Alternating Currents
Alternating currents (AC) are electrical currents that periodically change direction, oscillating back and forth. Unlike direct currents (DC), which flow in one direction, AC reverses direction at regular intervals. This type of current is commonly used in homes and businesses to power electrical devices and is the standard form of electricity delivered to households.
8 Key excerpts on "Alternating Currents"
eBook - ePub- Lawrence Thompson(Author)
- 2006(Publication Date)
- International Society of Automation(Publisher)
...Chapter 9 AC FUNDAMENTALS Alternating current (AC) is the most naturally occurring form of energy in the universe. If you have a fair grasp of direct current (DC) then alternating current is a relatively easy concept. It is essential that you understand the behavior of alternating current. Most of the modern world uses these behaviors to run industry, provide information, support medical therapies, the list of uses is endless. To understand AC is to understand the why of modern technology. ALTERNATING CURRENT DEFINED Alternating current (AC) is defined as an electrical current that changes amplitude continuously and periodically changes polarity. A little investigation will show that we have already discussed most of the concepts of AC. For example, it still obeys Ohm’s Law (for the instantaneous amplitude and polarity it exhibits at any selected moment). Understanding alternating current only requires a modification of what you’ve already learned. The following explanation, though simplistic, it is also quite true: we can simulate AC by a switched or square wave and this will meet our definition for changing amplitude and periodically changing phase. Figure 9–1 is an illustration of the procedure for mechanically generating a form of AC using two batteries and a switch. The wave-form is the voltage across the resistor as a result of the present switch condition plus each switch condition prior to this condition, so there is history in the wave-form (in all wave-forms). The wave-form is a graphic (or actually, a graph) of the voltage across the resistor for a period of time and, in our case, in a number of different switch conditions. Note that the switched wave-forms fit the description (almost) of alternating current...
- Dale Crane, Dennis Wilt(Authors)
- 2017(Publication Date)
- Aviation Supplies & Academics, Inc.(Publisher)
...It is current that produces heat and uses power, so by decreasing the current, large amounts of electrical power can be moved with very small losses. At the point the electricity is used, it is passed through another transformer to lower its voltage to a usable value and step its current back up. Alternating Current Terms and Values Before discussing the generation of AC, some of its unique terms and flow characteristics must be understood. Waveform waveform. The visual or graphic shape of an electromagnetic wave as seen on a cathode-ray oscilloscope. cycle. A complete series of events that recur regularly. alternation. One half of a cycle of alternating current or voltage. frequency. The number of cycles of alternating current that takes place in one second. period. The length of time required for one cycle of alternating current. In AC, current begins to flow in one direction, reaches a peak, slows down, and stops. Then it reverses its direction. One complete sequence of events, starting and stopping the flow in both directions, is called one cycle, and the number of cycles that take place in one second is called the frequency of the AC. Commercially produced AC in the United States has a frequency of 60 cycles per second and is called 60-hertz AC. Some foreign countries use 50-hertz AC, and most aircraft AC electrical systems use 400-hertz AC. Alternating current can be produced with almost any wave shape needed for special applications, and with almost any frequency. High-frequency AC produces electromagnetic radiation that makes radio and television possible, and AC can be easily and efficiently rectified, or converted to DC, when it is needed to keep batteries charged and for other applications that require DC. AC produced by a rotary generator has a smooth waveform whose amplitude follows a sine curve. The instantaneous value of the AC is proportional to the sine of the angle through which the conductor has moved through the magnetic field. Figure 3-1...
eBook - ePubFundamentals of Electric Machines: A Primer with MATLAB
A Primer with MATLAB
- Warsame Hassan Ali, Matthew N. O. Sadiku, Samir Abood(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
...3 Alternating Current Power Setting goals is the first step in turning the invisible into the visible. Anthony Robbins Alternating Current (AC) is used in large areas and in all different life facilities, for ease of generating. AC generators are electrical machines that operate on the principle of electromagnetic induction to generate electric power. AC is defined as the current whose value and direction change continuously over a period on a wave called the sinusoidal wave and as shown in Figure 3.1. The advantages of alternating current are as follows: 1. Changes in value and direction and the polarity are not fixed 2. Generates mechanical methods by cutting magnetic fields such as generators 3. Widely used 4. Low cost of production, especially when generated with large power 5. It can be changed to constant current using electrical components 6. It can be converted from low voltage to high voltage and vice versa using electric transformers 7. It can transfer to long distances using high voltage towers. 3.1 Sinusoidal Wave Cycle and Frequency The complete cycle of the sinusoidal, or the sine wave, is called the period, and the number of oscillations per second is called the frequency, and it is denoted by the letter F. From Figure 3.2, the portion between the two points (A–B) is called the full wave, the part bound between (A–C) is called half the positive wave, and (C–B) is called half the negative wave...
