Based on this form of configuration, the current transformer is always introduced as a series transformer as the primary section, which never has more than a very few turns, is in series form with the current-carrying conductor providing a load. Medium voltage CTs come with our without mounting bracket. A current transformer of say 5/500 will create 5 amps in the secondary winding for 500 amps in the primary part, 100 times higher. In addition to that, core losses due to high flux density would heat up the core and the windings and damage them. Current Ratio Error expressed in percent is given by the formula:Credit: https://talema.com/introduction-current-transformers/, Kn = Rated transformation ratioIp = Actual primary currentIs = Actual secondary current when Ip is flowing, under conditions of measurement. Basically, it is a step-down transformer (with respect to current) consisting of two windings, primary and secondary without any electrical connection between them. Current Transformers (600 Volt, Indoor Bar Type) Specifications File Reference: Title: Publish Date: Format: JCM-3/4/5: Models JCM-3/JCM-4/JCM-5: 2017-11-08 [417k] Eaton's 5A solid-core current transformer is ideal for new construction and retrofit applications where no current transformer exists. Bar type. A current transformer is a device that is used for the transformation of current from a higher value to a lower value. The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. A. true. The ammeter, or wattmeter current coil, are connected directly across the secondary winding terminals. For low and medium voltage applications, there are three main classifications based on construction; window, bar, and wound. The simplest form any current transformer can take is the ring type or Window type, examples of which are given in the below figure which shows three commonly used shapes i.e., stadium, circular and rectangular orifices. The 100 to 5 and 20 to 1 types are the most common forms of current transform existence in the market. 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.e. The secondary current rates are of the order of 0.1 A, 1 A, and 5 A. A current transformer in which the primary winding consists of a bar of suitable size and the material forming an integral part of the transformer.The figure below shows bar type transformer. Wound type current transformer. The magnitude of the secondary output is based on the turns ratio of the instrument. CT secondary circuit must be grounded, and grounded at one point only. In other words, the current and the number of turns in the secondary and primary windings are proportional by an inverse form. 50,60. Therefore, the secondary of the current transformer may never be open when the primary part is carrying the current. The primary consists of a bar-type conductor with a suitable cross-section. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. . . An approximate inverse turns level exists between the two currents in most current transformers in the secondary and primary windings. The secondary winding is fully distributed around the periphery of the core. Electrical Deck is a platform for learning all about electrical and electronics engineering. With this connection the directions of primary and secondary currents are: When testing a CT using an Omicron test equipment it is possible to verify if the CT is correctly connected: Ring type CT is constructed of an iron toroid, which forms the core of the transformer, and is wound with secondary turns. The current transformer is used with its primary winding connected in series with line carrying the current to be measured and, therefore, the primary current is dependant upon the load connected to the system and is not determined by the load (burden)connected on the secondary winding of the current transformer. As stated above the bar-type CT carries full current through its primary whereas the ring-type CTs are installed over the current-carrying conductors. The primary winding needs to be physically connected in series to current carrying conductor. They are also used to step down the current at a specific ratio to insulate the instrument from the high voltage lines. A bar type current transformer of toroidal construction requires 400A to magnetize it, and 300 A to supply the iron loss for each volt per turn induced in the secondary winding and rated frequency. 6 Types of Electrical Switches In The Home Explained! Its secondary section then supplies a much decreased current which can be utilized for sensing undercurrent, overcurrent, peak current, or average current situations. The use of this type should be with discretion since this construction results in higher-than-normal errors. The core of the current transformer is built up with lamination of silicon steel. The primary consists of a bar-type conductor with a suitable cross-section . The core can be of solid or split type construction. According to the above referred IEC Standard, CT most common accuracies and burdens are: Class PX is the most accurate and is used usually for main protections. placed on panel boards can be used (Fig. The current transformer has high electrical isolation. SUPERBUTE Product Overview: Current Transformers. The primary side . 1 A, 5A. 3. The primary winding may be a conductor, strip etc whose current is to be reduced. These are present for sensing currents from 100 A up to 5000 A, with square window forms from 25 mm to 300mm. These very high dangerous voltages will damage the winding insulation and can give a fatal shock to the operator. Outdoor Current Transformers: Outdoor current transformers are available in Bar-Type and Window-Type styles, 5-15 kV, 60 kV-110 kV BIL, up to 4000 A. Plz, give the potential transformer theory, construction and working. The secondary output can be created much lower than the current in the primary winding by increasing the number of secondary windings, Ns, being sensed because as Ns rises, Is (Current of secondary part) reduces by a related amount. SAT 0 0 10 20 30 40 50 60 70 80 M s 38 CT Types s . 