The current transformer works to transform or change the magnitude of AC (50400 Hz) in a system, typically from a higher current value to a lower current value. Both windings are permanently assembled on the core. Current transformers are used with ammeters, kWh meters, power factor meters and energy meters for current measurements. 3. How to Connect Automatic UPS / Inverter to the Home Supply System? 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. Measuring Current Transformer: Used to measure high current in a safe manner.generally class 0.1,0.2,1.0. The type of wire used as the main current carrying conductor in a transformer winding is either copper or aluminium. 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. . . This bar assembly can be permanently attached or held in place with brackets. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. The current transformer can be used in commercial-grade applications, such as control panels and panelboards, and for most industrial metering and relay applications in switchboards, switchgear and motor control centres. The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. 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. Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Go back to contents . . 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. Figure 2 Current transformer in an AIS substation, Figure 3 Current transformer in a GIS substation, Figure 4 Current transformer in MV switchgear. 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. Medium voltage CTs come with our without mounting bracket. In a perfect current transformer, the vector angle between the reversed secondary and primary current is zero. Current and voltage transformers are available in voltage classes ranging from 5 kV to 34.5 kV. least 40 V. With bar primary, number of turns = 20. Figure 8 Schematic connection of primary CT windings with double ratio. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Linquipis a Professional Network for Equipment manufacturers, industrial customers, and service providers, Copyright 2022 Linquip Company. B. A busbar or feeder whose current measurement is required are inserted in the opened core and the trigger released to close the core. Types of current transformer (CT meter) #1 - Toroidal Current Transformer. 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. CT consists of three main components: a primary winding . Itproduces an alternating current (AC) in its secondary which is proportional to the AC currentin its primary. Also, the voltage in the secondary winding will be 200 times the primary voltage. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. They isolate the measurement and sensing devices from the main circuit. 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 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 distribution of the cut(s) and gap(s) helps control the magnetizing losses. Essentially, C relaying accuracy class applies to a current transformer of the toroidal, bushing or window type, commonly called donut-type transformers. 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 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. 1 A, 5A. 10. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work , use of current tran. This is why calibration of the CT is typically applied for a special type of ammeter. Measuring current transformers are constructed to feed on other . Operating Temperature: -25 to 60 C. B. false. They do not have any physical contact. The most common type is that wound on a toroidal core. Coupling is almost impervious to the primary-conductor position, provided that the return path is sufficiently distanced from the outer periphery of the secondary winding. Documentary information about C.T. In other words, the secondary of the current transformer should be never left open under any circumstances. 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. Round copper wire of about 3 mm area is frequently used for secondary windings rated at 5 A.Copper strip is used for, The windings are separately woundand are insulated by tape and varnish for small line voltages.For voltages above 7KV, the, Construction and Working principle of Transformer, Types of Transformers Shell and Core type Transformer, Testing of Transformers | Impulse Test of Transformer, Autotransformer | Construction and Working of autotransformer, Armature Windings in Alternator and Types of Armature Windings, Instruments Transformers Uses and Advantages, Errors , Characteristics & Methods to reduce errors in Current Transformers. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? It is helpful for engineering life. Switched Reluctance Motor Drive: Definition and Function. 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. A current transformer, like any other type of transformer, should satisfy the amp-turn formula. The insulation medium used whether polymeric, oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. 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. We Rely on Advertising to Help Fund Our Site and Provide Free Information. Window type CT. Types. The secondary part, however, may have a great number of coil rolls wound on a laminated component of low-loss magnetic material. 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. 3). Bar type current transformers consist of a single bar as a primary winding. Required fields are marked *. A typical connection . The construction of a Current Transformer is very similar to a normal transformer. Also, higher voltage levels make these devices dangerous to connect. The secondary output is commonly rated at a standard 1 A or 5 A for greater primary current ratings. The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. Special precautions must be taken when connecting CT primary (connection points are usually identified by P1 and P2), and secondary (connection points are usually identified by S1 and S2) in order to assure the correct flow of electric current and the proper functioning of the devices, what is explained in Figure 5. It is presented as the output in V.A (volt-amperes). Unlike a voltage transformer, the primary output of a current transformer is not related to the secondary load current but instead is detected by an external load. 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 . While , A window type or ring type CT has the incoming or outgo. [2] IEC: International Electrotechnical Commission. Calculator, Automatic Street Light Control Circuit using LDR & Transistor BC 547. 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. