difference between single phase and three phase

KeepItSimpleStupid

Homework, again?

KingsX

Ya, wouldn't wikipedia be easier and faster? When I was in school, I had to look it up in an encyclopedia. Granted back then, they were books. No wait, punchcards! Nah, just books...

KeepItSimpleStupid

Oh, remember the keypunch machine. Definately not instant gratification. And 65 MB removeable disc drives the size of a washing machine.

KingsX

Those were the days though! You programmed computers to do what you wanted, you didn't just turn them on and go to facebook or whatever. It was kind of like building a car and then driving it, as apposed to just buying one and driving it. Well sort of anyway...

KeepItSimpleStupid

When the 4004 and the 8008 processors were out, for class our group built a computer of sorts out of small scale integrated circuits like flip-flops, 16 bits x 16 word memory chips, gates etc. The designed microcode was 16 bits wide and the memory was 16 words. We designed an instruction set and program that could sort numbers in ascending or decending order. It was fun to watch.

sarnian

sean58

See this Wikipedia link that provides details on single and three phase

Another simple but interesting link on the same

Success

brianfray

First off, unless you are an industrial business you can't really get three phase power. It takes special wiring and meters from the power company.

Three phase works by using three supply wires that carry different voltage, 220-240 volts like most homes and another one that is split off to 110-120 volts. The difference is, in three phase, different voltage is delivered on 3 legs, not 2. One example is two legs of 110-120 volts and a third leg of 208 volts. While there are different world standards of "three phase", It is basically, 3 times the line to neutral voltage ratio.

This saves energy, because the motor does not work as hard, just like 220 volt air conditioners and clothes dryers don't work as hard as 110 volt models do.

KeepItSimpleStupid

brianfray's post has a LOT of innacuracies.

1. Three phase power IS available to RESIDENTAL users in SELECT locations.
2. 3 phase "Y" is norally delivered as 208V at the lower voltages. 120 V has to come from a transformer.

2 legs and 3 legs may be confusing as the term does not include the neutrals and grounds.

Saves energy. Not necessarily. The energy savings really depends on the motors load. 3 phase motors will get you higher starting torque. They also have less moving parts.

Higher voltages are used because the current is less and it makes the wirig more manageable. Ranges, air conditioners, water heaters all use higher voltages.

3 phase makes it easier to control the speed, so your actually seeing three phase motors in a single phase appliance such as a heater

Newton1Law

Depending on where you live you may find that three phase 208 Wye / 120 volt is the normal supply for a Customer. In many Urban areas the normal supply will be from an underground network operating on 208 Wye/120 volt system using 4 wire (three phase wires and one netural wire) systems. Many utilities require you to take a three phase service if your load levels require a 200 amp service or greater. If you take service at 100 amps then you are supplied 208/120 volt service. This actually 2 of the 3 phase wires and one netural wire from the utility.

As to your question as to what is the difference between 3 phase and single phase, the vast majority of generators in this country operate as three phase ground Y (wye) systems. This will mean that the system will typically have 4 wires extending from the generator usually at about 13,000 to 15,000 volts as measured between any two of the three phase wires. A check of the voltage between any phase wire to the grounded fourth wire will give a voltage around 7500 volts.

They utility company may use all three phase wires and the fourth netural wire to connect a transformer bank (multiple single phase transformers connected across all three phases) and supply a three phase service. They may also use only one of the phase wires and connect a transformer between that phase and the ground wire. When they do this, the service is usually refered to a a "Single Phase" service.

Hope this helps.