2.5.3 Core-Balance Current Transformers. Since the secondary coil is wound over the core, an alternating current is induced in it. SUPERBUTE Product Overview: Current Transformers. The key distinction between the two types lies in the core and winding placement. Visit here to explore more about the construction of a current transformer. 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. Let us see the construction of the current transformer. The reassembly of the core halves is critical. "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. . Thus a current transformer operates its secondary winding nearly under short circuit conditions. The primary of a CT is connected in series to the current-carrying conductor and measurement devices are connected to its secondary. Current Transformer Types and Applications- Current transformers (CT) are employed in Medium-Voltage (MV) and High-Voltage (HV) installations to give an image of electrical output to protection units and relays and metering instruments. Transformer Basics and working principle,Construction,Types of . Our articles are written by the electrical engineers in a simple and easy way. 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. There is an ongoing development and limited use of optical-type current transducers (OCT), which rely on the principles of light deflection. Frequency Range: 0.0480 to 0.0620 kHz. 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. 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. Burden: 2 to 30 VA. The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. The center of the current transformer is accumulated with lamination of silicon steel. The primary and the secondary sections are insulated from the cores and each other. Where Is is the secondary current, Es is the secondary induced voltage, Ip is the primary current, Ep is the primary induced voltage, Kt is turn ratio, or the number of secondary turn/number of primary turn, I0 is the excitation current, Im is the magnetizing current, Iw is the working component, and s is main flux. Thus a CT must not be opened in working condition, it must always be earthed. Why Cant a Transformer Be Operated on DC Supply? Shell Type Transformer Construction. A CT consists of one or a very few primary turns and can have several hundreds of secondary turns. Where required for test purposes, terminals in the form of test blocks are provided on the switchgear for the connection of external instruments and metering equipment. The current transformers are assembled on to the secondary conductors "on site" for either permanent or temporary duty. This causes excessive core losses and produces excessive heat. A bar-type current transformer has no primary winding. The current transformer includes two problematic errors that are ratio error and a phase angle error. The phasor diagram of the current transformer is illustrated in the figure below. If the load (or ammeter) should be removed, a short-circuit must be set across the secondary terminals primarily to remove the risk of shocking. EE-Tools, Instruments, Devices, Components & Measurements, What is Potential Transformer (PT)? Usually HV CT use oil or gas (SF6) as insulation medium and MV CT use synthetic resins. 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 core of the current transformer is built up with lamination of silicon steel. In some, the bar carrying high current may act as a primary. By using Linquip RFQ Service, you can expectto receive quotations from various suppliers across multiple industries and regions. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). should have an output of at. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. b) primary winding consists of a bar of suitable size and material. Current Transformers Resolution: A bar type CT is an in-line CT, much more costly and is mounted in line with the bus bars (bolted on both sides). Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work , use of current tran. As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. In short, it should be never operated at no-load condition when the current is flowing through the primary. The working or operation of a current transformer is similar to that of a normal two-winding transformer. 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. The secondary winding of the current transformer has a larger number of turns, the exact number being determined by the turns ratio. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. A current transformer, like any other type of transformer, should satisfy the amp-turn formula. Therefore, once the current ratio of the current transformer is known then we can determine the line current on the primary side by measuring the current on the secondary side. In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. Wound type CT is similar to the two winding conventional transformer. The . 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. 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 primary winding and secondary winding(s) are insulated from each other and from the core(s) and are . Switched Reluctance Motor Drive: Definition and Function. Notify me of follow-up comments by email. Basically, it is a step-down transformer (with respect to current) consisting of two windings, primary and secondary without any electrical connection between them. [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. They should be capable of transforming high fault currents to allow protection relays to measure and disconnect the fault. In a ring-type core structure, the secondary winding is wound on the inner core of the bakelite former. . The figure below shows thewound type transformer. The secondary output is commonly rated at a standard 1 A or 5 A for greater primary current ratings. 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. Both windings are permanently assembled on the core. The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. These small currents in the secondary winding are then measured by the low-range ammeter connected across it. 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. It is helpful for engineering life. They come with lead wires that are equipped with connectors and housings if required. A true bar type current transformer is a toroidal type transformer with a bus bar as an integral part of the current transformer which . oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. The construction of the current transformer consists of many features according to its design. 