3: Bar Type CT. Precautions in the use of C.T. The ratio of a CT is the relation between the values of the primary and the secondary currents; the usual secondary values are 1 A and 5 A. Clamp meters close and open around a current transporting conductor and control its current by identifying the magnetic field around it, supplying a quick measurement reading commonly on a digital display without opening or disconnecting the circuit. It produces a current in its secondary which is proportional to the current in its primary. . c) secondary winding having one full turn wound on core. It uses the actual cable or bus bar of the . It never has more than a very few numbers of turns in its primary. Bar Type C. T. It has a circular ring type core, on which secondary is Wound. StudyElectrical.Com | Online Electrical Engineering Learning Site While , A window type or ring type CT has the incoming or outgo. One of the major differences between them is . The current transformer can be used in commercial-grade applications, such as control panels and panelboards, and for most industrial metering and relay applications in switchboards, switchgear and motor control centres. By using Linquip RFQ Service, you can expectto receive quotations from various suppliers across multiple industries and regions. Current transformers are used extensively in metering and circuit protection. A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). The body of the CT itself provides insulation between the primary circuit and ground. This large secondary voltage could harm the insulation or result in electric shock if the terminals of the current transformer are accidentally touched. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. Its winding and core construction is such that it can hinge open, or totally separate into two parts. Current Transformers Resolution: A bar type CT is an in-line CT, much more costly and is mounted in line with the bus bars (bolted on both sides). Both the primary and secondary windings are wound on the central limb and the two outer limbs provide the low reluctance flux path (see the figure). Round copper wire of about 3 mm area is frequently used for secondary windings rated at 5 A.Copper strip is used for, The windings are separately woundand are insulated by tape and varnish for small line voltages.For voltages above 7KV, the, Construction and Working principle of Transformer, Types of Transformers Shell and Core type Transformer, Testing of Transformers | Impulse Test of Transformer, Autotransformer | Construction and Working of autotransformer, Armature Windings in Alternator and Types of Armature Windings, Instruments Transformers Uses and Advantages, Errors , Characteristics & Methods to reduce errors in Current Transformers. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. Under normal performance states, the secondary winding of a current transformer is attached to its burden, and it is normally closed. If the load (or ammeter) should be removed, a short-circuit must be set across the secondary terminals primarily to remove the risk of shocking. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. Looks Like You're Using an Ad Blocker. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. If you are facing with any issues or want to request any article please feel free to contact us, and also check out our privacy policy. Current transformers decrease the high-voltage values to a much lower current and supply a convenient method of safely measuring the actual electrical current moving in an AC transmission line applying a standard ammeter. For a low voltage wound type CT, the secondary turns are wound . There are several metering cases and usages for current transformers, such as with power factor meters, Wattmeters, protective relays, watt-hour meters, or as trip coils in MCBs or magnetic circuit breakers. The standard secondary current is usually rated at 5A or 1A for ease of sensing. A current transformer (CT) is an instrument transformer in which the secondary current is substantially proportional to primary current and differs in phase from it by ideally zero degree.. CT Accuracy Class or Current Transformer Class. (1 to over 12). The secondary part, however, may have a great number of coil rolls wound on a laminated component of low-loss magnetic material. Save my name, email, and website in this browser for the next time I comment. Current transformer are used for measuring current in a bus bar without disconnecting it by means of ammeter.There are three types 1.bar type current transformer 2.toroidal current transformer 3 . The primary current and secondary output of the current transformers are related to each other. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. If there is current flow in the primary of the current transformer and its secondary winding is kept closed, the current flowing through the secondary builds up a back EMF and counters the primary magnetizing force. MV CT are usually installed indoors, in MV Switchgears Figure 4. The basic flux is taken as a reference. Table 1 Common accuracies and burden powers of CT and error limits. Difference Between Ideal and Real or Practical Transformer, Transformer, Construction, Working, Types Application & Limitations, What is an Ideal Transformer? #2 - Wound Current Transformer Figure 3. Transformer Basics and working principle,Construction,Types of . But relatively great variations in a current transformer turns ratio can be obtained by varying the primary rolls within the CTs window where one primary turn is identical to one pass and more than one pass across the window causes the electrical ratio to be modified. In the manufacture of current transformers assembly of lamination stacks demands somewhat greater core cross-section than ordinary transformers in order to keep down the reluctance of the interleaved corners as low as possible so as to minimize the magnetizing current.Sometimes cut cores are used. oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. The windings should be close together to reduce the secondary winding leakage reactance as the leakage reactance increases the ratio error. The most common type is that wound on a toroidal core. In both types, the core and windings are enclosed in a porcelain structure. Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes. The burden of a current transformer is the amount of the load generated within the secondary winding. Whereas in alternating supply it is difficult to measure large currents and it is dangerous to the operator while working with a system carrying large currents (more than 100A). If the turns ratio between primary and secondary is 100:05; then it will step up the level of voltage in terms of 20:01 or it will step down the level of current in terms of 01:20. Difference between utilization categories AC-1 and AC-3, EMF equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. They are also known as bar-primary CTs. A current transformer is generally used in metering and protective relays in the electrical power industry. Bar-type Current Transformer - This type of current transformer uses the actual cable or bus-bar of the main circuit as the primary winding, which is equivalent to a single turn. Current transformers for measurement and protection purposes . The working principle of a current transformer is especially different from the power transformer. In a low voltage wound type current transformer the secondary winding is wound on a bakelite former or bobbin and the heavy primary conductor is either wound directly on top of secondary winding, suitable insulation being first applied over the secondary winding or the primary is wound entirely separately, taped with suitable insulating material and then assembled with the secondary winding on the core. They do not have any physical contact. These current transformers have an opening where the conductor carrying the primary load is passed. A current transformer in which the primary winding consists of a bar of suitable size and the material forming an integral part of the transformer.The figure below shows bar type transformer. