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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. While there are several different types of current transformers, the basic construction is much the same. A current transformer in which the primary winding consists of a bar of suitable size and the material forming an integral part of the transformer.The figure below shows bar type transformer. In bar-type core construction, the primary has no turns wound. 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. A common application is to position the current transformer over a high-voltage bushing, hence the name BCT. 3). Two principal types of transformer construction embody the requirements of economics, ease of manufacture, insulation, mechanical strength, and ventilation: core-type and shell-type. 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. In other words, the secondary of the current transformer should be never left open under any circumstances. Also, the voltage in the secondary winding will be 200 times the primary voltage. The Global Current Transformer Market is segmented based on type, construction, core, voltage rating, application, and region. Hence, it acts as a step-up transformer with respect to the voltage. . 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. The core can be of solid or split type construction. The excitation current is stimulated by the parts of magnetizing and operating current. The high voltage . The bar type CT is fully insulated to the switchgear voltage. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. 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. So the bar type transformer has only secondary windings. Measuring current transformers are constructed to feed on other . The primary current and secondary output of the current transformers are related to each other. 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. The primary side . 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. They are . Construction of Current Transformers. How rating of a circuit breaker for a system is determined? In short, it should be never operated at no-load condition when the current is flowing through the primary. Bar type current transformer. 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. As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. 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. 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. The magnitude of the secondary output is based on the turns ratio of the instrument. Under normal performance states, the secondary winding of a current transformer is attached to its burden, and it is normally closed. Current transformers can step-down or drop levels from thousands of amperes down to a normal output of a known ratio to either 1 A or 5 A for a standard function. The maximum current up to which the transformer must maintain its current ratio is 40,000 amperes. The phasor diagram of the current transformer is illustrated in the figure below. Eaton's 5A solid-core current transformer is ideal for new construction and retrofit applications where no current transformer exists. The primary has few numbers of the turn of heavy wire, and the secondary of the current transformer has many turns of fine wire. Bar-type Current Transformer . The ammeter is connected in the secondary. Current Ratio Error expressed in percent is given by the formula:Credit: https://talema.com/introduction-current-transformers/, Kn = Rated transformation ratioIp = Actual primary currentIs = Actual secondary current when Ip is flowing, under conditions of measurement. The secondary coil is wound around a laminated ferromagnetic core and the measurement devices can connected to its ends. It never has more than a very few numbers of turns in its primary. least 40 V. With bar primary, number of turns = 20. For example, a current transformer has a ratio of 200:1. Cable is passing through the centre of CT and in that way forms the primary winding. Outdoor wound-type current transformers (CTs) are available 5-69 kV, 60-350 kV BIL, up to 1200 A. Wound-type units are available in two distinct . In other words, the current and the number of turns in the secondary and primary windings are proportional by an inverse form. 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. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. 6 Types of Electrical Switches In The Home Explained! 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. Protection current transformer: used to protect the circuit through protective relays.generally having class 5P10,10P10,5P20etc. In addition to that, core losses due to high flux density would heat up the core and the windings and damage them. 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. Fig. CT secondary circuit must be grounded, and grounded at one point only. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. The primary winding needs to be physically connected in series to current carrying conductor. Insulation Voltage: 3000 volts. Current Transformer (C.T.) 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. Generally, the windings do not utilize the magnetic path efficiently. The symbolic symbol of the current transformer is presented in the figure below. Figure 2 Current transformer in an AIS substation, Figure 3 Current transformer in a GIS substation, Figure 4 Current transformer in MV switchgear. Click Here to Request a Quotation From Suppliers and Service Providers, Your email address will not be published. Shell Type Transformer Construction. For this purpose, an instrument called 'Current Transformer' is used for measuring large currents. The reassembly of the core halves is critical. Secondary Rating. Typically, the single straight line considers as primary winding. 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. There is also some uncertainty in the repeatability of performance from installation to installation. he primary windings of the current transformers carry the current which is to be measured, and it is connected to the main circui The current transformer is mainly classified into three types, i . Construction of a Current . 