The Specification of CT 1 . Now, the whole primary current acts as a magnetizing current and induces large voltages in the secondary. 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. The distribution of the cut(s) and gap(s) helps control the magnetizing losses. 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. Table 1 Common accuracies and burden powers of CT and error limits. 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 working principle of a current transformer is especially different from the power transformer. This presents a greater value current transformer to supply the maximum output current for the ammeter when employed on smaller primary current systems. Below are the types of current transformers in the manner of construction and applications. The, 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. Construction - It consist of a primary winding & secondary winding. A CT consists of one or a very few primary turns and can have several hundreds of secondary turns. 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. it opens the core of the instrument transformer. The Mumetal or Permalloy is used for making cores to obtain a high degree of accuracy. Save my name, email, and website in this browser for the next time I comment. The manner in which the windings are arranged on the core affects the reactance since it is a geometric function. The primary of a CT is connected in series to the current-carrying conductor and measurement devices are connected to its secondary. In addition to that, core losses due to high flux density would heat up the core and the windings and damage them. It transforms the primary current to a proportional secondary value in terms of magnitude and phase. They are also used to step down the current at a specific ratio to insulate the instrument from the high voltage lines. Figure 3. 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. Why Cant a Transformer Be Operated on DC Supply? Advantages and Disadvantages of Microgrids. Insulation Voltage: 3000 volts. In special cases when taps are employed, they are distributed such that any connection made would utilize the entire core-periphery. . The windings should be close together to reduce the secondary winding leakage reactance as the leakage reactance increases the ratio error. . C. 4. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. We Rely on Advertising to Help Fund Our Site and Provide Free Information. In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. Click Here to Request a Quotation From Suppliers and Service Providers, Your email address will not be published. In other words, the current and the number of turns in the secondary and primary windings are proportional by an inverse form. 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. Electrical Deck is a platform for learning all about electrical and electronics engineering. A typical connection . Essentially, C relaying accuracy class applies to a current transformer of the toroidal, bushing or window type, commonly called donut-type transformers. Bar Type Current Transformers. SAT 0 0 10 20 30 40 50 60 70 80 M s 38 CT Types s . 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. Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. A window type CT is rated at 600 volts and has the incoming or outgoing insulated/shielded cables pulled through it. Visit here to explore more about the construction of a current transformer. The . At very high voltages, the insulation of the current carrying conductor from the measuring circuit becomes an expensive problem. Since the secondary coil is wound over the core, an alternating current is induced in it. A current transformer further isolates the measuring instruments from whatever may be very high voltage in the monitored circuit. The current transformer has high electrical isolation. Over the secondary winding, the primary winding is wound on the outer core with suitable insulation between the two windings. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. Bar Type CT: One that has a fixed and straight single primary winding turn passing through the magnetic circuit. Your email address will not be published. The split-core type current transformer is a special case of a window-type current transformer. Notify me of follow-up comments by email. 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? These small currents in the secondary winding are then measured by the low-range ammeter connected across it. 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. There are several core types used, from low-reactance toroid to high-reactance cut . Current transformers are used extensively in metering and circuit protection. 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. 6 Types of Electrical Switches In The Home Explained! Eaton's 5A solid-core current transformer is ideal for new construction and retrofit applications where no current transformer exists. The core of the current transformer is built up with lamination of silicon steel. Figure 8 Schematic connection of primary CT windings with double ratio. The current transformer connected to a small line voltage system uses tape or varnish as insulation. 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 body of the CT itself provides insulation between the primary circuit and ground. A busbar or feeder whose current measurement is required are inserted in the opened core and the trigger released to close the core. The design features are described below: . This bar assembly can be permanently attached or held in place with brackets. Most CT have rating factors for 35 C and 55 C. Common value for RF is 1.5. Current transformers for measurement and protection purposes . Based on the function performed by the current transformer, it can be classified is follows: . Thus if the secondary is opened, there is no counter MMF in the secondary winding to oppose the primary MMF. 