Physics
Real Transformer
A real transformer is an electrical device that consists of two or more coils of insulated wire and is used to transfer electrical energy between circuits. It operates on the principle of electromagnetic induction, where a changing current in one coil induces a voltage in another coil. Real transformers are commonly used in power distribution and electrical systems to step up or step down voltage levels.
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12 Key excerpts on "Real Transformer"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- The English Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 4 Transformer Pole-mounted split-phase transformer with center-tapped secondary winding (note use of grounded conductor, right, as one leg of the primary feeder) ________________________ WORLD TECHNOLOGIES ________________________ A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or voltage in the secondary winding. This effect is called mutual induction. If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding ( V s ) is in proportion to the primary voltage ( V p ), and is given by the ratio of the number of turns in the secondary ( N s ) to the number of turns in the primary ( N p ) as follows: By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be stepped up by making N s greater than N p , or stepped down by making N s less than N p . In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter-2 Transformer Pole-mounted power distribution transformer with center-tapped secondary winding (note use of grounded conductor, right, as one leg of the primary feeder). It transforms the high voltage of the overhead distribution wires to the lower voltage used in house wiring. A transformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This ____________________ WORLD TECHNOLOGIES ____________________ varying magnetic field induces a varying electromotive force (EMF) or voltage in the secondary winding. This effect is called mutual induction. If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding ( V s ) is in proportion to the primary voltage ( V p ), and is given by the ratio of the number of turns in the secondary ( N s ) to the number of turns in the primary ( N p ) as follows: By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be stepped up by making N s greater than N p , or stepped down by making N s less than N p . In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide.
eBook - PDFElectronic and Electrical Engineering
Principles and Practice
- Lionel Warnes(Author)
- 2017(Publication Date)
- Red Globe Press(Publisher)
298 Figure 16.1 The parts of a transformer (16.1) 16 Transformers P ROPERLY-DESIGNED transformers are highly efficient (up 99.5% for some multi-MVA transformers) devices that are chiefly used to step down (or step up) alternating voltages and also for matching loads. They range in size from multi-tonne, multi-MVA transformers in electricity distribution systems to 1VA, PCB-mounted transformers for portable instruments. Besides their high efficiencies, they are also notable for their reliability and freedom from the need for maintenance virtues stemming from their lack of moving parts. AC became standard partly because transformers have these attractive properties, relegating DC to special purposes. 16.1 The ideal transformer A transformer comprises two coils wrapped around a magnetic (more correctly ferromagnetic) core which channels nearly all the magnetic flux through them. Figure 16.1 shows a transformer, one coil of which the primary is connected to the supply, while the other coil the secondary is connected to the load. The coils are wound onto the limbs of the core, which are connected by a yoke . Transformers are reversible because primary can become secondary and vice versa: the primary is the coil connected to the primary supply, that is all. Current passing through the primary coil produces magnetic flux in the core; if all this flux passes through the secondary coil then the e.m.f. induced in it can be found from Faraday’s law of electromagnetic induction: The voltages are proportional to the numbers of turns in the coils: the coil with the most turns Chapter 16 299 (16.3) (16.2) (16.4) (16.5) Figure 16.2 The dot convention has the higher voltage . An ideal transformer is 100% efficient and the power put into the primary coil is equal to the power put out by the secondary: P 1 = P 2 . That is Substituting for V 1 / V 2 from Equation 16.1 gives where n is the turns ratio of the transformer.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Orange Apple(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 2 Transformer Pole-mounted power distribution transformer with center-tapped secondary winding (note use of grounded conductor, right, as one leg of the primary feeder). It transforms the high voltage of the overhead distribution wires to the lower voltage used in house wiring. ________________________ WORLD TECHNOLOGIES ________________________ A transformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or voltage in the secondary winding. This effect is called mutual induction. If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding ( V s ) is in proportion to the primary voltage ( V p ), and is given by the ratio of the number of turns in the secondary ( N s ) to the number of turns in the primary ( N p ) as follows: By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be stepped up by making N s greater than N p , or stepped down by making N s less than N p . In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide.
