Physics
Electrical Power
Electrical power is the rate at which electrical energy is transferred by an electric circuit. It is measured in watts and is the product of voltage and current in a circuit. In practical terms, electrical power is the amount of energy consumed or produced per unit of time.
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eBook - ePub- Stephen Sangwine, Stephen Sangwine(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
Power sources and power supplies 4 ObjectivesTo introduce the main sources of electrical energy used in electronic systems, including mains supplies, batteries, and photovoltaic cells.To introduce the concept of a power supply.To discuss the characterization and performance of power supplies.To explain the functions of the main subcircuits found in a power supply.To explain the operation of linear and switching voltage regulators.All electronic circuits and systems require energy to operate. Energy is required to move electric charge; to produce heat, light, or sound; to produce mechanical movement; and to manipulate information (as in a computer). Energy is a conserved physical quantity: in a closed system energy can be neither created nor destroyed, although it can be converted from one form to another. In electronic engineering, we are usually concerned with electrical energy, although other forms of energy are also important. Heat, for example, is produced in electronic circuits, usually as a by-product of a useful function, and is discussed in Chapter 7 . Energy may be stored as chemical energy in a cell or battery. Chemical energy sources are discussed later in this chapter.Energy is the capacity to do work. The International System of Units (SI) unit of energy is the joule (J).While the importance of energy should not be forgotten, electronic engineers more frequently use the concept of power. Power can be used to quantify the rate at which heat is produced in a resistor, the mechanical output of a motor, or the rate at which an electronic system takes energy from its energy source.Power is the rate of conversion, utilization, or transport of energy. The SI unit of power is the watt (W), which is 1 J s−1 .The terms a.c. and d.c. stand for alternating current and direct current respectively. We customarily talk about a.c. voltage and d.c. voltage, even though technically this is nonsense — what is an “alternating- current voltage?” We can avoid the term d.c
- Dale R. Patrick, Stephen W. Fardo(Authors)
- 2020(Publication Date)
- River Publishers(Publisher)
Unit V ), is probably the most complex of all the parts of the Electrical Power system. There are almost unlimited types of devices, circuits, and equipment used to control Electrical Power systems.Figure 2-4. Electrical Power Systems ModelEach of the blocks shown in Figure 2-4 represents one important part of the Electrical Power system. Thus, we should be concerned with each one as part of the Electrical Power system, rather than in isolation. In this way, we can develop a more complete understanding of how Electrical Power systems operate. This type of understanding is needed to help us solve problems that are related to Electrical Power. We cannot consider only the production aspect of Electrical Power systems. We must understand and consider all parts of the system.TYPES OF ELECTRICAL CIRCUITS
There are several basic fundamentals of Electrical Power systems. Therefore, the basics must be understood before attempting an in-depth study of Electrical Power systems. The types of electrical circuits associated with Electrical Power production or power conversion systems are (1) resistive, (2) inductive, and (3) capacitive. Most systems have some combination of each of these three circuit types. These circuit elements are also called loads. A load is a part of a circuit that converts one type of energy into another type. A resistive load converts electrical energy into heat energy.In our discussions of electrical circuits, we will primarily consider alternating current (AC) systems at this time, as the vast majority of the Electrical Power that is produced is alternating current. Direct current (DC) systems will be discussed in greater detail in Chapter 7 .POWER IN DC ELECTRICAL CIRCUITS
In terms of voltage and current, power (P) in watts (W) is equal to voltage (in volts) multiplied by current (in amperes). The formula is P = V × I. For example, a 120-V electrical outlet with 4 A of current flowing from it has a power value ofP = V × I = 120 V × 4 A = 480 W .The unit of Electrical Power is the watt. In the example, 480 W of power are converted by the load portion of the circuit. Another way to find power is:
eBook - ePub- Adrian Waygood(Author)
- 2018(Publication Date)
- Routledge(Publisher)
