Three-Phase Power Explained

This video will take a close look at three-phase power and explain how it works. Three-phase power can be defined as the common method of alternating current power generation, transmission, and distribution. It is a type of polyphase system, and is the most common method used by electric grids worldwide to transfer power.

[daneabc]

I remember my EE professor from my undergraduate days filling three chalk boards with a beautiful derivation of WHY three phase power, why not 4, 5 or n phase power? Answer: Because three phases was the minimum number of phases whose average power was a constant. Additional phases require additional windings and transformers, so go with THREE phases for the most efficient power grid. Beautiful. How I wish I had a video of his derivation. Even after over forty years as a now semi-retired Electrical Engineer who dealt with RF systems (FM broadcast, TV broadcast, and microwave), it was masterful derivation.

[jamesspash]

Great explanation of three phase. My son is entering the generation field and this will surely help him better understand three phase vs single phase. Me, 30+ years in hydro generation, so sometimes Dads explanations might be a little over whelming. Thanks.

[jakefeisel]

I've was only wondering about 3 phase for about 25 years now, thank you.

[johnkenneally]

Best explanation of 3 phase power I have come across. Currently I am an apprentice electrician.

[ALM]

120V/240V "residential" power comes from a single 240V phase supply line produced from a step-down transformer (secondary side). The primary side of the transformer is fed by one phase (1 of the 3 phases) from the substation (commonly 12kV). The secondary side of the transformer is stepped down to a 240V SINGLE phase output. Because the secondary of the transformer is split into two halves with the neutral (or ground) at the middle of the transformer's secondary winding, two 120V reference-to-ground signals are produced. So there are 3 wires coming from the secondary of that transformer, (2 hot--1 wire on each end of the winding, 1 neutral/ground wire tap at the middle of the winding). Measuring the voltage potential from each hot wire to the neutral wire yields 120V. Measuring the potential difference from one end of the winding to the other end yields 240V (ie. 120V + 120V...actually, 120V minus a negative 120V). This configuration is also called a split-phase system. I added this comment because at 8:00 of this video, it's not clear enough, because it says "it's 2 single phase lines". Technically, it's one phase split into two halves and the waveforms are "out of phase" only because they are referenced to ground at the middle of the transformer winding.

[jamestaylor]

You are a true educator, not only do you make it understandable, you also create the desire to learn more, many thanks

[ZZZZ-zgzb]

as an EE I want this video to be tough in colleges, it explains it perfectly, I want to go back to college, who would not want to be in college -all you have to do i study nothing else lol kids these days have it made with the internet, this is a great video, I watched it twice because its so well done, who ever did the animation I want them to do my power point stuff and make it like this

[goedelite]

This begins with faulty description of the effect of the north pole of a magnet rotating by a fixed linear conductor. Electrons do not flow towards the north pole of the magnet. According to Lenz's Law, the electrons in the conductor flow in such a direction as to oppose the motion of the passing north pole. That means that as the north pole approaches the end of the linear conductor, the electrons flow in such a way as to create a north pole at its end. As the north pole passes and receded from the conductor, the electron reverse their flow so as to produce a south pole at its end, to attract the receding pole. Lenz's Law is really a consequence of Faraday's Law of Induction, which states in mathematical terms that the direction the induced magnetic field is always opposite to the direction in which the magnetic field is increasing. The electrons in the conduction flow in the direction required to produce that opposing field. In the mathematical expression, the negative sign is what Lenz's Law expresses in words.

[janyjozsef]

The conductors between a voltage source and a load are called lines, and the voltage between any two lines is called line voltage. The voltage measured between any line and neutral is called phase voltage. For example, for a 208/120 volt service, the line voltage is 208 Volts, and the phase voltage is 120 Volts.(9:32)
EU:
230VAC => Phase voltage
400VAC => Line voltage.

[niallm-is]

This is one of the best descriptions and explanations on the Internet. Thank you

[coloradowilderness]

Simple, Easy, Concise, Thoughtful .
Thanks

[johng.]

thanks for this. I'm a recruiter and working with construction and 3 phase power is a huge plus for what I'm hiring for. Your videos do a great job explaining this to a layperson w/o the background.

[kevinbutler]

This is one of the best explanations/animations I've seen.

[sdj]

Been studying for an upcoming test and needed some refresher material. You explain the material beautifully. Definitely have a knack for explaining complex processes in a simplified manner.

[paulfrischknecht]

Errata: At 0:40, the sine waves are 60 degrees apart, but they should be 120. Magnets do not attract or repulse electrons. Varying magnetic fields cause electrons to experience a perpendicular force, which is why you need coils in a generator and motor, straight wires would not work properly...

[wiserdaley]

Thanks for the professional breaking down of information to simple yet informative points. It's great to have instructors like you.

[brightwriter]

Another, unmentioned, benefit of 3-phase power is that 3-phase AC induction motors are much simpler, not needing a shaded-pole device on the field windings or a special startup motor to get the principal motor started. A 2-phase AC induction motor, like an internal-combustion engine, can keep itself going but needs a separate device to get it started.

[garysinghsidhu]

this is the best explanation I have watched so far

[Sarcastix]

Super video. The detailed graphics and annotations are really helpful

[josephb]

Very good very clear explanation, l have been looking at this stuff for years and for some reason for me it just takes one mind and l a life ...does it ever puzzle you why we have to search for so long before we find the right answer ....why can't we get it straight away