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. Rating factor of a CT is largely dependent upon ambient temperature. 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. 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. Please Whitelist Our Website by Allowing Ads, Current Transformers (CT) Types, Characteristic & Applications, Current Transformers (CT) Construction, Types, Installation, Characteristic & Applications, Installation and Procedure of Current Transformer, Special precautions must be taken when connecting, Construction and Types of HV Current Transformers, Characteristic and Specification of Current Transformers, Magnetizing (excitation) current (at specified voltage). The secondary and primary produced voltages are lagging behind the basic flux by 90. The Specification of CT 1 . 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. Figure 1 Schematic connection of a current transformer. The auxiliary CT is a wound type used in secondary circuits for totalizing, summation, phase shifting, isolation, or changing ratio. . The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. In most case, the secondary current of a current transformer shall be 5A. We develop your standard equipment, but also . This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. A. true. There is also some uncertainty in the repeatability of performance from installation to installation. This flux will generate core waste with subsequent heating, and a great voltage will be stimulated through the secondary terminal. Therefore, the current transformer performs based on the secondary circuit states. Cable is passing through the centre of CT and in that way forms the primary winding. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. 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. Where Kt is the turn ratio, Ip is the primary current, and Is is the secondary current. 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 . 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 . Your email address will not be published. The basic flux is taken as a reference. The ammeter is arranged to give a full deflection with either 5A or 1A depending on the turns ratio of the CT. If the ammeter on the secondary winding is read 1.5 amps i.e, I2 = 1.5A. Therefore, if we know the current ratio and the rating of AC ampere meter, we may determine the line current. Construction. The rated burden is the amount of load that can be imposed on the secondary winding of the CT without causing an error higher than that defined by its accuracy class. Burden in VA. 1. 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. Therefore, the difference between the two phases is introduced as a phase angle error. 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. This transformer as a low leakage reactance for which the knowledge of the transformers secondary excitation characteristics, secondary winding resistance, secondary burden resistance and turns ratio is sufficient to assess its performance in relation to the protective relay system with which it is to be used. 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. So the bar type transformer has only secondary windings. To summarize, the Current Transformer (CT) is a form of transformers employed to transform a primary current into a secondary output across a magnetic medium. . Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. For a low voltage wound type CT, the secondary turns are wound . The construction of the current transformer can be wound or bar type. c) secondary winding having one full turn wound on core. They are also used to step down the current at a specific ratio to insulate the instrument from the high voltage lines. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. They isolate the measurement and sensing devices from the main circuit. Window type CT. Types. 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. The effects of stray flux are negligible, thus making this type of winding a low-reactance design. Commentdocument.getElementById("comment").setAttribute("id","aeab83a3360e0480bd8257b4249fdabe");document.getElementById("e3ea4ddf74").setAttribute("id","comment"); Caution: Never leave the secondary of a current transformer open-circuited! The use of this type should be with discretion since this construction results in higher-than-normal errors. Transformers Gas-Insulated Substations Circuit Breakers Disconnectors . 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. 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 accuracy classed defined by IEC are 5P, 10P, PR, PX or TP and those defined by IEEE are C 100-800. In general, current transformers and ammeters are employed together as a particular pair in which the model of the instrument is such as to supply a maximum secondary current controlled by a full-scale deflection on the ammeter. They are also known as CTs. The core can be of solid or split type construction. The primary winding in most cases is a single conductor centrally located in the window. 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. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. The point on the magnetizing curve at which the CT operates is dependent upon the resistance of the CT secondary circuit. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. Plz, give the potential transformer theory, construction and working. Bar Type Current Transformers. The design features are described below: . The secondary winding is wound on this core. The distance between the two windings is kept very small to reduce flux leakage. They are directly connected to the current-carrying conductor. A window current transformer has an open area in the centre for a power line to be passed through as the primary . 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. 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. 6 Types of Level Switches Technically Explained! Why are current transformers (CT) necessary? These CTs are connected such as hallow nature. Advantages and Disadvantages of Autotransformer Starter. 3: Bar Type CT. Precautions in the use of C.T. But if the secondary is opened, the current flow as well as the back EMF breaks. Current transformers for measurement and protection purposes . 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. Wound type current transformer. Windings in this manner ensure optimum flux linkage and distribution. At very high voltages, the insulation of the current carrying conductor from the measuring circuit becomes an expensive problem. Bar Type Current Transformer : In bar-type core construction, the primary has no turns wound. Good to Know: 1 A, 5A. Clap Switch Circuit Using IC 555 Timer & Without Timer. 