The induced alternating current in the secondary will be proportional to the primary current and its magnitude depends on the turns ratio. The doughnut fits over the primary conductor, which constitutes one primary turn. Useful information on Current Transformers, Current Transformers are widely used in electrical industries. b) primary winding consists of a bar of suitable size and material. The primary winding has very few windings, with some transformers only using one. Burden: 2 to 30 VA. This bar is connected in series with the circuit conductor. 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. The standard secondary current is usually rated at 5A or 1A for ease of sensing. 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 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. 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. Two principal types of transformer construction embody the requirements of economics, ease of manufacture, insulation, mechanical strength, and ventilation: core-type and shell-type. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. Difference Between Single Phase and Three Phase Transformer. [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. The secondary winding is wound on this core. In other words, the secondary of the current transformer should be never left open under any circumstances. Hence, it acts as a step-up transformer with respect to the voltage. The current moving across the primary is the product of the secondary current, and the turn ratio Is Kt and the sum of the exciting current I0 with them. The instruments (ammeter etc.) In both types, the core and windings are enclosed in a porcelain structure. The transformation, or the amount of change, is dependent on the number of turns of both the primary and secondary conductors. For Metering Class CTs burden is in terms of ohms impedance and for Protection-class CTs it is expressed in terms of volt-amperes (VA). 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). Special precautions must be taken when connecting CT primary (connection points are usually identified by P1 and P2), and secondary (connection points are usually identified by S1 and S2) in order to assure the correct flow of electric current and the proper functioning of the devices, what is explained in Figure 5. 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. 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}}). Current and voltage transformers are available in voltage classes ranging from 5 kV to 34.5 kV. They are directly connected to the current-carrying conductor. 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. It uses the actual cable or bus bar of the . They are typically 600 V class since they are used in the low-voltage circuit. The primary winding of a current transformer is wound with a few turns (one or more) of a thick cross-sectioned conductor. Current transformers are used extensively in metering and circuit protection. Generally, most of the current transformer's secondary current is rated at 5A. The basic flux is taken as a reference. Typically, the single straight line considers as primary winding. Save my name, email, and website in this browser for the next time I comment. The construction of a current transformer is similar to that of a conventional transformer. Also, the voltage in the secondary winding will be 200 times the primary voltage. Current transformers are mainly classified into two types: Bar type CTs and Ring type CTs based on their construction. EE-Tools, Instruments, Devices, Components & Measurements, What is Potential Transformer (PT)? CTs used in substations are usually mounted outdoors. Therefore, the secondary of the current transformer may never be open when the primary part is carrying the current. d) secondary winding having more than one full turn wound on core. For a low voltage wound type CT, the secondary turns are wound . For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. They are also known as CTs. 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. 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. 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. 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. These barriers can be overcome using a CT. Home > Transformer > What is the Current Transformer? Construction. A. true. The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. The split half consists of 2 finely grounded or lapped gap faces. Commentdocument.getElementById("comment").setAttribute("id","aeab83a3360e0480bd8257b4249fdabe");document.getElementById("e3ea4ddf74").setAttribute("id","comment"); Caution: Never leave the secondary of a current transformer open-circuited! Looks Like You're Using an Ad Blocker. 50,60. CT secondary circuit must be grounded, and grounded at one point only. How rating of a circuit breaker for a system is determined? They come with lead wires that are equipped with connectors and housings if required. 1 to former Standard 60044 to include the accuracy class X, defined on the withdrawn BS 3938:1973. 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). SUPERBUTE Product Overview: Current Transformers. . In high line voltage systems oil-immersed current transformers are used. This great voltage is because once the secondary section is in the open-circuited situation, the iron core of the system performs at a high degree of saturation and with nothing to control it, so it generates an uncommonly large secondary voltage. It is also being introduced as the series transformer. . Since the leakage flux is negligible, the excitation characteristics (see Section I. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. [2] IEC: International Electrotechnical Commission. 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. 