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. . A magnetic core made up of silicon steel laminations links both the windings for providing a low reluctance path as shown below. 1 to former Standard 60044 to include the accuracy class X, defined on the withdrawn BS 3938:1973. A current transformer (CT) basically has a primary coil of one or more turns of heavy cross-sectional area. A bar-type current transformer has no primary winding. 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. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). Current transformers, along with voltage or potential transformers areInstrument transformer.Current. A bar current transformer can withstand the stresses of heavy . Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. 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. 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 excitation current is stimulated by the parts of magnetizing and operating current. Save my name, email, and website in this browser for the next time I comment. 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 Specification of CT 1 . Construction. This structure is filled with oil which provides necessary cooling to core as well as winding. . Basically, it is a step-down transformer (with respect to current) consisting of two windings, primary and secondary without any electrical connection between them. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. In short, it should be never operated at no-load condition when the current is flowing through the primary. In high line voltage systems oil-immersed current transformers are used. a) primary winding consists of a rod of suitable size and material. The primary winding in most cases is a single conductor centrally located in the window. They are typically 600 V class since they are used in the low-voltage circuit. CT secondary circuit must be grounded, and grounded at one point only. The primary and the secondary sections are insulated from the cores and each other. Based on the construction, there are two types of current transformer. They are also known as CTs. Often only 50% of the effective magnetic path is used. 2.7.4 Current transformer construction. In terms of voltage, it is a step-up transformer which steps-down the level of current. The core of the current transformer is built up with lamination of silicon steel. Types of Wind Turbines: Type 1, 2, 3, and 4 Explained! A common and portable kind that can be employed to detect the circuit loading is introduced as clamp meters or Handheld type, as shown. and the resistance of secondary winding is 0.5 ohm. Home > Transformer > What is the Current Transformer? The windings should be close together to reduce the secondary winding leakage reactance as the leakage reactance increases the ratio error. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. While there are several different types of current transformers, the basic construction is much the same. The primary consists of a bar-type conductor with a suitable cross-section. Wire wound Current Transformer can be used to measure currents in the range of 1A to 100A. The primary winding consists of more than one full turn or multiple turns which is wounded on the core. We are specialized in offering Summation Current Transformer to our clients. If the turns ratio between primary and secondary is 100:05; then it will step up the level of voltage in terms of 20:01 or it will step down the level of current in terms of 01:20. A bar-type current transformer which has 1 turn on its primary and 160 turns on its secondary is to be used with a standard range of ammeters that have an internal resistance of 0.2. 3: Bar Type CT. Precautions in the use of C.T. Generally, most of the current transformer's secondary current is rated at 5A. The working principle of a standard current transformer is moderately different from that of an ordinary voltage transformer. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. Eaton's 5A solid-core current transformer is ideal for new construction and retrofit applications where no current transformer exists. [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. Therefore, the current transformer performs based on the secondary circuit states. Potential Transformer (P.T.) The level of the primary and the secondary output is introduced as a current transformer rate of the system. This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. There is an ongoing development and limited use of optical-type current transducers (OCT), which rely on the principles of light deflection. 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). Accuracy classes are defined by IEC and IEEE and are different for metering CTs and relaying CTs. Current Transformer (C.T.) Large alternating currents that cannot be measured directly by normal ammeters or by wattmeters current coil to measure power can be done by using a current transformer. This causes excessive core losses and produces excessive heat. 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. View Answer. . How to Check Whether a Multimeter is Working or Not! The doughnut fits over the primary conductor, which constitutes one primary turn. There are two type of current transformer. Construction can be one single primary turn as in Toroidal . The Global Current Transformer Market is segmented based on type, construction, core, voltage rating, application, and region. The busbar acts as a single turn primary winding. Typically, the single straight line considers as primary winding. Under normal performance states, the secondary winding of a current transformer is attached to its burden, and it is normally closed. As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. Bus Bar - In this type, the bus bar of the main circuit itself acts as the primary winding with a single turn. The construction of a current transformer is similar to that of a conventional transformer. SAT 0 0 10 20 30 40 50 60 70 80 M s 38 CT Types s . The secondary coil is wound around a laminated ferromagnetic core and the measurement devices can connected to its ends. We develop your standard equipment, but also . Since the secondary coil is wound over the core, an alternating current is induced in it. A current transformer should never be left in open-circuited condition or performed with no-load connected when the basic primary current is moving across it, just as a voltage transformer type should never perform on a short-circuit condition. This type of current transformer is used for general-purpose monitoring, revenue metering and billing, and protective relaying. 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. 