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. 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. 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. Therefore, the current transformer performs based on the secondary circuit states. c) secondary winding having one full turn wound on core. 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. 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. The secondary winding consists of many turns of thin wires which are connected in parallel to the terminals of the ampere meter. Save my name, email, and website in this browser for the next time I comment. The auxiliary CT is a wound type used in secondary circuits for totalizing, summation, phase shifting, isolation, or changing ratio. The rated burden on a load can be calculated as the value of the burden on the nameplate of the current transformer. This is the same concept used in the clamp meters. In a current transformer, there exists an inverse ratio relation between the current and the number of turns in the primary and secondary windings. this type of system has severe limitation in its power output which has to be amplified in order to operate relays etc. 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. Types of Current Transformers CTs are manufactured in various sizes, shapes, and ratings for a broad range of applications. 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. . ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. Our offered transformer is manufactured using the finest quality raw material and the most recent technology in compliance with the international quality standards. 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. The distance between the two windings is kept very small to reduce flux leakage. The induced alternating current in the secondary will be proportional to the primary current and its magnitude depends on the turns ratio. Most CT have rating factors for 35 C and 55 C. Common value for RF is 1.5. Your email address will not be published. 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 . By using Grain-oriented cold-rolled silicon steel. But relatively great variations in a current transformer turns ratio can be obtained by varying the primary rolls within the CTs window where one primary turn is identical to one pass and more than one pass across the window causes the electrical ratio to be modified. 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 current transformers are assembled on to the secondary conductors "on site" for either permanent or temporary duty. While , A window type or ring type CT has the incoming or outgo. Transformer Basics and working principle,Construction,Types of . TRue Engineer on October 24, 2019: Figure 8 Schematic connection of primary CT windings with double ratio. We develop your standard equipment, but also . The design features are described below: . Current Transformer (C.T.) The secondary winding is fully distributed around the periphery of the core. A CT consists of one or a very few primary turns and can have several hundreds of secondary turns. The basic flux is taken as a reference. 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. Bar type current transformers - A bar type current transformer doesn't have a primary winding of its own. 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. 6 Types of Electrical Switches In The Home Explained! 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. 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. Bar-type Current Transformer . Some CT has special primary coils that allow a double ratio, when an increase of the installation is foreseen (example: 200-400/1 A) see Figure 8. The point on the magnetizing curve at which the CT operates is dependent upon the resistance of the CT secondary circuit. The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. 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. They are also used to step down the current at a specific ratio to insulate the instrument from the high voltage lines. 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. For this purpose, an instrument called 'Current Transformer' is used for measuring large currents. 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 conductor itself acts as a single turn primary winding. In both types, the core and windings are enclosed in a porcelain structure. . A bar-type current transformer has no primary winding. Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? Answer: A. Clarification: The split core transformer consists of a split core. The bus bar type MV CTs construction usually have resin cast CT with bur bar built into the construction. The potential transformer is mainly classified into . Based on the construction, there are two types of current transformer. [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. oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. Types of Wind Turbines: Type 1, 2, 3, and 4 Explained! 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. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. In special cases when taps are employed, they are distributed such that any connection made would utilize the entire core-periphery. The TTR transformers with bar primary conductor are constructed to be used as a bushing. 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. The ammeter is required to give a full scale deflection when the primary current is 800 Amps. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. C. 4. For core-type transformers, the windings encircle the core, while in shell-type transformers, the core encircles the windings. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. The split-core type current transformer is a special case of a window-type current transformer. 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. In short, it should be never operated at no-load condition when the current is flowing through the primary. Bus Bar - In this type, the bus bar of the main circuit itself acts as the primary winding with a single turn. Types of current transformer based on construction. As stated above the bar-type CT carries full current through its primary whereas the ring-type CTs are installed over the current-carrying conductors. 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. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. These CTs are connected such as hallow nature. MV CT are usually installed indoors, in MV Switchgears Figure 4. Below are the types of current transformers in the manner of construction and applications. They isolate the measurement and sensing devices from the main circuit. This is due to the fact the ratio of 100/5 presents the input/output current rating and not the practical ratio of the primary to the secondary outputs. Often only 50% of the effective magnetic path is used. It is considered to be an incomplete transformer assembly since it consists only of a secondary winding wound on its core. 