Ring core cts are available for measuring currents from 50 to 5000 amps, with windows power conductor opening size from 1 to 8 diameter. The magnitude of the secondary current is dependent on the turns ratio of the transformer. Voltage transformers are designed so the through impedance rs,r,xp, and x is as low as possible, while current transform. Comprehensive without being overwhelming, this readerfriendly book combines a detailed. Basic electrical theory overview of ac motors, transformers and measuring instruments instructor. From the symmetry it is easy to see that an application of amperes law will produce. If it increase the input voltage, it is called step up transformer and if it decreases the input voltage, it is called step down transformer. If the book is written in a language the reader does not understand, then. Introduction to transformer the transformer is a electrostatic device which is used to transfer electrical energy voltage or current from one circuit to another by mutual induction of two electric circuits without change in frequency, which is working under the principle of electromagnetic induction.
It is used to raise or lower voltage and current between one circuit and the other, and plays a major role in almost all ac circuits. Due to the long lead time for repair of and replacement of transformers, a major goal of transformer protection is limiting the damage to a faulted transformer. Theory of heating by induction induction heating was first noted when it was found that heat was produced in transformer and motor windings, as mentioned in the chapter heat treating of metal in this book. The magnetic field around the winding is constantly in motion. Current transformers cts are used throughout the world as current transducers for protective relays in industrial. A distinction has to be made between a metering class and a protection class current transformer. These current transformers are used along with the protection equipments such as trip coils, relays, etc. Apprentice electrical technician test ett preparation guide.
Therefore there is a need for a method which enables the calculating of transient transformation errors. Electrical and magnetic circuits are similar in many respects. Transformers typically used because a change in voltage is needed. Then to summarise, the current transformer, ct is a type of instrument transformer used to convert a primary current into a secondary current through a magnetic medium. Preface this book is based on notes for the transformer applications course offered.
Presentation on current transformers submitted by roopal pancholi b. Chapter 31 alternating current phasors and alternating currents resistance and reactance magneticfield energy the lrc series circuit power in alternatingcurrent circuits resonance in alternatingcurrent circuits transformers. Wound current transformer the transformers primary winding is physically connected in series with the conductor that carries the measured current flowing in the circuit. Tests have shown values ranging from 500 to 11,000 volts. Pdf calculation of current transformer transient errors. Abaout ttt eocneccbivbycosnabcyaecntecagcnl mr transformers are used to accurately measure high alternating primary currents, converting the primary current into a.
Accordingly, the theory of induction heating was studied so that motors and transformers could be. The basics of current transformers nk technologies. Current transformers current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. Generally, aircore transformers are used when the voltage source has a high frequency above 20 khz. Find the current in the secondary if the voltage is stepped up to 500 v.
Transformers the current in the first coil is usually called the primary current and the current in the second wire is the secondary current. This protects connected metering devices from overloading in the presence of fault level current flows. Current transformer white paper the basics of current transformers ratio the ct ratio is the ratio of primary current input to secondary current output at full load. Module transformers this module introduces transformer theory and includes the types of transformers, voltage current relationships, and application. A transformer has no moving parts and is a completely. The voltage transformer can be thought of as an electrical component rather than an electronic component. Table 121 lists voltage and current ratios for the circuits, shown in figures 1211 through figures 1214 for inductive output filters. Copper loss is ohmic power lost in the primary and secondary windings of a. Ac enables use of transformers to change voltage from high to low and back. Theory of operation of singlephase transformers definition of transformer an electrical power transformer is a static device, which transforms electrical energy from one circuit to another without any direct electrical connection. The current transformer function is different than that of a voltage transformer. Current transformers cts basic theory basic formula.
Pdf to assess the quality of electricity supply through the power networks it is necessary to use instrument transformers or other devices for. Theory and practice, fifth edition, provides a thorough, engaging introduction to the theory, design, and analysis of electrical circuits. Current transformer basics and the current transformer. The academic background of the authors has ensured that a thorough theoretical treatment is given to important topics.
This is called electromagnetic induction because the current in the first coil causes or induces. Current transformer circuits for power electronics. Module 14 test instruments and measuring devices this module describes electrical measuring and test equipment and includes the. Reference materials ett test contains questions on the following. Toroidal current transformer these do not contain a primary winding.
Coates 2007 2010 introduction transformers have been an essential component in electrical and electronic circuits since the 1830s and although new technologies in some electronic circuits have reduced the. Each of these materials is suitable for certain applications. Consider the case of charging up a capacitor c which is connected to very long wires. Tech electrical, iii year, v semester k72 submitted to mr. Power transformers are defined as transformers rated 500 kva and larger in figure 1 is shown typical power transformer. Pdf application of instrument transformers in power quality. Pdf power transformersprinciples and applications book.
Figure 144 shows the magnetic field during one cycle. The composition of a transformer core depends on voltage, current, and frequency. Load loss is present only when the transformer is loaded, since the magnitude of the noload current is so small as to produce negligible resistive loss in the windings. Youve probably noticed i didnt get heavily into the science or theory. In principle, the only difference between a current transformer and a voltage transformer normal type is that the former is fed with a constant currentwhile the latter is fed with a constant voltage, where constant has the strict circuit theory meaning. Basics, maintenance, and diagnostics ix contents continued page 6. All merlin gerin instrument transformers are in conformity with iec standards. The electrical current flowing in a transformer is al ternating current. The parallel auxiliary winding effectively keeps the leakage flux out of the core so that the leakage reactance in the equivalent circuit is effectively ahead of the exciting branches. It buffers the meter from experiencing excessive torques that might be. Chapter 16 current transformer design university of north. A transformer consists of two electrically isolated coils and operates on faradays principal of mutual induction, in which an emf is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil.
