What is three phase?

[[2574]]

Can anyone offer a succinct explanation of 3 phase please? I think it is 440v but other than that I don't know much; how does it differ from 240v and what is the purpose? I understand that it is typically used for heavy commercial applications; is it just a higher voltage to deliver more power through thin wires? (as do the high voltage (400kv) national power distribution lines)

 

[Highndry]

From Wikipedia:

Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors. A single-phase supply connected to an alternating current electric motor does not produce a revolving magnetic field; single-phase motors need additional circuits for starting, and such motors are uncommon above 10 or 20 kW in rating.

In contrast, in a three-phase system, the currents in each conductor reach their peak instantaneous values sequentially, not simultaneously; in each cycle of the power frequency, first one, then the second, then the third current reaches its maximum value. The waveforms of the three supply conductors are offset from one another in time (delayed in phase) by one-third of their period. When the three phases are connected to windings around the interior of a motor stator, they produce a revolving magnetic field; such motors are self-starting.

Standard frequencies of single-phase power systems are either 50 or 60 Hz. Special single-phase traction power networks may operate at 16.67 Hz or other frequencies to power electric railways.

I remember in my first job on leaving school I worked for a manufacturer of woodworking machines which for the UK were all 415 volts, three phase, 50Hz.

 

[Salty John]

It's a system of power distribution that reduces the wiring cost of an installation, especially when high voltages and large electric motors are involved. Single phase systems require two wires of a particular size to carry a particular current - in a 3 phase system 50% more power can be carried with the addition of only one more wire. And it simplifies the wiring of large HP electric motors in the system.

Clear as mud?

 

[tommydortez]

Can anyone offer a succinct explanation of 3 phase please? I think it is 440v but other than that I don't know much; how does it differ from 240v and what is the purpose? I understand that it is typically used for heavy commercial applications; is it just a higher voltage to deliver more power through thin wires? (as do the high voltage (400kv) national power distribution lines)

I'd speak to these guys in regards to anything electrical, really pleasant mannered and had alot of time for me on the phone... http://thepowersite.co.uk/

 

[[3889]]

Also used to supply a building with separate single phase supplies e.g. three flats in a block which will each use a 230V single supply.

 

[sailorman]

Can anyone offer a succinct explanation of 3 phase please? I think it is 440v but other than that I don't know much; how does it differ from 240v and what is the purpose? I understand that it is typically used for heavy commercial applications; is it just a higher voltage to deliver more power through thin wires? (as do the high voltage (400kv) national power distribution lines)

How does this fit into a yacht

 

[Daydreamer]

A simple way of visualising it is as three single phase lives with a common neutral (although a neutral is not necessarily used). The single phases are each 120degrees (1/3 of a circle) separated so there is a potential difference between any two and all three wires. Its this phase difference that is used to power motors in particular.

 

[sailorman]

More a Lounge question. This has nothing to do with the average Practical boat

 

[tommydortez]

More a Lounge question. This has nothing to do with the average Practical boat

answering your own question?...

 

[sailorman]

answering your own question?...

NO Stating fact

 

[tommydortez]

NO Stating fact

Me too...

 

[VicS]

More a Lounge question. This has nothing to do with the average Practical boat

Its a request for practical information. .... This is therefore the appropriate forum ...... it is not restricted to boaty subjects ......

Lounge is for views, observations, ramblings, rants, jokes and banter and other simmilar krap and bullsh-it

 

[Lakesailor]

A simple way of visualising it is as three single phase lives with a common neutral (although a neutral is not necessarily used). The single phases are each 120degrees (1/3 of a circle) separated so there is a potential difference between any two and all three wires. Its this phase difference that is used to power motors in particular.

I found this diagram made it easier to visualise

 

[sailorman]

Me too...

Share practical, hands-on information, hosted by Practical Boat Owner magazine.

 

[VicS]

Can anyone offer a succinct explanation of 3 phase please? I think it is 440v but other than that I don't know much; how does it differ from 240v and what is the purpose? I understand that it is typically used for heavy commercial applications; is it just a higher voltage to deliver more power through thin wires? (as do the high voltage (400kv) national power distribution lines)

Succinct ..... difficult!

Three phase used for generation and distribution uses three live conductors but no neutral. Various voltages used, stepping up from the generator to the very high supergrid voltages then back down again progresively to the consumer.

The voltage in the three phases are out of step with each other by 120° and the quoted voltage is what you will measure between any two of them.

A neutral is introduced at the final local step down transformer.

Domestic properties will normally be supplied with a single phase and the neutral but different properties in the road will be connected to different phases to equalise the load. The quoted voltage is what you will measure between the live phase and the neutral.

Commercial properties may have a full 3 phase supply. there phase eqipment will use the three live phases but single phase equpment will be connected to circuits using just one phase and the neutral.

Large commercial users may have higher voltage 3 phase supplies connected.

Lakesaillor has found a good diagram ( although the red, blue, yellow colour code is out of date)

 

[chewi]

A simple way of visualising it is as three single phase lives with a common neutral (although a neutral is not necessarily used). The single phases are each 120degrees (1/3 of a circle) separated so there is a potential difference between any two and all three wires. Its this phase difference that is used to power motors in particular.

The power provided by each phase varies throughout the cycle, but they add up so that the total power is smooth and consistent throughought the 50hz cycle, not pulsing at 50hz like single phase motor does.


nb 3 phase is also used in some small generators, eg motorcycle engines, where the AC generated then goes through a 3 phase rectifier to get a smooth DC output.

 

[oldvarnish]

More a Lounge question. This has nothing to do with the average Practical boat

Actually, it does. On my pontoon, there a strong warnings that sockets one one side of the pontoon may be on a different phase to those on the others. Therefore, there may be 415V between them.

The practical advice, from a boaty point of view, is to stay well clear of three phase at all times.

 

[Bru]

Succint explanation of the difference ...

Single phase 230v shock ... "ow, bugger"

Three phase 415v shock ... "aaaaaaarrrrrrgggggghhhhhhh" <smoulder> <shake> <die>

Ask me how I know! (I managed to narrowly avoid the final stage though)

 

[sailorman]

Actually, it does. On my pontoon, there a strong warnings that sockets one one side of the pontoon may be on a different phase to those on the others. Therefore, there may be 415V between them.

The practical advice, from a boaty point of view, is to stay well clear of three phase at all times.

Especially on a pontoon where single phase is obviously safer

 

[Lakesailor]

Lakesaillor is out of date

An accusation that seems to follow me around.