Three Phase Power Simplified 

By on April 17th, 2012

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


comments powered by Disqus

  1. Jetstar's avatar Jetstar says:
    6/7/2012 10:59 AM

    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 4:03 AM

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

  2. Matt's avatar Matt says:
    9/18/2012 12:35 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



Latest Questions:

  1. Lightning Protection calculation Free Software
  2. How many motors, or of what kind, do I need to get the output to be 5 Volts under load?
  3. Three winding transformer impedance
  4. Short Circuit Fault Current (comprehensive)
  5. help for electricity distribution (HTA) through underground cables (6 circuits)
  6. CT Secondary Rating
  7. Embedded system design
  8. PV system design - advice

most popular notesMost Popular Notes:







newsletter logo

Our Newsletter

Receive updates on new posts by email
down arrow

Electric Power Distribution Engineering, Third Edition
Electric Power Distribution Engineering, ...
Turan Gonen
Hardcover - 1061 pages
$119.96
The Ultimate Solar Power Design Guide: Less Theory More Practice (The Missing Guide For Proven Simple Fast Sizing Of Solar Electricity Systems For Your Home or Business)
The Ultimate Solar Power Design Guide: Less ...
Lacho Pop MSE, Dimi ...
Kindle Edition - 221 pages
Solar Electricity Handbook - 2015 Edition: A simple, practical guide to solar energy - designing and installing solar PV systems.
Solar Electricity Handbook - 2015 Edition: ...
Michael Boxwell
Paperback - 204 pages
$16.64
Renewable and Efficient Electric Power Systems
Renewable and Efficient Electric Power ...
Gilbert M. Masters
Hardcover - 712 pages
$99.68
Power System Relaying
Power System Relaying
Stanley H. Horowitz, ...
Hardcover - 398 pages
$122.30
Design of Smart Power Grid Renewable Energy Systems
Design of Smart Power Grid Renewable Energy ...
Ali Keyhani
Hardcover - 592 pages
$111.84
Energy Systems Engineering: Evaluation and Implementation, Second Edition
Energy Systems Engineering: Evaluation and ...
Francis Vanek, Louis ...
Hardcover - 672 pages
$60.99
Power Systems and Renewable Energy: Design, Operation, and Systems Analysis (Power Generation Collection)
Power Systems and Renewable Energy: Design, ...
Gary D. Price
Paperback - 192 pages
$56.95
Standard Handbook for Electrical Engineers Sixteenth Edition
Standard Handbook for Electrical Engineers ...
H. Wayne Beaty, ...
Hardcover - 2144 pages
$107.84
Solar Energy Engineering, Second Edition: Processes and Systems
Solar Energy Engineering, Second Edition: ...
Soteris A. Kalogirou
Hardcover - 840 pages
$86.96
Photovoltaic Systems Engineering, Third Edition
Photovoltaic Systems Engineering, Third ...
Roger A. Messenger, ...
Hardcover - 528 pages
$106.58
Do It Yourself 12 Volt Solar Power, 2nd Edition (Simple Living)
Do It Yourself 12 Volt Solar Power, 2nd ...
Michael Daniek
Paperback - 128 pages
$12.86
Power Generation and the Environment
Power Generation and the Environment
Anco S. Blazev
Hardcover - 1333 pages
$223.66
Principles of Sustainable Energy Systems, Second Edition (Mechanical and Aerospace Engineering Series)
Principles of Sustainable Energy Systems, ...
Frank Kreith, Susan ...
Hardcover - 790 pages
$100.63
Large-Scale Solar Power Systems: Construction and Economics (Sustainability Science and Engineering)
Large-Scale Solar Power Systems: ...
Dr Peter Gevorkian
Paperback - 400 pages
$49.99
Electric Power Substations Engineering, Third Edition (Electrical Engineering Handbook)
Electric Power Substations Engineering, ...
Hardcover - 536 pages
$134.96
Renewable and Efficient Electric Power Systems
Renewable and Efficient Electric Power ...
Gilbert M. Masters
Hardcover - 680 pages
Power Electronics and Renewable Energy Systems: Proceedings of ICPERES 2014 (Lecture Notes in Electrical Engineering)
Power Electronics and Renewable Energy ...
Hardcover - 1607 pages
$399.00
Submarine Power Cables: Design, Installation, Repair, Environmental Aspects (Power Systems)
Submarine Power Cables: Design, ...
Thomas Worzyk
Hardcover - 296 pages
$189.00
Renewable Energy in Power Systems
Renewable Energy in Power Systems
Leon Freris, David ...
Hardcover - 300 pages
$77.60
Convex Optimization of Power Systems
Convex Optimization of Power Systems
Joshua Adam Taylor
Hardcover - 209 pages
$90.77
Electric Energy: An Introduction, Third Edition (Power Electronics and Applications Series)
Electric Energy: An Introduction, Third ...
Mohamed A. El-Sharkawi
Hardcover - 606 pages
$100.35
How to Solar Power Your Home Everything You Need to Know Explained Simply (Back-To-Basics Conserving)
How to Solar Power Your Home Everything You ...
Martha Maeda
Paperback - 336 pages
$12.02
Alternative Energy Systems and Applications
Alternative Energy Systems and Applications
B. K. Hodge
Paperback - 432 pages
Electric Energy: An Introduction, Second Edition (Power Electronics and Applications Series)
Electric Energy: An Introduction, Second ...
Mohamed A. El-Sharkawi
Hardcover - 496 pages
Solar Electricity Handbook - 2012 Edition: A Simple Practical Guide to Solar Energy - Designing and Installing Photovoltaic Solar Electric Systems
Solar Electricity Handbook - 2012 Edition: ...
Michael Boxwell
Paperback - 200 pages
Hydro Plant Electrical Systems
Hydro Plant Electrical Systems
David M. Clemen
Hardcover - 194 pages
$89.00
Solar Energy Conversion Systems
Solar Energy Conversion Systems
Jeffrey R. S. Brownson
Hardcover - 480 pages
$91.50


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