# Help:3 phase application

Discussion in 'Homework Help' started by kra1ne, Jul 29, 2010.

1. ### kra1ne Thread Starter New Member

Nov 16, 2009
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Help: Can you give me some application of 3 phase system..other that motors and transformers..

2. ### tom66 Senior Member

May 9, 2009
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This is homework... really belongs in the homework help section.

Anyway, I'll give you a tip. When you rectify three-phase AC, the output never goes to 0V, which means any DC equipment connected to it (say, an electronic controller) needs smaller filter caps, sometimes they can be omitted altogether.

Also, with three phase AC, you can transmit more power with less copper overall. (Think carefully about this one.)

Three phase motors are also cheaper to make in higher power ratings.

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3. ### dsp_redux Active Member

Apr 11, 2009
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More stable DC output from a rectifying bridge? Less ripple... is it for a homework?

4. ### debjit625 Well-Known Member

Apr 17, 2010
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In power systems it lowers shock hazard as the total voltage is divided into three parts.

Good Luck​

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5. ### rvh002@gmail.com Active Member

May 15, 2009
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Just like motor car alternators, all power station alternators generate 3 phase power. As stated above it is cheaper to transport via high voltage networks and at the user side it is effectively transformed into useable voltage for the consumer. The point being (without going into all the calculations) that 3phase wiring needs to be only a third of single phase wiring. If you look at the thousands of kilometers that electricity is transported in most countries it would be madness to do it in single phase.

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6. ### marshallf3 Well-Known Member

Jul 26, 2010
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In addition to other managerial duties I serve as the Facilities Engineer for a 250,000 ft*sq building and we've got 6,500 Amps of 480V three phase service coming in. In addition to motors and step down transformers running off the 480V single legs of it are used to operate the lighting which is 277V.

480V is typically served up as 480Y-277 meaning that across any two of the three phases you have 480V but from any one of the three phases to neutral you have 277V. Since it takes less current at 277V to power a specific wattage lighting fixture you can operate more fixtures (or utilize longer runs) on a single 20A circuit using the same #12 AWG wire which would be required in an equivalent 120V 20A circuit.

So, I would say in the case of a commercial 480Y-277 system you have a dual advantage - three phase motors are far more efficient and 277V lighting provides a substantial savings in copper and associated wiring costs.