Nearly all window-type current transformers manufactured today are rated 600 V class. The manner in which the windings are arranged on the core affects the reactance since it is a geometric function. While there are several different types of current transformers, the basic construction is much the same. There are several core types used, from low-reactance toroid to high-reactance cut cores and laminations. 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. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. 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. Why are current transformers (CT) necessary? The effects of stray flux are negligible, thus making this type of winding a low-reactance design. The induced alternating current in the secondary will be proportional to the primary current and its magnitude depends on the turns ratio. The transformation, or the amount of change, is dependent on the number of turns of both the primary and secondary conductors. This type of current transformer is used for general-purpose monitoring, revenue metering and billing, and protective relaying. Thus if the secondary is opened, there is no counter MMF in the secondary winding to oppose the primary MMF. The accuracy classed defined by IEC are 5P, 10P, PR, PX or TP and those defined by IEEE are C 100-800. 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 . The primary winding may be a conductor, strip etc whose current is to be reduced. Instrument transformers are of two types - Current Transformer (C.T.) 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. The window-type current transformer is the simplest form of instrument transformer. How to Check Whether a Multimeter is Working or Not! The primary winding and secondary winding(s) are insulated from each other and from the core(s) and are . Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. 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). Accuracy classes are defined by IEC and IEEE and are different for metering CTs and relaying CTs. The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. D. 5. For this purpose, an instrument called 'Current Transformer' is used for measuring large currents. Cable is passing through the centre of CT and in that way forms the primary winding. The loads impedance or burden on the secondary component has moderately differed from the power types in a current transformer. The secondary winding is fully insulated from the primary that is at CT rated voltage. if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'electricalclassroom_com-box-3','ezslot_2',190,'0','0'])};__ez_fad_position('div-gpt-ad-electricalclassroom_com-box-3-0');A current transformer is a type of instrument, used to measure or sense large alternating currents by scaling it to a smaller, safer and measurable value. There are two type of current transformer. The construction of a current transformer is similar to that of a conventional transformer. CTs used in substations are usually mounted outdoors. The primary and the secondary sections are insulated from the cores and each other. The symbolic symbol of the current transformer is presented in the figure below. Insulation Voltage: 3000 volts. Difference Between Ideal and Real or Practical Transformer, Transformer, Construction, Working, Types Application & Limitations, What is an Ideal Transformer? Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. Generally, most of the current transformer's secondary current is rated at 5A. d) secondary winding having more than one full turn wound on core. 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. Now, the whole primary current acts as a magnetizing current and induces large voltages in the secondary. See Terms of Use and Privacy Policy. 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. The primary has few numbers of the turn of heavy wire, and the secondary of the current transformer has many turns of fine wire. Measuring current transformers are constructed to feed on other . Below are the types of current transformers in the manner of construction and applications. 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}}. Your email address will not be published. While , A window type or ring type CT has the incoming or outgo. 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. 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. For example, a current transformer has a ratio of 200:1. Rated primary currents from 400 A to 3200 A. Bus- bar type split core current transformer Class 1 accuracy Currents from 400 A to 3200 A Up to 10 Bus- bar isolated. 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. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. this type of system has severe limitation in its power output which has to be amplified in order to operate relays etc. 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 uses are the same as the window type. The construction of a Current Transformer is very similar to a normal transformer. 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. The secondary coil is wound around a laminated ferromagnetic core and the measurement devices can connected to its ends. CT consists of three main components: a primary winding . In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. Burden in VA. 1. The current transformer is used in meters for sensing the current up to 100 A. 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. 5, 7.5, 3C, 40. In addition to that, core losses due to high flux density would heat up the core and the windings and damage them. The secondary rolls will be 1% and 2% less than the primary ones, and the difference being employed in the magnetizing core. Wound-type current transformers, T-type classification, are . The core of the current transformer is built up with lamination of silicon steel. A bar current transformer can withstand the stresses of heavy . Required fields are marked *. [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. Your email address will not be published. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. They are classified into four basic types: Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage type. . The current transformer includes two problematic errors that are ratio error and a phase angle error. 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 . 2.5.3 Core-Balance Current Transformers. The bar may be of rectangular or circular cross-section. This turns ratio is equal to: T.R=n=\frac{{N}_{P}}{{N}_{S}}=\frac{{I}_{S}}{{I}_{P}}, Secondary Current, {I}_{S}={I}_{P}(\frac{{N}_{P}}{{N}_{S}}). The current into the secondary winding depends upon the current flowing in the primary winding. It uses the actual cable or bus bar of the . The construction of the current transformer can be wound or bar type. 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. Medium voltage CTs come with our without mounting bracket. Hence, it acts as a step-up transformer with respect to the voltage. 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 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. All Rights Reserved. The key distinction between the two types lies in the core and winding placement. Over the secondary winding, the primary winding is wound on the outer core with suitable insulation between the two windings. . The maximum current up to which the transformer must maintain its current ratio is 40,000 amperes. The center of the current transformer is accumulated with lamination of silicon steel. . The Mumetal or Permalloy is used for making cores to obtain a high degree of accuracy. Buy Equipment or Ask for a Service. SUPERBUTE Product Overview: Current Transformers. Our offered transformer is manufactured using the finest quality raw material and the most recent technology in compliance with the international quality standards. 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. As the name suggests in wound type current transformers both primary and secondary windings are of wound type with a suitable number of turns. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. There is an ongoing development and limited use of optical-type current transducers (OCT), which rely on the principles of light deflection. They are also used to step down the current at a specific ratio to insulate the instrument from the high voltage lines. Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. In high line voltage systems oil-immersed current transformers are used. 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. They should be capable of transforming high fault currents to allow protection relays to measure and disconnect the fault. In a ring-type core structure, the secondary winding is wound on the inner core of the bakelite former. 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 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. Answer.1. Transformers Gas-Insulated Substations Circuit Breakers Disconnectors . The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. 5A ammeter). RITZ offers a large portfolio with a variety of different products. It never has more than a very few numbers of turns in its primary. In bar-type current transformer construction, the primary winding is a bar of suitable size. The split half consists of 2 finely grounded or lapped gap faces. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). Across the secondary terminal is connected an impedance of 2 ohm with a phase angle . There are several core types used, from low-reactance toroid to high-reactance cut . The proper combination of core type and coil arrangement can greatly reduce the total reactance, thus reducing errors. When the current moves across the primary part, it often flows within secondary windings, and amperes turns of each section are subsequently identical and opposite.
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