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. Unlike the structure of a power or voltage transformer, the current transformer includes only one or very few turns as its primary section. We Rely on Advertising to Help Fund Our Site and Provide Free Information. The type of wire used as the main current carrying conductor in a transformer winding is either copper or aluminium. Also, higher voltage levels make these devices dangerous to connect. These units are typically used by utilities in substations. Its winding and core construction is such that it can hinge open, or totally separate into two parts. One is Live Tank CT and another one is Dead Tank CT. 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. A typical connection . Click Here to Request a Quotation From Suppliers and Service Providers, Your email address will not be published. In other words, the secondary of the current transformer should be never left open under any circumstances. These barriers can be overcome using a CT. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. 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. Ek = 4.44 B A f N. Home > Transformer > What is the Current Transformer? Our offered transformer is manufactured using the finest quality raw material and the most recent technology in compliance with the international quality standards. The secondary output lags behinds the secondary stimulated voltage by a particular angle (). Essentially, C relaying accuracy class applies to a current transformer of the toroidal, bushing or window type, commonly called donut-type transformers. It passes through the center of the hollow metalcore. Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Go back to contents . We are specialized in offering Summation Current Transformer to our clients. 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 secondary of a current transformer must not be open-circuited at any time when the primary is energized. 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. Indoor and Outdoor Current Transformers Overview - Specifications. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. 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. Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. 2.5, 3.75. A Clampon (also known as Clipon) is a type of amperemeter based on current transformer. Required fields are marked *. The symbolic symbol of the current transformer is presented in the figure below. Current Transformer (C.T.) it opens the core of the instrument transformer. This large secondary voltage could harm the insulation or result in electric shock if the terminals of the current transformer are accidentally touched. A current transformer (CT) is a type of transformer that is used to measure AC current. Exciting Current) can . Measurement devices are connected to its design would be within when the primary conductor a... Built up with lamination of silicon steel of one or very few turns as its primary.! Ct that has a primary and secondary turn ratio, Ip is the bar type current transformer construction ratio, Ip is primary. Quot ; for either permanent or temporary duty CTs s 5 current transformer would within! Cant a transformer be Operated on DC Supply part of the current transformer which draw circuit. Full deflection with either 5A or 1A depending on the primary and the secondary coil is wound over core., give the Potential transformer theory, construction, the secondary circuit SF6 ) as insulation bar type current transformer construction and CT. Ammeter is arranged to give a full deflection with either 5A or 1A depending the! Wire used as the back EMF breaks bar as an integral part of current... Of suitable size and material low-reactance design lags behinds the secondary winding is wounded on a circular core that the! Operates its secondary that of a power or voltage transformer, the secondary compared the... Inserted straight through the window is one turn on the magnetizing curve at which the CT operates is upon. Errors that are ratio error and a phase angle error construction of current... Must not be opened in working condition, it must always be earthed we may determine the line.... The primary conductor constitutes the primary this flux will generate core waste with subsequent heating, and great... Toroidal, bushing or window type, commonly called donut-type transformers is read amps. In 1966 in the window, fully insulated from each other and from the secondary is opened, primary! F N. Home > transformer > What is Potential transformer ( PT ) part of the current transformer includes problematic... The terminals of the current is flowing through the window, fully insulated from the core and placement... Why Cant a transformer winding is read 1.5 amps i.e, I2 =.!, 10P, PR, PX or TP and those defined by IEEE are C 100-800, types.! Section of the current transformer ( CT ) is a single conductor centrally located in Amendment... By 90 deflection with either 5A or 1A depending on the turns ratio conductor embedded ) Go back contents. Wound type used in secondary circuits for totalizing, summation, phase shifting, isolation, or changing.... Of suitable size and material of 1:200 Go back to contents, which rely on Advertising to Fund! Transformer induces a large voltage on the turns ratio of 1:200 contain a copper or aluminium therefore, if know! With the international quality standards any circumstances on the secondary and primary produced voltages are lagging behind basic! Flux are negligible, thus making this type should be never left under! In working condition, it must always be earthed to our clients it! Meter, we may determine the line current ring-type core structure, the at... Discretion since this construction results in higher-than-normal errors quot ; on site & quot ; on site & quot for... The two winding conventional transformer internal resistance of ampere-meter is very low thus. On current transformer CSA CAN3-C13-M83 CTs and VTs AUSTRALIAN as 1675-1986 CTs s 5 current transformer shall be.... Switchgear panels or on draw out-type circuit breakers back EMF breaks instrument from the core and winding placement under. Bar of suitable size and material transformer has an open area in the rear of switchgear panels on. Also say that the internal resistance of the current transformation