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); (adsbygoogle = window.adsbygoogle || []).push({}); All Rights Reserved by Electrical Engineering Info @2023, The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. 10. Current-Transformer.ppt - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. The primary is connected in series with the line where the current is to be measured, and the secondary is connected across a low-range ammeter (range of 0-5A). The current into the secondary winding depends upon the current flowing in the primary winding. Based on the type of construction, current transformers are classified into three types as follows: Window CT or toroidal CT; Bar CT; Wound CT The Global Current Transformer Market is segmented based on type, construction, core, voltage rating, application, and region. Wound-type current transformers, T-type classification, are . Advantages & Application, Working Principle of Transformer: Discover the Mechanism Involved in the Operation, Difference between Power Transformer and Distribution Transformer, Easy Guide to Cooling Tower Efficiency & How To Increase it, Parts of Boiler and Their Function in the Boilers, Types of Alternator: Features, Advantages, and Vast Usage, Ball Valve Parts: An Easy-to-Understand Guide (2022 Updated). Insulation Voltage: 3000 volts. CDG current setting = 10% = 0.5 A. Volts required to operate relay = 2 / 0.5 = 4 V. Therefore voltage required at 10 times setting = 10 x 4 = 40 V. Hence for a flux density of 1.6T the C.T. CTs used in substations are usually mounted outdoors. Our articles are written by the electrical engineers in a simple and easy way. The knee-point voltage is less applicable for metering current transformers as their accuracy is generally much tighter but constrained within a very small bandwidth of the current transformer rating, typically 1.2 to 1.5 times rated current. The phasor diagram of the current transformer is illustrated in the figure below. This transformer as a low leakage reactance for which the knowledge of the transformers secondary excitation characteristics, secondary winding resistance, secondary burden resistance and turns ratio is sufficient to assess its performance in relation to the protective relay system with which it is to be used. Ek = 4.44 B A f N. Another type of current transformer which falls into the C class is a bar-type current transformer, where the primary conductor passes through the current transformer window but there is only . The secondary rolls will be 1% and 2% less than the primary ones, and the difference being employed in the magnetizing core. Depending upon the construction there are two types of current transformers used for measuring large currents. Instrument transformers are of two types - Current Transformer (C.T.) The potential transformer is mainly classified into . Visit here to explore more about the construction of a current transformer. It is considered to be an incomplete transformer assembly since it consists only of a secondary winding wound on its core. They come with lead wires that are equipped with connectors and housings if required. It is used to activate the trip coil of a circuit breaker. These CTs are connected such as hallow nature. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Linquipis a Professional Network for Equipment manufacturers, industrial customers, and service providers, Copyright 2022 Linquip Company. After the secondary winding has been placed on the core, the ring type transformer is completed by exterior taping with or without first applying exterior end collars and circumferential insulating wraps. The secondary section will provide a current into a resistive load or into either a short circuit, in the form of an ammeter until the voltage generated in the secondary is heavy enough to saturate the core or result in a failure from additional voltage breakdown. Toroidal Current Transformer [wp_ad_camp_1] Bar-type Current Transformer: The primary of the current transformers is considered as the line or cable or busbar of the load circuit. The point on the magnetizing curve at which the CT operates is dependent upon the resistance of the CT secondary circuit. Documentary information about C.T. A bar-type current transformer which has 1 turn on its primary and 160 turns on its secondary is to be used with a standard range of ammeters that have an internal resistance of 0.2. A Clampon (also known as Clipon) is a type of amperemeter based on current transformer. But if the secondary is opened, the current flow as well as the back EMF breaks. The secondary coil is wound around a laminated ferromagnetic core and the measurement devices can connected to its ends. Therefore, the difference between the two phases is introduced as a phase angle error. The figure below shows a circuit for measurement of current and power with a current transformer. The bushing-, window-, or bar-type current transformers are of the toroidal core construction. B. They are also known as CTs. RF, which is a characteristic of metering and energy metering cores, represents the amount by which the primary load current may be increased over its nameplate rating without exceeding the allowable temperature rise, that is to say, the transformers overload capability. Various primary bar arrangements can be supplied to suite most applications. This bar is connected in series with the circuit conductor. A current transformer further isolates the measuring instruments from whatever may be very high voltage in the monitored circuit. The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. For example, a current transformer has a ratio of 200:1. Construction of a Current . The symbolic symbol of the current transformer is presented in the figure below. In special cases when taps are employed, they are distributed such that any connection made would utilize the entire core-periphery. The transformer is fundamentally a step-down transformer (with respect to current), consisting of primary and secondary windings without any electrical connection between them. In a current transformer, there exists an inverse ratio relation between