AC and DC can coexist and each serve a purpose.
Ac voltage symbol
Here is a short animation showing this principle: Video credit: Khurram Tanvir Generating AC can be compared to our previous water analogy : To generate AC in a set of water pipes, we connect a mechanical crank to a piston that moves water in the pipes back and forth our "alternating" current. Alternating current AC is the flow of electric charge that periodically reverses direction. But what else is AC good for? The degree marks on the horizontal axis of the graph represent the domain of the trigonometric sine function, and also the angular position of our simple two-pole alternator shaft as it rotates: Figure below Alternator voltage as function of shaft position time. Certain sources of electricity most notably, rotary electromechanical generators naturally produce voltages alternating in polarity, reversing positive and negative over time. This is the basic operating principle of an AC generator, also known as an alternator: Figure below Alternator operation Notice how the polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by. The AC in most homes and offices have an oscillating voltage that produces a sine wave. For most purposes, we can assume that the voltage is constant.
The magnitude of the current remains constant as well. At higher frequencies, the power lost to this dissipation becomes unacceptably large.
Time period of sine wave is shown on oscilloscope. Even in the worst-case unbalanced linear load, the neutral current will not exceed the highest of the phase currents.
Ac voltage source
Certain sources of electricity most notably, rotary electromechanical generators naturally produce voltages alternating in polarity, reversing positive and negative over time. When transmitting electrical power over long distances, it is far more efficient to do so with stepped-up voltages and stepped-down currents smaller-diameter wire with less resistive power losses , then step the voltage back down and the current back up for industry, business, or consumer use. If the source varies periodically, particularly sinusoidally, the circuit is known as an alternating current circuit. 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. It is often given as a number between 0 and and measured in degrees. A twisted pair must be used with a balanced signalling system, so that the two wires carry equal but opposite currents. Of course, direct current may be interrupted pulsed through the primary winding of a transformer to create a changing magnetic field as is done in automotive ignition systems to produce high-voltage spark plug power from a low-voltage DC battery , but pulsed DC is not that different from AC.
DC Thomas Edison Image courtesy of biography. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world.
Difference between ac voltage and dc voltage
To explain the details of why this is so, a bit of background knowledge about AC is necessary. As useful as transformers are, they only work with AC, not DC. Find peak and rms value of current. Coaxial cables with an air rather than solid dielectric are preferred as they transmit power with lower loss. In reality, a battery will slowly lose its charge, meaning that the voltage will drop as the battery is used. Cells, batteries and regulated power supplies provide steady DC which is ideal for electronic circuits. Peak voltage is another name for amplitude.
Techniques for reducing AC resistance[ edit ] For low to medium frequencies, conductors can be divided into stranded wires, each insulated from one another, with the relative positions of individual strands specially arranged within the conductor bundle.
For most purposes, we can assume that the voltage is constant.
Often, the number of turns in each coil is set to create a voltage increase or decrease from the powered primary coil to the unpowered secondary coil. Step-up transformer steps voltage up and current down. Transformers provided an inexpensive method to step up the voltage of AC to several thousand volts and back down to usable levels. This current has a unique direction and flows from the negative terminal of a battery to positive terminal. In addition to this mechanical feasibility, electrical resistance of the non-ideal metals forming the walls of the waveguide cause dissipation of power surface currents flowing on lossy conductors dissipate power. Peak voltage is another name for amplitude. If the atmosphere surrounding the machine contains flammable or explosive vapors, the practical problems of spark-producing brush contacts are even greater. This milestone marked the decline of DC in the United States. The use of lower frequencies also provided the advantage of lower impedance losses, which are proportional to frequency. Waveguides[ edit ] Waveguides are similar to coaxial cables, as both consist of tubes, with the biggest difference being that the waveguide has no inner conductor. However, with AC it is possible to build electric generators, motors and power distribution systems that are far more efficient than DC, and so we find AC being used predominantly across the world in high power applications. Generating DC DC can be generated in a number of ways: An AC generator equipped with a device called a "commutator" can produce direct current Use of a device called a "rectifier" that converts AC to DC Batteries provide DC, which is generated from a chemical reaction inside of the battery Using our water analogy again, DC is similar to a tank of water with a hose at the end. Notice that the pinched section of pipe still provides resistance to the flow of water regardless of the direction of flow.
This will likely damage the equipment. A similar method is used for a different reason on construction sites in the UK.
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