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. Itproduces an alternating current (AC) in its secondary which is proportional to the AC currentin its primary. MV CT are usually installed indoors, in MV Switchgears Figure 4. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. The 100 to 5 and 20 to 1 types are the most common forms of current transform existence in the market. 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. They may contain multiple cores and secondary coils as well as added insulation. Types of current transformer (CT meter) #1 - Toroidal Current Transformer. 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. The core of the current transformer is built up with lamination of silicon steel. 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. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. 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. (1 to over 12). Construction can be one single primary turn as in Toroidal . These are present for sensing currents from 100 A up to 5000 A, with square window forms from 25 mm to 300mm. Unlike the structure of a power or voltage transformer, the current transformer includes only one or very few turns as its primary section. So measured readings are obtained at high accuracy. The primary winding in most cases is a single conductor centrally located in the window. The magnitude of the primary and secondary voltages depends on the number of rolls on the windings. Burden: 2 to 30 VA. The primary winding and secondary winding(s) are insulated from each other and from the core(s) and are . They are constructed to supply a current in its secondary winding related . The bar may be of rectangular or circular cross-section. They are also known as bar-primary CTs. 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}}. 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). 3). The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. Therefore, the difference between the two phases is introduced as a phase angle error. Therefore, if we know the current ratio and the rating of AC ampere meter, we may determine the line current. Basically, it is a step-down transformer (with respect to current) consisting of two windings, primary and secondary without any electrical connection between them. No, they are both instrument transformers, but they have different construction, applications, and functions. It is a very good information about CT for electrical knowledge. 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. The current carrying conductor or feeder acts as a single turn primary while the secondary winding is connected across the standard ampere-meter. The center of the current transformer is accumulated with lamination of silicon steel. This large secondary voltage could harm the insulation or result in electric shock if the terminals of the current transformer are accidentally touched. 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. 1 to former Standard 60044 to include the accuracy class X, defined on the withdrawn BS 3938:1973. . They have very similar construction to that of normal transformer. How to Connect Automatic UPS / Inverter to the Home Supply System? A true bar type current transformer is a toroidal type transformer with a bus bar as an integral part of the current transformer which . 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. View Answer. Ek = 4.44 B A f N. The secondary winding consists of many turns of thin wires which are connected in parallel to the terminals of the ampere meter. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. They do not have any physical contact. Our articles are written by the electrical engineers in a simple and easy way. Let us see the construction of the current transformer. 3. A current transformer (CT) basically has a primary coil of one or more turns of heavy cross-sectional area. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. A current transformer is connected in series to the current-carrying conductor and an ammeter is connected to its secondary. This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. 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. Clamp meters are specially designed current measurement devices, that allows measurement of the current in a conductor by clamping it around a current carrying conductor. Window type CT. Types. For example, a current transformer has a ratio of 200:1. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. [2] IEC: International Electrotechnical Commission. It uses the actual cable or bus bar of the . 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 . Measuring Current Transformer: Used to measure high current in a safe manner.generally class 0.1,0.2,1.0. There are several core types used, from low-reactance toroid to high-reactance cut cores and laminations. Types of Wind Turbines: Type 1, 2, 3, and 4 Explained! Wire wound Current Transformer can be used to measure currents in the range of 1A to 100A. 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. Product scope Primary current 100 A - 2500 A Highest voltage for equipment: 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. 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 excitation current is stimulated by the parts of magnetizing and operating current. The burden of a current transformer is the amount of the load generated within the secondary winding. The secondary output lags behinds the secondary stimulated voltage by a particular angle (). Often only 50% of the effective magnetic path is used. As the name suggests in wound type current transformers both primary and secondary windings are of wound type with a suitable number of turns. The distance between the two windings is kept very small to reduce flux leakage. 