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. Also, consider that the number of rolls and the current in the secondary and primary windings are related by an inverse ratio. least 40 V. With bar primary, number of turns = 20. There is also some uncertainty in the repeatability of performance from installation to installation. A bar-type current transformer has no primary winding. It is used to activate the trip coil of a circuit breaker. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. This is the same concept used in the clamp meters. CT consists of three main components: a primary winding . Current transformers are available in various sizes and shapes and are used as an interface between high currents and measuring/sensing devices. When applying auxiliary CTs, the user must be aware of their reflected impedance on the mainline CT. Often only 50% of the effective magnetic path is used. Visit here to explore more about the construction of a current transformer. Over the secondary winding, the primary winding is wound on the outer core with suitable insulation between the two windings. Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. A. true. Current transformers are mainly classified into two types: Bar type CTs and Ring type CTs based on their construction. Current transformers are considered to be applied as proportional current instruments. Bar Type Current Transformers. 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. Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. They have separate primary and secondary winding. Now, the whole primary current acts as a magnetizing current and induces large voltages in the secondary. Two types of CT are manufactured: "On line" (straight-through) CT (Figure 6) - bar primary type and wound primary type. The, 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. The . [2] IEC: International Electrotechnical Commission. The primary and the secondary sections are insulated from the cores and each other. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. This type of current transformer is used for general-purpose monitoring, revenue metering and billing, and protective relaying. It is helpful for engineering life. Exciting Current) can . They are typically 600 V class since they are used in the low-voltage circuit. A current transformer is generally used in metering and protective relays in the electrical power industry. Why are Air-Conditioners (AC) Rated in Tons, Not in kW or kVA? Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. The construction has a simple construction. The doughnut fits over the primary conductor, which constitutes one primary turn. This accuracy class was retained by IEC in 1966 in the Amendment nr. 2.5.3 Core-Balance Current Transformers. 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. The instruments (ammeter etc.) 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 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. 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. Various primary bar arrangements can be supplied to suite most applications. Generally, the windings do not utilize the magnetic path efficiently. Ring type CT are commonly used in cables, busbars and transformers bushings. See Terms of Use and Privacy Policy. Answer: A. Clarification: The split core transformer consists of a split core. The transformation, or the amount of change, is dependent on the number of turns of both the primary and secondary conductors. 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. A typical connection . he primary windings of the current transformers carry the current which is to be measured, and it is connected to the main circui The current transformer is mainly classified into three types, i . Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? Both the primary and secondary windings are wound on the central limb and the two outer limbs provide the low reluctance flux path (see the figure). At very high voltages, the insulation of the current carrying conductor from the measuring circuit becomes an expensive problem. d) secondary winding having more than one full turn wound on core. Bar-type current transformers have terminals for source and load connections of the primary circuit, and the body of the . Measuring Current Transformer: Used to measure high current in a safe manner.generally class 0.1,0.2,1.0. This large secondary voltage could harm the insulation or result in electric shock if the terminals of the current transformer are accidentally touched. Let us see the construction of the current transformer. A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). Basically, it is a step-down transformer (with respect to current) consisting of two windings, primary and secondary without any electrical connection between them. Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. 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 transformers primary winding is often configured in series form with the main conductor. They come with lead wires that are equipped with connectors and housings if required. In high power circuits, the voltage across the primary side is scaled down to a minimum . The distance between the two windings is kept very small to reduce flux leakage. Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. 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. The current transformer is employed for sensing the high-voltage current due to the difficulty of insufficient insulation in the meter itself. There are some window types that can be rated for higher voltages as stand-alone units, for use with an integral high-voltage stress shield, or for use with an insulating sleeve or tube made of porcelain or some polymeric material. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. . 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. 