eBook - PDFPragmatic Electrical Engineering
Fundamentals
- William Eccles(Author)
- 2022(Publication Date)
- Springer(Publisher)
We are going to look at the ideal transformer first, one that is 100% efficient. Then we’ll model the Real Transformer and see how to measure the parameters needed to do this. Finally, we’ll embed transformers into power systems. 4.1 IDEAL TRANSFORMERS A transformer is very simple. Take an iron core, wrap a couple of coils of wire around it, and you have a transformer. Figure 4.1 shows this. Note the current directions. On the left, the “1” side, the current is labeled into the transformer. On the other side, the “2” side, the current is labeled outward. This is done to imply that there is power moving from left to right. Now and then I’ll call the left side the primary and the right side, the secondary. Energy flow is generally from the primary to the secondary. 1 It is left as an exercise for the reader to determine the source and relevance of this quote. 100 4. TRANSFORMERS Figure 4.1: Transformer The numbers of turns on the coils is given, an important parameter when describing a trans- former and determining how it works. Instead of actually enumerating turns, we often state just the ratio of the turns of the two coils. Figure 4.2 is a cutaway photo of a common pole-mounted transformer.This one, compliments of Cooper Power Systems of Waukesha, Wisconsin, is kind of nondescript, but it is probably in the range of 10 to 25 kVA and a few thousand volts. How does the transformer work? I’ll introduce a little about magnetic fields here, but we won’t really deal with them until Chapter 6. The basic physics is described by Faraday’s Law: v t d t dt ( ) ( ) = φ This law says that a time-varying magnetic flux ø(t) produces a voltage in a loop of wire. Now apply this to the transformer using the voltages and currents described in Fig. 4.1: v t n d t dt v t n d t dt 1 1 2 2 ( ) ( ) ( ) ( ) = = φ φ That’s not enough, though, because it doesn’t include the currents in the drawing.
eBook - PDF- Jan De Kock, Cobus Strauss(Authors)
- 2004(Publication Date)
- Newnes(Publisher)
5 Transformer theory 5.1 Transformer theory Transformer is an essential device in electrical AC power distribution system, which is used to transform AC voltage magnitudes of any value obtained from a source to any desired value for the purpose of distribution and/or consumption. The development of power transformer dates back to 19th century. The main feature of a transformer is its constant VA rating whether referred to its primary side or the secondary side. With VA being constant ( V refers to the voltage magnitude and A refers to the current magnitude in a transformer winding), it is possible to get a higher V with lower A or a lower V with a higher A , by choosing suitable ratio for the transformer. The major benefit of such a device is its ability to take in the high current produced at relatively low voltage from the electrical generators and transform this power at a higher voltage level with lower current. This ensures that the power generated in the order of several megavolt amperes (MVA) is being transmitted at low current magnitudes in a cable of practical dimensions over very long distances. Today’s transmission and distribution systems are heavily dependent upon this technology and transformers are used extensively throughout the world. The standard transformer A standard transformer typically consists of a pair of windings, primary and secondary linked together by a magnetic core. The windings can be connected in any of the following types, which in turn decides to which category a transformer belongs. There are two basic types of the transformer viz., (a) shell type and (b) core type. These are illustrated in Figure 5.1. In Figure 5.1, the windings are the concentric portions and the white solid portions refer to the metallic part of a transformer (laminations), which either surround the windings (shell type) or where the windings surround the core (core type).