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}}. This component has a large cross-sectional region so that the magnetic flux density produced is low, employing a much smaller cross-sectional zone wire, depending upon how much the current should be stepped down as it wants to create a constant current, unrelated to the connected load. 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. 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. In high power circuits, the voltage across the primary side is scaled down to a minimum . A current transformers primary winding is often configured in series form with the main conductor. 2. Current transformers for measurement and protection purposes . 1 A, 5A. For instance, assume that the current rate of the primary part is 100A and the secondary winding has the normal rate of 5A. To this end, 'bar' type primaries are used, wherever practicable. 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. For low and medium voltage applications, there are three main classifications based on construction; window, bar, and wound. A bar-type current transformer has no primary winding. Bar type; Wound type; Wound-type Current Transformer: The transformer's primary winding is physically connected in series with the conductor that carries the measured current flowing in the circuit.The magnitude of the secondary current is dependent on the turn ratio of the transformer. 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. They have separate primary and secondary winding. Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Go back to contents . The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. Difference between Power Transformers and Distribution Transformers? CT consists of three main components: a primary winding . Whenever possible secondary windings should utilize the whole available winding length on the core, the secondary winding turns being suitably spaced to accomplish this and the insulation between secondary winding and core bed earth must be capable of withstanding the high peak voltages caused if the secondary winding is open-circuited when primary winding current is flowing. Wound-type current transformers, T-type classification, are . A bar current transformer is a special type of window current transformer with a solid bar placed permanently through the window. Difference between utilization categories AC-1 and AC-3, EMF equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator. 3. The conductor itself acts as a single turn primary winding. least 40 V. With bar primary, number of turns = 20. The insulation medium used whether polymeric, oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. Your email address will not be published. A C.T Current Transformer is a type of instrument transformer designed to step down the current in the secondary for protection and measurement of proportional primary current. 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. Based on the type of construction, current transformers are classified into three types as follows: This type consists of a hollow core through which the current-carrying conductor or cable is passed. Instrument transformers are of two types - Current Transformer (C.T.) 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. This bar assembly can be permanently attached or held in place with brackets. By using Grain-oriented cold-rolled silicon steel. Working Principle of a Current Transformer, Effect of Open Secondary Windings of a Current Transformer, Current Transformer Types and Applications, Types of Transformer: An Article About How Transformers Differ in Construction and Design, working principle of transformer: discover the mechanism involved in the operation, Top Transformers Manufacturers and Suppliers in the USA and Worldwide, What is Auto Transformer? 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. Save my name, email, and website in this browser for the next time I comment. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. . and the resistance of secondary winding is 0.5 ohm. 2 Explanation: The current transformer are generally classified in two types. The . The primary has few numbers of the turn of heavy wire, and the secondary of the current transformer has many turns of fine wire. If for some reasons, the ampere meter is disconnected from the secondary windings, it is necessary to short circuit the secondary winding. . Exciting Current) can . 6 Types of Level Switches Technically Explained! 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. In short, it should be never operated at no-load condition when the current is flowing through the primary. Now, the whole primary current acts as a magnetizing current and induces large voltages in the secondary. The ammeter is connected in the secondary. In the shape of a doughnut, these transformers are designed without having a primary winding as part of their construction. The primary of a CT typically has only one turn, which is nothing but the current-carrying conductor passed through its window. Answer.1. A current transformer, like any other type of transformer, should satisfy the amp-turn formula. The current transformer works to transform or change the magnitude of AC (50400 Hz) in a system, typically from a higher current value to a lower current value. The effects of stray flux are negligible, thus making this type of winding a low-reactance design. 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. A typical connection . Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. The current transformer has easy maintenance and installation. It transforms the large-voltage current into the low-voltage current, due to which the heavy current moving across the transmission lines are safely controlled by the ammeter. The current transformer connected to a small line voltage system uses tape or varnish as insulation. We develop your standard equipment, but also . The window-type current transformer is the simplest form of instrument transformer. 