# Three Phase Electricity...

Do power plants have three generators each 120 dgr out of phase to deliver three-phase electricity? This is just a WAG as a starting point, but I’m really just tossing darts blindly at the dartboard here! How is this done? I assume it is three phase from the factory, or is there a way to “create” three-phase downstream, as needed? I never quite understood this… - Jinx

One generator (strictly, alternator), three windings. The windings are spaced 120[sup]o[/sup] apart.

You could also do it with 6, 9, 12… windings.

No, each armature of three armatures of the generator has windings arranged 120 degrees apart from each other. BTW, there are other polyphase systems in use, sucH as four-phase and nine-phase.

Of course I meant to say “each of three armatures”, etc.

Sort of right. Each phase is created within wiring in the generator. Three phase power is produced by tripling the wiring. An explanation is here and here in more detail.

Referring to the OP there, not the replies that snuck in.

Also, FWIW, there are two distint types of three-phase loads used. One is called a “delta” and is essentially three balanced loads arranged in a triangle shape with three linesa feeding the vertices, and the other is a “Y” with three unbalanced loads arranged in a Y shape, with a fourth neutral line at the apex of the the three feedpoints.

Thanks, everyone! Truly Shocking! (Hey, I couldn’t resist!)

The alternator in your car is likely three phase…

AFAIKJ, automotive alternators are single phase. The number of phases depends not only upon the number of armatures, but the winding configuration of the armatures as well.

Airplanes use 400hz 3 phase power.

Check out Alternator Secrets by T.J.Lindsay. They are multple phase (not necessarily three) and then rectified thru diodes into rippled DC and regulated at the required voltage. Pretty cool.

Q.E.D., please stop referring to multiple armatures.

On most polyphase machines, the stator is the armature. It has multiple windings, but there’s only one stator.

It’s possible to make one where the rotor is the armature, but again, only one rotor with multiple windings.

I was using the term "armature"in this sense:

From this sense.

Yes, and I’m suggesting that you are using the term incorrectly.

I’ve always thought of an “armature” as an arm of the rotor assembly. I see now that is incorrect.

The armature is the bit that isn’t the field.

Thank you. I’ve dealt plenty with magnetics and three-phase circuits in transformer testing, but almost never with alternators, so I’m unfamiliar with terms which apply to them. I appreciate the information, Desmostylus.

Q.E.D. I believe you’re confusing armature with pole. The armature (rightly as you noted in your link) consists of a series of coils. The number and configuration of the coils (poles) determine how many phases are produced (i.e. multiples of 3 would produce 3Ø power). The armature is stationary and the rotor turns inside of it at a rate to produce the proper frequency. The rotor also consists of a number of coils which are energized (excited) to produce a magnetic field. This is accomplished either with an ‘exciter’ as an integral part of the generator, or with an outside excitation transformer which requires an outside source of power. So, a generator consists of a single rotor turning inside a single armature. I’m sorry, i can’t find my copy of the Standard Handbook for Electrical Engineers so my explaination is not as concise as it should be. Perhaps David Simmons or Crafter Man will chime in with the proper language.

Also, it would be more correct to say there are 2 distinct type of 3Ø systems; delta and wye. A 3Ø load (motor for instance) does not require a neutral in order to operate, just the 3 phases. The neutral in the system serves 2 (main) purposes: 1) provides a path to the source should a phase come in contact with a ground. This allows the protection relays or breakers to open the circuit to prevent further damage to equipment and to eliminate an unsafe condition. 2) stabilizes the system voltage by providing a reference to ground. Depending on load balance, a strictly delta system may not read equally between all phases. Additionally, a wye system allows for more options in transformer connections.

Although i can’t say for sure, i don’t know of any ‘strictly’ 4Ø or 9Ø systems. If i understand your meaning, 4Ø is generally referred to as 2Ø - 4 wire. Special transformers known as ‘Scott connected’ which have a ‘teaser’ winding connection at a point about 86% along the length of the primary coil. A second transfomer with a connection point at the midpoint of the primary coil is also used. These transformers were originally developed by Charles F. Scott and were used to convert the 2Ø output of the Niagra Falls generators to 3Ø.