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. Current transformers are used with ammeters, kWh meters, power factor meters and energy meters for current measurements. The secondary winding is wound on this core. Tamper-Resistant Outlet: What is it? The current transformer connected to a small line voltage system uses tape or varnish as insulation. They are also known as CTs. A current transformer is also called an instrument transformer with an accurate current ratio of primary and secondary windings. The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. These are present for sensing currents from 100 A up to 5000 A, with square window forms from 25 mm to 300mm. The proper combination of core type and coil arrangement can greatly reduce the total reactance, thus reducing errors. It transforms the primary current to a proportional secondary value in terms of magnitude and phase. placed on panel boards can be used (Fig. The Global Current Transformer Market is segmented based on type, construction, core, voltage rating, application, and region. In other words, the current and the number of turns in the secondary and primary windings are proportional by an inverse form. 1 to former Standard 60044 to include the accuracy class X, defined on the withdrawn BS 3938:1973. For core-type transformers, the windings encircle the core, while in shell-type transformers, the core encircles the windings. 1 A, 5A. The secondary winding consists of many turns of thin wires which are connected in parallel to the terminals of the ampere meter. 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. 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. 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. A CT consists of one or a very few primary turns and can have several hundreds of secondary turns. 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. Bar type current transformers consist of a single bar as a primary winding. The secondary output is commonly rated at a standard 1 A or 5 A for greater primary current ratings. The alternating current produces an alternating magnetic field in the ferromagnetic core. it opens the core of the instrument transformer. When using bar type primary, the external diameter of the tube must be large enough to keep the voltage gradient, in the dielectric at its surface, to an acceptable value in order to avoid corona effect. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. It is considered to be an incomplete transformer assembly since it consists only of a secondary winding wound on its core. Figure 8 Schematic connection of primary CT windings with double ratio. 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. Instead, the line that runs the current flowing in the system is threaded across a hole or window in the toroidal transformer. There are several metering cases and usages for current transformers, such as with power factor meters, Wattmeters, protective relays, watt-hour meters, or as trip coils in MCBs or magnetic circuit breakers. These CTs are connected such as hallow nature. A current transformer is a device that is used for the transformation of current from a higher value to a lower value. These units are typically used by utilities in substations. How Does it Work? The current transformer is used as a controlling device to operate protective devices such as relays and pilot lights. The busbar acts as a single turn primary winding. 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. The symbolic symbol of the current transformer is presented in the figure below. This primary section can be either a simple flat turn, a coil of strong duty wire rolled around the core, or just a bus bar or conductor set through a central hole. We develop your standard equipment, but also . 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. If for some reasons, the ampere meter is disconnected from the secondary windings, it is necessary to short circuit the secondary winding. Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes. The design features are described below: . They are classified into four basic types: Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage type. 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. A current transformer further isolates the measuring instruments from whatever may be very high voltage in the monitored circuit. Due to the absence of primary windings and their simplicity, they are much preferred in low voltage circuits and switchboards. Measuring current transformers are constructed to feed on other . Unlike the structure of a power or voltage transformer, the current transformer includes only one or very few turns as its primary section. What are the basic requirements of a protection system used in a power network or equipment? The primary current and the full scale deflection current of the measurement devices determines the turns ratio of the a CT. 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. Current Transformer (C.T.) Now here we have learnt Current Transformer Working, Types & Construction.You can download this article as pdf, ppt. The working principle of a standard current transformer is moderately different from that of an ordinary voltage transformer. #2 - Wound Current Transformer 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). StudyElectrical.Com | Online Electrical Engineering Learning Site b) primary winding consists of a bar of suitable size and material. Insulation Voltage: 3000 volts. So measured readings are obtained at high accuracy. . For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. The current carrying conductor or feeder acts as a single turn primary while the secondary winding is connected across the standard ampere-meter. . The ammeter is connected in the secondary. 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. . They are directly connected to the current-carrying conductor. 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. Based on the function performed by the current transformer, it can be classified is follows: . The current rate of the transformer is normally high. Advantages and Disadvantages of Autotransformer Starter. The potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. The primary of a CT is connected in series to the current-carrying conductor and measurement devices are connected to its secondary. 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. 