In a power plant , energy is generated at a convenient voltage for the design of a generator , and then stepped up to a high voltage for transmission. Near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary somewhat depending on the country and size of load, but generally motors and lighting are built to use up to a few hundred volts between phases.
The voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world.
High-voltage direct-current HVDC electric power transmission systems have become more viable as technology has provided efficient means of changing the voltage of DC power. Transmission with high voltage direct current was not feasible in the early days of electric power transmission , as there was then no economically viable way to step down the voltage of DC for end user applications such as lighting incandescent bulbs.
Three-phase electrical generation is very common. In practice, higher "pole orders" are commonly used. The advantage is that lower rotational speeds can be used to generate the same frequency. If the load on a three-phase system is balanced equally among the phases, no current flows through the neutral point.
Even in the worst-case unbalanced linear load, the neutral current will not exceed the highest of the phase currents. Non-linear loads e. Harmonics can cause neutral conductor current levels to exceed that of one or all phase conductors.
For three-phase at utilization voltages a four-wire system is often used. When stepping down three-phase, a transformer with a Delta 3-wire primary and a Star 4-wire, center-earthed secondary is often used so there is no need for a neutral on the supply side. For smaller customers just how small varies by country and age of the installation only a single phase and neutral, or two phases and neutral, are taken to the property.
For larger installations all three phases and neutral are taken to the main distribution panel. From the three-phase main panel, both single and three-phase circuits may lead off. Three-wire single-phase systems, with a single center-tapped transformer giving two live conductors, is a common distribution scheme for residential and small commercial buildings in North America.
This arrangement is sometimes incorrectly referred to as "two phase". A similar method is used for a different reason on construction sites in the UK. Direct current DC is the flow of electric charge in only one direction.
It is the steady state of a constant-voltage circuit. Most well-known applications, however, use a time-varying voltage source. Alternating current AC is the flow of electric charge that periodically reverses direction. If the source varies periodically, particularly sinusoidally, the circuit is known as an alternating current circuit.
The most common type of AC is the sine wave. The AC in most homes and offices have an oscillating voltage that produces a sine wave. Other common forms of AC include the square wave and the triangle wave: Square waves are often used in digital and switching electronics to test their operation.
Triangle waves are found in sound synthesis and are useful for testing linear electronics like amplifiers. For this example, we will use the common sine wave. There are three parts to a sine wave: amplitude, frequency, and phase. Looking at just voltage, we can describe a sine wave as the mathematical function: V t is our voltage as a function of time, which means that our voltage changes as time changes.
The equation to the right of the equals sign describes how the voltage changes over time. VP is the amplitude. The sin function indicates that our voltage will be in the form of a periodic sine wave, which is a smooth oscillation around 0V. This is given in the form of hertz or units per second. The frequency tells how many times a particular wave form in this case, one cycle of our sine wave - a rise and a fall occurs within one second.
As time varies, our waveform varies. Phase is a measure of how shifted the waveform is with respect to time. It is often given as a number between 0 and and measured in degrees.
But it should be noted that in such cases, the projection of the rotating phasor on the vertical axis will not give the instantaneous value of that alternating quantity. There are three parts to a sine wave: amplitude, frequency, and phase. Harmonics can cause neutral conductor current levels to exceed that of one or all phase conductors. Voltage is simply energy or work per coulomb and cannot be classified as a vector. It is often given as a number between 0 and and measured in degrees.
Applications Home and office outlets are almost always AC. Voltage is simply energy or work per coulomb and cannot be classified as a vector.
But it should be noted that in such cases, the projection of the rotating phasor on the vertical axis will not give the instantaneous value of that alternating quantity. Three-phase electrical generation is very common. This device is a special type of electrical generator designed to produce alternating current. A low frequency eases the design of electric motors, particularly for hoisting, crushing and rolling applications, and commutator-type traction motors for applications such as railways. It is often given as a number between 0 and and measured in degrees.
We can turn to our trusty outlet for a good example of how an AC waveform works. Waveguides have dimensions comparable to the wavelength of the alternating current to be transmitted, so they are only feasible at microwave frequencies. Notice that, as we predicted, the voltage rise up to V and down to V periodically. The mathematical expression for is given by. Such lines are called the phasors and the diagrams in which phasors represent currents, voltages and their phase difference are known as phasor diagrams. The voltage and current are sinusoidal and are in phase for a simple resistance circuit.
Waveguides have dimensions comparable to the wavelength of the alternating current to be transmitted, so they are only feasible at microwave frequencies. Notice that the pinched section of pipe still provides resistance to the flow of water regardless of the direction of flow. When talking about AC since the voltage changes constantly , it is often easier to use an average or mean.
Higher voltages mean lower currents, and lower currents mean less heat generated in the power line due to resistance. Each wire in a twisted pair radiates a signal, but it is effectively cancelled by radiation from the other wire, resulting in almost no radiation loss.
The rotation of the wire can come from any number of means: a wind turbine, a steam turbine, flowing water, and so on. Phase Difference When two alternating quantities, say, two emfs, or two currents or one voltage and one current are considered simultaneously, the frequency being the same, they may not pass through a particular point at the same instant. This will likely damage the equipment. Three-phase electrical generation is very common. A low frequency eases the design of electric motors, particularly for hoisting, crushing and rolling applications, and commutator-type traction motors for applications such as railways. Effects at high frequencies[ edit ] Play media A Tesla coil producing high-frequency current that is harmless to humans, but lights a fluorescent lamp when brought near it A direct current flows uniformly throughout the cross-section of a uniform wire.
As time varies, our waveform varies.
Alternating current AC is the flow of electric charge that periodically reverses direction. Voltage is simply energy or work per coulomb and cannot be classified as a vector. However, if several voltage phasors are to be used in the same phasor diagram, they should all be drawn to the same scale. The phasor diagram drawn in rms values of the alternating quantities helps in understanding the behavior of the ac machines under different loading conditions.