This module introduces transformer theory and includes the types of transformers, voltagecurrent relationships, and application. Current transformers have their primary windings connected in series with the power circuit, and so also in series with the system impedance. There are four typical types of current transformers. They are mechanically strong and can bear shocks and impacts. 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. The primary winding can consist merely of the primary current conductor passing once through an aperture in the current transformer core window or bartype, or it may consist of two or more turns wound on the core together with the secondary winding wound type. 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. 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. A blend of theory and practice, this comprehensive book examines aspects of transformer engineering, from design to diagnostics. An alternating voltage v p applied to the primary creates an alternating current i p through the primary. Current transformer ebook free download as pdf file. Figure 144 shows the magnetic field during one cycle.
The primary winding is supplied an alternating electrical source. Current transformer circuits for power electronics. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load. Pdf calculation of current transformer transient errors. 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. Engineering books pdf articles electrical engineering articles current transformer, potential transformer. It thoroughly explains electromagnetic fields and the finite element method to help you solve practical problems related to transformers. If a ct test switch is used, the switch must have a makebeforebreak contact pattern to.
Module 14 test instruments and measuring devices this module describes electrical measuring and test equipment and includes the parameters measured and the principles of operation of common instruments. As long as the current to be measured are small and at low voltage, the direct method of connecting the instruments and relays in the circuits is convenient and adequate. Fundamentals of mosfet and igbt gate driver circuits. The current transformer is designed to connect in series with the line to transform the line current to the standard 5 amperes suitable for the. The alternate current transformer in theory and practice. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to.
Instrument transformer basic technical information and. Transformer theory quiz questions electrician practice tests. The essentials of current transformers in power circuits. Download fulltext pdf calculation of current transformer transient errors article pdf available in ieee transactions on power apparatus and systems 976. Theory of operation of singlephase transformers custom. The magnetic field around the winding is constantly in motion. All current transformers are subtractive polarity and will have the following designations to guide proper installation. The open circuit situation resolves to high voltages and lethal currents. Everyone involved in or with the subject area of this book, whether from academics or industry, knows that the last decade has been particularly dynamic. Enter your mobile number or email address below and well send you a.
The current twelfth edition has been prepared by martin j. Current transformer basics and the current transformer. This chapter explores the transformer theory in detail. The main purpose of this book is to examine the current state of transformer technology. Current transformers cts basic theory basic formula. If the wire forms a complete circuit, current will flow in the wire.
Polarity refers to the instantaneous direction of the primary current with respect to the secondary current and is determined by the way the transformer leads are brought out of the case. If a second coil of wire is placed in a moving magnetic field, then a voltage will be induced in this. In reality, however, it is not possible to neglect the excitation. Chapter 3 the unidirectional current pulse transformer with 46 diode rectification and natural resetting 3.
In an ideal transformer ignoring any losses, the power available in the secondary winding will be the same as the power in the primary winding, they are constant wattage devices and do not change the power only the voltage to current ratio. Tests have shown values ranging from 500 to 11,000 volts. When the circuit burden gets too large, the ct secondary voltage becomes distorted. Electrical tutorial about current transformer basics and current transformer theory on how the current transformer works with just one secondary winding. It produces a current in its secondary which is proportional to the current in its primary. Zb burden impedance ip primary current ns number of secondary turns ratio to 1 v 3. Current transformers current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. A special section deals with the gate drive requirements of the. The basics of current transformers nk technologies. Instrument transformers scale the large values of voltage or current to small. Current transformer, potential transformer working instrument.
Transformer theory quiz questions free online quiz test transformer theory and practice. Current transformer ebook electric current electricity scribd. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac. Its secondary winding then provides a much reduced current which can be used for detecting overcurrent, undercurrent, peak current, or average current conditions. The alternating current through the primary winding produces an alternating flux that surrounds the winding. Ring core cts are available for measuring currents from 50 to 5000 amps, with windows power conductor opening size from 1 to 8 diameter. Basics, maintenance, and diagnostics vii contents continued page 4. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the same. We did not build nor tested the technology presented in this book.
Calculation of cts if the current transformer has primary to secondary current ratio of 100. This flow of electricity is parallel to the one in the main circuit and can be. Basic transformer theory vp primary voltage ip primary current np primary turns pp primary power. Current transformers, along with voltage or potential transformers, are instrument transformers. This book presents transformer concepts that provide the fundamentals to understand the nonlinear characteristics, accuracy ratings, and transient behavior of current transformers. Another winding, also known as the secondary winding, is brought close to the primary. Voltage transformers are much like small power transformers, differing only in details of design that control ratio accuracy over the specified range of output. Basic transformer operation can be described by two formulae relating the transformation ratio to the turns ratio of the transformer windings. The singlephase distribution transformer consists of a primary winding and a secondary winding wound on a laminated steel core. Combinations of delta and wye transformer connections. A distinction has to be made between a metering class and a protection class current transformer. Todays transmission and distribution systems are, of course, vastly more extensive and greatly dependent on transformers that themselves are very much more efficient than those of a century ago. Transformer book is still in demand is a tribute to the publishers and to the authors who have carried the torch to light our way for 75 years.
This module introduces transformer theory and includes the types of transformers, voltage current relationships, and application. Lessons in electric circuits, volume ii ac by tony r. The output of a constantvoltage transformer is essentially a square wave, which is desirable for rectifier output applications while, also. A current transformer is an instrument transformer, used along with measuring or protective devices, in which the secondary current is proportional to the primary current under normal conditions of operation and differs from it by an angle that is approximately zero. Introduction transformers are a critical and expensive component of the power system. Instrument transformer theory and testing steve hudson, pe engineering manager 10737 lexington drive knoxville, tn 37932.
Morgan lacey in 1925, based on a series of pamphlets entitled transformer abstracts that were. The constantvoltage transformer cvt has a wide application, particularly where reliability and inherent regulating ability against line voltage changes are of prime importance. The current transformer function is different than that of a voltage transformer. If the load is disconnected from the secondary winding of the transformer and a high voltage is applied to the primary winding of the transformer, a magnetizing current will flow in the primary. Thus, in an ideal transformer the power ratio is equal to one unity as the voltage, v multiplied by.
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