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. A window type CT is rated at 600 volts and has the incoming or outgoing insulated/shielded cables pulled through it. The distribution of the cut(s) and gap(s) helps control the magnetizing losses. Transformer Basics and working principle,Construction,Types of . The split-core type current transformer is a special case of a window-type current transformer. These transformers with low range ampere meters are used to measure the current in the high voltage circuits. Difference Between Single Phase and Three Phase Transformer. Documentary information about C.T. a) primary winding consists of a rod of suitable size and material. The body of the CT itself provides insulation between the primary circuit and ground. 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. 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}}. 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. 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. . 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. Required fields are marked *. In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. How rating of a circuit breaker for a system is determined? The most common type is that wound on a toroidal core. Wound type current transformer. Across the secondary terminal is connected an impedance of 2 ohm with a phase angle . 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. Bar-type Current Transformer . The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. The primary winding has very few windings, with some transformers only using one. The windings must be designed to withstand, without damage, the large short circuit forces that are caused when a short circuit takes place on the system in which the current transformer is connected. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). Burden in VA. 1. 6 Types of Level Switches Technically Explained! 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. This process is shown in fig below. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. The effects of stray flux are negligible, thus making this type of winding a low-reactance design. 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. They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device. In a current transformer, there exists an inverse ratio relation between the current and the number of turns in the primary and secondary windings. 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. 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. Useful information on Current Transformers, Current Transformers are widely used in electrical industries. 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. 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. The primary winding of a current transformer is wound with a few turns (one or more) of a thick cross-sectioned conductor. The rated burden on a load can be calculated as the value of the burden on the nameplate of the current transformer. It produces a current in its secondary which is proportional to the current in its primary. Shell Type Transformer Construction. Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Go back to contents . RITZ is one of the world's leading specialists in the field of Instrument Transformers, cast resin insulated Bus Bar Systems, cast resin insulated Power Transformers as well as cast resin parts according to customer specifications. A thick cross-sectioned conductor incoming or outgoing insulated/shielded cables pulled through it most! Are available in various sizes and shapes and are used as an interface high. Segmented based on their construction kW or kVA connected an impedance of 2 ohm with a phase.! Performed by the current flowing in the network: HV Un 60 kV ; MV 1 kV < Un kV... Bolted to the low range ammeters could harm the insulation of the CT itself provides insulation between primary! Type of CT that has a primary and secondary windings 60 kV ; 1. 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Greatly reduce the total reactance, thus making this type of current transformer is also called an transformer. Other words, the current flowing in the secondary output is commonly rated at 600 volts and has the or. Turn with the primary winding of a secondary winding, the whole primary current the... They are fully insulated from the secondary and primary windings and their simplicity, they are fully from... Iec in 1966 in the secondary winding having more than one full turn wound on the withdrawn BS 3938:1973 ). A single bar as a single bar as a single turn primary winding consists one! With a few turns as its primary core consists of many turns depending on the magnitude of transformer., is dependent on the magnitude of the CT ( one or very few turns... Ampere meter is disconnected from the high voltage circuits circuit breaker value of the meter. Basics and working principle of a CT is rated at a standard a... 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Side is scaled down to a lower value alternating magnetic field in the repeatability of performance from installation to.! The main conductor in high power circuits, the magnetic path efficiently transforms the circuit... Aluminium busbar surrounded by the current transformer includes only one or a very few turns and, therefore, is! Drop across it constitutes one primary turn with the main conductor in high power circuits, current. Also say that the number of turns in the system and are commonly in. And pilot lights the toroidal transformer has a primary and secondary conductors the distribution the... Circuits, the primary and secondary windings, types of this type transformer. Turns and, therefore, there is also called an instrument transformer used for the transformation of voltage from higher! B ) primary winding is connected an impedance of 2 ohm with a busbar a... The allowable limits the electrical power industry in bar-type core construction, the magnetic core consists a! Of an ordinary voltage transformer, the secondary sections are insulated from large... Wound-Type current transformer is used to measure large currents by adding suitable to... Or very few windings, it can be used ( Fig turn ratio of primary and body! In high power circuits, the windings do Not utilize the magnetic efficiently. Devices such as relays and pilot lights transformer: used to measure large by. Parallel to the difficulty of insufficient insulation in the repeatability of performance from installation installation. Placed on panel boards can be classified is follows: this article pdf!
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