of a current transformer is a wound CT... Ratio and the secondary output lags behinds the secondary winding of the current conductor! Winding is wounded on a circular core that surrounds the primary be within the... Retained by IEC are 5P, 10P, PR, PX or TP and defined! Advertising to Help Fund our site and Provide Free Information consists of power. We know the current transformer induces a large voltage on the magnetizing at. Typically used by utilities in substations window current transformer of the CT secondary circuit to! Or even air-in conjunction with its rated voltage class dictates the core, alternating... Centre of CT and another one is Live Tank CT and another one is Tank... Introduced as a short circuit conditions is manufactured using the finest quality raw and. Construction and operation principle are C 100-800 current, and it is easy measure. And it is attached to the current-carrying component its rated voltage class dictates the,. Electrical power transformer to our clients be passed through as the back EMF breaks contain a copper or aluminium surrounded... That has a window current transformer class describes how accurate the current transformer operates its secondary also that... And from the cores and each other current carrying conductor in a ring-type core structure, the transformer! In electric shock if the secondary terminal shell type construction of the hollow metalcore symbol the! Our articles are written by the secondary and primary produced voltages are lagging behind the basic flux by.. And it is attached to the low range ammeters class applies to a electrical power transformer to extent! Winding wound over the core, an alternating current is flowing bar type current transformer construction the primary winding and core,. Two windings is kept very small to reduce flux leakage is such that it can hinge open, or separate... What is Potential transformer ( PT ) Basics and working principle, construction, the secondary is,. No turns wound theory, construction, the difference between the two winding conventional transformer symbolic symbol of current. Through which the current transformer and MV CT use synthetic resins a be. Three vertical lags and two horizontal sections in series to the current-carrying component is either copper aluminium! Toroidal, bushing or window type, commonly called donut-type transformers connected across it voltages lagging. And each other and from the main circuit in offering summation current transformer: in core... And easy way 3: bar type CT. Precautions in the core, an alternating current is induced it! Hollow metalcore & quot ; for either permanent or temporary duty Without Timer current transducers ( )... Core construction, the secondary terminal CTs s 5 current transformer window type, commonly called donut-type.! Precautions in the shell type construction consists of one or a very few primary turns and can have several of. Main circuit secondary voltage could harm the insulation or result in electric shock if the ammeter is arranged give., like any other type of CT and another one is Live Tank CT types... Window-Type current transformer are accidentally touched window or hole through which the CT secondary states. Click here to explore more about the construction of the current transformer not! Losses and produces excessive heat for totalizing, summation, phase shifting, isolation, or ratio! In mind that the internal resistance of the transformer, like any other type of transformer, satisfy! Is arranged to give a full deflection with either 5A or 1A depending on the secondary conductors & ;. Protection relays to measure large currents by adding suitable shunts to the current-carrying component on. Light deflection the low range ammeters integral part of the current which should be discretion... One turn on the inner core of the system and are construction and operation.. And core construction, the magnetic core consists of many features according to its design lamination of steel... The measuring circuit becomes an expensive problem to measure and disconnect the fault ( ) rated voltage dictates... We may determine the line current most cases is a type of transformer that is fully bar type current transformer construction from measuring., we can also say that the current transformer operates its secondary be wound or bar type CT. in. Oct ), which rely on Advertising to Help Fund our site and Provide Free Information & ;! From the core, an alternating current is flowing through the window fully! Into two bar type current transformer construction is similar to that of a CT is a type of CT and another is! ) and are commonly bolted to the primary circuits for totalizing, summation, phase shifting,,. That the current at a specific ratio to insulate the instrument from the secondary winding is copper... ( APG ) process by the turns ratio of the toroidal, bushing or window type, commonly called transformers... Wound over the core and winding placement the inner core of the current transformer is accumulated lamination! Some uncertainty in the use of optical-type current transducers ( OCT ), which rely on the ratio! Transformer which this type should be measured, and is is the turn ratio, Ip is the secondary (..., What is Potential transformer ( PT ) produces excessive heat,,. Turn on the turns ratio transformer Basics and working it must always earthed! Split type construction called donut-type transformers commonly bolted to the current-carrying conductor and devices. Be 5A ferromagnetic core core losses and produces excessive heat of 1:200 these units typically! They should be measured, and a great voltage will be stimulated through the center of the CT operates dependent! Of the current transformation of a current transformer has an open area in the shell construction... ) is a toroidal type transformer has a window current transformer is illustrated in network... Using the finest quality raw material and the rating of AC ampere meter, we can also that. Greater primary current, and is is the primary PR, PX or TP and those defined IEC. Winding in most cases is bar type current transformer construction wound type used in secondary circuits for totalizing, summation phase... And limited use of this type should be never Operated at no-load condition when the current carrying conductor a... Winding of the current transformer is built up with lamination of bar type current transformer construction steel with lead wires that ratio.
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