3 Phase Generator
A 3 phase generator is a type of electrical generator that produces three alternating currents, typically 120 degrees out of phase with each other. This design allows for a more constant and smoother power output compared to single-phase generators. It is commonly used in industrial and commercial applications to power large machinery and equipment.
8 Key excerpts on "3 Phase Generator"
eBook - ePub- Ray Powell(Author)
- 1995(Publication Date)
- Butterworth-Heinemann(Publisher)
...5 Three-phase a.c. circuits 5.1 INTRODUCTION Three-phase has a number of advantages over single-phase: • A three-phase machine of a given physical size gives more output than a single-phase machine of the same size and most electrical power generation is carried out by means of three-phase synchronous generators. • There is a considerable amount of saving in conductor material to be gained by using three-phase rather than single-phase for the purposes of power transmission by overhead lines or underground cables. • The three-phase induction motor is the cheapest and most robust of machines and accounts for the vast majority of the world’s industrial machines. 5.2 GENERATION OF THREE-PHASE VOLTAGES We saw in Chapter 4 that a single-phase a.c. voltage is generated by rotating a single coil in a magnetic field. A three-phase a.c. system is generated by rotating three coils in a magnetic field, the coils being mutually displaced in space by 2π/3 radians (120°) as shown in Fig. 5.1 (a). The waveforms of the three-phase system of voltages thus produced are shown in Fig. 5.1 (b). The coils in which the voltages are generated constitute the armature, while the system producing the magnetic field is called the field system. In the large generators found in power stations the armature system is stationary and it is the field system which is made to rotate. Figure 5.1 Coil A has two ends labelled a and a′; coil B has two ends b and b′; coil C has ends c and c′. End b of coil B is displaced by 2 π/3 radians from end a of coil A, and end c of coil C is displaced by 2π/3 radians from end b of coil B (in a clockwise direction). This means that if the coils are rotated in an anticlockwise direction at an angular frequency of ω radians per second then coil A passes the N-pole of the magnetic field 2π/3ω seconds ahead of coil B which in turn passes the N-pole 2 π/3ω seconds ahead of coil C. The phasor diagram of the voltages is given in Fig...
eBook - ePub- B. M. Weedy, B. J. Cory, N. Jenkins, Janaka B. Ekanayake, Goran Strbac(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
...Chapter 2 Basic Concepts 1 2.1 Three-Phase Systems The rotor flux of an alternating current generator induces sinusoidal e.m.f.s in the conductors forming the stator winding. In a single-phase machine these stator conductors occupy slots over most of the circumference of the stator core. The e.m.f.s that are induced in the conductors are not in phase and the net winding voltage is less than the arithmetic sum of the individual conductor voltages. If this winding is replaced by three separate identical windings, as shown in Figure 2.1(a), each occupying one-third of the available slots, then the effective contribution of all the conductors is greatly increased, yielding a greatly enhanced power capability for a given machine size. Additional reasons why three phases are invariably used in large A.C. power systems are that the use of three phases gives similarly greater effectiveness in transmission circuits and the three phases ensure that motors always run in the same direction, provided the sequence of connection of the phases is maintained. Figure 2.1 (a) Synchronous machine with three separate stator windings a, b and c displaced physically by 120°. (b) Variation of e.m.f.s developed in the windings with time. The three windings of Figure 2.1(a) give voltages displaced in time or phase by 120°, as indicated in Figure 2.1(b). Because the voltage in the (a) phase reaches its peak 120° before the (b) phase and 240° before the (c) phase, the order of phase voltages reaching their maxima or phase sequence is a-b-c. Most countries use a, b, and c to denote the phases; however, R (Red), Y (Yellow), and B (Blue) has often been used. It is seen that the algebraic sum of the winding or phase voltages (and currents if the winding currents are equal) at every instant in time is zero...
