrical Equation

myElectrical Equation

myElectrical Equation

Line to Neutral Voltage (VLN)

myElectrical Equation

myElectrical Equation

 myElectrical Equation
 

 

Solving Three Phase Problems

 Tip - to solve a three phase problem, convert it to a single phase problem.

In a balanced three phase system
- each phase delivers/uses 1/3 of the total power
- convert three phase problems to single phase

Resources



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus

  1. Jetstar's avatar Jetstar says:
    6/7/2012 3:59 PM

    The 4th line down from TERMINOLOGY reads.

    The voltage across each winding (for example between 'L1' and 'L2' is called the line to neutral (or phase voltage).

    Should it not be (for example between 'L1 and 'N'...)?

    Regads...

    The voltage across each winding (for example between 'L1' and 'L2' is called the line to neutral (or phase voltage).

    • Steven's avatar Steven says:
      6/8/2012 9:03 AM

      Jetstar, thanks for spotting that - your right. I've corrected the error.

  2. Matt's avatar Matt says:
    9/18/2012 5:35 AM

    What about 3 phase unbalanced loads?


Comments are closed for this post:
  • have a question or need help, please use our Questions Section
  • spotted an error or have additional info that you think should be in this post, feel free to Contact Us



Material Properties

Everything physical in electrical engineering from insulations to conductors revolves around materials. Here we are listing common materials along with...

Network Theory – Introduction and Review

In electrical engineering, Network Theory is the study of how to solve circuit problems. By analyzing circuits, the engineer looks to determine the various...

Medium Voltage Switchgear Room Design Guide

Many medium voltage (MV) indoor switchgear rooms  exist worldwide. The complexity of these rooms varies considerably depending on location, function and...

Battery Sizing

This article gives an introduction to IEEE 485 method for the selection and calculation of battery capacity.

Software Usage Guidelines

Using software in our  work is essential for most of us and we are becoming even more dependant on it's use.  While software is a great asset, many times...

Contribute to myElectrcial

Have an opinion or something to say, want to ask or answer questions, share your knowledge then use our site to do it . As a community of people interested...

DC Motor Operation

Coils of wire on the rotor carry a d.c. current which generates a magnetic field. A stator magnetic field is created using either permanent magnets or...

Meeting room of the future

The IET site has a video of a visit showing of a high tech meeting room developed at Napier University in Edinburgh. It a good demonstration of innovative...

Capacitors - Energy Storage Application

Capacitors have numerous applications in electrical and electronic applications.  This note examines the use of capacitors to store electrical energy....

Dielectric loss in cables

Dielectrics (insulating materials for example) when subjected to a varying electric field, will have some energy loss.   The varying electric field causes...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note