Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [three-phase]

AC power with three legs run 120 degrees out of phase

Three-phase power is commonly used in power generation and distribution, as well as to drive industrial-sized motor loads. Most residences do not have three-phase power. Loads and transformers can be configured as line-to-line (delta) or line-to-neutral (wye).

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Why three-phase power? Why not a higher number of phases?

Is there a reason, beyond historical reasons, that three phases has become the dominant number of phases? I am aware of the advantages against one phase and two phase, namely the reduced amount of conductor needed, and that motors can provide torque…
Hugoagogo
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Why 3 phase and not 1 phase power transmission?

Why does power transmission use three lines with three different phases? Why not three lines all in the same phase? Does it have to do with the alternators used for generating the power, or is there less loss when the phases of the three lines are…
Geremia
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What do the line-and-circle symbols mean on these electric meters?

I was looking at an electrical installation and came across unfamiliar symbols on the front of a pair of meters. These are from three-phase 240v meters running on a timed system. One each for peak/off-peak usage. On the first image, I recognise part…
Ben
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Why is three-phase offset by 120 degrees?

For three phase electricity the wave is offset by 120 degrees(2\$\pi/3\$ Rad). Why aren't the phases closer together? Is it because it will affect the frequency of the phases? How was this 120 degrees chosen?
Dean
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Why don't three-phase transformers use toroidal cores?

When looking at different transformer core designs, three phased, I never see any core designed as a circle or torus. Why is that so? Will it not work as well as the common B-shaped core?
E. l4d3
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Why are the letters U, V and W used in AC motors to represent the windings?

I am connecting up an AC motor and was wondering if this labeling system was representative of something? Or just another set of letter like X,Y,Z? I could not find any information regarding this in IEC 60034-8, Rotating electrical machines – Part…
ElecEnthusiast
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Why does a delta/wye transformer make 30 degrees phase shift ?

I'v heard that a delta/delta or Wye/Wye transformers do not make any phase shift. In delta/wye or wye/delta transformers, There is a 30 degrees phase shift between the primary and secondary coils. So, Why is there a phase shift ? and Why is it 30…
Michael George
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Why are there only 3 wires on this power line?

When I was in Alaska, I saw a high voltage line, but I didn't see the Neutral. Is this because the water is conductive enough next to it to use as neutral? Or is it just two Phases. Where I live, Colorado, all of the power lines have the two…
skyler
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Is 3-phase power in any way better than split-phase power in a residential setting?

My understanding is that in the US (and Canada?) residential units receive split-phase 120V/240V power meaning the voltage between two phases is 2x the line-to-neutral voltage. Here in Europe residential units receive 3-phase 230V/400V power meaning…
QuantumWiz
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Y or Delta connections advantages / disadvantages

I have been studying three-phase systems for the whole course of a subject (on the first year of the university degree). I have finished now, and I know both "Y" (star) or "Delta" (triangle) connections. I have made a lot of computations with them,…
user3780731
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Is there a convention for the ordering of phases in three-phase power in the US?

I recently moved my small machine shop to a new location. Both locations had 3-phase power, and I wired up a 3-phase air compressor in both locations. In both locations, I used the convention of black-red-blue wiring on L1-L2-L3 bus bars in the…
Rick
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How is transition from three-phase distribution without neutral to three-phase consumption with neutral achieved?

A typical distribution grid supplies 6 or 10 kilovolts AC to a substation near the consumers. This is typically done with a three-phase line without neutral - just three wires going in parallel. Then there's a transformer that lowers the voltage to…
sharptooth
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What's the use of the 100 kΩ resistors in this schematic?

I saw a schematic for measuring AC voltage on a 3-phase mains supply (R/Y/B are the 3 phases and N is the neutral) I understand that the 1 MΩ and 2.7 kΩ resistors are for stepping down the voltage (240 V) to a measurable voltage by the…
Saksham Jain
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Single-phase to 3-phase conversion

I have seen some boxes (with some capacitor circuits inside) which do single-phase power supply to 3-phase power supply conversion. The problem with them is that they cause the load motor to heat up, because the phase difference between the legs is…
vivek
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3 phase induction motors with poles not equal to 3x

I am having trouble finding diagrams to show induction motors with poles not equal to 3x. Everything I find is 2 poles per phase. Can anyone explain and help me visualize, for example, a 4 pole 3 phase induction motor?
blindguy
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