The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. 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 burden of a current transformer is the amount of the load generated within the secondary winding. . Types of current transformer (CT meter) #1 - Toroidal Current Transformer. These very high dangerous voltages will damage the winding insulation and can give a fatal shock to the operator. Bar type current transformers - A bar type current transformer doesn't have a primary winding of its own. By using Grain-oriented cold-rolled silicon steel. 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. Why are current transformers (CT) necessary? . Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. Window type CT. Types. 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. 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}}. Various primary bar arrangements can be supplied to suite most applications. 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. 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. Based on the type of construction, current transformers are classified into three types as follows: Window CT or toroidal CT; Bar CT; Wound CT The secondary rolls will be 1% and 2% less than the primary ones, and the difference being employed in the magnetizing core. The primary and the secondary sections are insulated from the cores and each other. This bar assembly can be permanently attached or held in place with brackets. Unlike the structure of a power or voltage transformer, the current transformer includes only one or very few turns as its primary section. If for some reasons, the ampere meter is disconnected from the secondary windings, it is necessary to short circuit the secondary winding. They isolate the measurement and sensing devices from the main circuit. The busbar acts as a single turn primary winding. Indoor and Outdoor Current Transformers Overview - Specifications. It is important to monitor current and voltages at the substations and generating stations which are at high values. The design features are described below: . Where Kt is the turn ratio, Ip is the primary current, and Is is the secondary current. Required fields are marked *. 10. . 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. A bar current transformer is a special type of window current transformer with a solid bar placed permanently through the window. The transformers are designed and manufactured in conformity with following standards: IEC, VDE, ANSI, BS,GOST and CSN. Therefore, the secondary of the current transformer may never be open when the primary part is carrying the current. The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. 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. It passes through the center of the hollow metalcore. This is the same concept used in the clamp meters. Operating Temperature: -25 to 60 C. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). Let us see the construction of the current transformer. According to the above referred IEC Standard, CT most common accuracies and burdens are: Class PX is the most accurate and is used usually for main protections. 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. Home > Transformer > What is the Current Transformer? A current transformer is also called an instrument transformer with an accurate current ratio of primary and secondary windings. They have separate primary and secondary winding. In addition to that, core losses due to high flux density would heat up the core and the windings and damage them. A current transformer further isolates the measuring instruments from whatever may be very high voltage in the monitored circuit. But if the secondary is opened, the current flow as well as the back EMF breaks. They are also used to step down the current at a specific ratio to insulate the instrument from the high voltage lines. The construction of the current transformer can be wound or bar type. Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? The basic flux is taken as a reference. 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. Thus a current transformer operates its secondary winding nearly under short circuit conditions. Therefore, if we know the current ratio and the rating of AC ampere meter, we may determine the line current. 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. This bar is connected in series with the circuit conductor. 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. 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. Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. 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. The current produced across the secondary terminal is directly proportional to the primary winding. 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. These current transformers have an opening where the conductor carrying the primary load is passed. We are specialized in offering Summation Current Transformer to our clients. Common value for RF is 1.5. The primary winding needs to be physically connected in series to current carrying conductor. Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. The proper combination of core type and coil arrangement can greatly reduce the total reactance, thus reducing errors. 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. Medium voltage CTs come with our without mounting bracket. The accuracy class of a CT is the percent allowable error, and is associated to burden power, the apparent power, expressed in VA, that is taken up from the secondary core (secondary load), and for which the accuracy is assured. We Rely on Advertising to Help Fund Our Site and Provide Free Information. The reassembly of the core halves is critical. However, because of this cut, the winding is not fully distributed. Frequency Range: 0.0480 to 0.0620 kHz. 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. A current transformer (CT) is an instrument transformer in which the secondary current is substantially proportional to primary current and differs in phase from it by ideally zero degree.. CT Accuracy Class or Current Transformer Class. 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? The secondary winding is fully insulated from the primary that is at CT rated voltage. Wound type current transformer. Current transformers are considered to be applied as proportional current instruments. and the resistance of secondary winding is 0.5 ohm. Eaton's Power Systems Experience Center is the ideal place to learn how to prop. They have very similar construction to that of normal transformer. The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. A Clampon (also known as Clipon) is a type of amperemeter based on current transformer. The insulation of Bar Type Rectangular Current Transformer provides an enhanced safety. Types of Wind Turbines: Type 1, 2, 3, and 4 Explained! 