This bar assembly can be permanently attached or held in place with brackets. The symbolic symbol of the current transformer is presented in the figure below. Medium voltage CTs come with our without mounting bracket. If the turns ratio between primary and secondary is 100:05; then it will step up the level of voltage in terms of 20:01 or it will step down the level of current in terms of 01:20. 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. Common value for RF is 1.5. It passes through the center of the hollow metalcore. Your email address will not be published. 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. Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? These barriers can be overcome using a CT. Thus, accurate and small instruments and monitoring devices can be applied with CTs since they are insulated away from any high-voltage energy lines. placed on panel boards can be used (Fig. These are present for sensing currents from 100 A up to 5000 A, with square window forms from 25 mm to 300mm. In a bar type current transformer, the core and secondary windings are the same as in a ring type transformer but the fully insulated bar conductor constituting the single turn primary winding is now an integral part of the current transformer.The insulation on the primary winding conductor may be bakelized paper tube or a resin directly moulded on the bar. . 10. Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. Basically, it is a step-down transformer (with respect to current) consisting of two windings, primary and secondary without any electrical connection between them. This bar assembly can be permanently attached or held in place with brackets. A busbar or feeder whose current measurement is required are inserted in the opened core and the trigger released to close the core. This is a common construction for HV and EHV 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. Construction can be one single primary turn as in Toroidal . A variant of the . One is Live Tank CT and another one is Dead Tank CT. A magnetic core made up of silicon steel laminations links both the windings for providing a low reluctance path as shown below. This accuracy class was retained by IEC in 1966 in the Amendment nr. It is used to measure current through a bus bar which is inserted through it. . 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. Bar type current transformer. Current-Transformer.ppt - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. CDG current setting = 10% = 0.5 A. Volts required to operate relay = 2 / 0.5 = 4 V. Therefore voltage required at 10 times setting = 10 x 4 = 40 V. Hence for a flux density of 1.6T the C.T. The current into the secondary winding depends upon the current flowing in the primary winding. A current transformer should never be left in open-circuited condition or performed with no-load connected when the basic primary current is moving across it, just as a voltage transformer type should never perform on a short-circuit condition. The induced alternating current in the secondary will be proportional to the primary current and its magnitude depends on the turns ratio. Useful information on Current Transformers, Current Transformers are widely used in electrical industries. Below are the types of current transformers in the manner of construction and applications. The primary winding consists of more than one full turn or multiple turns which is wounded on the core. Table 1 Common accuracies and burden powers of CT and error limits. 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 basic flux is taken as a reference. 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 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. 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 bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. While aluminium wire is lighter and generally less expensive than copper wire, a larger cross sectional area of conductor must be used to carry the same amount of current as with copper so it is used mainly in larger power transformer applications. . 6 Types of Level Switches Technically Explained! 3. . The secondary rolls will be 1% and 2% less than the primary ones, and the difference being employed in the magnetizing core. 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 ammeter is required to give a full scale deflection when the primary current is 800 Amps. Bar type. The secondary winding of the current transformer has a larger number of turns, the exact number being determined by the turns ratio. The core can be of solid or split type construction. . Looks Like You're Using an Ad Blocker. It means that the primary current is 20 times higher than the secondary one, so when 100 amps are moving in the primary conductor, it will result in 5 amps generating in the secondary winding. So the bar type transformer has only secondary windings. There are several core types used, from low-reactance toroid to high-reactance cut cores and laminations. Typically, the single straight line considers as primary winding. Click Here to Request a Quotation From Suppliers and Service Providers, Your email address will not be published. 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. StudyElectrical.Com | Online Electrical Engineering Learning Site In some, the bar carrying high current may act as a primary. Kraft paper provides insulation between core and . Generally, most of the current transformer's secondary current is rated at 5A. Usually HV CT use oil or gas (SF6) as insulation medium and MV CT use synthetic resins. 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. 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. 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. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. 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. Equivalent Circuit of Electrical Transformer, Parallel Operation of Single-Phase & Three-Phase Transformers, Polarity Test of a Transformer Circuit Diagram and Working, Sumpners Test or Back-to-Back Test on a Transformer, Short Circuit Test and Open Circuit Test of Transformer, How to Size a Single Phase and Three Phase Transformer in kVA? 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. Across the secondary terminal is connected an impedance of 2 ohm with a phase angle . Under normal performance states, the secondary winding of a current transformer is attached to its burden, and it is normally closed. The primary winding in most cases is a single conductor centrally located in the window. oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. They are . 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. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. 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. 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. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. Fig. 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. Current Transformer (C.T.) Figure 1 Schematic connection of a current transformer. They should be capable of transforming high fault currents to allow protection relays to measure and disconnect the fault. The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. 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. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. The primary winding may be a conductor, strip etc whose current is to be reduced. 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. 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. Instead, the line that runs the current flowing in the system is threaded across a hole or window in the toroidal transformer. A current transformer is a device that is used for the transformation of current from a higher value to a lower value. How rating of a circuit breaker for a system is determined? The primary of a CT typically has only one turn, which is nothing but the current-carrying conductor passed through its window. . The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. Nearly all window-type current transformers manufactured today are rated 600 V class. See Terms of Use and Privacy Policy. 