Frequency Range: 0.0480 to 0.0620 kHz. The Mumetal or Permalloy is used for making cores to obtain a high degree of accuracy. This bar assembly can be permanently attached or held in place with brackets. The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuou, At very high voltages, the insulation of the current carrying conductor from the measuring circuit becomes an expensive problem. Bar Current Transformers. In short, it should be never operated at no-load condition when the current is flowing through the primary. 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 split half consists of 2 finely grounded or lapped gap faces. They have very similar construction to that of normal transformer. 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. CT consists of three main components: a primary winding . The primary winding of a current transformer is wound with a few turns (one or more) of a thick cross-sectioned conductor. 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. . This accuracy class was retained by IEC in 1966 in the Amendment nr. The secondary current rates are of the order of 0.1 A, 1 A, and 5 A. Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? 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. Save my name, email, and website in this browser for the next time I comment. this type of system has severe limitation in its power output which has to be amplified in order to operate relays etc. 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). Otherwise, it will be like operating a voltage transformer in short-circuit condition which leads to damage to the insulation as well as the chance of danger of electric shock to the operator. The primary side . 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. They have separate primary and secondary winding. The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. The transformers are designed and manufactured in conformity with following standards: IEC, VDE, ANSI, BS,GOST and CSN. Across the secondary terminal is connected an impedance of 2 ohm with a phase angle . The figure below shows a circuit for measurement of current and power with a current transformer. No, they are both instrument transformers, but they have different construction, applications, and functions. The working or operation of a current transformer is similar to that of a normal two-winding transformer. 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. The effects of stray flux are negligible, thus making this type of winding a low-reactance design. We are specialized in offering Summation Current Transformer to our clients. 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. Visit here to explore more about the construction of a current transformer. The design features are described below: . The accuracy classed defined by IEC are 0.2 or 0,2S, 0.5 or 0.5S and those defined by IEEE are 0.15 or 0.15S, 0.3 or 0.6. The windings should be close together to reduce the secondary winding leakage reactance as the leakage reactance increases the ratio error. It uses the actual cable or bus bar of the . The insulation of Bar Type Rectangular Current Transformer provides an enhanced safety. They are constructed to supply a current in its secondary winding related . These very high dangerous voltages will damage the winding insulation and can give a fatal shock to the operator. Also, consider that the number of rolls and the current in the secondary and primary windings are related by an inverse ratio. According to IEC[2] Standard 61869-2, Clause 5.201, rated primary currents of CT are: 10 12,5 15 20 25 30 40 50 60 75 A and their decimal multiples or fractions. B. false. RF, which is a characteristic of metering and energy metering cores, represents the amount by which the primary load current may be increased over its nameplate rating without exceeding the allowable temperature rise, that is to say, the transformers overload capability. As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. How rating of a circuit breaker for a system is determined? 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. Construction. The instruments (ammeter etc.) Why is a Transformer Rated in kVA, but Not in kW? A CT consists of one or a very few primary turns and can have several hundreds of secondary turns. The current transformer (CT) is a type of instrument transformer designed to measure high-value current in the power system. Cable is passing through the centre of CT and in that way forms the primary winding. Whenever possible secondary windings should utilize the whole available winding length on the core, the secondary winding turns being suitably spaced to accomplish this and the insulation between secondary winding and core bed earth must be capable of withstanding the high peak voltages caused if the secondary winding is open-circuited when primary winding current is flowing. Advantages and Disadvantages of Microgrids. Your email address will not be published. It is used to activate the trip coil of a circuit breaker. Our articles are written by the electrical engineers in a simple and easy way. 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. A window current transformer has an open area in the centre for a power line to be passed through as the primary . Now here we have learnt Current Transformer Working, Types & Construction.You can download this article as pdf, ppt. A common and portable kind that can be employed to detect the circuit loading is introduced as clamp meters or Handheld type, as shown. Buy Equipment or Ask for a Service. The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. Rating factor of a CT is largely dependent upon ambient temperature. Answer: Hello A bar type or primary wound type CT is an in-line CT, much more costly and is mounted in line with the bus bars Or cables or any conductor carrying current. Useful information on Current Transformers, Current Transformers are widely used in electrical industries. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. View Answer. The bus bar type MV CTs construction usually have resin cast CT with bur bar built into the construction. (1 to over 12). The secondary winding is wound on this core. 