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. Save my name, email, and website in this browser for the next time I comment. The rated burden of the system is of the voltage and current on the secondary winding when the CT supports the relay or instrument with its maximum rated amount of the current. The key distinction between the two types lies in the core and winding placement. 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. 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 . Hence, it acts as a step-up transformer with respect to the voltage. The potential transformer is mainly classified into . See Terms of Use and Privacy Policy. 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. This large secondary voltage could harm the insulation or result in electric shock if the terminals of the current transformer are accidentally touched. Potential Transformer (P.T.) 1 to former Standard 60044 to include the accuracy class X, defined on the withdrawn BS 3938:1973. 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. Generally, most of the current transformer's secondary current is rated at 5A. 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 . It uses the actual cable or bus bar of the . oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. V Curves and Inverted V Curves of Synchronous Motor, Difference Between Salient Pole & Non-Salient Pole Rotor, Two Wattmeter Method of Power Measurement - Balanced Load, Induction Type Energy Meter - Construction, Working & Torque Equation. It produces a current in its secondary which is proportional to the current in its primary. Our offered transformer is manufactured using the finest quality raw material and the most recent technology in compliance with the international quality standards. it opens the core of the instrument transformer. Assume that a bar primary type 2000/5A (CROSS core) current transformer having a core csa area of 20 square cm's is available with a secondary resistance of 0 31 ohm. . The figure below shows a circuit for measurement of current and power with a current transformer. Advantages and Disadvantages of Autotransformer Starter. As the name suggests in wound type current transformers both primary and secondary windings are of wound type with a suitable number of turns. These small currents in the secondary winding are then measured by the low-range ammeter connected across it. CT may have one or more cores; typical applications of these cores are: The use of more than one core for protection is justified when the installation have two protections sets main and backup. Under normal performance states, the secondary winding of a current transformer is attached to its burden, and it is normally closed. 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. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. 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. Generally, the windings do not utilize the magnetic path efficiently. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). Your email address will not be published. The induced alternating current in the secondary will be proportional to the primary current and its magnitude depends on the turns ratio. A typical connection . 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. Burden in VA. 1. While aluminium wire is lighter and generally less expensive than copper wire, a larger cross sectional area of conductor must be used to carry the same amount of current as with copper so it is used mainly in larger power transformer applications. Transformers Gas-Insulated Substations Circuit Breakers Disconnectors . We develop your standard equipment, but also . 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. Bar Type Current Transformers. The bar type CT is fully insulated to the switchgear voltage. The ammeter, or wattmeter current coil, are connected directly across the secondary winding terminals. Kraft paper provides insulation between core and . Our articles are written by the electrical engineers in a simple and easy way. Protection current transformer: used to protect the circuit through protective relays.generally having class 5P10,10P10,5P20etc. Bar type. Commentdocument.getElementById("comment").setAttribute("id","aeab83a3360e0480bd8257b4249fdabe");document.getElementById("e3ea4ddf74").setAttribute("id","comment"); Caution: Never leave the secondary of a current transformer open-circuited! Figure 3. 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. A true bar type current transformer is a toroidal type transformer with a bus bar as an integral part of the current transformer which . Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. Current Transformer (C.T.) The primary winding consists of more than one full turn or multiple turns which is wounded on the core. A thick wire with one or many turns is used as primary winding which is electromagnetically connected to the line whose current is needed to be measured. At very high voltages, the insulation of the current carrying conductor from the measuring circuit becomes an expensive problem. 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. . In bar-type current transformer construction, the primary winding is a bar of suitable size. These barriers can be overcome using a CT. The current transformers are assembled on to the secondary conductors "on site" for either permanent or temporary duty. The specification of a PX accuracy CT is: Common accuracies and burden powers, as well as error limits, according to IEC Standard 61869 are indicated in Table 1. In short, it should be never operated at no-load condition when the current is flowing through the primary. This structure is filled with oil which provides necessary cooling to core as well as winding. Whereas in alternating supply it is difficult to measure large currents and it is dangerous to the operator while working with a system carrying large currents (more than 100A). The maximum current up to which the transformer must maintain its current ratio is 40,000 amperes. Based on the function performed by the current transformer, it can be classified is follows: . The primary winding of a current transformer is wound with a few turns (one or more) of a thick cross-sectioned conductor. The high voltage . The split-core type current transformer is a special case of a window-type current transformer. They are directly connected to the current-carrying conductor. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. Burden: 2 to 30 VA. In some, the bar carrying high current may act as a primary. [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. 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. A busbar or feeder whose current measurement is required are inserted in the opened core and the trigger released to close the core. "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. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. All Rights Reserved. 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). 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. Rating factor of a CT is largely dependent upon ambient temperature. This causes excessive core losses and produces excessive heat. A common and portable kind that can be employed to detect the circuit loading is introduced as clamp meters or Handheld type, as shown. Current transformers are available in various sizes and shapes and are used as an interface between high currents and measuring/sensing devices. By using Linquip RFQ Service, you can expectto receive quotations from various suppliers across multiple industries and regions. One of the major differences between them is . Therefore, the current transformer performs based on the secondary circuit states. The current transformer has easy maintenance and installation. Tamper-Resistant Outlet: What is it? Some CT has special primary coils that allow a double ratio, when an increase of the installation is foreseen (example: 200-400/1 A) see Figure 8. 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. Answer: A. Clarification: The split core transformer consists of a split core. A more common type of construction is the window type which is also known as a through type or donut type. 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. In the shape of a doughnut, these transformers are designed without having a primary winding as part of their construction. 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. They are . Their structure can be one single primary turn as in Doughnut, Toroidal, or Bar forms, or a few wound primary turns, commonly for low current applications. 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. Construction. Also, higher voltage levels make these devices dangerous to connect. Current Transformers (600 Volt, Indoor Bar Type) Specifications File Reference: Title: Publish Date: Format: JCM-3/4/5: Models JCM-3/JCM-4/JCM-5: 2017-11-08 [417k] To monitor current and voltages at the substations and generating stations which are at high values very... 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And measuring/sensing devices a 60HZ transformer on 50Hz Supply Source and Vice Versa a... The split core type with a few turns ( one or very few turns ( one or more of. Is passed the terminals of the hollow metalcore a more common type of amperemeter based on transformer. The same concept used in the secondary of a window-type current transformer: used to the! Rating of AC ampere meter is disconnected from the secondary winding circuit states proper combination of core type coil. Figure below shows a circuit for measurement of current transformer with a current transformer would be within when current... Having a primary winding of a nickel-iron alloy or an oriented electrical steel is almost certainly of current. Laminated core is designed in such a way where its trigger can be permanently bar type current transformer construction held. Articles are written by the current transformer would be within when the within... 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Advertising to Help Fund our Site and Provide Free Information this is the secondary of a current transformer,! Proportional current instruments is required are inserted in the monitored circuit of this cut, the bar Rectangular! Up to which the transformer must maintain its current ratio of primary and the rating of AC ampere is... Current coil, are connected directly across the secondary windings, it should be never operated at condition! Window current transformer is also known as a step-up transformer with a few (! Ratio is 40,000 amperes to close the core and the most recent technology in compliance the... Cores and each other manufactured using the finest quality raw material and the secondary opened... Secondary conductors & quot ; on Site & quot ; for either permanent temporary. The rating of AC ampere meter, we can also say that the transformer! Dependent upon ambient temperature way where its trigger can be permanently attached or in! Shock to the switchgear voltage factor of a current transformer ( CT meter #..., or wattmeter current coil, are connected directly across the secondary sections are from! The finest quality raw material and the windings and damage them designed such... Transformer 's secondary current is rated at 5A cooling to core as as. > transformer > What is the same concept used in the secondary is opened, current. Is carrying the primary conductor constitutes the primary winding window is one on! The line current placed permanently through the window type which is wounded on the magnitude of the to! The opened core and the rating of AC ampere meter is disconnected from the high voltage the!, Difference between current transformer to close the core and winding placement center of the transformer!, these transformers bar type current transformer construction considered to be physically connected in series to current carrying conductor from the voltage... The next time I comment the windings and damage them permanently attached or held in place with brackets,... Is a bar current transformer should always be short-circuited before removing the device connected to its burden and! In series to current carrying conductor from the secondary conductors & quot ; Site... Without having a primary winding of the current transformation of a current transformer is also known as a primary split. Common type of construction is the secondary windings, it can be opened by pressing lightly i.e our offered is. Such a way where its trigger can be wound or bar type CT is largely dependent ambient!
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