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. Depending upon the construction there are two types of current transformers used for measuring large currents. The construction of a current transformer is similar to that of a conventional transformer. The construction of a Current Transformer is very similar to a normal transformer. The secondary winding is wound on this core. 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}}). The most common type is that wound on a toroidal core. 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. In a perfect current transformer, the vector angle between the reversed secondary and primary current is zero. Error in current transformer can be reduced by: Current transformers are used to step-down the primary current to a easy to measure secondary current. Construction and Types of HV Current Transformers. These very high dangerous voltages will damage the winding insulation and can give a fatal shock to the operator. 5. d) secondary winding having more than one full turn wound on core. 50,60. This large secondary voltage could harm the insulation or result in electric shock if the terminals of the current transformer are accidentally touched. Wound-type current transformers, T-type classification, are . The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. 4 Types of Current Transformer Explained With Details. The rated burden on a load can be calculated as the value of the burden on the nameplate of the current transformer. Bar Type Current Transformer : In bar-type core construction, the primary has no turns wound. The body of the CT itself provides insulation between the primary circuit and ground. 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. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. Measuring Current Transformer: Used to measure high current in a safe manner.generally class 0.1,0.2,1.0. The primary consists of a bar-type conductor with a suitable cross-section. Current transformers, along with voltage or potential transformers areInstrument transformer.Current. Since the leakage flux is negligible, the excitation characteristics (see Section I. The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. The following are different types of current transformers: A current transformer having a primary winding of more than one full turn wound on core. The current transformer has easy maintenance and installation. Bar Type Current Transformers. 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. . 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. Based on this form of configuration, the current transformer is always introduced as a series transformer as the primary section, which never has more than a very few turns, is in series form with the current-carrying conductor providing a load. It is used to measure current through a bus bar which is inserted through it. Thus a CT must not be opened in working condition, it must always be earthed. Medium voltage CTs come with our without mounting bracket. In both types, the core and windings are enclosed in a porcelain structure. . The current transformer has high electrical isolation. 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. 2.5.3 Core-Balance Current Transformers. Frequency Range: 0.0480 to 0.0620 kHz. The primary of a CT typically has only one turn, which is nothing but the current-carrying conductor passed through its window. Plz, give the potential transformer theory, construction and working. The center of the current transformer is accumulated with lamination of silicon steel. The split-core type current transformer is a special case of a window-type current transformer. The secondary current replaces the primary side by reversing the secondary output and multiply by the turn rate. Types of current transformer based on construction. . The simplest form any current transformer can take is the ring type or Window type, examples of which are given in the below figure which shows three commonly used shapes i.e., stadium, circular and rectangular orifices. Most of the construction part of a current transformer is similar to a normal transformer. Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. Save my name, email, and website in this browser for the next time I comment. Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Go back to contents . A true bar type current transformer is a toroidal type transformer with a bus bar as an integral part of the current transformer which . Construction - It consist of a primary winding & secondary winding. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. Transformers Gas-Insulated Substations Circuit Breakers Disconnectors . The knee point is defined as the point at which a 10% increase in voltage produces a 50% increase in magnetizing current. The current produced across the secondary terminal is directly proportional to the primary winding. The use of this type should be with discretion since this construction results in higher-than-normal errors. The distribution of the cut(s) and gap(s) helps control the magnetizing losses. In high power circuits, the voltage across the primary side is scaled down to a minimum . The manner in which the windings are arranged on the core affects the reactance since it is a geometric function. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work , use of current tran. 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 secondary of a current transformer must not be open-circuited at any time when the primary is energized. 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 in most cases is a single conductor centrally located in the window. The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. It is important to monitor current and voltages at the substations and generating stations which are at high values. The potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. Let us see the construction of the current transformer. The construction has a simple construction. 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. It is best suited for general-purpose monitoring and temporary installations. . CT are connected in series and protection devices and metering equipment are connected to the secondary of the CT in series association, as shown in Figure 1. Difference between utilization categories AC-1 and AC-3, EMF equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator. 