# Current transformer design theory pdf

It transforms the high voltage current into the low voltage current due to which the heavy current flows through the transmission lines is safely monitored by the ammeter. Transformer tlt some baluns are narrowband because they depend on a section of transmission line that is a particular fraction of a wavelength. Cable is passing through the centre of ct and in that way forms the primary winding. Modeling current transformer ct saturation for detailed. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to. The internal process is the same, which is when an. The choice of circuit topology obviously has great impact on the transformer design. The current transformer function is different than that of a voltage transformer. Generally current transformers are designed such a way that, its. He has vast experience in the design and development of transformers. Figure 144 shows the magnetic field during one cycle. Current sense transformer application design guidelines by ariel general applications engineer, datatronic distribution inc. Currentsense transformer application design guidelines by ariel general applications engineer, datatronic distribution inc.

Ring type is the most usual type of corebalance current transformer cbct. The electrical current flowing in a transformer is al ternating current. Pdf optimal design of protective current transformer using pso. Current transformer basics and the current transformer. Primary of this transformer is connected across the phase and ground. The primary wire size is much larger than the secondary wire size. Pdf saturation analysis of current transformer researchgate. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work, use of current transformer.

Voltage transformer or potential transformer theory. They are accurate, easy to implement, and reliable under harsh. 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. I want to make a current transformer using toroidal ferrites to measure 2205060hz ac current40a max.

A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. Morgan lacey in 1925, based on a series of pamphlets entitled transformer abstracts that were. The fundamentals of current sense transformer design patrick a. A study of the current transformer with particular. Allentown, pa abstract more and more substations are retrofitted with numerical relays, meters and monitoring devices. Current transformer design guide an effective design of a ring type c. A voltage transformer theory or potential transformer theory is just like a theory of general purpose step down transformer. The essentials of current transformers in power circuits. It becomes very difficult to optimize a power transformer design. The voltage, current and flux due to the current in. Basic transformer theory vp primary voltage ip primary current np primary turns pp primary power.

Current transformers are used to measure, or monitor, the current in the lead of an ac power circuit. The current flows first in one direc tion, stops, then reverses and flows in the other direc274 unit 74 transformers tion. This current is known as the magnetizing or exciting. The minimum primary inductance required l p is a function of how accurate and linear the volts per ampere versus current transfer function of the transformer needs to be. What is the working principle of a current transformer. Instrument transformer basic technical information and. Power transformers operating theory butler winding. If a ct test switch is used, the switch must have a makebeforebreak contact pattern to. If there is a zero sequence impedance of transformer, the power and leakage impedance rating of the transformer may be calculated. Continue reading current transformers theory of operation. Testing current transformers burden test only if we cannot get to the primary side of the ct we can. The designer should consider the maximum gate trigger current as the minimum trigger current value that must be applied to the device in order to assure its proper triggering. Calculation of cts if the current transformer has primary to secondary current ratio of 100.

The output of a constantvoltage transformer is essentially a square wave, which is desirable for rectifier output applications while, also. 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 meter or relay. Its electrical purpose is to transfer power from the primary winding to the other windings with no energy storage or loss. The basics of current transformers nk technologies. Electrical tutorial about current transformer basics and current transformer theory on how the current transformer works with just one secondary winding. When an ac voltage is applied to the primary winding, a timevarying current flows in the primary winding and causes an ac magnetic flux to appear in the transformer core. Ring core cts are available for measuring currents from 50 to 5000 amps, with windows power conductor opening size from 1 to 8 diameter. Figure 6 bar primary type current transformer ct having single primary turn with the primary conductor embedded go back to contents 2. It details both the theory and practice of inductors and transformers employed to filter currents, store electromagnetic energy, provide physical isolation between circuits, and perform stepping up and down of dc. 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. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load. The regulation characteristics at various lines and loads are shown in figure 116. A distinction has to be made between a metering class and a protection class current transformer.

In high frequency transformers eddy current losses are reduced by using a core made of a ceramic. Most power transformer designers use an electrical model that allows them to approximate a transformer design. Thus, in an ideal transformer the power ratio is equal to one unity as the voltage, v multiplied by. 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. Nov 15, 2019 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 which is approximately zero. The magnetic field around the winding is constantly in motion. Some most recent works are also discussed to give readers a feel for the latest trends in transformer technology. H i g h p o w e r e d r e s e a r c h f o r t h e r e a l w o r l d december 2011 issue 1 modeling current transformer ct saturation for detailed protection studies 6 the wound rotor wr and squirrel. 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. Basics, maintenance, and diagnostics vii contents continued page 4. In the ideal transformer the current value is zero. Igt gate trigger current the maximum value of gate current required to switch the device from the off. The preliminary approximate design will be evaluated, then adjusted as needed to achieve desired objectives. Pdf current transformers ct are the key device in power system protection.

