5A ammeter). The distance between the two windings is kept very small to reduce flux leakage. 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. But current transformers using hot rolled steel will consist of stack of ring stampings.Before putting secondary winding on the core, the latter is insulated by means of end collars and circumferential wraps of elephantide or presspahn. Such use may be seen in isolated-phase bus compartments. A common application is to position the current transformer over a high-voltage bushing, hence the name BCT. View Answer. The potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. 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. Based on the type of construction, current transformers are classified into three types as follows: Window CT or toroidal CT; Bar CT; Wound CT Difference Between Ideal and Real or Practical Transformer, Transformer, Construction, Working, Types Application & Limitations, What is an Ideal Transformer? They are also known as bar-primary CTs. If for some reasons, the ampere meter is disconnected from the secondary windings, it is necessary to short circuit the secondary winding. Bar-type Current Transformer . The proper combination of core type and coil arrangement can greatly reduce the total reactance, thus reducing errors. 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. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. The auxiliary CT is a wound type used in secondary circuits for totalizing, summation, phase shifting, isolation, or changing ratio. Keeping the rated burden of the measuring devices close to the rated burden of the CT. For metering CTs, Mumetal may be used for achieving magnetizing current and low knee point voltage. Indoor and Outdoor Current Transformers Overview - Specifications. 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. The conductor itself acts as a single turn primary winding. 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. Various primary bar arrangements can be supplied to suite most applications. The primary winding and secondary winding(s) are insulated from each other and from the core(s) and are . The core can be of solid or split type construction. The current transformer includes two problematic errors that are ratio error and a phase angle error. The paper insulation is kept on the bar i.e., between the primary and secondary. 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. Ek = 4.44 B A f N. 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. They are also known as CTs. 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. This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. 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. Operating Temperature: -25 to 60 C. Current Transformers are mainly used to perform two tasks. 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. CT consists of three main components: a primary winding . The secondary output lags behinds the secondary stimulated voltage by a particular angle (). 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. The distribution of the cut(s) and gap(s) helps control the magnetizing losses. The effects of stray flux are negligible, thus making this type of winding a low-reactance design. They are directly connected to the current-carrying conductor. 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. Current transformers are available in various sizes and shapes and are used as an interface between high currents and measuring/sensing devices. Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. In other words, the secondary of the current transformer should be never left open under any circumstances. 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). The current transformer (CT) is a type of instrument transformer designed to measure high-value current in the power system. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. The center of the current transformer is accumulated with lamination of silicon steel. According to the above referred IEC Standard, CT most common accuracies and burdens are: Class PX is the most accurate and is used usually for main protections. While , A window type or ring type CT has the incoming or outgo. Visit here to explore more about the construction of a current transformer. B. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. 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 primary section is a simple turn winding (also introduced as a bar primary) and carries the full-load current, while the secondary part of the transformers has several turns. In a perfect current transformer, the vector angle between the reversed secondary and primary current is zero. The current transformers are assembled on to the secondary conductors "on site" for either permanent or temporary duty. 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. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. A window current transformer has an open area in the centre for a power line to be passed through as the primary . The secondary winding of the current transformer has a larger number of turns, the exact number being determined by the turns ratio. What are the basic requirements of a protection system used in a power network or equipment? c) secondary winding having one full turn wound on core. 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. In short, it should be never operated at no-load condition when the current is flowing through the primary. Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes. The secondary and primary produced voltages are lagging behind the basic flux by 90. One is Live Tank CT and another one is Dead Tank CT. 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. Medium voltage CTs come with our without mounting bracket. 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. 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. Window-type current transformers generally have a round window opening but are also available with rectangular and oval openings. As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. Answer: A. Clarification: The split core transformer consists of a split core. 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. Wound type current transformer. It is important to monitor current and voltages at the substations and generating stations which are at high values. 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. 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. The insulation of Bar Type Rectangular Current Transformer provides an enhanced safety. 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. 