eBook - ePub- S. Bobby Rauf(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...So, AC could be generated at, for instance, 4,000 V, stepped up to 100,000 V – through the application of transformers – for transmission purposes, and miles away, it could be stepped down to usable levels, such as 480 V, 240 V, or 120 V. That is, mostly, the way AC is generated, transmitted, and distributed to consumers today. We learned earlier that movement of electrons, or other charged particles, constitutes electrical current. When the charged particles move in one specific direction – such that there is a net displacement in their position or when the charged particles travel a net distance – direct current or DC is said to exist. On the other hand, when the electrons or charged particles oscillate or vibrate about a point – similar to a pendulum – such motion of charged particles constitutes alternating current or AC. If voltage and current were plotted on Cartesian coordinates, the resulting graphs would be as depicted in Figures 3.2 and 3.3, respectively. In fact, if AC voltage, DC voltage, and current were compared using an oscilloscope, the graph displayed on the screen would be similar to voltage and current graphs shown in Figures 3.2 and 3.3, respectively. However, the inception of AC voltage or current is better depicted in Figure 3.1, where X represents voltage or current, X(°/t) simply denotes a voltage or current signal varying as a function of time, +X m represents the positive maximum or peak value of voltage or current signal, and −X m represents the negative minimum value of voltage or current signal. FIGURE 3.1 AC generation, a plot of amplitude versus degrees of rotation. FIGURE 3.2 Voltage comparison, AC versus DC. FIGURE 3.3 Current comparison, AC versus DC. Examination of Figures 3.2 and 3.3 shows that the Y-axis (or abscissa) represents time, t, in seconds...
eBook - ePub- Bill Mantovani(Author)
- 2019(Publication Date)
- In Easy Steps Limited(Publisher)
...5 Single Phase AC Circuits Learn how AC differs from DC, and of the phase relationship between current and voltage. Also learn new measurement terms and how waveforms can be observed with an oscilloscope. AC (Alternating Current) AC Terminology Series AC Circuits R, L, and C in Series Power in an AC Circuit AC Circuit Measurements Rectifier Circuits Safety First AC (Alternating Current) So far we have mainly considered voltage as being from a DC source, such as a battery where the voltage delivered is of a positive value even when the battery loses energy and needs recharging or replacing. The polarity is fixed; so, too, is the direction of the “direct current” as (by convention) it travels from the positive to the negative terminal. However, not all electronic circuits or devices use a battery as a power source. Many derive the necessary DC from an AC mains adapter that converts the high-voltage AC supply into a low-voltage DC supply to power the equipment. Such power supplies are covered later in Chapter 11, but first we need to look at alternating current in more detail. Mains electricity is a term used in the UK and Canada, whereas US terms include wall power, domestic power, and grid power. They all refer to the alternating current (AC) electric power supply. Mains electricity supply You will remember from the section on magnetism that alternating current electricity is generated by means of a coil rotating within a magnetic field. It is easier and cheaper to produce AC than DC, plus AC is far easier to distribute. Domestic mains electricity in the UK is historically stated as a single phase 240 V AC supply (but see below) with a frequency of 50 Hz (Hertz) and is delivered to houses via the National Grid. Transformers at the power stations where the electricity is generated step up the voltage into many kilovolts so that it can be easily distributed along power lines with little energy loss...