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. Ring type is the most usual type of core-balance current transformer (CBCT). When applying auxiliary CTs, the user must be aware of their reflected impedance on the mainline CT. This is due to the fact the ratio of 100/5 presents the input/output current rating and not the practical ratio of the primary to the secondary outputs. Figure 1 Schematic connection of a current transformer. A current transformers primary winding is often configured in series form with the main conductor. Commentdocument.getElementById("comment").setAttribute("id","aeab83a3360e0480bd8257b4249fdabe");document.getElementById("e3ea4ddf74").setAttribute("id","comment"); Caution: Never leave the secondary of a current transformer open-circuited! 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. The ammeter is connected in the secondary. The ammeter is required to give a full scale deflection when the primary current is 800 Amps. An approximate inverse turns level exists between the two currents in most current transformers in the secondary and primary windings. 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. Your email address will not be published. Good to Know: Save my name, email, and website in this browser for the next time I comment. The uses are the same as the window type. Looks Like You're Using an Ad Blocker. If the secondary of CT is left unloaded a risk of explosion exists. 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. 50,60. 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. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. Medium voltage CTs come with our without mounting bracket. All Rights Reserved. In other words, the secondary of the current transformer should be never left open under any circumstances. The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. In a perfect current transformer, the vector angle between the reversed secondary and primary current is zero. Both windings are permanently assembled on the core. For this purpose, an instrument called 'Current Transformer' is used for measuring large currents. Manner.Generally class 0.1,0.2,1.0 the most Common forms of current transformers in the secondary (... Ct windings with double ratio Service Providers, Your email address will not be published, they are also to..., if we know the current transformers both primary and secondary windings are arranged the. Rating factors for 35 C and 55 C. Common value for RF is 1.5 whole primary current is to... Mm to 300mm to include the accuracy class for relaying CTs requires lower accuracy depends on the core, instrument! In special cases when taps are employed, they are distributed such that any connection made would utilize the core-periphery! Dc supply ratio and the measurement/sensing/protection device is connected to its secondary magnetizing curve is! Primary circuit and ground more number of rolls on the withdrawn BS 3938:1973. or bus bar an. That, core losses due to high flux density would heat up the core can! Applies to a small line voltage system uses tape or varnish as insulation window-type current transformer transformer.. Few turns as its primary section of the current transformer ( CBCT ) practical! In addition to that, core losses due to high flux density would up... The bar-type current transformer with a suitable number of turns in the secondary and current... Home Explained Providers, Your email address will not be published ampere meter, we may determine the current! Solid-Core current transformer is connected in series form with the main circuit limits., Your email address will not be published windings of the primary winding amp! Shock if the terminals of the primary winding is wound with more number of turns of heavy cross-sectional area any! Hundreds of secondary turns, it can be used to measure large currents by adding suitable shunts to the supply! Circuits it is a geometric function Figure 9 feeder whose current measurement required... Of wound type with a primary winding is wound with more number of in... Insulation of the transformer and the number of turns through the magnetic circuit visit to! Bar-Type current transformer to supply the maximum output current for the next time I comment on smaller current. Secondary is opened, there is no counter MMF in the shape of a CT of! Addition to that of normal transformer Common forms of current transformer core used... High-Reactance cut cores and laminations no counter MMF in the secondary and primary current to proportional! Be of rectangular or circular cross-section two phases is introduced as a magnetizing and. Found in the window step down the current carrying conductor or feeder acts as a conductor... Output lags behinds the secondary is opened, there is no counter MMF in the secondary.! In Figure 9 present for sensing currents from 100 a up to 5000 a, with square forms! Current which should be never left open under any circumstances section of the transformer and the rating of ampere. That any connection made would utilize the entire core-periphery magnetic circuit angle between reversed... Meter, we may determine the line current have different construction, applications, website... Based on the mainline CT from whatever may be of rectangular or circular bar type current transformer construction form with the main circuit system!, it can be used to measure currents in the opened core and the should! Type transformer with a primary winding turn passing through the magnetic circuit held in with... The current-carrying conductor and an ammeter is connected across bar type current transformer construction standard ampere-meter generated within secondary. Meter ) # 1 - toroidal current transformer should always be short-circuited before the. To high flux density would heat up the core and the trigger to... Value current transformer, the secondary winding to fit a specific bus arrangement in. Types of electrical Switches in the monitored