Definition of Phase in Electricity
In electrical phase it is the expression of relative displacement between waves that have the same frequency. There are two different ways of looking at phases. First, it is when the voltages are out of phase with each other, as with three-phase power, and second, when the voltage is out of phase with the current.
If you have two different electrical generators, even if they are operating at the same frequency, 60 hertz for example, if you connect them together, you must make sure that they are in phase. In the simplest way, it just means that the voltages should increase and decrease together. If they are not synchronized, they will fight each other. Sometimes, if you do it right, you want your voltages to be out of sync. In industrial situations, particularly with motors, you can get what is called «three-phase» power. This is where you have three wires with the voltages separated from each other by 120 degrees.
The peak of the second sine wave occurs 120 degrees later than the first and the top of the third sine wave occurs another 120 degrees after that. A fourth wire generally provides a reference to ground, making it more efficient than a typical single-phase or «single-phase» power supply, where you only have one wire with a variable voltage and one wire to ground. In addition to efficiency, three-phase power is better than single-phase because there is a constant power output. With only one phase, you may have a good average power, but it constantly changes and has moments, many times per second, where the output power is zero.
If you have three-phase power for the motors, the motors can be smaller and more efficient and do not pulse on their torque because of the constant power input. These three phases also mean that the motors do not require separate starting circuits and give them more torque when they are starting. Finally, obtaining single-phase power from three-phase power is extremely simple: simply do not connect the other two inputs. The other type of phase you should think about is whether the voltage and current are in phase.
With a purely resistive load, as the voltage increases, the current increases at the same exact time. An inductive or capacitive load can cause its current to *lead* or *delay* behind the voltage. So, if you have an inductive load like a motor on your blender or vacuum cleaner, or even a capacitive load, which is less common in residential circumstances, the current and voltage will not synchronize. The current is delayed when the load is inductive.
If you remember, power is voltage times current, so every time the voltage or current is 0, no power is emitted. When it is out of phase in this way, it is called reactive power and is measured in reactive volt-amperes or VAR. Engineers like to use imaginary numbers and phase angles to describe this, and while it may seem scary, those are just mathematical ways of describing that phase difference.
What Is Single Phase ?
A single phase installation means that the line is connected to one of the phases and also to the neutral. The electricity flowing into your building is alternating current and flows in and out continuously by reversing its direction 50 times per second. In power systems, single-phase supply is usually used for appliances where the amount of load required is small.
From the secondary distribution, we get one wire as phase and the other wire as neutral. One phase and neutral are used together to provide a single-phase power supply. The single-phase power supply uses alternating current (AC) to distribute to domestic homes. In a 1-phase supply, the voltage varies sinusoidally with respect to the time period.
Since the voltage of a single-phase supply meets the maximum value of twice, the instantaneous power is not constant. For a single-phase system, 240V is supplied that sufficiently satisfies the needs of domestic users. A single-phase system is not suitable for motors with high ratings. The standard frequency of the single-phase system is 50 Hz and varies from country to country.
Advantages of a Single-Phase System
- The single-phase system can be applied to small loads.
- The complexity of the 1 phase system design is less.
- The operating cost is less.
Disadvantages of the Single Phase System
- Single-phase cannot be applied for heavy loads.
- Single-phase, when connected to an electric motor, cannot develop a rotating magnetic field.
- Single-phase motors require some additional equipment for starting.
- The disadvantages of the single-phase system can be overcome in a three-phase supply system.
What is a Three-Phase System ?
It operates a three-phase system at 415v that is supplied to industries where heavy engines will be executed. In a three-phase system, waves travel at one frequency and current waves vary alternately between zero and peak values. The individual phases are separated from each other by an angle of 120 degrees.
Advantages of a Three-Phase System
- A three-phase system is more economical than a single-phase system because it requires less conductive material than a single-phase system.
- High industrial loads can be operated by a three-phase system.
- Highly reliable.
- Requires less maintenance.
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