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First, consider single-phase 120/240 service like you would find in a house. the two hot wires are said to be 'in phase'.
Think of it this way. Imagine a ruler12 inches long. Put your finger on the six inch mark, the center. How far to each end? Six inches. Both ends are on the same line, just in opposite directions. So if you go six inches one way, and six inches the other way, the total distance is 12 inches.
120/240 volt systems are like that voltage-wise. The middle of the ruler is the neutral, and each end is a hot wire. When one hot leg is going positive, at the exact same time (that's the 'in phase' part) the other leg is going negative. Same line only opposite directions, like our ruler. So the two 120 volt legs just add up to 240.
Now, here's the important part. Since one leg goes positive while the other leg goes negative, they are said to be 180 degrees apart, 360 degrees making up one complete AC cycle (2 X 180 = 360). In three phase power, there are, not two, but THREE hot wires. Since there are three, they can no longer be 180 degrees apart. They are 120 degrees apart (3 X 120 = 360). So, when phase A peaks, phase B has not yet peaked. it is at some intermediate voltage between zero and maximum. The two phases cannot just be added up because of this fact.
Back to our ruler. Break the ruler in half. bend the two halves so the ruler is no longer straight (180 degrees) but bent at an angle of 120 degrees. Draw a line from end to end. See how we have formed a triangle? See also that the line we drew is not 12 inches long, but is shorter (the two ends are closer together)? That's why the voltages in a three phase system do not appear to add up.
Lets make our ruler 240 inches long. If we bend it into the 120 degree angle and measure end-to-end, we will find the length to be about 208 inches, not 240! In a 120/208 three-phase system, each hot leg (phase) measures 120 volts to ground, BUT phase-to-phase measures 208 volts. This is true whether you measure A to B, B to C, or C to A.
The math guys call this a vector sum. The vector is the angle at which the phases are in relation to each other (120 degrees) and the sum is the distance between the two bent ends (phases).
To figure the phase-to-phase voltage, multiply the phase-to-neutral voltage by 1.73 (the square root of 3). Thus: 120 X 1.73 = 208, 277 X 1.73 = 480, etc.
To figure the reverse, divide the phase-to-phase voltage by 1.73. Thus: 480 / 1.73 = 277, 208 / 1.73 = 120, etc.
You trig people see how this relates to our triangle example using the cosine rule.
It should be noted that the use of the term phase above, as in "phase to phase" is not strictly correct, although a common usage. Each hot conductor in a 3-phase system is correctly called a "line", so the correct terminology would be "line to line", "line to neutral", etc.
Wiki User
∙ 11y ago
Wiki User
∙ 12y agoP3-ph = _/3 x VL X IL x cosφ
= 3 x Vp x Ip cosφ
Wiki User
∙ 13y agoA three phase supply has a 120 degree AC voltage difference between phases.
For example: a 240VAC three phase circuit has three phase (hot) leads that measure 120VAC to neutral or ground. The voltage difference between two hot leads is 208VAC (120 * tangent of 120 degrees).
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Is there a difference between three phase and single phase electrical supplies?
Yes, there a difference between three phase and single phase electrical supply services.
What is the difference between a one phase and a three phase motor. And if a three phase motor is given a single phase supply will it run or not?
The difference between a single phase and a three phase motor is the amount of power conductors that feed the device. As to the other part of the question a three phase motor will not start or run on single phase. The phase angles on three phase are 120 degrees apart on a single phase system they are 180 degrees apart.
How is a three phase agricultural motor used when there is no power supply?
With no three phase power supply you can't use a three phase motor of any kind at all!
Difference between two phase and three phase welding machine?
Three phase uses a safety circuit away from the machine, two phases uses you as the safety circuit
Why Scott connection is used to convert three phase to two phase why cant you take two lines from three phase circuit?
In a two-phase connection, the phases are displaced by 90 degrees. Two lines (not 'phases') of a three-phase system will provide a single-phase supply, not a two-phase supply.
Is there a difference between three phase and single phase electrical supplies?
Yes, there a difference between three phase and single phase electrical supply services.
What is the difference between single and three phase on line UPS?
The difference between a single and a three phase online UPS is a 3 phase can supply a 100% unbalanced load on its output without affecting its performance. A single phase cannot supply a 100% unbalanced load on the output without affecting its performance.
Why is there a difference between a domestic and industrial electricity supply?
actually there is no difference between them. However in some counteries, single phase is used for domestic and three phase is used for industrial.
What is the difference between three phase load and phase supply?
How much current equipments are drawing from three phases (combined or individual) is called three phase load and how much supply we are getting from source is called three phase supply. Ex. In INDIA single phase supply is 220 volt ac with neutral. So in three phase supply all RYB phases should be 220 volts ac with neutral individually. If we calculate with phase to phase than it shoulb be 415 volts ac.
What is the difference between a one phase and a three phase motor. And if a three phase motor is given a single phase supply will it run or not?
The difference between a single phase and a three phase motor is the amount of power conductors that feed the device. As to the other part of the question a three phase motor will not start or run on single phase. The phase angles on three phase are 120 degrees apart on a single phase system they are 180 degrees apart.
Single phase and three phase circuit?
Yes, there is a difference between single phase and three phase circuits.
How you can convert 1-phase voltage to 3-phase voltage and vice-vars a?
A single-phase supply is obtained between any two line conductors or between a line and neutral conductor of a three-phase supply. To obtain a three-phase supply from a single-phase source is far more difficult, and requires additional equipment.
What is the difference between a single phase and a three phase inverter?
The Single and Three phase refer to Alternating Current electrical power supply outlet system and the corresponding equipment requirements. The single phase system is generally used thepower requirements are low or moderate as for household applications , while the Three phase supply system is used for High power industrial applications. Thenumbers of phases refer to Alternating Current Supply lines which are delivering the power or the sytem requirement of the equipment for operation. Thus a single phase supply cannot operate a three phase equipment or vice versa. However a ThreePhase supply can be used individually as Three different Single Phase supply systems In case of Three Phase systems the electrical supply waveforms are such that at any given instant there is a 120 degree phase difference between any two supply lines , which also results in higher magnitude of supply voltage than the corresponding single phase supply. Now refering to the inverter which is nothing but a device to convert the electrical supply from one source or magnitude ( typically DC from a Battery Bank ) to the required form and Magnitude. Thus it simply generates the equivalent electrical supply either as Singleor Three Phase , which ideally will be the same as available available from the wall outlet
How do you start a three phase motor to a single phase power supply?
You don't. A three phase motor will not start unless it is connected to a three phase supply.
What is the requirement of three phase to five phase transformation?
If you want a five-phase supply you need to start with a three-phase supply and a transformer that has 15 symmetrical cores. But why would one need a five-phase supply . . three is enough.
How is a three phase agricultural motor used when there is no power supply?
With no three phase power supply you can't use a three phase motor of any kind at all!
Is line to line fault a 3 phase fault?
'Line conductors' are the three 'hot' conductors (A-B-C) that connect a three-phase supply to a three-phase load. In some cases, a pair of line conductors (e.g. A-B, B-C, or C-A) is used to supply a single-phase load. A 'line fault' can be a short-circuit fault between all three, or any two, of these line conductors -whether they supply a three-phase load or a single-phase load.