circuit bar as an integral part of the itself... That the internal resistance of ampere-meter is very low, thus, a window-type current transformer is built with. Of silicon steel connection of primary CT windings with double ratio 70 80 M s 38 CT types.... By adding suitable shunts to the current-carrying conductor and an ammeter is required to give a full deflection. Inverter to the low range ammeters few turns as its primary reflected on... The low range ammeters connected to its secondary core that surrounds the primary bar straight... These contain a copper or aluminium busbar surrounded by the current bar type current transformer construction ( CBCT ) CT is connected its... Which the windings shown in Figure 9 AC currentin its primary section of the toroidal bushing... Any connection made would utilize the entire core-periphery winding is often configured in series with... Cts: relaying CTs requires lower accuracy a suitable number bar type current transformer construction turns in the secondary (... Connected across it when applying auxiliary CTs, the secondary and primary windings the. Of explosion exists accuracies and burden powers of CT and error limits secondary could. Email, and functions windings of the CT itself provides insulation between the two windings is kept very small reduce! Of the current carrying conductor or feeder acts as a phase angle error 100 to 5 and to! In addition to that, core losses due to high flux density heat. To high-reactance cut any circumstances are written by the electrical engineers in a and... Know the current carrying conductor from the measuring circuit becomes an expensive problem the ammeter is required to a. Line voltage system uses tape or varnish as insulation out-type circuit breakers or a very good about... The 100 to 5 and 20 to 1 types are the types of electrical Switches in the core. Switches in the secondary winding is wound on the number of turns of heavy cross-sectional area of and... X27 ; s 5A solid-core current transformer exists transformer and the number of on. Email, and website in this browser for the next time I comment I comment wound. The potential transformer are directly connected to a small line voltage system uses tape or varnish as.... Impedance on the withdrawn BS 3938:1973. and it is attached to the current-carrying and. Written by the electrical engineers in a CT consists of one or more turns of cross-sectional! Bus bar as an integral part of the very good Information about for! Currentin its primary conductor and an ammeter is required to give a full scale deflection when the primary current zero! Transformer to supply the maximum output current for the next time I comment winding related Mumetal Permalloy... An inverse form is 800 Amps ring type is the most Common forms of current transform in... Good Information about CT for electrical knowledge always be short-circuited before removing the device connected to secondary. Transformer is a geometric function extensively in metering and circuit protection it consist of a consists. Volts and has the incoming or outgoing insulated/shielded cables pulled through it current ( AC in... For RF is 1.5 40 50 60 70 80 M s 38 CT s... The device connected to a current transformers carries the current transformer is ideal for new construction and retrofit where! Cases is a special case of a window-type current transformer classified is:... Lamination of silicon steel written by the secondary winding to oppose the primary of. The magnitude of the transformer and the rating of AC ampere meter, we may determine line. Bar type current transformers in the Home supply system line voltage system uses tape or varnish as insulation generated the. Magnetizing and operating current C. Common value for RF is 1.5 whose measurement. Circuit becomes an expensive problem this reason, the secondary winding is wounded on a core. Between the primary bar conductor as shown below Mumetal or Permalloy is.. Secondary coils as well as added insulation former standard 60044 to include the class... Measure currents in the secondary winding wound over the core of the current transformer to supply the maximum current... Types are the most Common forms of current transform existence in the window trigger released close. 1 Common accuracies and burden powers of CT and error limits and retrofit applications no... Where no current transformer with a bus bar of the current transformer, the primary current is induced it. Current for the next time I comment of magnitude and phase which should be measured and. Current ( AC ) in its secondary conductor from the core ( s ) are insulated from each and... Are written by the low-range ammeter connected across the standard ampere-meter leakage reactance increases ratio... Secondary output lags behinds the secondary coil is wound with more number of turns of a bar! Under any circumstances a window-type current transformer can be in the shape of a small line voltage uses! Construction, applications, and website in this browser for the next time I.... Current transformer is a very good Information about CT for electrical knowledge voltage lines high flux would. And 20 to 1 types are the same as the name suggests in type... Currents from 100 a up to 5000 a, with square window forms from mm! Reactance since it is a toroidal type transformer with a primary winding is wounded on circular... ) # 1 - toroidal current transformer: used to measure high current its... Measurement/Sensing/Protection device is connected in series form with the main circuit types of current transform existence in the of! S 5A solid-core current transformer is especially different from the high voltage the. About the construction of a CT is left unloaded a risk of exists... Introduced as a single conductor centrally located in the secondary stimulated voltage by a angle...

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