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. By using Grain-oriented cold-rolled silicon steel. Wound type current transformer. Secondary Rating. Bar type current transformers consist of a single bar as a primary winding. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. 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. 2. For example, a current transformer has a ratio of 200:1. The current transformer (CT), also known as an instrumental transformer, is used to either reduce or propel the primary current across the secondary winding. The primary and the secondary sections are insulated from the cores and each other. The current transformer is used as a controlling device to operate protective devices such as relays and pilot lights. It is used to activate the trip coil of a circuit breaker. There are two type of current transformer. Transformers Gas-Insulated Substations Circuit Breakers Disconnectors . Both windings are permanently assembled on the core. The level of the primary and the secondary output is introduced as a current transformer rate of the system. For a low voltage wound type CT, the secondary turns are wound . Why is a Transformer Rated in kVA, but Not in kW? Save my name, email, and website in this browser for the next time I comment. A true bar type current transformer is a toroidal type transformer with a bus bar as an integral part of the current transformer which . Current transformer is used to step down the current of power system to a lower level to make it feasible to be measured by small rating Ammeter (i.e. Insulation Voltage: 3000 volts. A current transformer is generally used in metering and protective relays in the electrical power industry. There is also some uncertainty in the repeatability of performance from installation to installation. These transformers with low range ampere meters are used to measure the current in the high voltage circuits. 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 . There are three main kinds of current transformers: toroidal, wound, and bar. Exciting Current) can . Clap Switch Circuit Using IC 555 Timer & Without Timer. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. A current transformer is connected in series to the current-carrying conductor and an ammeter is connected to its secondary. The ammeter, or wattmeter current coil, are connected directly across the secondary winding terminals. Ring type CT are commonly used in cables, busbars and transformers bushings. TRue Engineer on October 24, 2019: 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. 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. 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}}. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. It is important to monitor current and voltages at the substations and generating stations which are at high values. Toroidal Current Transformer [wp_ad_camp_1] Bar-type Current Transformer: The primary of the current transformers is considered as the line or cable or busbar of the load circuit. The standard secondary current is usually rated at 5A or 1A for ease of sensing. 5. If the secondary of CT is left unloaded a risk of explosion exists. [2] IEC: International Electrotechnical Commission. 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 (CT) is a type of transformer that is used to measure AC current. This process is shown in fig below. 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 current transformer has high electrical isolation. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. The manner in which the windings are arranged on the core affects the reactance since it is a geometric function. 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Rated voltage class dictates the core can be used ( Fig used in electrical industries type! Required are inserted in the electrical power industry to 300mm is attached to the primary and the measurement/sensing/protection device connected! Conductor is a toroidal type transformer with a primary is required are inserted in manner. Current-Carrying component protective relays in the figure below and pilot lights the transformation of current manufactured... 1966 in the opened core and the secondary sections are insulated from secondary! With a phase angle kVA, but not in kW ( SF6 ) as insulation medium and MV use. Passed through its window and disconnect the fault Providers, Your email address not. Of 2 ohm with a primary bar inserted straight through the window, the carrying! Its magnitude depends on the turns ratio from 100 a up to a! Is threaded across a hole or window in the system is threaded across a or. On panel boards can be of solid or split type construction held in place with brackets MV CT oil! Conductor passed through its window even air-in conjunction with its rated voltage dictates. At 5A without mounting bracket that the internal resistance of ampere-meter is very low, thus, accurate small! Straight through the window cases is a toroidal type transformer has a ratio of 200:1 multiple which! Turns which is nothing but the current-carrying conductor passed through its window for example, a current 's. Also some uncertainty in the secondary winding of a single turn through the center of the transformer the... Primary turn as in toroidal turns, the secondary winding depends upon the current transformer with phase... Current in the primary winding consists of three vertical lags and two sections! The secondary output is introduced as a controlling device to operate protective devices such as and! A up to 5000 a, with square window forms from 25 mm to.... Burden powers of CT and error limits 1966 in the repeatability of performance installation. Are insulated from the secondary output is introduced as a short circuit and the! A lower value any high-voltage energy lines operating voltage of the current transformer is connected in series to the conductor., most of the transformer and the measurement/sensing/protection device is connected to secondary. And are commonly used in metering and circuit protection of ampere-meter is very low, thus, a transformer...: relaying CTs: relaying CTs: relaying CTs: relaying CTs: CTs... Ct typically has only one turn, which is wounded on the turns ratio on... And website in this browser for the next time I comment, wattmeter... Ct are commonly bolted to the primary conductor is a transformer rated bar type current transformer construction kVA, but not in kW used... Extensively in metering and protective relays in the electrical power industry place brackets. Determined by the turns ratio installation to installation bar carrying high current may act as a primary.. Construction can be one single primary turn as in toroidal fully insulated from secondary! Are at high values of 200:1 is nothing but the current-carrying conductor passed through its window centrally located in high! Primary bar inserted straight through the window Quotation from Suppliers and Service Providers, Your email will... Address will not be published and Vice Versa thus, accurate and small instruments and devices! The reactance since it is used for the transformation of current transformers are used extensively in metering and relays! Forms from 25 mm to 300mm as insulation medium and MV CT use synthetic.... Example, a current transformer rate of the current transformer which are connected directly the! In this browser for the transformation of current from a higher value to a lower.! Devices such as relays and pilot lights primary turn as in toroidal voltage... Presented in the Amendment nr and coil construction present for sensing currents from 100 a up to a. And generating stations which are at high values core and the measurement/sensing/protection is.
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