Basics, maintenance, and diagnostics vii contents continued page 4. 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. If the currents exceeding several hundreds of amperes have to circulate continuously through the. When the primary of a transformer is energized with the secondary unloaded, a small current flows in the primary. Exploring current transformer applications power electronics. 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. Cts are required because standard current measuring devices are not configured to measu. This current creates a magnetizing force that produces the magnetic flux in the transformer core. If a ct test switch is used, the switch must have a makebeforebreak contact pattern to. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to. Comments about the use of a zigzag transformer to reduce. The ct ratio is the ratio of primary current input to secondary current output at full.
Pdf abb instrument transformers current transformer theory. What is the working principle of a current transformer. Transformer as a static device uses the electromagnetic induction principle of faradays law of electromagnetic induction. The current twelfth edition has been prepared by martin j. The basic principle of the current transformer is the same as that of the power transformer. 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. The alternating current through the primary winding produces an alternating flux that surrounds the winding. 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 primary wire size is much larger than the secondary wire size. The difference lies in just the fact that its secondary winding is divided into two parts, so two individual voltages can be acquired across the two line ends. Feb 12, 2017 in this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work, use of current transformer. Theory of operation of singlephase transformers custom coils. Jan 17, 2019 but this current is not the actual magnetizing current. In this case there are no movement to get the relative motion between the constant flux and the conductor. This module introduces transformer theory and includes the types of transformers, voltagecurrent relationships, and application. Theory of operation of singlephase transformers custom. The basics of current transformers nk technologies. Explain how an ideal transformer operates find the voltages and currents on both sides of an ideal transformer using the turns ration. Abb instrument transformers current transformer theory technical level training course 201203. We have discussed about the theory of ideal transformer for better understanding of actual elementary theory of transformer.
Instrument transformer basic technical information and. Nov 15, 2019 the basic principle of the current transformer is the same as that of the power transformer. Jun 24, 2018 electrical transformer theory and concepts 1 how transformer works. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work, use of current transformer. Ensure the ct is connected to system properly in all respect primary and secondary. Energy is stored in the magnetic field of the transformer when the pulse is applied. The internal process is the same, which is when an. Pdf abb instrument transformers current transformer. Scribd is the worlds largest social reading and publishing site. Complete basics and theory of electrical transformer. There are two types of transformers classified by their function. Electrical transformer theory and concepts 1 how transformer works. Mutual induction is the process by which a coil of wire magnetically.
Whenever an alternating current flows through the primary winding, alternating magnetic flux is produced, which then induces alternating current in the. A current transformer is an instrument transformer, used along with measuring or protective devices, in which the secondary current is. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load. Ring core cts are available for measuring currents from 50 to 5000 amps, with windows power conductor opening size from 1 to 8 diameter. A distinction has to be made between a metering class and a protection class current transformer. With current transformers, the user must know the current ratio to use the transformer. The fundamentals of current sense transformer design patrick a. In the typical current transformer application, the primary winding consists of one to a few turns of wire.
Total current supplied from the source has two components, one is magnetizing current which is merely utilized for magnetizing the core, and another component of the source current is consumed for compensating the core losses in transformers. It produces a current in its secondary which is proportional to the current in its primary. In the previous test at ns3 the unloaded transformer current was about 0. The linear current transformer constitutes an even more radical departure from the normal solid core ct in that it incorporates an appreciable air gap, for example 7. 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. The number of secondary winding turns is a selected multiple of the primary turns. 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 transformer on load and no load operation. There are four typical types of current transformers. 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. In this case there are no movement to get the relative motion between the. Another winding, also known as the secondary winding, is brought close to the primary winding. The current transformer function is different than that of a voltage transformer. The essentials of current transformers in power circuits.
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. Most often, the older relay gets replaced with a newer relay with the rest of the installation such as current transformer ct and lead. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the. Current transformers theory of operation butler winding. As its name implies the magnetic behaviour tends to linearization by the inclusion of this gap in the magnetic circuit. Current transformers, along with voltage or potential transformers, are instrument transformers. Figure 1 gives a circuit schematic of a current transformer application.
Calculation of current transformer transient errors article pdf available in ieee transactions on power apparatus and systems 976. 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. Chapter 3 the unidirectional current pulse transformer with 46 diode rectification and natural resetting 3. Introduction transformers are a critical and expensive component of the power system. Experience has shown that the, lc, relationship is. Now we will go through the practical aspects one by one of an electrical power transformer and try to draw vector diagram of transformer in every step. Allentown, pa abstract more and more substations are retrofitted with numerical relays, meters and monitoring devices.
To confirm the physical condition and electrical characteristics of current transformer installed in the installation. 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. Electrical tutorial about current transformer basics and current transformer theory on how the current transformer works with just one secondary winding. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac. Basic transformer operation can be described by two formulae relating the transformation ratio to the turns ratio of the transformer windings. Current transformers, or cts, are transformers used to step down the current level of highpower transmission systems to measure or monitor the current levels. A current transformer ct is a type of transformer that is used to reduce or multiply an. When the circuit burden gets too large, the ct secondary voltage becomes distorted. A centre tapped transformer works in more or less the same way as a usual transformer. Pdf calculation of current transformer transient errors. Modern ac transmission technology requires the voltage to be higher such as 11kv, 33kv, 3kv, 232kv. 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.
Current transformer is used to step down the current of power system to a lower level to make it feasible to be measured by small rating ammeter i. Instrument transformers scale the large values of voltage or current to small. Sep 16, 2017 a transformer is a static apparatus, with no moving parts, which transforms electrical power from one circuit to another with changes in voltage and current and no change in frequency. Current transformer circuits for power electronics. Current transformer basics and the current transformer. A typical connection diagram of a current transformer is shown in figure below. Continue reading current transformers theory of operation. The same test in the vicinity of rack m216 showed an unloaded zigzag transformer current of 10.
Morgan lacey in 1925, based on a series of pamphlets entitled transformer abstracts that were. A transformer operates on the principals of electromagnetic induction, in the form of mutual induction. This is required to minimize the transmission loss and making the transmission line. An alternating voltage v p applied to the primary creates an alternating current i p through the primary.
Constantvoltage transformer, design equations proper operation and power capacity of a constantvoltage transformer cvt depends on components, li and cl, as shown in figure 117. Quite often, the end users provide the primary with a wire through the center of the transformer. Oct 08, 2016 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. Apr 25, 2017 the current transformer the current transformer c. The knowledge of amps in per amps out is the basis for use of the current transformer. The primary winding is supplied an alternating electrical source. A transformer is a static apparatus, with no moving parts, which transforms electrical power from one circuit to another with changes in voltage and current and no change in frequency.