This can be expressed as: E = W Q where: E = voltage, in volts W = work, in joules Q = electric charge, in coulombs Rearranging this equation, to make W the subject: W = E Q but we have also learnt that Q= It, so, substituting for Q in equation (1), we have: W = E I t —equation (1) where: W = work, in joules E = voltage, in volts I = current, in amperes t = time, in seconds The above equation is the fundamental equation for the work done, or energy expended, by an electric circuit. As power is defined as the rate of doing work, we can express this as: P = W t... substituting the fundamental equation for work into equation (2), we have: P = E I t⃥ t⃥ which is simplified to: P = E I —equation (2) where: P = power, in watts E = voltage, in volts I = current, in amperes As resistance is the ratio of voltage to current, we can derive alternative equations for both work and power: W = I 2 R t Again, from Ohm’s Law, I = E R Substituting for I, in eq.1: W = E (E R) t W = E 2 R t P = I 2 R Again, from Ohm’s Law, I = E R Substituting for I,. in eq.2: P = E (E R) P = E 2 R Summary of equations for work and power For work : W = E I t W = I 2 R t W = E 2 R t W = P t... and for power: P = E I P = I 2 R P = E 2 R P = W t Worked example 1 Calculate the work done by a resistor when connected across a 230-V supply, if it draws a current of 10 A for 1 min. Solution Important
eBook - ePubElectrical Engineering
Fundamentals
- Viktor Hacker, Christof Sumereder(Authors)
- 2020(Publication Date)
- De Gruyter Oldenbourg(Publisher)
B have to be fulfilled.Figure 1.17: Superconducting surface.1.11 Energy and Electrical Power
Electrical energy is provided by the combination of electric current and electric potential in an electrical circuit. The mechanical workW = ∫is comparable to electrical work done on a charged particle by an electric field.F ⃗⋅ ds ⃗If the force (F ) is used to lift an object by the distance (s), mechanical work is carried out. The object now has higher energy content by that amount (potential energy). This energy can perform work by e.g. letting the object drop.Electric energy the following applies:W = Q ⋅ V = V ⋅ I ⋅ tV Voltage in VI Current in At Time in sQ Electric charge in AsW Electrical work/energy in WsThe electric charge represents the product of current I multiplied by time (Q = I ⋅ t ). Therefore, the following applies:W =⋅ t = P ⋅ tPV ⋅ I⏟P Power in WThe work performed per time unit is called power P.P =W tWith direct current, the electric power P that is transformed in an electric load is the result of the voltage V multiplied by the current I :P = V ⋅ IPower is one of the most important parameters for electrical machines and devices. By insertion of the Ohm’s law, the equation can be transformed to:P = Wor also:Power hyperbola
All V-I pairs of values that lead to the same power, e.g.P = 2 W
eBook - ePubElectrical Energy Systems
Second Edition
- Mohamed E. El-Hawary(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
Chapter 2 BASICS OF ELECTRIC ENERGY SYSTEM THEORY 2.1 Introduction This chapter lays the groundwork for the study of electric energy systems. We develop some basic tools involving fundamental concepts, definitions, and procedures. The chapter can be considered as simply a review of topics utilized throughout this work. We start by introducing the principal electrical quantities. 2.2 Concepts of Power in Alternating Current Systems Generally, the electric power systems specialist is more concerned with electric power in the circuit rather than the currents. The value of instantaneous power flowing into an element is the product of voltage across and current through it. It seems, then, reasonable to exchange the current for power without losing any information. In treating sinusoidal steady-state behavior of circuits, some further definitions are necessary. To illustrate the concepts, we use a cosine representation of the waveforms. Consider the impedance element Z = Z ∠ ϕ. For a sinusoidal voltage, v (t) given by υ (t) = V m cos ω t The instantaneous current in the circuit is i (t) = I m cos (ω t − ϕ) Here I m = V m / | Z | The instantaneous power into the element is given by p (t) = υ (t) i (t) = V m I m [ cos (ω t) cos (ω t − ϕ) ] This reduces. to p (t) = V m I m 2 [ cos ϕ + cos (2 ω t − ϕ) ] Since the average of cos (2 ωt - ϕ) is zero, through 1 cycle, this term therefore contributes nothing to the average of p, and the average power p av is given by p a v = V m I m 2 cos ϕ (2.1) Using the effective (rms) values of voltage and current and substituting V m = 2 (V rms), and I m = 2 (I rms), we. get p a v = V r m s I r m s cos ϕ (2.2) The power entering any network is the product of the effective values of terminal voltage and current and the cosine of the phase angle ϕ, which is, called the power factor (PF). This applies to sinusoidal voltages and currents only
eBook - ePub- S. Bobby Rauf(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
1 Fundamental Electrical Engineering Concepts and PrinciplesIntroduction
