Nevertheless, the primary winding is still connected to electricity and forms a closed circuit. This is required to minimize the transmission loss and making the transmission line. In other words, for a transformer there is no direct electrical connection between the two coil windings, thereby giving it the name also of an isolation transformer. Current transformers theory of operation butler winding. The basics of current transformers nk technologies. 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. Instrument transformers are also used with protective relays for protection of power system. Apr 25, 2017 the current transformer the current transformer c. What is the working principle of a current transformer. An alternating voltage v p applied to the primary creates an alternating current i p through the primary. 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. The number of secondary winding turns is a selected multiple of the primary turns. A distinction has to be made between a metering class and a protection class current transformer.
Current flowing in a wire produces a magnetic field. Instrument transformers are used in ac system for measurement of electrical quantities i. Transient saturation of current transformers may cause maloperation of protective devices. Download fulltext pdf calculation of current transformer transient errors article pdf available in ieee transactions on power apparatus and systems 976. It can be designed to step up or step down voltages and works on the magnetic induction principle. Primary of this transformer is connected across the phase and ground. Like the power transformer, the current transformer also contains a primary and a secondary winding. Therefore there is a need for a method which enables the calculating of transient transformation errors. Instrument transformer basic technical information and. Instrument transformer theory and testing steve hudson, pe. The essentials of current transformers in power circuits. The primary winding is supplied an alternating electrical source. In the typical current transformer application, the primary winding consists of one to a few turns of wire.
Current transformers cts are an indispensable tool to aid in the measurement of ac current. Similarly, current transformers take a high current and reduce it to typically 5 amps on the secondary winding so that it can be used with a watthour meter, ammeter. Figure 1 gives a circuit schematic of a current transformer application. Current transformers have their primary windings connected in series with the power circuit, and so also in series with the system impedance. The secondary winding of ct has large number of turns which is determined by the secondary.
The transformer does this by linking together two or more electrical circuits using a common oscillating magnetic circuit which is produced by the transformer itself. 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 basics of current transformers ratio the ct ratio is the ratio of primary current input to secondary current output at full load. Technical level training course 201203 abb instrument transformers current transformer theory current transformers why instrument transformers. Free online quiz test transformer theory and practice. Current transformers of various shapes and sizes are used as an interfacing solution. Instrument transformers potential transformer, current transformers for high voltage and current measurement. Recommendations are provided by manufacturers see application guides. Voltage is produced in any conductor in a changing magnetic field current flowing in the coil on one side of the transformer induces a voltage in the coil on the other side. Ideal transformer theory equations example problems.
Like a traditional voltage transformer, the ratio of the windings determines the relation between the input and output currents. It buffers the meter from experiencing excessive torques that might be. Current transformers cts basic theory basic formula. Commercially available relays and meters used for protection and metering, are designed for low voltage. The basic principle of the current transformer is the same as that of the power transformer. Kod ktf remanence only considered in extra high voltage systems ehv k tfvalues acc. Basic transformer theory vp primary voltage ip primary current np primary turns. 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. Transformers the current in the first coil is usually called the primary current and the current in the second wire is the secondary current.
Abaout ttt eocneccbivbycosnabcyaecntecagcnl mr transformers are used to accurately measure high alternating primary currents, converting the primary current into a. Voltage transformer or potential transformer theory. Current transformers 101 publications give the burdens of individual relays, meters, etc. This is the first part of video series called as current transformer in this video i have discussed about definition of current transformer and working principle of it. Pdf abb instrument transformers current transformer theory. Testing current transformers burden test only if we cannot get to the primary side of the ct we can. Generally, the primary winding of a transformer is connected to the input voltage supply and converts or transforms the electrical power into a magnetic field. 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. The current twelfth edition has been prepared by martin j. Transformer theory quiz questions electrician practice tests. In a current transformer its primary winding is connected in series with the line carrying the load current. Current and power when a load resistor is connected to the secondary winding, there is a current through the resulting secondary circuit because of the voltage induced in the secondary coil this results in current in both the primary and secondary coils which is also effected by the turns ratio.
Selecting current transformers janitza electronics. The ct burden impedance decreases as the secondary current increases, because of saturation in the magnetic circuits of relays and other devices. Constantvoltage transformer, regulating characteristics the basic twocomponent cvt ferroresonant regulator is shown in figure 111. Whenever an alternating current flows through the primary winding, alternating magnetic flux is produced, which then induces alternating current in the. Nov 26, 2017 instrument transformers potential transformer, current transformers for high voltage and current measurement.
Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering. This protects connected metering devices from overloading in the presence of fault level current flows. A transformer has no moving parts and is a completely. A transformer operates on the principals of electromagnetic induction, in the form of mutual induction. Current transformer circuits for power electronics. Dec 30, 2018 voltage transformer or potential transformer theory. Mar 25, 2015 introduction to current transformers part 2. 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. 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. Another winding, also known as the secondary winding, is brought close to the primary. Cts current transformers pts potential transformers. Voltage transformers are much like small power transformers, differing only in details of design that control ratio accuracy over the specified range of output.
Theory of operation of singlephase transformers custom coils. Basic function of instrument transformers is to step down the ac system voltage and current. In this case, the primary winding behaves as a coil with a core. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the same. The output of a constantvoltage transformer is essentially a square wave, which is desirable for rectifier output applications while, also. Voltage is produced in any conductor in a changing magnetic field current flowing in the coil on one side of the transformer induces a. Current transformers current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. Zb burden impedance ip primary current ns number of secondary turns ratio to 1 v 3. When current flow exceeds that rating, the metering core will become saturated, thereby limiting the amount of current level within the device. A voltage transformer theory or potential transformer theory is just like a theory of general purpose step down transformer.
Current transformers perform the following functions. Ring core cts are available for measuring currents from 50 to 5000 amps, with windows power conductor opening size from 1 to 8. Potential transformer or voltage transformer gets used in electrical power system for stepping down the system voltage to a safe value which can be fed to low ratings meters and relays. Current transformer basics and the current transformer. Pdf current transformers ct are the key device in power system protection. Presentation on current transformers submitted by roopal pancholi b. 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 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. 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.
Tech electrical, iii year, v semester k72 submitted to mr. Instrument transformers potential transformer, current transformers for high voltage. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the. Modern ac transmission technology requires the voltage to be higher such as 11kv, 33kv, 3kv, 232kv. Generally current transformers are designed such a way that. This is a simplest form of potential transformer definition. Module transformers this module introduces transformer theory and includes the types of transformers, voltage current relationships, and application.
Concept of current transformer with examples current transformer c. Theory of operation of singlephase transformers custom. Complete basics and theory of electrical transformer. Nov 15, 2019 the basic principle of the current transformer is the same as that of the power transformer. While the latter configuration would not be used today, one may be required to make this calculation on an existing system. There are four typical types of current transformers. Concept of current transformer with examples paktechpoint.
Pdf abb instrument transformers current transformer. Mutual induction is the process by which a coil of wire magnetically. A current transformer ct is a type of transformer that is used to reduce or multiply an. The ct ratio is the ratio of primary current input to secondary current output at full. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. Current transformer circuits for power electronics applications. Abb instrument transformers current transformer theory technical level training course 201203. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an ac. K tf values required in practice depend on relay type and design.
Transformer as a static device uses the electromagnetic induction principle of faradays law of electromagnetic induction. The alternating current through the primary winding produces an alternating flux that surrounds the winding. In this case there are no movement to get the relative motion between the constant flux and the conductor. Whilst measurement current transformers are intended to reach saturation point as quickly as possible once they exceed their operational current range expressed by the overcurrent factor fs in order to avoid an increase in the secondary current with a fault e. 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. Current transformers of various shapes and sizes are used as an interfacing solution between high currents and instrumentation devices. Module transformers this module introduces transformer theory and includes the types of transformers, voltagecurrent relationships, and application. Electrical tutorial about current transformer basics and current transformer theory on how the current transformer works with just one secondary winding. Pdf calculation of current transformer transient errors. 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. This is called electromagnetic induction because the current in the first coil causes or induces.
Current transformers are devices used to scale large primary currents to a smaller, easy to measure, secondary currents. Chapter 3 the unidirectional current pulse transformer with 46 diode rectification and natural resetting 3. The primary winding of ct consists of very few turns usually 1. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. They provide a means of scaling a large primary input current into a smaller, manageable output secondary. Current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. Unique to a current transformer the current transformer function is different than that of a voltage transformer. Module 14 test instruments and measuring devices this module describes electrical measuring and test equipment and includes the. Continue reading current transformers theory of operation.
The function of current and voltage transformers collectively known as. The voltage transformer can be thought of as an electrical component rather than an electronic component. The primary wire size is much larger than the secondary wire size. What weve done here is pass an electric current through empty space from one coil of wire to another.
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