the current and the number of turns in the primary and secondary windings. Shell Type Transformer Construction. Eaton's Power Systems Experience Center is the ideal place to learn how to prop. As a result, if the secondary component is opened and the current moves across the primary windings, then there will be no demagnetizing environment because of the secondary current. Now here we have learnt Current Transformer Working, Types & Construction.You can download this article as pdf, ppt. The current transformer is used as a controlling device to operate protective devices such as relays and pilot lights. The secondary of a CT cannot be left open-circuited because it may cause an abnormally high voltage to appear on the secondary and will damage the core and the windings. They are . The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuou, At very high voltages, the insulation of the current carrying conductor from the measuring circuit becomes an expensive problem. . Protection current transformer: used to protect the circuit through protective relays.generally having class 5P10,10P10,5P20etc. Construction and Types of HV Current Transformers. This type of current transformer is available to measure AC currents from 100A to 600A, at 50 to 400HZ. Circuit, Working & Phasor Diagram, Transformers Fire Protection System Causes, Types & Requirements, Efficiency of Transformer All Day Efficiency & Maximum Efficiency, Transformer Phasing: The Dot Notation and Dot Convention, Transformer Losses Types of Energy Losses in a Transformer. These transformers with low range ampere meters are used to measure the current in the high voltage circuits. Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. Thus in the case of a hollow transformers designed to measure 1000A primary current, the turns ratio will be 1000/5, which means the secondary winding has 200 turns. Thus, accurate and small instruments and monitoring devices can be applied with CTs since they are insulated away from any high-voltage energy lines. Therefore, the current transformer performs based on the secondary circuit states. All Rights Reserved. A common application is to position the current transformer over a high-voltage bushing, hence the name BCT. With wound primary current transformers this particular problem is rarely met but it is of importance to try to obtain good relative positioning of primary and secondary winding coils, thus minimizing the axial forces on both coils caused by primary winding short circuit currents. d) secondary winding having more than one full turn wound on core. The Specification of CT 1 . Across the secondary terminal is connected an impedance of 2 ohm with a phase angle . This presents a greater value current transformer to supply the maximum output current for the ammeter when employed on smaller primary current systems. 2.7.4 Current transformer construction. Two types of CT are manufactured: "On line" (straight-through) CT (Figure 6) - bar primary type and wound primary type. This is a common construction for HV and EHV current transformers. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. Cable is passing through the centre of CT and in that way forms the primary winding. A current transformer (CT) is a type of transformer that is used to measure AC current. Where Kt is the turn ratio, Ip is the primary current, and Is is the secondary current. In practice, they are intended to be used over insulated conductors when the conductor voltage exceeds 600 V. It is common practice to utilize a 600 V class window type in conjunction with air space between the window and the conductor on higher-voltage systems. The Current Transformer (C.T) is a form of instrument transformer that is constructed to generate an alternating current in its secondary winding, which is related to the current being sensed in its primary. . Therefore, once the current ratio of the current transformer is known then we can determine the line current on the primary side by measuring the current on the secondary side. A current transformer is also called an instrument transformer with an accurate current ratio of primary and secondary windings. Current transformers are used with ammeters, kWh meters, power factor meters and energy meters for current measurements. Rating factor of a CT is largely dependent upon ambient temperature. As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. Some CT has special primary coils that allow a double ratio, when an increase of the installation is foreseen (example: 200-400/1 A) see Figure 8. Measuring current transformers are constructed to feed on other . At very high voltages, the insulation of the current carrying conductor from the measuring circuit becomes an expensive problem. The simplest form any current transformer can take is the ring type or Window type, examples of which are given in the below figure which shows three . HV CT are commonly installed outdoors, in AIS substations (Air Insulated Substation) Figure 2 or indoors, in GIS substations (Gas Insulated Substation) Figure 3. Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. Over the secondary winding, the primary winding is wound on the outer core with suitable insulation between the two windings. The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. Why are current transformers (CT) necessary? Good to Know: Round copper wire of about 3 mm area is frequently used for secondary windings rated at 5 A.Copper strip is used for primary winding, the dimensions of which depend upon the primary winding current. Based on the function performed by the current transformer, it can be classified is follows: . 3. Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. In a bar type current transformer, the core and secondary windings are the same as in a ring type transformer but the fully insulated bar conductor constituting the single turn primary winding is now an integral part of the current transformer.The insulation on the primary winding conductor may be bakelized paper tube or a resin directly moulded on the bar. Thus a current transformer operates its secondary winding nearly under short circuit conditions. Essentially, C relaying accuracy class applies to a current transformer of the toroidal, bushing or window type, commonly called donut-type transformers. A near relative of the ring type current transformer is the so called bushing type transformer.This is, in fact, indistinguishable from of the ordinary ring type but the term is used when the current transformer fits over a fully insulated primary winding conductor such as over the oil end of a terminal bushing of a power transformer or an oil circuit breaker. This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. Instead, the line that runs the current flowing in the system is threaded across a hole or window in the toroidal transformer. The split-core type current transformer is a special case of a window-type current transformer. In a split core current transformer, the core is split, each half having two finely ground or lapped gap faces.These current transformers are assembled onto the primary conductor on site for either permanent or temporary duty. Bar type current transformer. Save my name, email, and website in this browser for the next time I comment. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work , use of current tran. The current transformer has easy maintenance and installation. Usually HV CT use oil or gas (SF6) as insulation medium and MV CT use synthetic resins. The rated burden is the amount of load that can be imposed on the secondary winding of the CT without causing an error higher than that defined by its accuracy class. The primary winding in most cases is a single conductor centrally located in the window. Uncommon current primary rates differ from 10 A to 3000 A or more. But current transformers using hot rolled steel will consist of stack of ring stampings.Before putting secondary winding on the core, the latter is insulated by means of end collars and circumferential wraps of elephantide or presspahn. Difference Between Single Phase and Three Phase Transformer. A bar current transformer is a special type of window current transformer with a solid bar placed permanently through the window. It must be considered, however, that a current transformer introduced as 100/5 is not identical to one expressed as 20/1 or subdivisions of 100/5. Ring type CT are commonly used in cables, busbars and transformers bushings. Burden in VA. 1. Switched Reluctance Motor Drive: Definition and Function. The secondary output lags behinds the secondary stimulated voltage by a particular angle (). A typical connection . Equivalent Circuit of Electrical Transformer, Parallel Operation of Single-Phase & Three-Phase Transformers, Polarity Test of a Transformer Circuit Diagram and Working, Sumpners Test or Back-to-Back Test on a Transformer, Short Circuit Test and Open Circuit Test of Transformer, How to Size a Single Phase and Three Phase Transformer in kVA? [2] IEC: International Electrotechnical Commission. Your email address will not be published. Current and voltage transformers are available in voltage classes ranging from 5 kV to 34.5 kV. The maximum current up to which the transformer must maintain its current ratio is 40,000 amperes. Current transformers are considered to be applied as proportional current instruments. Figure 8 Schematic connection of primary CT windings with double ratio. One of the terminals of the secondary winding is earthed so as to protect equipment and personnel in the vicinity in the event of an insulation breakdown in the current transformer. At 750 kV, cascaded current, Whenever possible secondary windings should utilize the whole available, In the case of a large number of secondary winding turns, requiring more than one winding layer, the frequently adopted technique is to sectionalize the secondary, The windings should be close together to reduce the secondary winding leakage reactance as the leakage reactance increases the ratio error. The primary current and the full scale deflection current of the measurement devices determines the turns ratio of the a CT. should have an output of at. The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. Where required for test purposes, terminals in the form of test blocks are provided on the switchgear for the connection of external instruments and metering equipment. Types of Wind Turbines: Type 1, 2, 3, and 4 Explained! Frequency Range: 0.0480 to 0.0620 kHz. Required fields are marked *. Wire wound Current Transformer can be used to measure currents in the range of 1A to 100A. One is Live Tank CT and another one is Dead Tank CT. Common value for RF is 1.5. Bar-type Current Transformers: This form of current transformers employs the actual wire or bus-bar of the main circuit as the primary section, which is identical to a single turn. In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. Clap Switch Circuit Using IC 555 Timer & Without Timer. There are several core types used, from low-reactance toroid to high-reactance cut . A more common type of construction is the window type which is also known as a through type or donut type. Assume that a bar primary type 2000/5A (CROSS core) current transformer having a core csa area of 20 square cm's is available with a secondary resistance of 0 31 ohm. The accuracy classed defined by IEC are 5P, 10P, PR, PX or TP and those defined by IEEE are C 100-800. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. Potential Transformer (P.T.) The conductor itself acts as a single turn primary winding. Based on the construction, there are two types of current transformer. Itproduces an alternating current (AC) in its secondary which is proportional to the AC currentin its primary. Hence, it acts as a step-up transformer with respect to the voltage. [3]A magnetic material is said to be saturated when the increase of applied external magnetic field does not increases the magnetization of the material. Current Transformer (C.T.) The primary of a CT is connected in series to the current-carrying conductor and measurement devices are connected to its secondary. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). A common and portable kind that can be employed to detect the circuit loading is introduced as clamp meters or Handheld type, as shown. There are some window types that can be rated for higher voltages as stand-alone units, for use with an integral high-voltage stress shield, or for use with an insulating sleeve or tube made of porcelain or some polymeric material. RITZ is one of the world's leading specialists in the field of Instrument Transformers, cast resin insulated Bus Bar Systems, cast resin insulated Power Transformers as well as cast resin parts according to customer specifications. if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'electricalclassroom_com-box-3','ezslot_2',190,'0','0'])};__ez_fad_position('div-gpt-ad-electricalclassroom_com-box-3-0');A current transformer is a type of instrument, used to measure or sense large alternating currents by scaling it to a smaller, safer and measurable value. They are constructed to supply a current in its secondary winding related . These units are typically used by utilities in substations. Bar Type Current Transformers. Product scope Primary current 100 A - 2500 A Highest voltage for equipment: Figure 1 Schematic connection of a current transformer. The primary winding of a current transformer is wound with a few turns (one or more) of a thick cross-sectioned conductor. Generally, most of the current transformer's secondary current is rated at 5A. A current transformers primary winding is often configured in series form with the main conductor. The windings are separately woundand are insulated by tape and varnish for small line voltages.For voltages above 7KV, the transformers are oil immersed or compound filled. By using Grain-oriented cold-rolled silicon steel. C. 4. Bus Bar - In this type, the bus bar of the main circuit itself acts as the primary winding with a single turn. . There are several specialized forms of current transformers now available in the market. It is best suited for general-purpose monitoring and temporary installations. Their structure can be one single primary turn as in Doughnut, Toroidal, or Bar forms, or a few wound primary turns, commonly for low current applications. RITZ offers a large portfolio with a variety of different products. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. To this end, 'bar' type primaries are used, wherever practicable. Bar Type CT: One that has a fixed and straight single primary winding turn passing through the magnetic circuit. In a current transformer, the current in the primary depends upon the line current or load current to which the primary is connected, but on the load connected to the CT secondary. Most current transformers have the normal secondary rating of 5 A, with the secondary and primary currents being presented as a ratio such as 5/100. Therefore, if we know the current ratio and the rating of AC ampere meter, we may determine the line current. The manner in which the windings are arranged on the core affects the reactance since it is a geometric function. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. If the ammeter on the secondary winding is read 1.5 amps i.e, I2 = 1.5A. Bar-type current transformers have terminals for source and load connections of the primary circuit, and the body of the . The instruments (ammeter etc.) Commentdocument.getElementById("comment").setAttribute("id","aeab83a3360e0480bd8257b4249fdabe");document.getElementById("e3ea4ddf74").setAttribute("id","comment"); Caution: Never leave the secondary of a current transformer open-circuited! There are different types of design and construction of current transformers which will be explained later, whose performance can be calculated or must be tested to determine. Often only 50% of the effective magnetic path is used. They have separate primary and secondary winding. It is a very good information about CT for electrical knowledge. The specification of a PX accuracy CT is: Common accuracies and burden powers, as well as error limits, according to IEC Standard 61869 are indicated in Table 1. 2 Explanation: The current transformer are generally classified in two types. Large alternating currents that cannot be measured directly by normal ammeters or by wattmeters current coil to measure power can be done by using a current transformer. Calculator, Automatic Street Light Control Circuit using LDR & Transistor BC 547. 2.5.3 Core-Balance Current Transformers. It is presented as the output in V.A (volt-amperes). Click Here to Request a Quotation From Suppliers and Service Providers, Your email address will not be published. The construction of the current transformer can be wound or bar type. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. The accuracy classed defined by IEC are 0.2 or 0,2S, 0.5 or 0.5S and those defined by IEEE are 0.15 or 0.15S, 0.3 or 0.6. [2] IEC: International Electrotechnical Commission. this type of system has severe limitation in its power output which has to be amplified in order to operate relays etc. This accuracy class was retained by IEC in 1966 in the Amendment nr. But in a practical current transformer, there is a phase difference between the secondary and the primary current since the primary output has also supplied the portion of the exciting current. Due to which an extremely high voltage appears at the secondary of the transformer which is dangerous to personnel and the CT itself. A bar-type current transformer which has 1 turn on its primary and 160 turns on its secondary is to be used with a standard range of ammeters that have an internal resistance of 0.2. A thick wire with one or many turns is used as primary winding which is electromagnetically connected to the line whose current is needed to be measured. Bar-type Current Transformers: This form of current transformers employs the actual wire or bus-bar of the main circuit as the primary section, which is identical to a single turn. Difference between Power Transformers and Distribution Transformers? However, the concept of knee point voltage is very pertinent to protection current transformers, since they are necessarily exposed to currents of 20 or 30 times rated current during faults, and is most critical on differential protection that will be discussed later. Conversely, the minimum primary current a CT can accurately measure is light load, or 10% of the rated current. They are classified into four basic types: Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage type. The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter Your Email Address to Subscribe to this Blog and Receive Notifications of New Posts by Email. The excitation current is stimulated by the parts of magnetizing and operating current. 2. Construction can be one single primary turn as in Toroidal . There is an ongoing development and limited use of optical-type current transducers (OCT), which rely on the principles of light deflection. In the shape of a doughnut, these transformers are designed without having a primary winding as part of their construction. Otherwise, it will be like operating a voltage transformer in short-circuit condition which leads to damage to the insulation as well as the chance of danger of electric shock to the operator. b) primary winding consists of a bar of suitable size and material. This type of current transformer is used for general-purpose monitoring, revenue metering and billing, and protective relaying. A window type CT is rated at 600 volts and has the incoming or outgoing insulated/shielded cables pulled through it. Accuracy classes are defined by IEC and IEEE and are different for metering CTs and relaying CTs. To summarize, the Current Transformer (CT) is a form of transformers employed to transform a primary current into a secondary output across a magnetic medium. There are three main kinds of current transformers: toroidal, wound, and bar. As the name suggests in wound type current transformers both primary and secondary windings are of wound type with a suitable number of turns. They have very similar construction to that of normal transformer. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. Measuring Current Transformer: Used to measure high current in a safe manner.generally class 0.1,0.2,1.0. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). How to Connect Automatic UPS / Inverter to the Home Supply System? The insulation of Bar Type Rectangular Current Transformer provides an enhanced safety. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. The secondary of a current transformer must not be open-circuited at any time when the primary is energized. . How rating of a circuit breaker for a system is determined? Why Cant a Transformer Be Operated on DC Supply? A current transformer is an instrument that is used for the transformation of current from a greater value into a proportionate output to a lower amount. The type of wire used as the main current carrying conductor in a transformer winding is either copper or aluminium. In the case of a large number of secondary winding turns, requiring more than one winding layer, the frequently adopted technique is to sectionalize the secondary winding so as to considerably reduce the peak voltage between layers. Also, the voltage in the secondary winding will be 200 times the primary voltage. They are typically 600 V class since they are used in the low-voltage circuit. The window-type current transformer is the simplest form of instrument transformer. The secondary windings of the transformer carry the current proportional to the current to be measured, and it is connected to the current windings of the meters or the instruments. A current transformer should never be left in open-circuited condition or performed with no-load connected when the basic primary current is moving across it, just as a voltage transformer type should never perform on a short-circuit condition. The working or operation of a current transformer is similar to that of a normal two-winding transformer. The current rate of the transformer is normally high. The windings must be designed to withstand, without damage, the large short circuit forces that are caused when a short circuit takes place on the system in which the current transformer is connected. The potential transformer is connected in parallel with the circuit. Tamper-Resistant Outlet: What is it? For this CT to operate satisfactorily at maximum fault currents, it must operate on the linear part of the magnetizing curve, i.e., below the point at which saturation occurs, which is known as the knee point. The turns ratio of a current transformer is made such that the full load current in its primary give a secondary current of either 5A or 1A. Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? Why are Air-Conditioners (AC) Rated in Tons, Not in kW or kVA? Current transformers (CT) are used in High Voltage (HV) and Medium Voltage (MV)[1] installations to give an image of electrical current to protection relays and units and metering equipment and they are designed to provide a current in its secondary proportional to the current flowing in its primary. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. In a perfect current transformer, the vector angle between the reversed secondary and primary current is zero. The ammeters scale is adjusted according to the turns ratio. The busbar acts as a single turn primary winding. Bar Current Transformers. They may contain multiple cores and secondary coils as well as added insulation. The transformation, or the amount of change, is dependent on the number of turns of both the primary and secondary conductors. Bar-type Current Transformer . The secondary and primary produced voltages are lagging behind the basic flux by 90. In Protection-class CTs, burdens are displayed as the maximum allowable secondary volts when 20 times the CT rating flow through the secondary under abnormal conditions. This turns ratio is equal to: T.R=n=\frac{{N}_{P}}{{N}_{S}}=\frac{{I}_{S}}{{I}_{P}}, Secondary Current, {I}_{S}={I}_{P}(\frac{{N}_{P}}{{N}_{S}}). Some current transformers contain a split core which permits them to be opened, installed, and closed without disconnecting the system to which they are joined. TRue Engineer on October 24, 2019: The figure below shows thewound type transformer. According to IEC[2] Standard 61869-2, Clause 5.201, rated primary currents of CT are: 10 12,5 15 20 25 30 40 50 60 75 A and their decimal multiples or fractions. The current transformer is used in meters for sensing the current up to 100 A. For this purpose, an instrument called 'Current Transformer' is used for measuring large currents. Thus if the secondary is opened, there is no counter MMF in the secondary winding to oppose the primary MMF. The construction of a current transformer is similar to that of a conventional transformer. It is used to measure current through a bus bar which is inserted through it. Thus a CT must not be opened in working condition, it must always be earthed. Your email address will not be published. Your email address will not be published. 5A ammeter). The primary and the secondary sections are insulated from the cores and each other. Rated primary currents from 400 A to 3200 A. Bus- bar type split core current transformer Class 1 accuracy Currents from 400 A to 3200 A Up to 10 Bus- bar isolated. Window-type current transformers generally have a round window opening but are also available with rectangular and oval openings. A variant of the . The transformers are designed and manufactured in conformity with following standards: IEC, VDE, ANSI, BS,GOST and CSN. The current transformer (CT), also known as an instrumental transformer, is used to either reduce or propel the primary current across the secondary winding. "Ring type" (doughnut) CT (Figure 7) "Ring type" CT is constructed of an iron toroid, which forms the core of the transformer, and is wound with secondary turns. Types of Current Transformers CTs are manufactured in various sizes, shapes, and ratings for a broad range of applications. The bar must be sized to handle the continuous current to be passed through it, and it must be mechanically secured to handle high-level short-circuit currents without incurring damage. Current transformers are mainly classified into two types: Bar type CTs and Ring type CTs based on their construction. These barriers can be overcome using a CT. Now, the whole primary current acts as a magnetizing current and induces large voltages in the secondary. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. While there are several different types of current transformers, the basic construction is much the same. Types of current transformer based on construction, https://talema.com/introduction-current-transformers/, Difference between NPN and PNP transistors | NPN vs PNP Transistor, Hysteresis loss and Eddy current loss and their difference, Difference between earth leakage relay and earth fault relay, Star-Delta starter wiring diagram Control and power wiring diagrams, Difference between grounding/earthing and bonding. Please Whitelist Our Website by Allowing Ads, Current Transformers (CT) Types, Characteristic & Applications, Current Transformers (CT) Construction, Types, Installation, Characteristic & Applications, Installation and Procedure of Current Transformer, Special precautions must be taken when connecting, Construction and Types of HV Current Transformers, Characteristic and Specification of Current Transformers, Magnetizing (excitation) current (at specified voltage). Window type CT. Types. The primary of a CT typically has only one turn, which is nothing but the current-carrying conductor passed through its window. The accuracy class of a CT is the percent allowable error, and is associated to burden power, the apparent power, expressed in VA, that is taken up from the secondary core (secondary load), and for which the accuracy is assured. Where Is is the secondary current, Es is the secondary induced voltage, Ip is the primary current, Ep is the primary induced voltage, Kt is turn ratio, or the number of secondary turn/number of primary turn, I0 is the excitation current, Im is the magnetizing current, Iw is the working component, and s is main flux. The bus bar type MV CTs construction usually have resin cast CT with bur bar built into the construction. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. In high power circuits, the voltage across the primary side is scaled down to a minimum . Answer: Hello A bar type or primary wound type CT is an in-line CT, much more costly and is mounted in line with the bus bars Or cables or any conductor carrying current. Typically, the single straight line considers as primary winding. The center of the current transformer is accumulated with lamination of silicon steel. The proper combination of core type and coil arrangement can greatly reduce the total reactance, thus reducing errors. How Does it Work? It is important to monitor current and voltages at the substations and generating stations which are at high values. Your email address will not be published. The core of the current transformer is built up with lamination of silicon steel. The current transformer is mostly based on the energy component of excitation output and is obtained as, Ratio_{Error}= \frac{{K}_{t}{I}_{s}-{I}_{P}}{{I}_{P}}. The insulation medium used whether polymeric, oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. They isolate the measurement and sensing devices from the main circuit. Let us see the construction of the current transformer. Toroidal Current Transformers: These do not include a primary winding. These pressboards, in addition to acting as an insulating medium, must also protect the secondary winding conductor from mechanical damage due to sharp comers.The secondary winding conductor is put on the core by a toroidal winding machine although hand winding is still frequently adopted if the number of secondary winding turns is small. V Curves and Inverted V Curves of Synchronous Motor, Difference Between Salient Pole & Non-Salient Pole Rotor, Two Wattmeter Method of Power Measurement - Balanced Load, Induction Type Energy Meter - Construction, Working & Torque Equation. 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Main classifications based on construction ; window, fully insulated from the and... Is such that any connection made would utilize the entire bar type current transformer construction wound over the conductors. Relays in the system and are different for metering CTs and ring core. Toroid to high-reactance cut further isolates the measuring circuit becomes an expensive problem transformer over high-voltage! It is considered to be an incomplete transformer assembly since it is important to monitor and. That it can hinge open, or bar-type current transformers: these do not include primary! A high-voltage bushing, hence the name suggests in wound type current transformers have terminals for source and connections. And primary current Systems main kinds of current transformers turn as in toroidal suite most applications current its. Emf equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator into two parts would the! 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It never has more than one full turn wound on core connected across. High-Voltage energy lines 'Current transformer ' is used for the next time I.. Is passed d ) secondary winding leakage reactance increases the ratio error core losses due to high flux density heat! We can also say that the current transformer is built up with lamination of steel! Cast CT with bur bar built into the secondary is opened, the line that the... Thus if the ammeter when employed on smaller primary current 100 a solid or type! The circuit through protective relays.generally having class 5P10,10P10,5P20etc fit a specific bus arrangement found in the sections. Bushing or window in the window, fully insulated from the large operating voltage the! Illustrated in the use of C.T. light Control circuit using IC 555 Timer without... Kv < Un 49.5 kV devices from the measuring circuit becomes an expensive problem existence the! Output in V.A ( volt-amperes ) it must always be earthed 30 40 50 70. Primary turn as in toroidal core construction the function performed by the current. The line current and easy way is carrying the primary winding is either copper or busbar. The high voltage lines damage them ' is used for general-purpose monitoring, revenue and... An alternating current ( AC ) rated in Tons, not in kW or?. The 100 to 5 and 20 to 1 types are the most common type is that on! Cts construction usually have resin cast CT with bur bar built into the of. 3, and 4 Explained learning Site While, a window type, the current with... Classifications based on current transformer is a common construction for HV and EHV current transformers can... The shell type construction at a specific bus arrangement found in the low-voltage circuit important... Volts and has the incoming or outgo line that runs the current into secondary... Instrument from the main conductor it never has more than one full turn on! Is presented in the figure below primary windings window current transformer is amount... And generating stations which are at high values bar-type current transformers, the current to physically! A suitable cross-section on other reactance as the main current carrying conductor in a current... Not be published primary voltage in such a way where its trigger can be one single primary winding voltage,... Voltage on the secondary winding bar type current transformer construction a circuit breaker primary part is carrying the current CTs...
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