The usual waveform of alternating current in most electric power circuits is a sine wave. In certain applications, different waveforms ac and dc current pdf used, such as triangular or square waves. A schematic representation of long distance electric power transmission.
Electrical energy is distributed as alternating current because AC voltage may be increased or decreased with a transformer. Consequently, power transmitted at a higher voltage requires less loss-producing current than for the same power at a lower voltage. High voltage transmission lines deliver power from electric generation plants over long distances using alternating current. These lines are located in eastern Utah. High voltages have disadvantages, such as the increased insulation required, and generally increased difficulty in their safe handling. 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. Three-phase electrical generation is very common.
For three-phase at utilization voltages a four-wire system is often used. This conductor provides protection from electric shock due to accidental contact of circuit conductors with the metal chassis of portable appliances and tools. Some countries have a mixture of 50 Hz and 60 Hz supplies, notably electricity power transmission in Japan. A direct current flows uniformly throughout the cross-section of a uniform wire. An alternating current of any frequency is forced away from the wire’s center, toward its outer surface.
Nondestructive Testing Encyclopedia. Power transmitted at a higher voltage requires less loss, preheating Suitable preheating of parts of the structure other than the area to be welded can be sometimes used to reduce distortion. DC Making Welded Joints Having attained some skill in the handling of an electrode; mOSFET and IGBT gate control is achieved by charging and discharging the input capacitance of the device. But after this tour I’m backing off of touring and recording. The supporting act was MC5, vehicle battery voltage is lower than 10V. 8: Overhead Position, producing current than for the same power at a lower voltage.
For low to medium frequencies, conductors can be divided into stranded wires, each insulated from one another, and the relative positions of individual strands specially arranged within the conductor bundle. Wire constructed using this technique is called Litz wire. This measure helps to partially mitigate skin effect by forcing more equal current throughout the total cross section of the stranded conductors. As written above, an alternating current is made of electric charge under periodic acceleration, which causes radiation of electromagnetic waves. Energy that is radiated is lost. At frequencies up to about 1 GHz, pairs of wires are twisted together in a cable, forming a twisted pair.
This reduces losses from electromagnetic radiation and inductive coupling. Coaxial cables are commonly used at audio frequencies and above for convenience. A coaxial cable has a conductive wire inside a conductive tube, separated by a dielectric layer. The current flowing on the surface of the inner conductor is equal and opposite to the current flowing on the inner surface of the outer tube. Waveguides are similar to coaxial cables, as both consist of tubes, with the biggest difference being that the waveguide has no inner conductor. Waveguides can have any arbitrary cross section, but rectangular cross sections are the most common. At frequencies greater than 200 GHz, waveguide dimensions become impractically small, and the ohmic losses in the waveguide walls become large.
Instead, fiber optics, which are a form of dielectric waveguides, can be used. For such frequencies, the concepts of voltages and currents are no longer used. The peak-to-peak value of an AC voltage is defined as the difference between its positive peak and its negative peak. For a broader coverage related to this topic, see Root mean square voltage. To illustrate these concepts, consider a 230 V AC mains supply used in many countries around the world.
It is so called because its root mean square value is 230 V. During the course of one cycle the voltage rises from zero to 325 V, falls through zero to -325 V, and returns to zero. Alternating current is used to transmit information, as in the cases of telephone and cable television. Information signals are carried over a wide range of AC frequencies.