- Barbara Renner(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...CHAPTER 6 Three-Phase Motors 6.01 Three-phase alternating-current (A-C) is the manner in which most utilities receive their electric power. Usually, the power is transmitted over high-voltage lines, but the requirements of the treatment plant are quite different. Understanding how three-phase power is generated, transmitted, and used within the plant is not complex, but a number of different pieces of equipment are needed to accomplish this process, and it is important to have a general idea of how each piece functions. THREE-PHASE POWER 6.02 The generation of A-C was discussed in Chapter 5, paragraphs 5.42-5.45. Although, the text was describing single-phase A-C, the same information applies to three-phase A-C. The major differences between the two types of power is that three-phase power can be transmitted more efficiently, it provides more energy, and three-phase motors do not require any extra components to get them to start. 6.03 A three-phase generator (more commonly referred to as an alternator) has three sets of windings on the armature. Each are spaced electrically and mechanically apart by 120°. As phase winding A passes through the magnetic field of the poles (Figure 6.1), it generates one cycle of power and is represented by sine wave A. Note that the sine wave is positive on the top and negative on the bottom. 6.04 However, as shown in Figure 6.1, before the phase A winding has completed one-half of its cycle (at 120°), the phase B winding enters the magnetic field between the poles and starts to generate power. The sine wave for phase B shows that the entire cycle trails the phase A sine wave by 120°. 6.05 Finally, as shown in Figure 6.1, the phase C winding enters the magnetic field between the poles shortly after phase A has passed its half-way position (180°) and starts to generate one cycle of power. The sine wave for phase C shows that it trails the phase A sine wave by 240° for the entire cycle...
eBook - ePub- C R Robertson(Author)
- 2010(Publication Date)
- Routledge(Publisher)
...Chapter 3 Three-Phase A.C. Circuits Learning Outcomes This chapter introduces the concepts and principles of the three-phase electrical supply, and the corresponding circuits. On completion you should be able to: 1 Describe the reasons for, and the generation of the three-phase supply. 2 Distinguish between star (3 and 4-wire) and delta connections. 3 State the relative advantages of three-phase systems compared with single-phase-systems. 4 Solve three-phase circuits in terms of phase and line quantities, and the power developed in three-phase balanced loads. 5 Measure power dissipation in both balanced and unbalanced three-phase loads, using the 1, 2 and 3-wattmeter methods, and hence determine load power factor. 6 Calculate the neutral current in a simple unbalanced 4-wire system. 3.1 Generation of a Three-Phase Supply In order to understand the reasons for, and the method of generating a three-phase supply, let us firstly consider the generation of a single-phase supply. Alternating voltage is provided by an a.c. generator, more commonly called an alternator. The basic principle was outlined in Fundamental Electrical and Electronic Principles, Chapter 5. It was shown that when a coil of wire, wound on to a rectangular former, is rotated in a magnetic field, an alternating (sinusoidal) voltage is induced into the coil. You should also be aware that for electromagnetic induction to take place, it is the relative movement between conductor and magnetic flux that matters. Thus, it matters not whether the field is static and the conductor moves, or vice versa. For a practical alternator it is found to be more convenient to rotate the magnetic field, and to keep the conductors (coil or winding) stationary. In any rotating a.c. machine, the rotating part is called the rotor, and the stationary part is called the stator. Thus, in an alternator, the field system is contained in the rotor. The winding in which the emf is generated is contained in the stator...
eBook - ePub- David Wyatt, Mike Tooley(Authors)
- 2018(Publication Date)
- Routledge(Publisher)
...4.22 it is possible to produce several cycles of output voltage for one single revolution of the rotor. The frequency of the output voltage produced by an AC generator is given by: f = p N 6 0 where/is the frequency of the induced e.m.f. (in Hz), p is the number of pole pairs, and N is the rotational speed (in rev/min). Example 4.1 An alternator is to produce an output at a frequency of 60 Hz. If it uses a 4-pole rotor, determine the shaft speed at which it must be driven. Re-arranging f = p N 6 0 to make N the subject gives: N = 6 0 f p A 4-pole machine has 2 pairs of poles, thus p = 2 and: N = 6 0 × 6 0 2 = 1, 8 0 0 r e v / min Key point In a practical AC generator, the magnetic field excitation is produced by the moving rotor whilst the conductors from which the output is taken are stationary and form part of the stator. 4.2.1 Two-phase AC generators By adding a second stator winding to the single-phase AC generator shown in Fig. 4.22, we can produce an alternator that produces two separate output voltages which will differ in phase by 90°. This arrangement is known as a two-phase AC generator. When compared with a single-phase AC generator of similar size, a two-phase AC generator can produce more power. The reason for this is attributable to the fact that the two-phase AC generator will produce two positive and two negative pulses per cycle whereas the single-phase generator will only produce one positive and one negative pulse. Thus, over a period of time, a multi-phase supply will transmit a more evenly distributed power and this, in turn, results in a higher overall efficiency. Key point Three-phase AC generators are more efficient and produce more constant output than comparable single-phase AC generators. 4.2.2 Three-phase AC generators The three-phase AC generator has three individual stator windings, as shown in Fig. 4.26. The output voltages produced by the three-phase AC generator are spaced by 120° as shown in Fig. 4.27...