- S. Bobby Rauf(Author)
- 2021(Publication Date)
- River Publishers(Publisher)
...Chapter 3 Alternating Current (AC) Fundamentals Introduction This chapter begins with an introduction to AC, i.e., alternating current, and segues into a comparison between AC and DC. This comparison accentuates the complexity of AC as compared with DC due to the use of complex numbers and vectors for complete representation of AC entities and parameters. In this chapter, we get an opportunity to appreciate how the complexity of AC is amplified by three-phase AC consideration in more common, industrial, and commercial applications. In an effort to allow readers ample opportunity to explore and learn basic, single, and three-phase AC principles and mathematical computations, we introduce various single and three-phase AC functions, equations, and mathematical techniques, reinforced by examples and self-assessments problems. The depth to which the readers may endeavor to explore the topics in this chapter depends on their need, appetite, and aptitude. Due to the practical applications of the process of electrodeposition in the coatings industry ― and the innate relationship between electrodeposition and electricity ― this process will be defined and illustrated through equations and practical numerical examples. This chapter provides the reader an introduction to AC electrical transformers of various types: single-phase and three-phase. Of course, similar to other topics in this text, the concepts, principles, equations, and applications in this chapter are illustrated with analogies, numerical examples, and end-of-the-chapter problems. All in all, this chapter provides an adequate introduction to alternating current and prepares the reader for intermediate level study of AC concepts. A LTERNATING C URRENT (AC) V ERSUS D IRECT C URRENT (DC) The contrast between AC and DC isn’t just rooted in physics but goes as far back as the 1800s when, for a period of time, both vied for the residential, commercial, and industrial markets...
eBook - ePubElectrical Engineering
Fundamentals
- Viktor Hacker, Christof Sumereder(Authors)
- 2020(Publication Date)
- De Gruyter Oldenbourg(Publisher)
...7 Alternating current technology Alternating current technology is an important area of electrical engineering as the public electricity supply happens through AC/three-phase AC technology. The high-power consumption in the public supply (which in Europe is a three-phase supply) is covered through power generation in power plants. 73 A generator creates sinusoidal alternating voltages. In order to transmit electric power over a great distance with little losses (power loss P = I 2 ⋅ R), the current I must be small. The current is low at the same power (P = V·I), if the voltage, in contrast to the current, is increased. 74 The level of voltages is technically adjusted with transformers in a simple and efficient way (“transformed”). Transformers work with Alternating Currents due to their mode of action. 75 Depending on the distance for the power to be bypassed and the power to be distributed, different specific voltage levels are chosen. By means of alternating current technology electrical energy can be produced and distributed easily. You can directly operate low-maintenance and technically simple engines (asynchronous motors) on a three-phase supply (three-phase current system). Before the current reaches the load, the voltages are transformed to a so-called low voltage level (400 V/230 V). Due to these advantages, AC technology has become established in the public electricity network. Direct current technology is, at the moment, mainly limited to electronics. 76 Definition of terms An alternating voltage constantly changes between a positive and a negative maximum value (peak amplitude v ˆ peak value or amplitude 77)...
eBook - ePub- Adrian Waygood(Author)
- 2018(Publication Date)
- Routledge(Publisher)
...Chapter 25 Introduction to alternating current Objectives On completion of this chapter, you should be able to: identify the five main components of the electricity supply industry. describe the function of each of these five main components. explain how the voltage induced into a conductor varies according to the angle at which the conductor moves through a magnetic field. apply Fleming’s Right-Hand Rule to determine the direction of the voltage induced into a conductor moving through a magnetic field. explain why a conductor or loop, rotating within a magnetic field, generates a sinusoidal voltage. explain each of the following terms specifying, where applicable, their SI units of measurement: amplitude instantaneous value period wavelength cycle frequency. given the peak value of an a.c. voltage or current, calculate its r.m.s. (or ‘effective’) value, and vice versa. describe the functions of a phasor and a phasor diagram. Introduction Electricity generation, transmission and distribution systems are almost* exclusively alternating current (a.c.) systems. The primary reason for this is because, as we learnt in an earlier chapter, high voltages are essential for the transmission and distribution of electrical energy, and a.c. voltages can be easily and efficiently changed using transformers. *High-voltage, direct current transmission systems do exist and are used for very long transmission lines (to reduce losses), to interconnect independent grid systems (to avoid frequency synchronisation difficulties), and for undersea cables (to avoid large capacitive currents). High voltages are essential for the transmission and distribution of electrical energy if we are to avoid (a) enormous voltage drops along the lines, (b) conductors with unrealistically high cross-sectional areas and weights, and (c) unacceptably high line losses. There are five components to any national electricity supply industry...
