But if the secondary is opened, the current flow as well as the back EMF breaks. It is used to activate the trip coil of a circuit breaker. Insulation Voltage: 3000 volts. 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 . Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? For this CT to operate satisfactorily at maximum fault currents, it must operate on the linear part of the magnetizing curve, i.e., below the point at which saturation occurs, which is known as the knee point. Typically, the single straight line considers as primary winding. The bar type CT is fully insulated to the switchgear voltage. Since the secondary coil is wound over the core, an alternating current is induced in it. Eaton's 5A solid-core current transformer is ideal for new construction and retrofit applications where no current transformer exists. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. There are several core types used, from low-reactance toroid to high-reactance cut . Difference between Power Transformers and Distribution Transformers? RF, which is a characteristic of metering and energy metering cores, represents the amount by which the primary load current may be increased over its nameplate rating without exceeding the allowable temperature rise, that is to say, the transformers overload capability. 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. Switched Reluctance Motor Drive: Definition and Function. Figure 3. They may contain multiple cores and secondary coils as well as added insulation. A near relative of the ring type current transformer is the so called bushing type transformer.This is, in fact, indistinguishable from of the ordinary ring type but the term is used when the current transformer fits over a fully insulated primary winding conductor such as over the oil end of a terminal bushing of a power transformer or an oil circuit breaker. . 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. 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. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. Why Cant a Transformer Be Operated on DC Supply? There are three main kinds of current transformers: toroidal, wound, and bar. Difference Between Ideal and Real or Practical Transformer, Transformer, Construction, Working, Types Application & Limitations, What is an Ideal Transformer? 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. The TTR transformers with bar primary conductor are constructed to be used as a bushing. The transformer is fundamentally a step-down transformer (with respect to current), consisting of primary and secondary windings without any electrical connection between them. Frequency Range: 0.0480 to 0.0620 kHz. For example, a current transformer has a ratio of 200:1. When applying auxiliary CTs, the user must be aware of their reflected impedance on the mainline CT. For low and medium voltage applications, there are three main classifications based on construction; window, bar, and wound. Your email address will not be published. The insulation of Bar Type Rectangular Current Transformer provides an enhanced safety. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. 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. 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. There is an ongoing development and limited use of optical-type current transducers (OCT), which rely on the principles of light deflection. A current transformer, like any other type of transformer, should satisfy the amp-turn formula. The bar type CT is fully insulated to the switchgear voltage. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. Plz, give the potential transformer theory, construction and working. Wound-type current transformers, T-type classification, are . Visit here to explore more about the construction of a current transformer. There are several core types used, from low-reactance toroid to high-reactance cut cores and laminations. The construction of a current transformer is similar to that of a conventional transformer. 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. The instruments (ammeter etc.) Current transformers are available in various sizes and shapes and are used as an interface between high currents and measuring/sensing devices. 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. Thus if the secondary is opened, there is no counter MMF in the secondary winding to oppose the primary MMF. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). 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. . Buy Equipment or Ask for a Service. As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. Current Transformers (600 Volt, Indoor Bar Type) Specifications File Reference: Title: Publish Date: Format: JCM-3/4/5: Models JCM-3/JCM-4/JCM-5: 2017-11-08 [417k] . 1 A, 5A. The ammeter is arranged to give a full deflection with either 5A or 1A depending on the turns ratio of the CT. The accuracy classed defined by IEC are 5P, 10P, PR, PX or TP and those defined by IEEE are C 100-800. 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. A current transformer is generally used in metering and protective relays in the electrical power industry. The primary winding needs to be physically connected in series to current carrying conductor. 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. Ring type CT are commonly used in cables, busbars and transformers bushings. The primary of a CT typically has only one turn, which is nothing but the current-carrying conductor passed through its window. Now here we have learnt Current Transformer Working, Types & Construction.You can download this article as pdf, ppt. Indoor and Outdoor Current Transformers Overview - Specifications. The secondary of a current transformer must not be open-circuited at any time when the primary is energized. 2. Transformer Basics and working principle,Construction,Types of . These are present for sensing currents from 100 A up to 5000 A, with square window forms from 25 mm to 300mm. Toroidal Current Transformers, Bar type Current Transformers, and . The primary consists of a bar-type conductor with a suitable cross-section. A variant of the . 3). Thus a CT must not be opened in working condition, it must always be earthed. The secondary winding is fully insulated from the primary that is at CT rated voltage. The type of wire used as the main current carrying conductor in a transformer winding is either copper or aluminium. 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. While there are several different types of current transformers, the basic construction is much the same. The paper insulation is kept on the bar i.e., between the primary and secondary. 