Instrument transformers are of two types - Current Transformer (C.T.) It uses the actual cable or bus bar of the . The potential transformer is connected in parallel with the circuit. The high voltage . Wound type current transformer. The Mumetal or Permalloy is used for making cores to obtain a high degree of accuracy. 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. Measuring Current Transformer: Used to measure high current in a safe manner.generally class 0.1,0.2,1.0. Construction. 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. Also, consider that the number of rolls and the current in the secondary and primary windings are related by an inverse ratio. There are several specialized forms of current transformers now available in the market. Then the primary current or load current I1 is given as. . Typically, the single straight line considers as primary winding. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. The working principle of a current transformer is especially different from the power transformer. Window-type current transformers generally have a round window opening but are also available with rectangular and oval openings. Potential Transformer (P.T.) 50,60. Transformer Basics and working principle,Construction,Types of . 3. Based on the construction, there are two types of current transformer. Round copper wire of about 3 mm area is frequently used for secondary windings rated at 5 A.Copper strip is used for primary winding, the dimensions of which depend upon the primary winding current. For example, a current transformer has a ratio of 200:1. A busbar or feeder whose current measurement is required are inserted in the opened core and the trigger released to close the core. Secondary Rating. Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. This process is shown in fig below. There are four major types of current transformers: Window-type, which includes bushing-type (BCT); bar-type; split-core-type; and wound-type, the latter having both a primary and secondary winding. But in a practical current transformer, there is a phase difference between the secondary and the primary current since the primary output has also supplied the portion of the exciting current. 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. Wire wound Current Transformer can be used to measure currents in the range of 1A to 100A. The key distinction between the two types lies in the core and winding placement. 5, 7.5, 3C, 40. They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device. Useful information on Current Transformers, Current Transformers are widely used in electrical industries. So the bar type transformer has only secondary windings. and the resistance of secondary winding is 0.5 ohm. Based on the type of construction, current transformers are classified into three types as follows: This type consists of a hollow core through which the current-carrying conductor or cable is passed. The current transformer connected to a small line voltage system uses tape or varnish as insulation. Required fields are marked *. Toroidal Current Transformers, Bar type Current Transformers, and . Usually HV CT use oil or gas (SF6) as insulation medium and MV CT use synthetic resins. Operating Temperature: -25 to 60 C. 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. As a result, if the secondary component is opened and the current moves across the primary windings, then there will be no demagnetizing environment because of the secondary current. 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. 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). They are classified into four basic types: Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage type. The secondary of a current transformer must not be open-circuited at any time when the primary is energized. 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. 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. These are present for sensing currents from 100 A up to 5000 A, with square window forms from 25 mm to 300mm. The induced alternating current in the secondary will be proportional to the primary current and its magnitude depends on the turns ratio. Commentdocument.getElementById("comment").setAttribute("id","aeab83a3360e0480bd8257b4249fdabe");document.getElementById("e3ea4ddf74").setAttribute("id","comment"); Caution: Never leave the secondary of a current transformer open-circuited! Advantages and Disadvantages of Microgrids. placed on panel boards can be used (Fig. Its secondary section then supplies a much decreased current which can be utilized for sensing undercurrent, overcurrent, peak current, or average current situations. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. 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. Various primary bar arrangements can be supplied to suite most applications. The uses are the same as the window type. Table 1 Common accuracies and burden powers of CT and error limits. Types of Instrument Transformers. "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. 3. The potential transformer is mainly classified into . Current transformers are available in various sizes and shapes and are used as an interface between high currents and measuring/sensing devices. The following are different types of current transformers: A current transformer having a primary winding of more than one full turn wound on core. How Does it Work? Good to Know: Under normal performance states, the secondary winding of a current transformer is attached to its burden, and it is normally closed. [2] IEC: International Electrotechnical Commission. 3). The core of the current transformer is built up with lamination of silicon steel. 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. Construction of a Current . The working principle of a standard current transformer is moderately different from that of an ordinary voltage transformer. The bar type CT is fully insulated to the switchgear voltage. Two principal types of transformer construction embody the requirements of economics, ease of manufacture, insulation, mechanical strength, and ventilation: core-type and shell-type. A current transformer (CT) is a type of transformer that is used to measure AC current. 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. Accuracy classes for metering CTs: Metering devices such as ammeters, wattmeters, energy meters, kVar and kVarh meters requires high accuracy and has a low burden. The secondary winding is wound on this core. Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. 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 . 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. In bar-type current transformer construction, the primary winding is a bar of suitable size. 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}}. CT are connected in series and protection devices and metering equipment are connected to the secondary of the CT in series association, as shown in Figure 1. By using Linquip RFQ Service, you can expectto receive quotations from various suppliers across multiple industries and regions. Your email address will not be published. The paper insulation is kept on the bar i.e., between the primary and secondary. A CT consists of one or a very few primary turns and can have several hundreds of secondary turns. 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). Types of Current Transformers CTs are manufactured in various sizes, shapes, and ratings for a broad range of applications. The ammeter is connected in the secondary. 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. Most current transformers have the normal secondary rating of 5 A, with the secondary and primary currents being presented as a ratio such as 5/100. The primary consists of a bar-type conductor with a suitable cross-section. Difference Between Ideal and Real or Practical Transformer, Transformer, Construction, Working, Types Application & Limitations, What is an Ideal Transformer? Your email address will not be published. The primary side . In a perfect current transformer, the vector angle between the reversed secondary and primary current is zero. In practice, they are intended to be used over insulated conductors when the conductor voltage exceeds 600 V. It is common practice to utilize a 600 V class window type in conjunction with air space between the window and the conductor on higher-voltage systems. In the shape of a doughnut, these transformers are designed without having a primary winding as part of their construction. 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. Looks Like You're Using an Ad Blocker. . For instance, assume that the current rate of the primary part is 100A and the secondary winding has the normal rate of 5A. So measured readings are obtained at high accuracy. The current carrying conductor or feeder acts as a single turn primary while the secondary winding is connected across the standard ampere-meter. A current transformer, like any other type of transformer, should satisfy the amp-turn formula. Bar Current Transformers. Windings in this manner ensure optimum flux linkage and distribution. How to Check Whether a Multimeter is Working or Not! Construction can be one single primary turn as in Toroidal . For this purpose, an instrument called 'Current Transformer' is used for measuring large currents. Bar Type 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. 4 Types of Current Transformer Explained With Details. The Specification of CT 1 . The turns ratio of a current transformer is made such that the full load current in its primary give a secondary current of either 5A or 1A. The center of the current transformer is accumulated with lamination of silicon steel. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. Bar type current transformers consist of a single bar as a primary winding. 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 accuracy class of a CT is the percent allowable error, and is associated to burden power, the apparent power, expressed in VA, that is taken up from the secondary core (secondary load), and for which the accuracy is assured. This is the same concept used in the clamp meters. The knee-point voltage is less applicable for metering current transformers as their accuracy is generally much tighter but constrained within a very small bandwidth of the current transformer rating, typically 1.2 to 1.5 times rated current. At very high voltages, the insulation of the current carrying conductor from the measuring circuit becomes an expensive problem. We are specialized in offering Summation Current Transformer to our clients. b) primary winding consists of a bar of suitable size and material. CT may have one or more cores; typical applications of these cores are: The use of more than one core for protection is justified when the installation have two protections sets main and backup. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. 3: Bar Type CT. Precautions in the use of C.T. Frequency Range: 0.0480 to 0.0620 kHz. 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