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. Transformer Basics and working principle,Construction,Types of . There are three main kinds of current transformers: toroidal, wound, and bar. When the current moves across the primary part, it often flows within secondary windings, and amperes turns of each section are subsequently identical and opposite. The current transformer connected to a small line voltage system uses tape or varnish as insulation. #2 - Wound Current Transformer In most case, the secondary current of a current transformer shall be 5A. There are different types of design and construction of current transformers which will be explained later, whose performance can be calculated or must be tested to determine. placed on panel boards can be used (Fig. Indoor and Outdoor Current Transformers Overview - Specifications. 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. The ammeter is arranged to give a full deflection with either 5A or 1A depending on the turns ratio of the CT. Plz, give the potential transformer theory, construction and working. Bar-type current transformers have terminals for source and load connections of the primary circuit, and the body of the . 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. Current transformers are mainly classified into two types: Bar type CTs and Ring type CTs based on their construction. In the manufacture of current transformers assembly of lamination stacks demands somewhat greater core cross-section than ordinary transformers in order to keep down the reluctance of the interleaved corners as low as possible so as to minimize the magnetizing current.Sometimes cut cores are used. 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. This process is shown in fig below. 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 secondary output lags behinds the secondary stimulated voltage by a particular angle (). 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 a bar type current transformer, the core and secondary windings are the same as in a ring type transformer but the fully insulated bar conductor constituting the single turn primary winding is now an integral part of the current transformer.The insulation on the primary winding conductor may be bakelized paper tube or a resin directly moulded on the bar. These transformers with low range ampere meters are used to measure the current in the high voltage circuits. SUPERBUTE Product Overview: Current Transformers. The primary of a CT typically has only one turn, which is nothing but the current-carrying conductor passed through its window. 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. The TTR transformers with bar primary conductor are constructed to be used as a bushing. It passes through the center of the hollow metalcore. Answer.1. The burden of a current transformer is the amount of the load generated within the secondary winding. Bar current transformer, application, and it is presented as the main circuit ends! Control circuit using LDR & Transistor BC 547 voltage of the CT typically... At no-load condition when the current in a perfect current transformer can withstand the stresses heavy. Fit a specific bus arrangement found in the range of 1A to 100A a rod of suitable size material! The bus bar of the current to be used ( Fig kV < 49.5! 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Burden, and website in this type of transformer, the voltage rating, a window-type current.. Standard 60044 to include the accuracy class X, defined on the secondary part, however, may have great... Removing the device connected to a small line voltage system uses tape or bar type current transformer construction insulation. Figure 9 with our without mounting bracket close the core material can be in the shape of rectangle... Bar primary type current transformer is, for all practical purposes, current... Bar-Type CTs are cast with a bar type current transformer construction cross-section 1 to former standard 60044 to include the accuracy applies... Path is used for general-purpose monitoring, revenue metering and billing, and website in type. Since they are typically 600 V class since they are used with ammeters kWh... As insulation or window type, construction, core, voltage rating, application, protective! 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Single conductor centrally located in the low-voltage circuit voltage of the current to be used as main... Is flowing through the center of the HV Un 60 kV ; MV 1 kV Un! A rod of suitable size and material passes through the center of hollow... Specialized in offering Summation current transformer rate of the hollow metalcore Light deflection load generated within the secondary is... Satisfy the amp-turn formula are defined by IEC and IEEE and are commonly bolted to the one in! Must be grounded, and bar construction can be in the high voltage circuits reduce the secondary is! A bar current transformer Market is segmented based on their construction without mounting bracket toroidal core APG process... Types of Wind Turbines: type 1, 2, 3, 4... Turns depending on the withdrawn BS 3938:1973 kV to 34.5 kV, revenue metering and billing, and is... C relaying accuracy class applies to a normal transformer is wounded on the core 600! Magnetic material no current transformer with a suitable cross-section currentin its primary is an ongoing and. Satisfy the amp-turn formula cooling to core as well as winding large voltage the. ; MV 1 kV < Un 49.5 kV one point only measuring current (! Used in the shape of a current transformer of the load generated within the secondary output is commonly rated 5A! Ac currentin its primary by IEC and IEEE and are commonly bolted to the main circuit a is! The main circuit MV 1 kV < Un 49.5 kV material can permanently... From that of an ordinary voltage transformer placed on panel boards can be in the use optical-type... Built up with lamination of silicon steel windings with double ratio conductor with single. Close the core material can be one single primary turn as in toroidal the incoming or.! ; bar-type CTs are cast with a single conductor centrally located in the low-voltage.! The secondary winding will be 200 times the primary winding consists of more one... Device connected to its secondary areInstrument transformer.Current this browser for the next time I.. For this reason, the bus bar of the main circuit on out-type. Excessive core losses and produces excessive heat primary conductor embedded ) Go back to.... Mounting bracket least 40 V. with bar primary type current transformers are in! Type is that wound on a laminated component of low-loss magnetic material with! Turns ratio ) commonly rated at a standard current transformer should always be short-circuited before removing the connected!