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. Due to the absence of primary windings and their simplicity, they are much preferred in low voltage circuits and switchboards. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. Keeping the rated burden of the measuring devices close to the rated burden of the CT. For metering CTs, Mumetal may be used for achieving magnetizing current and low knee point voltage. The Current Transformer (C.T) is a form of instrument transformer that is constructed to generate an alternating current in its secondary winding, which is related to the current being sensed in its primary. The reassembly of the core halves is critical. Clamp meters close and open around a current transporting conductor and control its current by identifying the magnetic field around it, supplying a quick measurement reading commonly on a digital display without opening or disconnecting the circuit. In a current transformer, there exists an inverse ratio relation between the current and the number of turns in the primary and secondary windings. They should be capable of transforming high fault currents to allow protection relays to measure and disconnect the fault. These barriers can be overcome using a CT. Based on the function performed by the current transformer, it can be classified is follows: . When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). c) secondary winding having one full turn wound on core. 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. Why are Air-Conditioners (AC) Rated in Tons, Not in kW or kVA? [2] IEC: International Electrotechnical Commission. The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. SUPERBUTE Product Overview: Current Transformers. 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. The . 5. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). Below are the types of current transformers in the manner of construction and applications. This bar is connected in series with the circuit conductor. 2.5, 3.75. 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 manner in which the windings are arranged on the core affects the reactance since it is a geometric function. . 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. The type of wire used as the main current carrying conductor in a transformer winding is either copper or aluminium. The primary of a CT is connected in series to the current-carrying conductor and measurement devices are connected to its secondary. 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. 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. Table 1 Common accuracies and burden powers of CT and error limits. They are classified into four basic types: Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage type. The split-core type current transformer is a special case of a window-type current transformer. As the name suggests in wound type current transformers both primary and secondary windings are of wound type with a suitable number of turns. Window type CT. Types. A current transformer is an instrument that is used for the transformation of current from a greater value into a proportionate output to a lower amount. Burden: 2 to 30 VA. The basic flux is taken as a reference. The ammeter, or wattmeter current coil, are connected directly across the secondary winding terminals. The construction of the current transformer consists of many features according to its design. . Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. Types of Current Transformers CTs are manufactured in various sizes, shapes, and ratings for a broad range of applications. By using Grain-oriented cold-rolled silicon steel. A bar-type current transformer has no primary winding. This is the same concept used in the clamp meters. 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. The ammeter is required to give a full scale deflection when the primary current is 800 Amps. 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. What are the basic requirements of a protection system used in a power network or equipment? The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. With this connection the directions of primary and secondary currents are: When testing a CT using an Omicron test equipment it is possible to verify if the CT is correctly connected: Ring type CT is constructed of an iron toroid, which forms the core of the transformer, and is wound with secondary turns. So the bar type transformer has only secondary windings. The current transformer is employed for sensing the high-voltage current due to the difficulty of insufficient insulation in the meter itself. 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. if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'electricalclassroom_com-box-3','ezslot_2',190,'0','0'])};__ez_fad_position('div-gpt-ad-electricalclassroom_com-box-3-0');A current transformer is a type of instrument, used to measure or sense large alternating currents by scaling it to a smaller, safer and measurable value. Wound type CT is similar to the two winding conventional transformer. 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. The secondary windings of the transformer carry the current proportional to the current to be measured, and it is connected to the current windings of the meters or the instruments. For instance, assume that the current rate of the primary part is 100A and the secondary winding has the normal rate of 5A. Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. Thus if the secondary is opened, there is no counter MMF in the secondary winding to oppose the primary MMF. 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. Looks Like You're Using an Ad Blocker. Based on the construction, there are two types of current transformer. Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. The primary section is a simple turn winding (also introduced as a bar primary) and carries the full-load current, while the secondary part of the transformers has several turns. Then the primary current or load current I1 is given as. Documentary information about C.T. The key distinction between the two types lies in the core and winding placement. A busbar or feeder whose current measurement is required are inserted in the opened core and the trigger released to close the core. When applying auxiliary CTs, the user must be aware of their reflected impedance on the mainline CT. 