There is a nice blend of theory and practice in almost every topic discussed in the text. Hiziroglu designed for junior and seniorlevel courses in electromechanical energy conversion, electric machinery and transformers, continues the strong pedagogical tradition established by its successful previous editions. Eleven different topologies are compared on the basis of voltage and current rating of the transformer windings and. Current transformer ebook free download as pdf file. It can be designed to step up or step down voltages and works on the magnetic induction principle. Dec 18, 2017 ac circuits and power systems in practice pdf download, by graeme vertigan, isbn. Basic electrical theory transformers generators protection at the completion of the module the participant will be able to.
These ratios apply for sinusoidal ac input voltages. Current transformer ebook electric current electricity scribd. The name instrument transformer is a general classification applied to current and. The generator transformer is one of the most important and critical components of the power system. When current flow exceeds that rating, the metering core will become saturated, thereby limiting the amount of current level within the device. Zb burden impedance ip primary current ns number of secondary turns ratio to 1 v 3. Phase voltage, line voltage, and current in a wye system the relationship between the line voltage, and line current, and the winding, or phase voltage and phase current, in a threephase wye circuit can be seen in figure 128. Power generated at a generating station usually at a voltage in the range of 11 to 25 kv is stepped up by a generator transformer to a higher voltage 220, 345, 400 or 765 kv for transmission. If the voltage or current in a power circuit are too high to connect measuring instruments or relays directly, coupling is made through transformers. What is the working principle of a current transformer. Theory of operation of singlephase transformers custom.
This portable document format pdf file contains bookmarks, thumbnails, and hyperlinks to help you navigate through the document. Transient saturation of current transformers may cause maloperation of protective devices. Pdf power transformers principles and applications sebastian. Transformer windings are no exception and these give rise to the load loss or copper loss of the transformer. Unique to a current transformer the current transformer function is different than that of a voltage transformer. Values shown do not take into consideration voltage drops which occur in the power transformer or rectifier diodes. Youve probably noticed i didnt get heavily into the science or theory behind this. Current balance relay, directional type, 62 for line protection, 330 overcurrent type, 58 current biasing, for mho relay, 82 for offset impedance relay, 77 to avoid distancerelay misoperation on arcs, 346 current compensation for ground distance relays, 360 current switching for distance relays, 368 current transformers, accuracy calcula, 1. What weve done here is pass an electric current through empty space from one coil of wire to another. Current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. Apr 25, 2017 the current transformer the current transformer c. Instrument transformer theory and testing steve hudson, pe engineering manager 10737 lexington drive knoxville, tn 37932. Introduction transformers are a critical and expensive component of the power system.
It also improves the performance of current transformers and subjects their performance to simple calculation. Its secondary winding then provides a much reduced current which can be used for detecting overcurrent, undercurrent, peak current, or average current conditions. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to. Download electric machinery and transformers by bhag s. The drive shaft 46 is driven from the motor drive or manual.
Transformer book will update the knowledge of the current generation of engineers and will be of as. All current transformers are subtractive polarity and will have the following designations to guide proper installation. Figure 1 represents the essential elements for a transformer a magnetic core, with a primary and secondary coil wound on the limbs of the magnetic core. The alternate current transformer in theory and practice. Commonly used core materials are air, soft iron, and steel. Voltage and current relationship of a threephase delta circuit. Here is an example in which current does not gives rise to the magnetic field. Allentown, pa abstract more and more substations are retrofitted with numerical relays, meters and monitoring devices. These current transformers are used along with the measuring devices for the measurement of current, energy, and power. The essentials of current transformers in power circuits. This simplifies the calculation of the current bypassed through zo and zi.
Power transformer transformers transfer electrical energy. Transformers are a necessary part of all power supplies. This is a closed book test and calculators are allowed. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load.
A construction used in hv or ehv current transformers. An alternating voltage v p applied to the primary creates an alternating current i p through the primary. Ring core cts are available for measuring currents from 50 to 5000 amps, with windows power conductor opening size from 1 to 8. Typically current transformers consist of a silicon steel ring core wound with many. A transformer basically is very simple static or stationary electromagnetic passive electrical device that works on the principle of faradays law of induction by converting electrical energy from one value to another. Instrument transformer basic technical information and. A transformer is an electrical device for converting an alternating current at low voltage into that at high voltage or vice versa. Apprentice electrical technician test ett about the test there are 40 questions with a maximum time limit of three hours. Then we will step through each of these topics in detail.
Concept of coupled circuits, dot convention, writing network equilibrium equations in coupled circuits problems on coupled circuits excluded, principle of transformer action for voltage transformation, constructional details of shell type and core type singlephase and threephase transformers, description of the following types of transformers power transformer. The current flows first in one direc tion, stops, then reverses and flows in the other direc274 unit 74 transformers tion. A transformer changes the voltage level or current level on its input winding to another value on its output winding using a magnetic field. Oct 01, 2004 analyzing and applying current transformers stanley e. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another.
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