No longer available |Learn more- (Author)
- 2014(Publication Date)
- White Word Publications(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter-1 Transformer Pole-mounted power distribution transformer with center-tapped secondary winding (note use of grounded conductor, right, as one leg of the primary feeder). It transforms the high voltage of the overhead distribution wires to the lower voltage used in house wiring. A transformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the ____________________ WORLD TECHNOLOGIES ____________________ transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or voltage in the secondary winding. This effect is called mutual induction. If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding ( V s ) is in proportion to the primary voltage ( V p ), and is given by the ratio of the number of turns in the secondary ( N s ) to the number of turns in the primary ( N p ) as follows: By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be stepped up by making N s greater than N p , or stepped down by making N s less than N p . In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- College Publishing House(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter 7 Transformer Pole-mounted power distribution transformer with center-tapped secondary winding (note use of grounded conductor, right, as one leg of the primary feeder). It transforms the high voltage of the overhead distribution wires to the lower voltage used in house wiring. A transformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or voltage in the secondary winding. This effect is called mutual induction. ____________________ WORLD TECHNOLOGIES ____________________ If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding ( V s ) is in proportion to the primary voltage ( V p ), and is given by the ratio of the number of turns in the secondary ( N s ) to the number of turns in the primary ( N p ) as follows: By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be stepped up by making N s greater than N p , or stepped down by making N s less than N p . In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide.
Available until 25 Jan |Learn more- Turan Gonen(Author)
- 2011(Publication Date)
- CRC Press(Publisher)
The secondaries of both voltage and CTs are normally grounded. A transformer consists of a primary winding and a secondary winding linked by a mutual mag-netic field. Transformers may have an air core, an iron core, or a variable core, depending on their operating frequency and application. Transformers are also quite different in size and shape depending on the application. In power system applications, the single- or three-phase transformers with ratings up to 500 kVA are defined as distribution transformers , whereas those transformers with ratings over 500 kVA at voltage levels of 69 kV and above are defined as power transformers .* Figure 4.1 shows a cutaway view of a single-phase, overhead pole-mounted distribution transformer. Notice that it has two high-voltage bushings since it is built to operate under line-to-line voltage rather than line-to-neutral voltage. Figure 4.2 shows a three-phase, 345/161 kV autotransformer used as a power transformer. Its power ratings are 214/285/357 MVA for its OA/FA/FOA operations. Note that the OA/FA/FOA means oil-immersed, self-cooled/forced-air-cooled/forced-oil-cooled . † A transformer is basically made up of two or more windings coupled by a mutual magnetic field. Ferromagnetic cores are employed to develop tight magnetic coupling and high flux densities. When such a coupling exists, the transformer is called an iron-core transformer . Most distribution and power transformers are immersed in a tank of oil for better insulation ‡ and cooling purposes. The leads of the windings are brought to the outside of the tank through insulating bushings which are attached to the tank, as shown in Figure 4.1. Such transformers are used in high-power applications. § When there is no ferromagnetic material but only air present, such a transformer is called an air-core transformer . ¶ These transformers have poor magnetic coupling and are usually used in lower-power applications such as in electronic circuits.
- P. C. Sen(Author)
- 2013(Publication Date)
- Wiley(Publisher)
chapter two TRANSFORMERS A transformer is a static machine. Although it is not an energy conversion device, it is indis- pensable in many energy conversion systems. It is a simple device, having two or more electric circuits coupled by a common magnetic circuit. Analysis of transformers involves many principles that are basic to the understanding of electric machines. Transformers are so widely used as electrical apparatus that they are treated along with other electric machines in most books on electric machines. A transformer essentially consists of two or more windings coupled by a mutual magnetic field. Ferromagnetic cores are used to provide tight magnetic coupling and high flux densities. Such transformers are known as iron core transformers. They are invariably used in high-power applications. Air core transformers have poor magnetic coupling and are sometimes used in low- power electronic circuits. In this chapter we primarily discuss iron core transformers. Two types of core constructions are normally used, as shown in Fig. 2.1. In the core type (Fig. 2.1a), the windings are wound around two legs of a magnetic core of rectangular shape. In the shell type (Fig. 2.1b), the windings are wound around the center leg of a three-legged magnetic core. To reduce core losses, the magnetic core is formed of a stack of thin lamina- tions. Silicon-steel laminations of 0.014-inch thickness are commonly used for transformers operating at frequencies below a few hundred cycles. L-shaped laminations are used for core- type construction and E-shaped laminations are used for shell-type construction. To avoid a continuous air gap (which would require a large exciting current), laminations are stacked alternately, as shown in Figs. 2.1c and 2.1d. For small transformers used in communication circuits at high frequencies (kilocycles to megacycles) and low power levels, compressed powdered ferromagnetic alloys, known as permalloy, are used.