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. The symbolic symbol of the current transformer is presented in the figure below. In most case, the secondary current of a current transformer shall be 5A. Depending upon the construction there are two types of current transformers used for measuring large currents. 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. . A bar type current transformer of toroidal construction requires 400A to magnetize it, and 300 A to supply the iron loss for each volt per turn induced in the secondary winding and rated frequency. 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. The manner in which the windings are arranged on the core affects the reactance since it is a geometric function. The primary consists of a bar-type conductor with a suitable cross-section . They are also known as bar-primary CTs. 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. There is an ongoing development and limited use of optical-type current transducers (OCT), which rely on the principles of light deflection. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. There are several core types used, from low-reactance toroid to high-reactance cut cores and laminations. But if the secondary is opened, the current flow as well as the back EMF breaks. 3. A typical connection . This causes excessive core losses and produces excessive heat. Current transformers for measurement and protection purposes . Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. Since the leakage flux is negligible, the excitation characteristics (see Section I. 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. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. This is a common construction for HV and EHV current transformers. Figure 3. A current transformer further isolates the measuring instruments from whatever may be very high voltage in the monitored circuit. 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. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. The center of the current transformer is accumulated with lamination of silicon steel. Their structure can be one single primary turn as in Doughnut, Toroidal, or Bar forms, or a few wound primary turns, commonly for low current applications. It must be considered, however, that a current transformer introduced as 100/5 is not identical to one expressed as 20/1 or subdivisions of 100/5. Good to Know: If the ammeter on the secondary winding is read 1.5 amps i.e, I2 = 1.5A. The 100 to 5 and 20 to 1 types are the most common forms of current transform existence in the market. The primary winding needs to be physically connected in series to current carrying conductor. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). CT secondary circuit must be grounded, and grounded at one point only. Save my name, email, and website in this browser for the next time I comment. Window-type current transformers generally have a round window opening but are also available with rectangular and oval openings. b) primary winding consists of a bar of suitable size and material. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. The primary side . 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. Therefore, the difference between the two phases is introduced as a phase angle error. These units are typically used by utilities in substations. What are the basic requirements of a protection system used in a power network or equipment? For example, a current transformer has a ratio of 200:1. This process is shown in fig below. Difference between Power Transformers and Distribution Transformers? 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. The body of the CT itself provides insulation between the primary circuit and ground. Tamper-Resistant Outlet: What is it? A Clampon (also known as Clipon) is a type of amperemeter based on current transformer. While there are several different types of current transformers, the basic construction is much the same. Let us see the construction of the current transformer. Burden in VA. 1. Useful information on Current Transformers, Current Transformers are widely used in electrical industries. It transforms the primary current to a proportional secondary value in terms of magnitude and phase. A bar current transformer is a special type of window current transformer with a solid bar placed permanently through the window. In high line voltage systems oil-immersed current transformers are used. 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. The working or operation of a current transformer is similar to that of a normal two-winding transformer. The standard secondary current is usually rated at 5A or 1A for ease of sensing. Uncommon current primary rates differ from 10 A to 3000 A or more. 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 winding so as to considerably reduce the peak voltage between layers. 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. The alternating current produces an alternating magnetic field in the ferromagnetic core. These current transformers have an opening where the conductor carrying the primary load is passed. 3. A bar current transformer can withstand the stresses of heavy . Clap Switch Circuit Using IC 555 Timer & Without Timer. There is also some uncertainty in the repeatability of performance from installation to installation. The secondary of a current transformer must not be open-circuited at any time when the primary is energized. 6 Types of Level Switches Technically Explained! Visit here to explore more about the construction of a current transformer. They may contain multiple cores and secondary coils as well as added insulation. 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. Required fields are marked *. 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. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. 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. The current transformer is used in the AC device, meters, or monitoring apparatus where the current to be sensed is of such magnitude that the instrument coil or meter cannot conveniently be created from adequate current carrying capacity. The phasor diagram of the current transformer is illustrated in the figure below. Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. HV CT are commonly installed outdoors, in AIS substations (Air Insulated Substation) Figure 2 or indoors, in GIS substations (Gas Insulated Substation) Figure 3. 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. should have an output of at. Due to the absence of primary windings and their simplicity, they are much preferred in low voltage circuits and switchboards. SAT 0 0 10 20 30 40 50 60 70 80 M s 38 CT Types s . 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). From low-reactance toroid to high-reactance cut cores and secondary coils as well as added.! Electrical industries different types of removing the device connected to its secondary reason. 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