T&T: Why the Wye? (2 30a to 1 50a/240)

[Bob]

Phase isn't an incorrect term for describing 120/240 home power.  It's 
simply 120 Vac 2-phase.  Two phase power has two "hot" lines 180 degrees 
away from each other.  Three phase power has three lines 120 deg away from 
each other.  This concept can be extended to an arbitrary number of phases. 
For example in the aircraft electrical power world, we commonly use 
rectified six phase power for 28V buses.  When necessary for power quality 
requirements, we use twelve or fifteen phase power.  Fifteen phase power is 
just that; fifteen sine wave phases, spaced 24 deg apart.  The a/c 
generators are 3 phase, so the generation of the extra phases requires some 
electrical and magnetic wizardry.

Bob

----- Original Message ----- 
From: "Albin43SDtr" <Albin43SDtr at comcast.net>
To: <trawlers-and-trawlering at lists.samurai.com>
Sent: Saturday, September 19, 2009 12:00 AM
Subject: Re: T&T: Why the Wye? (2 30a to 1 50a/240)


> 'Lo All,
>
> It's probably just me, but this discussion seems to use the term "phase" 
> rather loosely. In one context, "phase" (correctly) alludes to the 
> 'phases' as generated by a rotating armature, where the rising 
> zero-crossing points of the three waveforms (of 3 phase power) are 120 
> degrees apart. Electricity is supplied to consumers as single or three 
> phase power and then used as single phase, as for a single phase motor, or 
> as 3 phase as in a 3-phase motor. Three phase power is used to improve the 
> power factor for consumers who use LOTS of power, thus reducing their 
> overall energy costs, but as it is more expensive to distribute to places, 
> such as our houses, where consumption usually is significantly less, 
> single phase power is normally used.
>
> For example, most houses and individual apartments are supplied only with 
> single phase 120/240 volt power, which is provided by center tapping the 
> single phase power at the supply transformer and running two 'hot' wires 
> and a neutral wire to the house. We then get the two 'legs' of 120 volt 
> power at the power panel by connecting each leg to one of the 'hot' wires 
> and to the common neutral to form a circuit. Again, this is usually all 
> single phase power.
>
> The other context seems to use the term "phase" when speaking of the 
> waveform of center-tapped single phase power. Admittedly, the two legs of 
> the single phase power line are 180 degrees out of sync, but I question 
> using the term "phase" to describe their relationship. In all of the 
> electrical classes I have attended, "phase" referred solely to power as 
> generated by a rotating armature - and never to the electrical waveform 
> from a center-tapped transformer. Then again, its been many, many years 
> since I attended any electrical classes.
>
> In reading the posts in this discussion, I have often wondered if the two 
> contexts of the term - "phase" - have not been confused - resulting in 
> additional confusion.
>
> Again, its probably just me, I am often confused......such as when I 
> ponder the concise communication of a concept of a phase of one leg of a 
> single phase power source, or worse, the concept of the relationship of a 
> single phase of one leg of a single phase of a three phase power source to 
> any other leg's phase.
>
>
> Take care and be safe.
>
> Wayne
> Celestial
> Albin 43 Sundeck
> Near Panama City, FL _______________________________________________
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