Optimiza tion techniques, programming and algorithm theory. Design requirements for current transformers for general protection purposes are frequently laid out in terms of kneepoint e. A current transformer is a device that is used for the transformation of current from a higher value into a proportionate current to a lower value. If there is a zero sequence impedance of transformer, the power and leakage impedance rating. The arrangement of primary and secondary windings on the transformer core is shown in figure 9 below. Isolation transformers can allow separate circuits to be physically isolated from each other whilst still allowing current and. They are very useful in highpower circuits, where the current. Generally, the metering its require high accuracy in the range of normal oper. The shortcircuit current is limited and set by the series inductance, l. Generally current transformers and ammeters are used together as a matched pair in which the design of the current transformer is such as to provide a maximum secondary current corresponding to a fullscale deflection on the ammeter. C indicates accuracy can be calculated based on design.

In the typical current transformer application, the primary winding consists of one to a few turns of wire. In case of a transformer of normal design, the no load current will generally be less than about 2% of the full load current. In nonideal transformers this current is greater than zero. The above theory is sufficient to give a general view. A transformer has no moving parts and is a completely. Current transformers theory of operation butler winding. 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. The basic theory covers all types from small high frequency transformers using ferrite core, current transformers typically a round wound core and a. It can be designed to step up or step down voltages and works on the magnetic induction principle. The current transformer is used in meters for measuring the current up to 100 amperes. Force is proportional to square of current transformer consulting services inc. A centre tapped transformer works in more or less the same way as a usual transformer. Currentsense transformer application design guidelines. Design procedure for compact pulse transformers with.

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. Most often, the older relay gets replaced with a newer relay with the rest of the installation such as current transformer ct and lead. Cattermole typically, the transformer is designed so that the impedance of the primary winding is much greather than the shunt resistance reflected into the primary side and thus the primary impedance is mostly resistive. When the circuit burden gets too large, the ct secondary voltage becomes distorted. 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. An alternating voltage v p applied to the primary creates an alternating current i p through the primary. The ideal transformer equations we use are sufficient to design a transformer that works under certain constraints.

Magnetics design 4 power transformer design texas instruments. 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. C indicates accuracy can be calculated based on design of this ct. A transformer uses the principles of electromagnetism to change one a. The number of secondary winding turns is a selected multiple of the primary turns. The constantvoltage transformer cvt has a wide application, particularly where reliability and inherent regulating ability against line voltage changes are of prime importance. Your load resistance should be small relative to the impedances of the inductors in the transformer, at least at the frequency you want it to work at. Instrument transformer theory and testing steve hudson, pe engineering manager 10737 lexington drive knoxville, tn 37932. Oct 08, 2016 calculation of cts if the current transformer has primary to secondary current ratio of 100. 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.

Figure 1 gives a circuit schematic of a current transformer application. Optimization techniques, programming and algorithm theory. The core of the current transformer is built up with lamination of silicon steel. Power transformer design involves many interdependent parameters. Current transformers current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. Aresistanceshunted byacondenserisplacedinthemovingcoilcircuitoftheseries. Based on the fundamentals of electromagnetics, this clear and concise text explains basic and applied principles of transformer and inductor design for power electronic applications. H i g h p o w e r e d r e s e a r c h f o r t h e r e a l w o r l d december 2011 issue 1 modeling current transformer ct saturation for detailed protection studies 6 the wound rotor wr and squirrel cage sq induction machine models. Detailed descriptions of many types of transformer are also given together with typical applications. Leakage inductance delays the transfer of current between switches. Basic transformer theory vp primary voltage ip primary current np primary turns. Instrument transformer theory and testing steve hudson, pe. Just like the transformer used for stepping down purpose, potential transformer i.

The voltage transformer is designed to connect in parallel. Chapter 16 current transformer design university of north. A study of the current transformer with particular reference. The current transformer is used for measuring the high voltage current because of the difficulty of inadequate insulation in the meter itself. Also, you should expect the transformer to have losses from the ideal value that. If the voltage is stepped up in the secondary, the current is stepped down by the same amount if the voltage is stepped down in the secondary, the current is stepped up by the same amount. However, most baluns are made from short sections of transmission lines compared to l surrounded by magnetic media with their ends connected to show transformerlike properties. Current transformer design example the following information is the design specification for a current transformer, as shown in figure 169. 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. The standard for precise current measurement in instrumentation and other high reliability equipment applications has been the current sense transformer. 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 first author worked in the transformer industry for 11 years before joining academia. Shortcircuit design basic theory radial force due to axial flux. For an ideal transformer, the power delivered in the secondary v sec isec equals the power in the primary v pri ipri therefore.

402 488 385 1156 457 321 785 1286 1009 385 1197 1204 350 1199 1300 291 1614 1251 1267 1598 471 947 798 983 506 1029 1526 157 826 918 1542 314 1614 910 1156 992 1115 1184 1437 651 203 366 1179 815 927