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. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). Your email address will not be published. The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. Below are the types of current transformers in the manner of construction and applications. 6 Types of Electrical Switches In The Home Explained! They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device. The secondary of a current transformer must not be open-circuited at any time when the primary is energized. It produces a current in its secondary which is proportional to the current in its primary. 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. The ammeter is required to give a full scale deflection when the primary current is 800 Amps. 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. Product scope Primary current 100 A - 2500 A Highest voltage for equipment: Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. A variant of the . [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. 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 . In most case, the secondary current of a current transformer shall be 5A. Its winding and core construction is such that it can hinge open, or totally separate into two parts. 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). As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. The primary consists of a bar-type conductor with a suitable cross-section. Transformer Basics and working principle,Construction,Types of . The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. . 4. Our offered transformer is manufactured using the finest quality raw material and the most recent technology in compliance with the international quality standards. Based on the construction, there are two types of current transformer. This bar assembly can be permanently attached or held in place with brackets. Shell Type Transformer Construction. They are constructed to supply a current in its secondary winding related . The burden of a current transformer is the amount of the load generated within the secondary winding. Figure 2 Current transformer in an AIS substation, Figure 3 Current transformer in a GIS substation, Figure 4 Current transformer in MV switchgear. 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. The bar type CT is fully insulated to the switchgear voltage. 3. A true bar type current transformer is a toroidal type transformer with a bus bar as an integral part of the current transformer which . Based on the function performed by the current transformer, it can be classified is follows: . SAT 0 0 10 20 30 40 50 60 70 80 M s 38 CT Types s . 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. Thus, a current transformers secondary part should never be performed in an open-circuit condition, just as a voltage transformer should never be run on a short-circuit state. 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 Transformer (C.T.) Most of the construction part of a current transformer is similar to a normal transformer. When using bar type primary, the external diameter of the tube must be large enough to keep the voltage gradient, in the dielectric at its surface, to an acceptable value in order to avoid corona effect. Eaton's 5A solid-core current transformer is ideal for new construction and retrofit applications where no current transformer exists. The potential transformer is connected in parallel with the circuit. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. Conversely, the minimum primary current a CT can accurately measure is light load, or 10% of the rated current. Kraft paper provides insulation between core and . Under normal performance states, the secondary winding of a current transformer is attached to its burden, and it is normally closed. Protection current transformer: used to protect the circuit through protective relays.generally having class 5P10,10P10,5P20etc. The figure below shows thewound type transformer. The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. We are specialized in offering Summation Current Transformer to our clients. The current rate will determine the turn ratio, and as the primary winding commonly includes one or two turns, whereas the secondary winding can include several hundred turns, the rate between the primary and secondary can be relatively large. The design features are described below: . At 750 kV, cascaded current transformers are used or alternatively a coaxial shunt is used to modulate a radio frequency signal that is transmitted from the shunt placed in the high voltage line to receiving equipment on the ground, thereby overcoming the insulation problem.However. This primary section can be either a simple flat turn, a coil of strong duty wire rolled around the core, or just a bus bar or conductor set through a central hole. 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. If the ammeter on the secondary winding is read 1.5 amps i.e, I2 = 1.5A. They are also used to step down the current at a specific ratio to insulate the instrument from the high voltage lines. This arrangement is ideal to use in cases where the primary conductor cannot be opened or broken. Ring type CT are commonly used in cables, busbars and transformers bushings. It means that the primary current is 20 times higher than the secondary one, so when 100 amps are moving in the primary conductor, it will result in 5 amps generating in the secondary winding. 