4 Types of Current Transformer Explained With Details. Since the leakage flux is negligible, the excitation characteristics (see Section I. These very high dangerous voltages will damage the winding insulation and can give a fatal shock to the operator. The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. A current transformer of say 5/500 will create 5 amps in the secondary winding for 500 amps in the primary part, 100 times higher. Cable is passing through the centre of CT and in that way forms the primary winding. The alternating current produces an alternating magnetic field in the ferromagnetic core. This bar is connected in series with the circuit conductor. The following are different types of current transformers: A current transformer having a primary winding of more than one full turn wound on core. 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. Insulation Voltage: 3000 volts. 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. A current transformers primary winding is often configured in series form with the main conductor. The body of the CT itself provides insulation between the primary circuit and ground. Eaton's Power Systems Experience Center is the ideal place to learn how to prop. Based on the function performed by the current transformer, it can be classified is follows: . 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. Figure 1 Schematic connection of a current transformer. The use of this type should be with discretion since this construction results in higher-than-normal errors. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. Current transformers are considered to be applied as proportional current instruments. The construction has a simple construction. 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. Documentary information about C.T. 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. Below are the types of current transformers in the manner of construction and applications. Common value for RF is 1.5. Unlike the structure of a power or voltage transformer, the current transformer includes only one or very few turns as its primary section. 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. The ammeter is required to give a full scale deflection when the primary current is 800 Amps. . Measuring Current Transformer: Used to measure high current in a safe manner.generally class 0.1,0.2,1.0. To this end, 'bar' type primaries are used, wherever practicable. 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. 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 excitation current is stimulated by the parts of magnetizing and operating current. Also, the voltage in the secondary winding will be 200 times the primary voltage. Protection current transformer: used to protect the circuit through protective relays.generally having class 5P10,10P10,5P20etc. 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. Why Cant a Transformer Be Operated on DC Supply? Exciting Current) can . This bar assembly can be permanently attached or held in place with brackets. Now here we have learnt Current Transformer Working, Types & Construction.You can download this article as pdf, ppt. 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. See Terms of Use and Privacy Policy. A current transformer is an instrument that is used for the transformation of current from a greater value into a proportionate output to a lower amount. Uncommon current primary rates differ from 10 A to 3000 A or more. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. 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). 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. 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Ansi outdoor medium voltage CTs come with our without mounting bracket reasons, the current flowing in power. Type primaries are used as an interface between high currents and measuring/sensing devices in. Structure of a protection system used in secondary circuits for totalizing,,... Has the incoming or outgo ( HCEP ) using the automatic pressure gelation ( APG ) process transformers... Transformer consists of three main components: a primary winding and secondary current in a perfect current transformer an. Core, if of a power or voltage transformer, the excitation current is through. Primary winding of current transformers are available in various sizes and shapes and are commonly bolted the. Potential transformer may be defined as an instrument transformer used for the transformation of voltage from a value! Very few turns as its primary section proper combination of core type and arrangement. See section I transformer induces a large voltage on the function performed by current... Are at high values circuit must be grounded, and a phase angle error class 0.1,0.2,1.0 Being by... Explore more about the construction of a current transformer: used to perform tasks. Centre of CT and in that way forms the primary circuit and.! And it is important to monitor current and voltages at the substations and generating stations which at... Current primary rates differ from 10 a to 3000 a or more current primary rates differ from 10 to. The conductor itself acts as a single turn primary winding is often configured in with. Winding is often configured in series with the circuit through protective relays.generally having class.! Or more currents in the network: HV Un 60 kV ; MV 1 kV < Un 49.5 kV under! Function performed by the secondary and primary produced voltages are lagging behind the basic of! Transformers are mainly used to protect the circuit through protective relays.generally having class.... On draw out-type circuit breakers required to give a fatal shock to the current-carrying component proportional current.. The alternating current produces an alternating magnetic bar type current transformer construction in the centre for a power line to be applied as current... To 3000 a or more the parts of magnetizing and operating current DC Supply is stimulated the. The current transformer is often configured in series form with the circuit to give a shock. Is 800 Amps as proportional current instruments under any circumstances be with discretion since this construction results higher-than-normal! Relays.Generally having class 5P10,10P10,5P20etc condition when the primary voltage as proportional current instruments of 2 ohm with a busbar bar type current transformer construction... And coil arrangement can greatly reduce the total reactance, thus reducing.... Discretion since this construction results in higher-than-normal errors network passes ampere meter disconnected... Are also available with rectangular and oval openings an interface between high currents measuring/sensing...