eBook - ePubElectrical Equipment
A Field Guide
- B. Koti Reddy(Author)
- 2021(Publication Date)
- Wiley-Scrivener(Publisher)
...3 Generators 3.1 Introduction An Electrical Generator, which is driven by a prime-mover, converts mechanical energy into electrical energy. There are various types of conventional generators, as shown in Figure 3.1. At present, most of the generators are of AC, which will be explained in subsequent sections. 3.2 Alternator Unlike DC generators, alternators have a stationary armature. The main advantages of stationary armature are: The output can be taken easily from armature which avoids brush gear thus avoids sparking and wear & tear problems. Ease in insulation and can built generators up to 30 KV or more. No slip rings and less maintenance. Low voltage is supplied to rotating field, thus avoids brush gear and other problems. Figure 3.1 Types of generators. The armature can be braced which prevents the deformation of windings due to mechanical forces on occurrence of severe faults such as short circuits. 3.3 Field Poles There are two type of poles, which are explained in Table 3.1. 3.4 Construction of Field Poles The basic construction model of salient pole and cylindrical pole type generators are shown in Figures 3.2 and 3.3, respectively. Table 3.1 Types of field poles of AC generators. S. no. Salient pole Cylindrical pole 1 Projected or protruding poles. Wound rotor type poles. 2 Used for low speeds like diesel driven Generators. Used for high speeds and large capacities like turbo Generators. 3 Needs damper winding. No need of damper winding since rotor body itself acts as a damper. 4 Has larger diameter of order of 2 to 6 meters to accommodate several poles and short axial length of around 1M. Has a small diameter of order of 1 meter and long axial length of order of 2 to 5 meters. 5 Little vibrating and noisy operation. Better balance of rotor and quite operation. 6 Have different axis reactances (x d and x q) which are to be analysed based on two reaction theory. Here, Have only one direct axis reactance...
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 - ePubElectrical Energy Systems
Second Edition
- Mohamed E. El-Hawary(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
...The choice between the two designs (salient or nonsalient) for a specific application depends on the prime mover. For hydroelectric generation, a salient-pole construction is employed, because hydraulic turbines run at relatively low speeds, and a large number of poles is required to produce the desired frequency as indicated by Eq. (3.1). Steam and gas turbines perform better at relatively high speeds, and two- or four-pole cylindrical rotor turboalternators are used to avoid the use of protruding parts on the rotor. Figure 3.5 A Cylindrical Rotor Two-Pole Machine. 3.3 Synchronous Machine Fields An understanding of the nature of the magnetic field produced by a polyphase winding is necessary for the analysis of polyphase ac machines. We will consider a two-pole, three-phase machine. The windings of the individual phases are displaced spatially from each other by 120 electrical degrees. The magnetomotive forces developed in the air gap due to currents in the windings will also be displaced from each other by 120 electrical degrees in space. Assuming sinusoidal, balanced three-phase operation, the phase currents are displaced by 120 electrical degrees in time. Assume that I m is the maximum value of the current, and the time origin is arbitrarily taken as the instant when the phase a current is a positive maximum. The phase sequence is assumed to be abc which means that any event such as the maximum of current will take place on phase a followed by phase b and then phase c. The magnetomotive force (MMF) of each phase is proportional to the corresponding current, and hence, the peak MMF is given by F max = K I m where K is a constant of proportionality that depends on the winding distribution and the number of series turns in the winding per phase...