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. With this connection the directions of primary and secondary currents are: When testing a CT using an Omicron test equipment it is possible to verify if the CT is correctly connected: Ring type CT is constructed of an iron toroid, which forms the core of the transformer, and is wound with secondary turns. The current transformer includes two problematic errors that are ratio error and a phase angle error. Accuracy classes are defined by IEC and IEEE and are different for metering CTs and relaying CTs. They are classified into four basic types: Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage type. A bar current transformer can withstand the stresses of heavy . 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. 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}}. Let us see the construction of the current transformer. It transforms the primary current to a proportional secondary value in terms of magnitude and phase. This component has a large cross-sectional region so that the magnetic flux density produced is low, employing a much smaller cross-sectional zone wire, depending upon how much the current should be stepped down as it wants to create a constant current, unrelated to the connected load. 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. There is also some uncertainty in the repeatability of performance from installation to installation. It is presented as the output in V.A (volt-amperes). The distribution of the cut(s) and gap(s) helps control the magnetizing losses. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. 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. Most CT have rating factors for 35 C and 55 C. Common value for RF is 1.5. In addition to that, core losses due to high flux density would heat up the core and the windings and damage them. If the secondary of CT is left unloaded a risk of explosion exists. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work , use of current tran. The secondary winding of the current transformer has a larger number of turns, the exact number being determined by the turns ratio. Across the secondary terminal is connected an impedance of 2 ohm with a phase angle . Figure 1 Schematic connection of a current transformer. In a ring-type core structure, the secondary winding is wound on the inner core of the bakelite former. The primary is connected in series with the line where the current is to be measured, and the secondary is connected across a low-range ammeter (range of 0-5A). A current transformer further isolates the measuring instruments from whatever may be very high voltage in the monitored circuit. Current Transformers are mainly used to perform two tasks. The knee point is defined as the point at which a 10% increase in voltage produces a 50% increase in magnetizing current. In terms of voltage, it is a step-up transformer which steps-down the level of current. It is a very good information about CT for electrical knowledge. [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. An approximate inverse turns level exists between the two currents in most current transformers in the secondary and primary windings. 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. The conductor itself acts as a single turn primary winding. Why is a Transformer Rated in kVA, but Not in kW? It never has more than a very few numbers of turns in its primary. Current transformers (CT) are used in High Voltage (HV) and Medium Voltage (MV)[1] installations to give an image of electrical current to protection relays and units and metering equipment and they are designed to provide a current in its secondary proportional to the current flowing in its primary. See Terms of Use and Privacy Policy. Your email address will not be published. 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. 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. Instrument transformers are of two types - Current Transformer (C.T.) Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. A current transformer (CT) is an instrument transformer in which the secondary current is substantially proportional to primary current and differs in phase from it by ideally zero degree.. CT Accuracy Class or Current Transformer Class. The high voltage . [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. The excitation current is stimulated by the parts of magnetizing and operating current. The primary consists of a bar-type conductor with a suitable cross-section . 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. 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. B. false. A current transformer is a device that is used for the transformation of current from a higher value to a lower value. Answer.1. SUPERBUTE Product Overview: Current Transformers. This arrangement is ideal to use in cases where the primary conductor cannot be opened or broken. Uncommon current primary rates differ from 10 A to 3000 A or more. This is the same concept used in the clamp meters. They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device. The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. The secondary output is commonly rated at a standard 1 A or 5 A for greater primary current ratings. The basic flux is taken as a reference. For core-type transformers, the windings encircle the core, while in shell-type transformers, the core encircles the windings. In special cases when taps are employed, they are distributed such that any connection made would utilize the entire core-periphery. 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. Therefore, if we know the current ratio and the rating of AC ampere meter, we may determine the line current. 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. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. The use of this type should be with discretion since this construction results in higher-than-normal errors. Why are Air-Conditioners (AC) Rated in Tons, Not in kW or kVA? Current transformers are used extensively in metering and circuit protection. 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. They do not have any physical contact. . Why are current transformers (CT) necessary? They are also known as CTs. Advantages and Disadvantages of Autotransformer Starter. It produces a current in its secondary which is proportional to the current in its primary. A current transformers primary winding is often configured in series form with the main conductor. 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. The Specification of CT 1 . 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