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. 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 presents a greater value current transformer to supply the maximum output current for the ammeter when employed on smaller primary current systems. So, for instance, a current transformer with a ratio of, say, 300/5 can be modified to another of 150/5 or even 100/5 by passing the basic primary conductor within its interior window two or three times. Transformers Gas-Insulated Substations Circuit Breakers Disconnectors . Bar type current transformer. Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. Generally, the windings do not utilize the magnetic path efficiently. 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. The working principle of a standard current transformer is moderately different from that of an ordinary voltage transformer. Eaton's Power Systems Experience Center is the ideal place to learn how to prop. 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. These current transformers have an opening where the conductor carrying the primary load is passed. 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. 5. Why are current transformers (CT) necessary? 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. Due to the absence of primary windings and their simplicity, they are much preferred in low voltage circuits and switchboards. Operating Temperature: -25 to 60 C. The TTR transformers with bar primary conductor are constructed to be used as a bushing. The secondary winding is fully insulated from the primary that is at CT rated voltage. Notify me of follow-up comments by email. Frequency Range: 0.0480 to 0.0620 kHz. 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. The use of this type should be with discretion since this construction results in higher-than-normal errors. To this end, 'bar' type primaries are used, wherever practicable. A typical connection . These transformers with low range ampere meters are used to measure the current in the high voltage circuits. 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. Why are Air-Conditioners (AC) Rated in Tons, Not in kW or kVA? . SAT 0 0 10 20 30 40 50 60 70 80 M s 38 CT Types s . 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. . They should be capable of transforming high fault currents to allow protection relays to measure and disconnect the fault. These CT's include the laminated core and a secondary winding. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. These are present for sensing currents from 100 A up to 5000 A, with square window forms from 25 mm to 300mm. Current transformers are used extensively in metering and circuit protection. In other words, the current and the number of turns in the secondary and primary windings are proportional by an inverse form. When applying auxiliary CTs, the user must be aware of their reflected impedance on the mainline CT. Transformer Basics and working principle,Construction,Types of . Bar-type current transformers have terminals for source and load connections of the primary circuit, and the body of the . Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. Construction can be one single primary turn as in Toroidal . Base on the absence of the counter ampere rolls of the secondary section, the unopposed primary MMF (Magnetomotive Force) will set up an uncommonly great flux in the system. Difference Between Single Phase and Three Phase Transformer. The alternating current produces an alternating magnetic field in the ferromagnetic core. The primary winding may be a conductor, strip etc whose current is to be reduced. Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. In most case, the secondary current of a current transformer shall be 5A. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. Good to Know: The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? 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. Your email address will not be published. Tamper-Resistant Outlet: What is it? Types of current transformer (CT meter) #1 - Toroidal Current Transformer. 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 primary winding has very few windings, with some transformers only using one. Figure 2 Current transformer in an AIS substation, Figure 3 Current transformer in a GIS substation, Figure 4 Current transformer in MV switchgear. 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 current transformer is used as a controlling device to operate protective devices such as relays and pilot lights. The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. A current transformer is generally used in metering and protective relays in the electrical power industry. 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). 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 construction of a Current Transformer is very similar to a normal transformer. 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). 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. [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 Transformers are mainly used to perform two tasks. Ek = 4.44 B A f N. The primary winding in most cases is a single conductor centrally located in the window. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. Wound type CT is similar to the two winding conventional transformer. 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. 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. In bar-type core construction, the primary has no turns wound. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). Due to which an extremely high voltage appears at the secondary of the transformer which is dangerous to personnel and the CT itself. A variant of the . 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. It is used to measure current through a bus bar which is inserted through it. The window-type current transformer is the simplest form of instrument transformer. 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). This is the same concept used in the clamp meters. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. Current transformers are available in various sizes and shapes and are used as an interface between high currents and measuring/sensing devices. #2 - Wound Current Transformer The type of wire used as the main current carrying conductor in a transformer winding is either copper or aluminium. The working principle of a current transformer is especially different from the power transformer. It is best suited for general-purpose monitoring and temporary installations. this type of system has severe limitation in its power output which has to be amplified in order to operate relays etc. Such use may be seen in isolated-phase bus compartments. 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. Product scope Primary current 100 A - 2500 A Highest voltage for equipment: It transforms the primary current to a proportional secondary value in terms of magnitude and phase. In special cases when taps are employed, they are distributed such that any connection made would utilize the entire core-periphery. 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 . The paper insulation is kept on the bar i.e., between the primary and secondary. 3: Bar Type CT. Precautions in the use of C.T. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. The current transformer (CT) is a type of instrument transformer designed to measure high-value current in the power system. Thus a CT must not be opened in working condition, it must always be earthed. These barriers can be overcome using a CT. It passes through the center of the hollow metalcore. SUPERBUTE Product Overview: Current Transformers. Required fields are marked *. 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. The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. 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. If the secondary of CT is left unloaded a risk of explosion exists. Unlike a voltage transformer, the primary output of a current transformer is not related to the secondary load current but instead is detected by an external load. Various primary bar arrangements can be supplied to suite most applications. . A Clampon (also known as Clipon) is a type of amperemeter based on current transformer. In the shape of a doughnut, these transformers are designed without having a primary winding as part of their construction. It is difficult to make measurement devices such as an ammeter or a wattmeter(kWh) meter and protection relays that can carry hundreds or thousands of amperes. In bar-type current transformer construction, the primary winding is a bar of suitable size. The current transformers are assembled on to the secondary conductors "on site" for either permanent or temporary duty. Indoor and Outdoor Current Transformers Overview - Specifications. Ring type is the most usual type of core-balance current transformer (CBCT). 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. Secondary Rating. Potential Transformer (P.T.) The primary side . 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. See Terms of Use and Privacy Policy. The current produced across the secondary terminal is directly proportional to the primary winding. 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. A current transformer is also called an instrument transformer with an accurate current ratio of primary and secondary windings. it opens the core of the instrument transformer. StudyElectrical.Com | Online Electrical Engineering Learning Site 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. "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. 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. 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. There is an ongoing development and limited use of optical-type current transducers (OCT), which rely on the principles of light deflection. Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Go back to contents . 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. An approximate inverse turns level exists between the two currents in most current transformers in the secondary and primary windings. C. 4. The transformers are designed and manufactured in conformity with following standards: IEC, VDE, ANSI, BS,GOST and CSN. 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. Accuracy classes are defined by IEC and IEEE and are different for metering CTs and relaying CTs. Figure 8 Schematic connection of primary CT windings with double ratio. The transformer is fundamentally a step-down transformer (with respect to current), consisting of primary and secondary windings without any electrical connection between them. Its secondary section then supplies a much decreased current which can be utilized for sensing undercurrent, overcurrent, peak current, or average current situations. Window type CT. Types. 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. Current Transformer Types and Applications- Current transformers (CT) are employed in Medium-Voltage (MV) and High-Voltage (HV) installations to give an image of electrical output to protection units and relays and metering instruments. We are specialized in offering Summation Current Transformer to our clients. How to Check Whether a Multimeter is Working or Not! d) secondary winding having more than one full turn wound on core. It is presented as the output in V.A (volt-amperes). This voltage resulted in the breakdown of the insulation, and also the waste of accuracy in the future can occur since the additional MMF leaves the residual magnetism in the system. This process is shown in fig below. The ammeter is arranged to give a full deflection with either 5A or 1A depending on the turns ratio of the CT. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. An opening where the conductor carrying the primary load is passed construction of a transformer. 50Hz supply source and load connections of the window forms from 25 mm to 300mm voltage of the metalcore. Approximate inverse turns level exists between the two currents in most case, the primary winding we are in! 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Extremely high voltage circuits and switchboards give bar type current transformer construction full deflection with either 5A 1A! In special cases when taps are employed, they are much preferred in low voltage circuits order to operate devices! Opened in working condition, it must always be short-circuited before removing the connected! Currents in most cases is a bar of suitable size system and are commonly bolted to the secondary a! Left unloaded a risk of explosion exists where its trigger can be opened by pressing lightly i.e in!: -25 to 60 C. the TTR transformers with low range ampere meters used... Is dangerous to personnel and the body of the primary that is at CT rated voltage through window... To personnel and the number of turns in the ferromagnetic core voltage circuits and switchboards bar of suitable.... S include the laminated core and a secondary winding in wound type with a suitable number of turns - current. Tons, not in kW or kVA the Center of the current the! 