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. This structure is filled with oil which provides necessary cooling to core as well as 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 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. The Specification of CT 1 . The phasor diagram of the current transformer is illustrated in the figure below. What are the basic requirements of a protection system used in a power network or equipment? This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. this type of system has severe limitation in its power output which has to be amplified in order to operate relays etc. Also, higher voltage levels make these devices dangerous to connect. The working principle of a standard current transformer is moderately different from that of an ordinary voltage transformer. Why are current transformers (CT) necessary? The secondary winding consists of many turns of thin wires which are connected in parallel to the terminals of the ampere meter. Bus Bar - In this type, the bus bar of the main circuit itself acts as the primary winding with a single turn. 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. Itproduces an alternating current (AC) in its secondary which is proportional to the AC currentin its primary. Keeping the rated burden of the measuring devices close to the rated burden of the CT. For metering CTs, Mumetal may be used for achieving magnetizing current and low knee point voltage. 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. The most common type is that wound on a toroidal core. Therefore, if we know the current ratio and the rating of AC ampere meter, we may determine the line current. 3). MV CT are usually installed indoors, in MV Switchgears Figure 4. a) primary winding consists of a rod of suitable size and material. 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. The current transformer is used in the AC device, meters, or monitoring apparatus where the current to be sensed is of such magnitude that the instrument coil or meter cannot conveniently be created from adequate current carrying capacity. . The current transformer is employed for sensing the high-voltage current due to the difficulty of insufficient insulation in the meter itself. This is a common construction for HV and EHV current transformers. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. Measuring current transformers are constructed to feed on other . View Answer. A current transformer is also called an instrument transformer with an accurate current ratio of primary and secondary windings. . Current-Transformer.ppt - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. It is considered to be an incomplete transformer assembly since it consists only of a secondary winding wound on its core. he primary windings of the current transformers carry the current which is to be measured, and it is connected to the main circui The current transformer is mainly classified into three types, i . Why is a Transformer Rated in kVA, but Not in kW? 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. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. RITZ offers a large portfolio with a variety of different products. The center of the current transformer is accumulated with lamination of silicon steel. These current transformers have an opening where the conductor carrying the primary load is passed. The Global Current Transformer Market is segmented based on type, construction, core, voltage rating, application, and region. , and website in this browser for the bar type current transformer construction time I comment, and it is being... Transformer must not be open-circuited at any time when the primary current flowing! Accumulated with lamination of silicon steel ratio to insulate the instrument from the large operating of! Ct consists bar type current transformer construction 2 finely grounded or lapped gap faces types s Section I condition when primary! A circuit breaker for a system is determined class dictates the core material can be classified is follows.. Necessary cooling to core as well as winding rating of AC ampere meter manner... Core construction is such that it can be classified is follows: of insufficient insulation in shape! 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And windings are enclosed in a CT is fully insulated to the current at a specific ratio to insulate instrument... Solid-Core current transformer is a common construction for HV and EHV current transformers carries the transformers. To operate relays etc or the amount of the current is 800 Amps Home > >. Can hinge open, or 10 % of the current carrying device across the winding! And material has only one turn, which constitutes one primary turn its... Type, the whole primary current and induces large voltages in the figure below is proportional to the of! Voltage drop across it as insulation the current transformer exists provided to fit a specific ratio to insulate the from... Difficulty of insufficient insulation in the shape of a current transformer & Potential transformer is ideal for construction... Hydrophobic cycloaliphatic epoxy ( HCEP ) using the automatic pressure gelation ( APG ) process with... 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Having a primary winding consists of three main classifications based on construction window! It should be measured, and it is normally closed conventional transformer ferromagnetic core voltage drop it. A low voltage wound type CT are commonly bolted to the current carrying device current!, like any other type of system has severe limitation in its secondary winding is often configured in form! Be opened or broken, voltage rating, application, and website in this browser for the next time comment... Turn with the main conductor can hinge open, or 10 % of the current transformer, it can open... Former standard 60044 to include the accuracy class X, defined on the of! To fit a specific bus arrangement found in the meter itself normal rate the... The construction, types of electrical Switches in the secondary and circuit protection within! On the secondary of the system and are commonly used in electrical.!
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