- Christopher Lavers, Edmund G.R. Kraal(Authors)
- 2014(Publication Date)
- Thomas Reed(Publisher)
The transformer, ‘the heart of the alternating current system’. William Stanley Jr A brief introduction to the static transformer principle was made in Volume 6, Chapter 6, but it is vital to stress the importance of understanding its operating principle and applications as these devices are of practical use to marine engineers. This device in its various forms and its applications will be discussed in some detail in the next three chapters. A transformer is an essential piece of equipment providing electrical energy in an A.C. current form, and it is often classed as a machine because, although it has no moving parts, it is capable of converting energy. However, unlike a generator, it receives the energy in an electrical and not a mechanical form; nevertheless energy conversion takes place, in that, electrical energy is given out at a higher or lower voltage than that in which it is received. If the output voltage is greater than the input voltage it is considered to be a step-up transformer. A transformer whose output voltage is less than its input voltage is known as a step-down transformer. Not wanting to state the obvious the transformer, although using Faraday’s laws raises or lowers A.C. voltage it cannot increase power , so that if voltage is raised, the current is proportionally lowered and vice versa . Since operation does not involve rotation of any armature, field system or commutator, rotational and windage losses do not occur and its effi ciency is thus high. For electrical ‘power’ purposes, i.e. transformers operating at 50 or 60 Hz, iron cores are essential and iron losses will occur. Winding copper losses are also present when current is supplied, nonetheless the transformer is the most effi cient of electrical machines and a full-load effi ciency of 95.5% for units of 5 kVA and 97.5% for units up to 1 MVA may be achieved. TRANSFORMER OPERATION 1
- S. B. Lal Seksena, Kaustuv Dasgupta(Authors)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
The electric energy is measured by the product of voltage and current. Thus, in a transformer V × I of input side should be equal to the V × I of the output side. This implies the current and voltage of output and input sides varies inversely proportional. When a transformer lowers down or steps down the voltage it also steps up the current and vice-versa. We generally call a transformer to be step up transformer if the voltage level is elevated from input side to output side. A step up transformation always steps down the current to maintain the constant power. Likewise a step down transformer always decreases the voltage and increases the current from input to output side. Fig. 9.1 will help us to understand the interrelation between an electric generator and transformer. 9 TRANSFORMER Transformer 433 Let us suppose there are two electromagnets A and B. B is placed inside a slit of A. A has winding terminals a 1 a 2 and that of B is b 1 b 2 . Now let us suppose our intention is to get some output voltage at b 1 b 2 terminals. According to Faraday’s law we must establish a rate of change in flux in B to get the voltage output at b 1 b 2 . A and B are magnetically coupled due to mutual induction effect. If we can set up a d ϕ – dt (rate of change of magnetic flux w.r.t. time) in coil A, the same rate of change of flux will be induced in B. There are two ways by which we can vary the flux associated with coil B with respect to time. a. By varying the position of the coil If we rotate B inside A the position of B with respect to A will vary. If we excite the coil of A by a constant DC source there will be no variation of ϕ in coil A. But due to the rotation there will be a continuous change in position of B with respect to A. Thus, the flux cut by B will be varied due to change in positional angle between the axis of B and constant magnetic lines of force. This is the principle of operation of an electric generator.
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