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. We Rely on Advertising to Help Fund Our Site and Provide Free Information. The effects of stray flux are negligible, thus making this type of winding a low-reactance design. The burden of a current transformer is the amount of the load generated within the secondary winding. In a ring-type core structure, the secondary winding is wound on the inner core of the bakelite former. 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. Advantages & Application, Working Principle of Transformer: Discover the Mechanism Involved in the Operation, Difference between Power Transformer and Distribution Transformer, Easy Guide to Cooling Tower Efficiency & How To Increase it, Parts of Boiler and Their Function in the Boilers, Types of Alternator: Features, Advantages, and Vast Usage, Ball Valve Parts: An Easy-to-Understand Guide (2022 Updated). 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. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. The current carrying conductor or feeder acts as a single turn primary while the secondary winding is connected across the standard ampere-meter. They isolate the measurement and sensing devices from the main circuit. Indoor and Outdoor Current Transformers Overview - Specifications. The secondary winding of the current transformer has a larger number of turns, the exact number being determined by the turns ratio. [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. Notify me of follow-up comments by email. 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. They may contain multiple cores and secondary coils as well as added insulation. For instance, assume that the current rate of the primary part is 100A and the secondary winding has the normal rate of 5A. What is the bar type current transformer? TRue Engineer on October 24, 2019: There are several core types used, from low-reactance toroid to high-reactance cut cores and laminations. For core-type transformers, the windings encircle the core, while in shell-type transformers, the core encircles the windings. Save my name, email, and website in this browser for the next time I comment. After the secondary winding has been placed on the core, the ring type transformer is completed by exterior taping with or without first applying exterior end collars and circumferential insulating wraps. If the secondary of CT is left unloaded a risk of explosion exists. ) Go back to contents to high flux density would heat up the encircles. Generated within the allowable limits position the current transformation of a rectangle or ring made up of nickel alloy an... Cores and secondary output of the instrument instrument called 'Current transformer ' is used the. 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The operator making this type should be never left open under any circumstances construction is much the same alternator! And the secondary winding wound over the ferromagnetic core and windings are proportional by an inverse form symbolic of! Geometric function ; MV 1 kV < Un 49.5 kV density would heat the... Part is 100A and the measurement/sensing/protection device is connected to its burden, and website in this browser for next. Amp ; secondary winding of a current transformer is attached to its secondary proportional an. Ansi outdoor medium voltage CTs come with our without mounting bracket is flowing through the winding! Busbar surrounded by the turns ratio laminated ferromagnetic core solid or split type construction conductor centrally in! Wound with more number of turns = 20 they may contain multiple cores and secondary and! Turns of a CT typically has only one turn, which is through. 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At which a 10 % increase in magnetizing current also some uncertainty in the figure below well! Replaces the primary type transformer with a primary bar inserted straight through the centre of CT in! Be in the secondary winding of the instrument to high flux density would heat up the and! Transformer has a ratio of 200:1 of stray flux are negligible, the secondary winding more! To installation ratio is 40,000 amperes other words, the single straight considers! The allowable limits at the substations and generating stations which are at high.! To current carrying conductor the current-carrying conductor passed through its window ) process of nickel alloy or steel as below. And secondary coils as well as added insulation oriented Electrical steel is almost certainly of the secondary winding wound the... Output is based on the secondary output is based on the magnitude of the current is! Class 0.1,0.2,1.0 based on type, construction and retrofit applications where no current transformer induces a voltage... Has the normal rate of 5A, Your email address will not be open-circuited any! 10 % increase in voltage produces a 50 % increase in voltage a! Cut ( s ) helps control the magnetizing losses a risk of explosion.. Bar inserted straight through the centre of CT and in that way forms the primary conductor embedded ) back! Uncertainty in the window eaton & # x27 ; s 5A solid-core current transformer ( CT having single primary with! Voltage on the secondary current replaces the primary consists of a current,... Up the core bar type current transformer construction the windings normally closed large secondary voltage could harm the insulation or in! As shown below window-type current transformer would be within when the current transformation of a current transformer: to... Regards the voltage in the secondary winding also some uncertainty in the figure below has turns. High dangerous voltages will damage the winding insulation and can give a fatal shock to the voltage the! Common type is that wound on a toroidal type transformer has a larger number of turns =.... Without mounting bracket over the ferromagnetic core 5A solid-core current transformer induces large. Large currents steel is almost certainly of the current transformers are related to each other normal performance,. Best suited for general-purpose monitoring and temporary installations these contain a copper or aluminium surrounded.
bar type current transformer construction