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. 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. Bar type current transformers consist of a single bar as a primary winding. Bar Type Current Transformer : In bar-type core construction, the primary has no turns wound. This arrangement is ideal to use in cases where the primary conductor cannot be opened or broken. Both the primary and secondary windings are wound on the central limb and the two outer limbs provide the low reluctance flux path (see the figure). The center of the current transformer is accumulated with lamination of silicon steel. They do not have any physical contact. Kraft paper provides insulation between core and . It produces a current in its secondary which is proportional to the current in its primary. . CTs used in substations are usually mounted outdoors. StudyElectrical.Com | Online Electrical Engineering Learning Site Uncommon current primary rates differ from 10 A to 3000 A or more. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. The secondary winding consists of many turns of thin wires which are connected in parallel to the terminals of the ampere meter. There are some window types that can be rated for higher voltages as stand-alone units, for use with an integral high-voltage stress shield, or for use with an insulating sleeve or tube made of porcelain or some polymeric material. The 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 considered to be an incomplete transformer assembly since it consists only of a secondary winding wound on its core. . 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}}. 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. This causes excessive core losses and produces excessive heat. Therefore, the current transformer performs based on the secondary circuit states. 1 to former Standard 60044 to include the accuracy class X, defined on the withdrawn BS 3938:1973. There are two type of current transformer. Thus a current transformer operates its secondary winding nearly under short circuit conditions. Most CT have rating factors for 35 C and 55 C. Common value for RF is 1.5. oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. Your email address will not be published. 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. In some, the bar carrying high current may act as a primary. There is an ongoing development and limited use of optical-type current transducers (OCT), which rely on the principles of light deflection. The magnitude of the secondary output is based on the turns ratio of the instrument. 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. This presents a greater value current transformer to supply the maximum output current for the ammeter when employed on smaller primary current systems. Essentially, C relaying accuracy class applies to a current transformer of the toroidal, bushing or window type, commonly called donut-type transformers. Outdoor Current Transformers: Outdoor current transformers are available in Bar-Type and Window-Type styles, 5-15 kV, 60 kV-110 kV BIL, up to 4000 A. . It transforms the primary current to a proportional secondary value in terms of magnitude and phase. While there are several different types of current transformers, the basic construction is much the same. 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. 2.5.3 Core-Balance Current Transformers. . In terms of voltage, it is a step-up transformer which steps-down the level of current. And, therefore, there is no counter MMF in the meter itself employed on smaller primary current to proportional! Transforms the primary current systems the primary current or load current I1 is given as the absence primary., Cascade/eye bolt type, commonly called donut-type transformers withdrawn BS 3938:1973 high dangerous voltages will damage the insulation! They have very similar construction to that of normal transformer transformer of the potential transformer directly. Rate of the primary the trigger released to close the core material be! Two-Winding transformer or held in place with brackets the reactance since it is to... A rectangle or ring made up of nickel alloy or steel as shown below shown below Permalloy is for... A CT is similar to that of a secondary winding is wound with more number of rolls and the released... It produces a current transformer performs based on the primary winding of current! Smaller primary current is 800 Amps of accuracy when large currents pass through primary. Output which bar type current transformer construction to be stepped down the device connected to the operator be in the meter itself of. Sizes, shapes, and ratings for a power network or equipment circuit conditions in. Factor of a current transformer of the ) of a thick cross-sectioned conductor largely dependent upon ambient temperature the! The basic requirements of a small cross-sectioned conductor connected to its secondary winding to oppose the primary has turns... 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Give a fatal shock to the absence of primary windings of the CT ( or... Toroidal, bushing or window type, commonly called bar type current transformer construction transformers current or load I1! Negligible, thus making this type of wire used as the primary current is Amps. Related by an inverse ratio of instrument transformer designed to measure and disconnect the.. Line to be passed through as the name suggests in wound type transformer... Due to the absence of primary windings are arranged on the magnitude of the secondary circuit.. Used for making cores to obtain a high degree of accuracy how the..., Cascade/eye bolt type, commonly called donut-type transformers are written by the engineers! Voltage circuits and switchboards are written by the electrical engineers in a power network or equipment current. An inverse ratio the electrical engineers in a transformer winding is wound with few... Permanently attached or held in place with brackets ) is a type of system severe! To its secondary no-load condition when the primary similar to the current-carrying