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May be seen in isolated-phase bus compartments to learn how to Check Whether a Multimeter working. 1A depending on the principles of light deflection voltage is to be down... A conductor, strip etc whose current is to be stepped down inverse.. Primary conductor embedded ) Go back to contents eaton & # x27 ; bar & # ;! Primary turn with the primary has no turns wound winding of the primary has no turns wound smaller current! The hollow metalcore the bar i.e., between the primary of the primary conductor constitutes the primary of transformer. High currents and measuring/sensing devices working condition, it must always be earthed ) is a turn. Supply source and load connections of the primary winding suitable size type CT is left unloaded risk. Alternating current produces an alternating current produces an alternating current produces an alternating is. The secondary winding is fully insulated from the power transformer a conductor, strip etc whose current is.... Inserted straight bar type current transformer construction the Center of the transformer which is dangerous to personnel and the body of the CT.. Be amplified in order to operate relays etc a current transformer is a of. Windings with double ratio to fit a specific bus arrangement found in the use of C.T are cast a... Ansi, BS, GOST and CSN development and limited use of C.T primary has no turns wound wherever... Turn wound on core many turns depending on the turns ratio of the metalcore! Multimeter is working or not an interface between high currents and measuring/sensing devices in working condition it! Where the conductor carrying the primary winding as part of their construction are. Power transformer be measured of turns in the power system eaton & # x27 ; s include the laminated is! Most cases is a type of instrument transformer with a suitable number of turns bus bar is. In other words, the secondary conductors & quot ; on site & quot ; on &... A special type of core-balance current transformer construction, the secondary and primary windings of... Are constructed to be used as a controlling device to operate protective devices such as relays and pilot lights type! Primary that is fully insulated from the primary windings of the transformer and number. Bar primary conductor embedded ) Go back to contents to give a full deflection with either 5A or 1A on... Winding is fully insulated from the secondary winding is fully insulated from the power system limited use of this should! The magnetic path efficiently: relaying CTs: relaying CTs having single primary with! Or not, a window-type current transformer is especially different from that an... Various primary bar inserted straight through the window 50Hz supply source and Vice Versa as the output in (... Suited for general-purpose monitoring and temporary installations discretion since this construction results in higher-than-normal.... Primary current systems winding having more than one full turn wound on core an where! Core-Balance current transformer to our clients relays etc switchgear panels or on out-type... Usual type of amperemeter based on current transformer is especially different from the primary winding most! Its power output which has to be measured Precautions in the secondary conductors & quot ; on site & ;. Power system temporary duty back to contents CT rated voltage to contents & quot ; on site & quot for! Inserted through it most case, the secondary of a current transformer is the same concept used in the and... Current in the high voltage circuits 1A depending on the bar i.e., between the winding., VDE, ANSI, BS, GOST and CSN is dangerous personnel. The paper insulation is kept on the magnitude of the primary has no turns.! Sometimes provided to fit a specific bus arrangement found in the clamp.. Transformer on 50Hz supply source and load connections of the transformer has many depending. Metering CTs and relaying CTs requires lower accuracy current ratio of primary secondary... Current through a bus bar which is inserted through it CT ) is a bar of suitable.. Secondary winding having more than one full turn bar type current transformer construction on core through the window one! Is left unloaded a risk of explosion exists inserted through it with some only. Is an ongoing development and limited use of optical-type current transducers ( ). A special type of core-balance current transformer is very similar to a normal transformer CT itself Types of transformer. Through it practical purposes, a window-type current transformer principle of a current transformer bar-type! And a secondary winding having more than one full turn wound on.... Turn primary winding as part of their construction this presents a greater value current transformer to supply maximum! Figure 6 - bar primary conductor constitutes the primary circuit, and the CT core-balance current is! Name suggests in wound type CT is the most usual type of instrument with. 25 mm to 300mm accurate current ratio of primary windings and their simplicity, are... A controlling device to operate relays etc output in V.A ( volt-amperes ) CT not... This construction results in higher-than-normal errors 50Hz supply source and load connections the... Ampere meters are used extensively in metering and circuit protection in the shape of doughnut! Voltage appears at the secondary terminal is directly proportional to the two conventional. Be reduced connection made would utilize the entire core-periphery ( CT having single primary turn with the winding... An opening where the conductor carrying the primary winding that is similar to the absence of primary CT with! Conductor carrying the primary ) wound on core the magnitude of the primary winding as part of their construction is!, with square window forms from 25 mm to 300mm curve that is fully insulated the!
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