This Answer is the same as the for the Question 'Why is power for a country's mains grid usually generated as 3-phase electricity not single phase?'
Single phase power has a sine wave voltage that crosses zero before reversing its polarity. In the region near the zero-crossing there is not much power. At zero there is none at all. So single phase loads often need some trickery to deliver output in this area. Often it is just the inertia of the motor or appliance.
Three phase power is always delivering power on one of its phases, and is thus preferred for machines, motors and appliances that use lots of power.
Three phase power generation is preferred if the application needs very high power, or nees relatively small power output but with with weight restrictions - as in automobiles, where the power is generated in a 3-phase alternator and then converted to DC using rectifiers!
Use of DC (Direct Current) is the next step up for smooth high-power devices but requires rectification, regulation and smoothing to be useful.
Another problem with DC is that, for efficient long distance transmission, it cannot be simply converted to much higher voltages than the voltage at which it was generated at the power station.
Similarly DC cannot - simply by using Transformers - be converted down to safer, much lower AC mains voltages for use by consumers.
Conversion of DC to AC requires the use of expensive high-power electronic "power inverter" systems and the opposite - the conversion of high-power AC to DC - requires the use of very big power rectifiers.
AC (Alternating Current) is used for high power generation and distribution because it can easily be transformed, using transformers, to achieve very efficient power transmission over very long distances and can then be transformed down to low voltages for distribution to consumers.
Two phase, and higher multi-phases are also used, but very rarely, for a few very specialised applications.
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A three phase system provides constant torque, whereas single phase does not.
With three phase you will get more power per kilogram of metal to generate electrical energy.
AnswerFor a given load, a three-phase supply uses less copper than a single-phase system. In other words, it's more economical!
In US residential single phase service you have two hots, in phase with each other.
In a 3 phase system you have 3 hots, out of phase with each other.
From Wikipedia:
Three phase power does "work" more efficiently than single phase power. The way the waveforms of the three different phases line up cause electric motors (for example) to output more torque with less current draw than the same voltage supplied through single phase power. Three phase power is usually used in industrial machinery where a lot of power is needed (and energy cost is a concern).
There is no particular disadvantage to having a residential three-phase supply; in fact, such supplies are quite common in some European countries, such as here in Cyprus.
There is absolutely no need to obtain special appliances, as ordinary single-phase appliances can be easily connected to a three-phase supply: they are simply connected between line and neutral (230 V in Europe).
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Motors of the same horsepower are smaller.
For other items since you usually have a higher voltage, it decreases the amps required and the size of wire necessary. You also seriously decrease the number of amps leaving the building on the neutral.
With three-phase transmission a given amount of power can be transmitted with half the amount of wire. That is because only three live wires are needed, while for single phase of the same voltage to earth, each of the three live wires needs a neutral wire of the same size.
If you are asking why do we use three-phase for transmission/distribution, then the answer is simple: economy. For both overhead and underground systems, it can be shown that three-phase distribution uses less copper(or aluminium) than single phase distribution for a given load. However, the most economical method, in terms of copper usage, is a direct-current system -but, of course, changing voltage levels of DC is far more complicated than for AC systems.
If, on the other hand, you are asking why a three-phase supply might be more useful than single phase to a consumer, then the answer is that three-phase motors are self-starting and, for a given load, more compact and lighter than the corresponding single-phase motor. So, for consumers with motor loads, three phase would be a better choice than single phase.
For a given load, a three-phase system uses less volume of copper in its conductors and supply equipment, so is more economical than a corresponding single-phase system. It also supplies energy continuously, rather than in a pulsing manner. Finally, three-phase supplies create naturally-rotating fields in induction motors -allowing them to self-start.
Three phase power is more efficient at running motors. The advantage of 3 phase becomes greater the larger the motor is. Three phase motors do not have to rely on capacitors to start or run.
The national electrical grid.
First house lighting systems are single phase not three phase. To connect a generator to the house lighting system for emergency power, it would take an electrician to do the job properly. The biggest concern would be to isolate the rest of the service from the main distribution supply service and then isolate the rest of the distribution panel loads from the lighting loads.
A series is an electric circuit with a single path.A parallel circuit is an electric circuit with multiple paths.
cheap,quiet,long lifetime for motor
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All high-voltage distribution systems are three-phase. Single-phase 'spurs' off the main line, supplying, for example, farm houses, are simply two lines of a three-phase system.
The national electrical grid.
Advantages to single-user, single-tasking operating systems are, the computer is dedicated to one particular task at a time. No other aspect of the computer is shared in that moment. Disadvantages are tasks may take much longer to complete.
Advantages to single-user, single-tasking operating systems are, the computer is dedicated to one particular task at a time. No other aspect of the computer is shared in that moment. Disadvantages are tasks may take much longer to complete.
Single-phase electric power refers to the distribution of electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors.Do you know that there is a proposed 800-mile high-voltage direct current transmission line from Oklahoma to Tennessee?Read more about it by clicking on the link.AnswerA single-phase transformer is a simple transformer which will either step up, or step down, a single-phase voltage. A single-phase supply is a two-conductor alternating-current system, comprising a line conductor and a neutral conductor.As most high-voltage electrical distribution systems are three-phase systems, comprising three line conductors, a single phase distribution transformer's primary (high voltage) winding is connected between any two of the three high-voltage line conductors. As far as the secondary (low voltage) winding is concerned:in Europe, one end of the winding is earthed and provides the neutral terminal , while the opposite end provides the line terminal (L)in North America, the winding is centre tapped and grounded, providing the neutral terminal, while opposite ends of the winding provide the line terminals L1 and L2
The primary advantage is that, for a given load, a three-phase system requires less copper for tranmission/distribution than an equivalent single-phase system would require. Other advantages include the fact that three-phase machines are smaller than single-phase machines of similar rating.
The mean of a sample is a single value and so its distribution is a single value with probability 1.
advantages of executive
Single Touch Systems was created in 2001.
Consider a binomial distribution with 10 trials What is the expected value of this distribution if the probability of success on a single trial is 0.5?
The binomial distribution is defined by two parameters so there is not THE SINGLE parameter.
Advantages to single-user, single-tasking operating systems are, the computer is dedicated to one particular task at a time. No other aspect of the computer is shared in that moment. Disadvantages are tasks may take much longer to complete.