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



Tips for a better Low Voltage Protection Discrimination Study

Carrying out a protection system discrimination study is critical to ensure the correct functioning of  the electrical system in the event of faults. ...

Post Editing Tips

If you at all familiar with programs like office and outlook, then adding and editing posts is pretty straightforward and intuitive.  However, there are...

Operational Amplifier

The fundamental component of any analogue computer is the operational amplifier, or op amp. An operational amplifier (often called an op-amp,) is a high...

Robotics - Home Innovations

We have a sister note to this (Robots - Interesting Video), in which I have posted some videos of interesting robots developed by commercial corporations...

Electromagnetic Fields - Exposure Limits

Exposure to time varying magnetic fields, from power frequencies to the gigahertz range can have harmful consequences.  A lot of research has been conducted...

Cold Fusion (or not?)

Recently I have seen a few interesting articles on viable cold fusion; the combining of atoms at room like temperatures to create boundless energy. Now...

Standard Cable & Wire Sizes

IEC 60228 is the International Electrotechnical Commission's international standard on conductors of insulated cables. Among other things, it defines a...

Switchboard - Forms of Internal Separation

IEC 61439 'Low-voltage switchgear and controlgear assemblies', specifies standard arrangements of switchboard (call forms of internal separation). The...

What is LED?

Light Emitting Diodes (LED ) are increasing gaining favour in both the domestic and commercial sectors; due to their efficiency, sustainability and durability...

Our internet address and Vanity URLs

Visitors who like to type web address rather then click menus may be interested in how our URL structure works.

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