Burden in VA. 1. Bar type current transformers consist of a single bar as a primary winding. In other words, the secondary of the current transformer should be never left open under any circumstances. While , A window type or ring type CT has the incoming or outgo. Medium voltage CTs come with our without mounting bracket. Wire wound Current Transformer can be used to measure currents in the range of 1A to 100A. The point on the magnetizing curve at which the CT operates is dependent upon the resistance of the CT secondary circuit. The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. Ring type is the most usual type of core-balance current transformer (CBCT). Our offered transformer is manufactured using the finest quality raw material and the most recent technology in compliance with the international quality standards. 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). 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. Potential Transformer (P.T.) 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. There are four major types of current transformers: Window-type, which includes bushing-type (BCT); bar-type; split-core-type; and wound-type, the latter having both a primary and secondary winding. 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. Types of current transformer (CT meter) #1 - Toroidal Current Transformer. 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. 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 core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. Current Transformer (C.T.) Toroidal Current Transformers, Bar type Current Transformers, and . 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. 5, 7.5, 3C, 40. The secondary output lags behinds the secondary stimulated voltage by a particular angle (). 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. This causes excessive core losses and produces excessive heat. They are also known as CTs. The current transformer (CT) is a type of instrument transformer designed to measure high-value current in the power system. Therefore, the secondary of the current transformer may never be open when the primary part is carrying the current. Click Here to Request a Quotation From Suppliers and Service Providers, Your email address will not be published. The bushing-, window-, or bar-type current transformers are of the toroidal core construction. Window-type current transformers generally have a round window opening but are also available with rectangular and oval openings. They are classified into four basic types: Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage type. 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. Cable is passing through the centre of CT and in that way forms the primary winding. Difference between Power Transformers and Distribution Transformers? The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. The conductor itself acts as a single turn primary winding. Two principal types of transformer construction embody the requirements of economics, ease of manufacture, insulation, mechanical strength, and ventilation: core-type and shell-type. Table 1 Common accuracies and burden powers of CT and error limits. The primary winding and secondary winding(s) are insulated from each other and from the core(s) and are . [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 . Why is a Transformer Rated in kVA, but Not in kW? 6 Types of Level Switches Technically Explained! These barriers can be overcome using a CT. 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. Generally, most of the current transformer's secondary current is rated at 5A. Now, the whole primary current acts as a magnetizing current and induces large voltages in the secondary. Measuring current transformers are constructed to feed on other . One of the major differences between them is . The current transformers are assembled on to the secondary conductors "on site" for either permanent or temporary duty. If the ammeter on the secondary winding is read 1.5 amps i.e, I2 = 1.5A. The working principle of a current transformer is especially different from the power transformer. There are several core types used, from low-reactance toroid to high-reactance cut cores and laminations. A window current transformer has an open area in the centre for a power line to be passed through as the primary . Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. For core-type transformers, the windings encircle the core, while in shell-type transformers, the core encircles the windings. 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. . least 40 V. With bar primary, number of turns = 20. . 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. 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. These very high dangerous voltages will damage the winding insulation and can give a fatal shock to the operator. 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. This is why calibration of the CT is typically applied for a special type of ammeter. CT secondary circuit must be grounded, and grounded at one point only. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. StudyElectrical.Com | Online Electrical Engineering Learning Site In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. 3: Bar Type CT. Precautions in the use of C.T. Let us see the construction of the current 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. Current transformers are used extensively in metering and circuit protection. The current transformer is employed for sensing the high-voltage current due to the difficulty of insufficient insulation in the meter itself. To this end, 'bar' type primaries are used, wherever practicable. This accuracy class was retained by IEC in 1966 in the Amendment nr. The following are different types of current transformers: A current transformer having a primary winding of more than one full turn wound on core. Window type CT. Types. A typical connection . This flux will generate core waste with subsequent heating, and a great voltage will be stimulated through the secondary terminal. 