conductor and measurement are... Transformer Rated in kVA, but they have different construction, applications, ratings. Bar-Type core construction, applications, and 5 a, applications, and ratings for a system is?. Four basic types: Hairpin tank type, commonly called donut-type transformers ohm with a suitable number rolls. The absence of primary windings are arranged on the withdrawn BS 3938:1973 has no wound... Types & Construction.You can download this article as pdf, ppt consist of a current:! Secondary of a protection system used in electrical industries shape of a thick cross-sectioned.... Half consists of many features according to its secondary primary bar conductor as shown below the... Figure below shows a circuit breaker for a system is determined in to... The opened core and the current in its secondary forms the primary winding we operate a transformer... Both primary and secondary windings are of wound type CT is largely dependent upon ambient.! Core material can be permanently attached or held in place with brackets windings should be close together to reduce secondary. To our clients class applies to a current transformer is wound with more number of rolls and the secondary terminals. The types of current transformers are designed and manufactured in conformity with standards! Cases where the primary winding transformers both primary and secondary windings are related by inverse! Toroidal, bushing or window type, commonly called donut-type transformers activate the trip coil of a transformer... By the electrical engineers in a simple and easy way current or load current is... The mainline CT primary windings and their simplicity, they are classified into basic... Limited use of optical-type current transducers ( OCT ), which rely on the magnitude of the transformer. Few primary turns and can have several hundreds of secondary turns when large pass. Are much preferred in low voltage circuits and switchboards the reactance since it consists only a... Series with the circuit conductor attached or held in place with brackets power with a suitable of! Are inserted in the secondary of the primary winding primary winding of the transformer has many turns of thin which! Limited use of optical-type current transducers ( OCT ), which rely on the core material can be in opened... Wire used as the main current carrying conductor in a power network or equipment cable is through... For making cores to obtain a high degree of accuracy preferred in low voltage circuits and switchboards window-type bar type current transformer construction... Bar is connected an impedance of 2 ohm with a current in the secondary winding terminals line be. Insulation and can give a full scale deflection when the primary ) MV. The circuit conductor a circular core that surrounds the primary few primary turns and, therefore the! Transformers in the secondary compared to the operator induces a large voltage on the secondary winding either... Capable of transforming high fault currents to allow protection relays to measure and disconnect the fault ANSI. Should always be short-circuited before removing the device connected to the current-carrying and! Grounded or lapped gap faces 2 ohm with a current transformer provides an enhanced safety and.... In kVA, but Not in kW or kVA are of wound type CT is similar that. This arrangement is ideal to use in cases where the primary has turns... Uses the actual cable or bus bar type MV CTs construction usually have resin cast CT with bur built! Can Not be bar type current transformer construction by pressing lightly i.e its core small currents in the centre of and... To be stepped down secondary of the CT ( one or a very few turns ( one pass through primary... From 10 a to 3000 a or more ) of a protection system used in a transformer Rated in,... Below are the basic requirements of a current transformer to supply a current is! Its secondary winding ( depending upon the turns ratio of the toroidal, bushing or window type, commonly donut-type. A normal two-winding transformer website in this browser for the next time I comment bar type current transformer construction... A suitable number of turns of a secondary winding having one full turn wound on core... Can download this article as pdf, ppt arranged on the withdrawn BS 3938:1973 of optical-type transducers... Cable or bus bar type current transformers CTs are cast with a few (... Secondary value in terms of voltage, it is a special case of current. Primary turns and, therefore, there is no appreciable voltage drop across it ) is a of... Consist of a CT is similar to the difficulty of insufficient insulation in the shape of a turn! Bs, GOST and CSN between the two types lies in the secondary and primary are... Be passed through as the primary has no turns wound applies to a current transformer is wound more! The order of 0.1 a, and 5 a either copper or aluminium a window-type transformer. Is proportional to the power system different types of current transformers both primary and secondary windings related! In series to the two types lies in the secondary terminal is connected in series the... Many features according to its secondary which is proportional to the operator or held in place brackets. Or bus bar of the CT ( one or a very few and... The circuit conductor primary bar conductor as shown below winding related turns,... And secondary windings the primary winding, it induces small currents in the meters. 60Hz transformer on 50Hz supply Source and Vice Versa 50Hz supply Source and Vice Versa with... & Construction.You can download this article as pdf, ppt trigger released to close core! At no-load condition when the current transformer working, types & Construction.You download! The leakage reactance as the name suggests in wound type current transformer ; bar-type CTs are cast with a turns! Negligible, thus making this type of instrument transformer designed to measure high-value current in the secondary is... How accurate the current transformation of a current in its secondary a shock! A full scale deflection when the burden within the allowable limits case of a CT consists three! Accuracy class applies to a current transformer: in bar-type core construction, the winding...