In this first chapter of the Electrical Engineering Fundamentals text, we will explore fundamental electrical engineering terms, concepts, principles, and analytical techniques and impart knowledge that is considered elemental in the discipline of electrical engineering. Readers who invest time and effort in studying this text are likely to do so for the key purpose of gaining an introduction into the field of electricity. In this chapter, we will lay the foundations in the electrical engineering realm by covering basic electrical engineering terms, concepts, and principles, without the understanding of which, discussion and study of terms that bear important practical significance, such as power factor, real power, reactive power, apparent power, and load factor, would be untenable.Most of the material in this chapter pertains to DC, or direct current, electricity. However, some entities discussed in this chapter such as capacitive reactance, inductive reactance, and impedance are fundamentally entrenched in the AC, alternating current, realm.This text affirms that electrical engineering is rooted in the field of physics and chemistry. Physics, chemistry, and electrical engineering, as most other subject matters in science, depend on empirical proof of principles and theories. Empirical analysis and verification require tools and instruments for measurement of various parameters and entities. Hence, after gaining a better understanding of the basic electrical concepts, we will conclude this chapter with an introduction to three of the most common and basic electrical instruments, namely, multi-meter, clamp-on ammeter, and a scope meter or oscilloscope.Voltage or EMF (Electromotive Force)
Voltage can be defined as a “force” that moves or pushes electrically charged particles like electrons, holes, negatively charged ions, or positively charged ions by forming an electric field. The term “electromotive” force stems from the early recognition of electrical current as something that consisted, strictly, of the movement of “electrons.” Nowadays, however, with the more recent breakthroughs in the renewable and non-traditional Electrical Power generating methods and systems like microbial fuel cells and hydrocarbon fuel cells, Electrical Power is being harnessed, more and more, in the form of charged particles that may not be electrons. In batteries, such as those used in automobiles, as we will see in the batteries chapter, the flow of current driven by voltage potential difference consists not only of negatively charged electrons, e− , but also types of ions, including H+ and HSO4 − ions.1
- S. Bobby Rauf(Author)
- 2021(Publication Date)
- River Publishers(Publisher)
Electrical engineering is largely rooted in the field of physics. Physics, and electrical engineering, as most other fields in science, depend on empirical proof of principles and theories. Empirical analysis and verification require measurement tools or instrumentation. So, after gaining a better understanding of the basic electrical concepts, we will conclude this chapter with an introduction to two of the most common and basic electrical instruments, i.e., multi-meter and clamp-on ammeter.VOLTAGE
Voltage is defined as an electromotive that moves or pushes electrically charged particles like electrons, holes, negatively charged ions, or positively charged ions. The term “electromotive” force stems from the early recognition of electricity as something that consisted, strictly, of the movement of “electrons.” Nowadays, however, with the more recent breakthroughs in the renewable and non-traditional Electrical Power generating methods and systems like microbial fuel cells and hydrocarbon fuel cells, Electrical Power is being harnessed, more and more, in the form of charged particles that may not be electrons.Two analogies for voltage in the mechanical and civil engineering disciplines are pressure and elevation. In the mechanical realm — or more specifically in the fluid and hydraulic systems — high pressure or pressure differential pushes fluid from one point to another and performs mechanical work. Similarly, voltage — in the form of voltage difference between two points, as with the positive and negative terminals of an automobile battery — moves electrons or charged particles through loads such as motors, coils, resistive elements, lamps, etc. Negatively charged ions or particles, like electrons, are attracted by positively charged electrodes — referred to as anodes or high potential terminals — and the positively charged ions or particles are drawn toward negatively charged electrodes referred to as cathodes, low potential terminals, commons, or grounds. As electrons or charged particles are pushed through loads like motors, coils, resistive elements, light filaments, etc., electrical energy is converted into mechanical energy, heat energy, or light energy. In equipment like rechargeable batteries, during the charging process, applied voltage can push ions from one electrode (or terminal) to another and thereby “charge” the battery. Charging of a battery, essentially, amounts to the restoration of the chemical composition of battery terminals or plates to “full strength.” So, in essence, the charging of a battery could be viewed as the “charging” of an electrochemical “engine.” Once charged, a chemical or electrochemical engine, when presented with an electrical load, initiates and sustains the flow of electrical current, and performs mechanical work through electrical or electromechanical machines.