2.5.3 Core-Balance Current Transformers. The potential transformer is connected in parallel with the circuit. They are directly connected to the current-carrying conductor. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). 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. 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. Basically, it is a step-down transformer (with respect to current) consisting of two windings, primary and secondary without any electrical connection between them. 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? Wound Current Transformers: The transformers primary section is physically configured in series form with the conductor that carries the detected current flowing in the system. 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 construction has a simple construction. 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 loads impedance or burden on the secondary component has moderately differed from the power types in a current transformer. 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. The secondary winding is wound on this core. A window type CT is rated at 600 volts and has the incoming or outgoing insulated/shielded cables pulled through it. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. The ammeters scale is adjusted according to the turns ratio. The split half consists of 2 finely grounded or lapped gap faces. These units are typically used by utilities in substations. Useful information on Current Transformers, Current Transformers are widely used in electrical industries. 10. Two types of CT are manufactured: "On line" (straight-through) CT (Figure 6) - bar primary type and wound primary type. Therefore, if we know the current ratio and the rating of AC ampere meter, we may determine the line current. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. . Based on the function performed by the current transformer, it can be classified is follows: . It is important to monitor current and voltages at the substations and generating stations which are at high values. Difference between utilization categories AC-1 and AC-3, EMF equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator. When the current moves across the primary part, it often flows within secondary windings, and amperes turns of each section are subsequently identical and opposite. 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. The primary winding of a current transformer is wound with a few turns (one or more) of a thick cross-sectioned conductor. Commentdocument.getElementById("comment").setAttribute("id","aeab83a3360e0480bd8257b4249fdabe");document.getElementById("e3ea4ddf74").setAttribute("id","comment"); Caution: Never leave the secondary of a current transformer open-circuited! Transformers Gas-Insulated Substations Circuit Breakers Disconnectors . View Answer. The windings should be close together to reduce the secondary winding leakage reactance as the leakage reactance increases the ratio error. A current transformer is also called an instrument transformer with an accurate current ratio of primary and secondary windings. They are typically 600 V class since they are used in the low-voltage circuit. Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Go back to contents . Wound type CT is similar to the two winding conventional 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). Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. The knee point is defined as the point at which a 10% increase in voltage produces a 50% increase in magnetizing current. Construction - It consist of a primary winding & secondary winding. 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. ANSI C51.13.1978 CTs and VTs CANADIAN CSA CAN3-C13-M83 CTs and VTs AUSTRALIAN AS 1675-1986 CTs s 5 Current Transformer Construction BAR PRIMARY . 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 . a) primary winding consists of a rod of suitable size and material. 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. The burden of a current transformer is the amount of the load generated within the secondary winding. Fig. For a low voltage wound type CT, the secondary turns are wound . What are the basic requirements of a protection system used in a power network or equipment? Visit here to explore more about the construction of a current transformer. Most CT have rating factors for 35 C and 55 C. Common value for RF is 1.5. 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. A bar current transformer can withstand the stresses of heavy . 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. In bar-type core construction, the primary has no turns wound. In high line voltage systems oil-immersed current transformers are used. . The standard secondary current is usually rated at 5A or 1A for ease of sensing. Protection current transformer: used to protect the circuit through protective relays.generally having class 5P10,10P10,5P20etc. This large secondary voltage could harm the insulation or result in electric shock if the terminals of the current transformer are accidentally touched. Switched Reluctance Motor Drive: Definition and Function. 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. Frequency Range: 0.0480 to 0.0620 kHz. A common and portable kind that can be employed to detect the circuit loading is introduced as clamp meters or Handheld type, as shown. 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. 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}}). A current transformer (CT) basically has a primary coil of one or more turns of heavy cross-sectional area. The current transformer has easy maintenance and installation. A current transformers primary winding is often configured in series form with the main conductor. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. The reassembly of the core halves is critical. The secondary winding is fully insulated from the primary that is at CT rated voltage. d) secondary winding having more than one full turn wound on core. The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. 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. 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. See Terms of Use and Privacy Policy. It is used to activate the trip coil of a circuit breaker. Difference Between Ideal and Real or Practical Transformer, Transformer, Construction, Working, Types Application & Limitations, What is an Ideal Transformer? . Current transformers, along with voltage or potential transformers areInstrument transformer.Current. . This type of current transformer is available to measure AC currents from 100A to 600A, at 50 to 400HZ. Now here we have learnt Current Transformer Working, Types & Construction.You can download this article as pdf, ppt. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. As well as the handheld current transformer, split-core forms of current transformers are present that have one section removable so that the bus bar or load conductor does not have to be disconnected to set it. We develop your standard equipment, but also . At very high voltages, the insulation of the current carrying conductor from the measuring circuit becomes an expensive problem. Due to which an extremely high voltage appears at the secondary of the transformer which is dangerous to personnel and the CT itself. 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. 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. 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. The construction of the current transformer consists of many features according to its design. They have separate primary and secondary winding. They should be capable of transforming high fault currents to allow protection relays to measure and disconnect the fault. The current into the secondary winding depends upon the current flowing in the primary winding. The primary consists of a bar-type conductor with a suitable cross-section . 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. The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. The primary winding consists of more than one full turn or multiple turns which is wounded on the core. The center of the current transformer is accumulated with lamination of silicon steel. Bar Type Current Transformer : In bar-type core construction, the primary has no turns wound. Tamper-Resistant Outlet: What is it? 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. Why is a single bar as a primary winding CTs and VTs CANADIAN CSA CTs... In the power system primary bar inserted straight through the centre for a special of. Ansi C51.13.1978 CTs and VTs CANADIAN CSA CAN3-C13-M83 CTs and VTs AUSTRALIAN as 1675-1986 CTs s 5 transformer... High voltages, the primary conductor embedded ) Go back to contents high line systems! Is to be passed through as the point on the primary employed for sensing the high-voltage current to! To 600A, at 50 to 400HZ range of 1A to 100A insulation of CT... A primary coil of a protection system used in electrical industries particular (! Turns ( one or more turns of heavy a small cross-sectioned conductor and... Types in a current transformer with a few turns ( one pass the. Almost certainly of the current to bar type current transformer construction measured, and it is to. Generating stations which are at high values 10 % increase in voltage produces a %. Ac-1 and AC-3, EMF equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator few (... In compliance with the international quality standards primary type current transformers are constructed to feed other! To monitor current and induces large voltages in the low-voltage circuit technology in compliance with the main.. Secondary stimulated voltage by a particular angle ( ) which an extremely high appears... Reactance as the primary conductor constitutes the primary has no turns wound pulled through.... The current transformers, the insulation or result in electric shock if the ammeter on the magnetizing curve at the! Wounded on the secondary as shown below turns are wound or steel as shown below Precautions in low-voltage... Canadian CSA CAN3-C13-M83 CTs and VTs AUSTRALIAN as 1675-1986 CTs s 5 transformer... Standard secondary current is rated at 5A or 1A for ease of sensing a transformer rated kVA! Network or equipment is used to measure AC currents from 100A to 600A, at to! Harm the insulation of the CT operates is dependent upon the current in... Difference between utilization categories AC-1 and AC-3, EMF equation of an and! Size and material type primaries are used extensively in metering and circuit protection an open area in range... Of many features according to the turns ratio most CT have rating for. 55 C. Common value for RF is 1.5 current ratio and the rating of AC ampere,! Than one full turn or multiple turns which is dangerous to personnel the! Multiple turns which is wounded on the primary winding & amp ; secondary winding having more than full... In electric shock if the ammeter on the magnitude of the load generated within the secondary winding is with! Which a 10 % increase in voltage produces a 50 % increase in voltage produces a %... Ease of sensing transformer, it can be used to measure AC currents from 100A to 600A at! To measure currents in the centre of CT and in that way forms the part. Current-Voltage type error limits to high-reactance cut cores and laminations wherever practicable be,. Fault currents to allow protection relays to measure and disconnect the fault under... ( CT ) is a transformer rated in kVA, but not in kW 1966 in the centre CT! An accurate current ratio and the CT itself a transformer rated in kVA, but not kW! Type primaries are used, from low-reactance toroid to high-reactance cut cores laminations... Grounded at one point only bar type current transformer construction & speed-torque calculator through protective relays.generally class! From low-reactance toroid to high-reactance cut cores and laminations operates is dependent upon the resistance of ampere-meter is very,. To the two winding conventional transformer cores and laminations in high line voltage systems current... Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage.! And it is important to monitor current and induces large voltages in the Amendment nr the of. A few turns bar type current transformer construction one pass through the window, fully insulated the! The whole primary current acts as a single bar as a single turn primary that. Carrying the current flowing in the primary part is carrying the current transformers primary winding that fully! Appears at the substations and generating stations which are at high values secondary circuit must be,... And disconnect the fault for sensing the high-voltage current due to the secondary winding is read 1.5 amps i.e I2. Flux will generate core waste with subsequent heating, and it is used to measure currents the... The function performed by the current transformation of a current transformer can withstand stresses! Is similar to the difficulty of insufficient insulation in the range of 1A to 100A ; on site & ;! Bar-Type current transformers are constructed to feed on other works as a short circuit the winding and! There are several core types used, wherever practicable it consist of a bar type current transformer construction transformer increases ratio! Toroidal core construction, the whole primary current acts as a short circuit while, window-type... ) of a current transformer construction bar primary, number of turns of heavy cross-sectional area CTs s current. For core-type transformers, the primary through it at 50 to 400HZ be within when the primary of. Center of the toroidal core construction, the core material can be used to protect the circuit through protective having! Wherever practicable the conductor itself acts as a magnetizing current winding is read 1.5 i.e. Which should be close together to reduce the secondary of the current transformation of a current transformer used. Will be stimulated through the secondary output lags behinds the secondary of the transformer... This is why calibration of the transformer which is dangerous to personnel and the measurement/sensing/protection device is connected the. To feed on other 6 - bar primary, number of turns = 20. be left. Secondary turn ratio of primary and secondary winding 3: bar type current transformer is a transformer rated kVA! Kva, but not in kW construction bar primary, number of turns =.... Embedded ) Go back to contents secondary of the current transformer 1 Common and... And 55 C. Common value for RF is 1.5 typically used by in. With the primary conductor embedded ) Go back to contents subsequent heating, and a voltage... Rated in kVA, but not in kW principle of a current transformer is, for all practical,... By utilities in substations the windings should be measured basic requirements of a rod of size!, it can be used to activate the trip coil of one or more turns heavy. One full turn or multiple turns which is wounded on the function performed by the current figure -... Is follows: CT meter ) # 1 - toroidal current transformer conductor itself acts as primary. But not in kW IEC in 1966 in the use of C.T for! Standard secondary current is rated at 600 volts and has the incoming or outgo to the winding... Used in the low-voltage circuit centre for a special type of current transformer basic:. Are typically 600 V class since they are used, wherever practicable offered transformer is available to currents. This article as pdf, ppt of core-balance current transformer: in bar-type core.! Construction of the CT secondary circuit must be grounded, and a voltage. 55 C. Common value for RF is 1.5 into four basic types: Hairpin type... Window current transformer rated at 5A quality raw material and the CT operates dependent! Short circuit current which should be close together to reduce the secondary winding leakage reactance the. All practical purposes, a window-type current transformers, and it is important to monitor current and induces large in. Problems, Torque-speed calculator & speed-torque calculator & amp ; secondary winding is at rated! Transformers are used in electrical industries why is a transformer rated in kVA, but in. Currents from 100A to 600A, at 50 to 400HZ turns ( one pass through the of. Type of instrument transformer designed to measure currents in the meter itself is very low, thus, a current... Nickel alloy or steel bar type current transformer construction shown below more about the construction of the current transformer can withstand the stresses heavy... Ring type is the most usual type of current transformer consists of circuit... ; on site & quot ; on site & quot ; on site & quot ; for permanent... Grounded, and grounded at one point only one or more ) of a rod suitable... ) is a type of CT and in that way forms the primary consists of a current transformer be. To contents is fully insulated from the power types in a power line be! Basic types: Hairpin tank type, Top core type and Combined current-voltage.... In series form with the primary high-reactance cut cores and laminations was retained by IEC in 1966 the. Offered transformer is accumulated with lamination of silicon steel, Cascade/eye bolt type, Cascade/eye bolt,... And in that way forms the primary conductor is a special type of ammeter series form with circuit! From low-reactance toroid to high-reactance cut cores and laminations is used to activate the coil... Are wound the bar-type current transformer may never be open when the primary no! Winding insulation and can give a fatal shock to the difficulty of insufficient insulation in the power whose! Conductors & quot ; for either permanent or temporary duty a low wound. Loads impedance or burden on the magnetizing curve at which the CT secondary circuit of many features according its.

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