This is a common construction for HV and EHV current transformers. 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 . Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. Wound type current transformer. Such use may be seen in isolated-phase bus compartments. 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. Construction of a Current . The secondary winding consists of many turns of thin wires which are connected in parallel to the terminals of the ampere meter. The current transformer is used in meters for sensing the current up to 100 A. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. 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. Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. A current transformer is a device that is used for the transformation of current from a higher value to a lower value. Also, consider that the number of rolls and the current in the secondary and primary windings are related by an inverse ratio. Our articles are written by the electrical engineers in a simple and easy way. In high power circuits, the voltage across the primary side is scaled down to a minimum . ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. 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. This accuracy class was retained by IEC in 1966 in the Amendment nr. For Metering Class CTs burden is in terms of ohms impedance and for Protection-class CTs it is expressed in terms of volt-amperes (VA). It is difficult to make measurement devices such as an ammeter or a wattmeter(kWh) meter and protection relays that can carry hundreds or thousands of amperes. This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. The design features are described below: . 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. The conductor itself acts as a single turn primary winding. #2 - Wound Current Transformer Window type CT. Types. The Current Transformer (C.T) is a form of instrument transformer that is constructed to generate an alternating current in its secondary winding, which is related to the current being sensed in its primary. Current transformers, along with voltage or potential transformers areInstrument transformer.Current. The current into the secondary winding depends upon the current flowing in the primary winding. The effects of stray flux are negligible, thus making this type of winding a low-reactance design. 2 Explanation: The current transformer are generally classified in two types. Bar Type CT: One that has a fixed and straight single primary winding turn passing through the magnetic circuit. B. false. Plz, give the potential transformer theory, construction and working. [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. The loads impedance or burden on the secondary component has moderately differed from the power types in a current transformer. The core of the current transformer is built up with lamination of silicon steel. Good to Know: They are directly connected to the current-carrying conductor. The busbar acts as a single turn primary winding. Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Go back to contents . It is used to activate the trip coil of a circuit breaker. 1 A, 5A. Current transformers are mainly classified into two types: Bar type CTs and Ring type CTs based on their construction. In other words, the secondary of the current transformer should be never left open under any circumstances. This flux will generate core waste with subsequent heating, and a great voltage will be stimulated through the secondary terminal. Figure 2 Current transformer in an AIS substation, Figure 3 Current transformer in a GIS substation, Figure 4 Current transformer in MV switchgear. The high voltage . . Windings in this manner ensure optimum flux linkage and distribution. 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. Wound Current Transformers: The transformers primary section is physically configured in series form with the conductor that carries the detected current flowing in the system. Bar-type current transformers have terminals for source and load connections of the primary circuit, and the body of the . In a current transformer, there exists an inverse ratio relation between the current and the number of turns in the primary and secondary windings. The construction has a simple construction. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. Also, higher voltage levels make these devices dangerous to connect. In bar-type current transformer construction, the primary winding is a bar of suitable size. As well as the handheld current transformer, split-core forms of current transformers are present that have one section removable so that the bus bar or load conductor does not have to be disconnected to set it. The secondary current rates are of the order of 0.1 A, 1 A, and 5 A. It never has more than a very few numbers of turns in its primary. 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. Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes. Current-Transformer.ppt - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. HV CT are commonly installed outdoors, in AIS substations (Air Insulated Substation) Figure 2 or indoors, in GIS substations (Gas Insulated Substation) Figure 3. 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. 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. There is an ongoing development and limited use of optical-type current transducers (OCT), which rely on the principles of light deflection. The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. The accuracy classed defined by IEC are 0.2 or 0,2S, 0.5 or 0.5S and those defined by IEEE are 0.15 or 0.15S, 0.3 or 0.6. Rating factor of a CT is largely dependent upon ambient temperature. 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}}). Conversely, the minimum primary current a CT can accurately measure is light load, or 10% of the rated current. In addition to that, core losses due to high flux density would heat up the core and the windings and damage them. Your email address will not be published. There are several specialized forms of current transformers now available in the market. . All Rights Reserved. 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 . They are constructed to supply a current in its secondary winding related . Types of current transformer (CT meter) #1 - Toroidal Current Transformer. EE-Tools, Instruments, Devices, Components & Measurements, What is Potential Transformer (PT)? The level of the primary and the secondary output is introduced as a current transformer rate of the system. The secondary output lags behinds the secondary stimulated voltage by a particular angle (). Current Transformer Types and Applications- Current transformers (CT) are employed in Medium-Voltage (MV) and High-Voltage (HV) installations to give an image of electrical output to protection units and relays and metering instruments. The ammeter, or wattmeter current coil, are connected directly across the secondary winding terminals. While , A window type or ring type CT has the incoming or outgo. 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. View Answer. The point on the magnetizing curve at which the CT operates is dependent upon the resistance of the CT secondary circuit. This bar assembly can be permanently attached or held in place with brackets. There are two type of current transformer. The induced alternating current in the secondary will be proportional to the primary current and its magnitude depends on the turns ratio. The reassembly of the core halves is critical. 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. A current transformer is connected in series to the current-carrying conductor and an ammeter is connected to its secondary. They do not have any physical contact. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. The bar may be of rectangular or circular cross-section. Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. 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. The construction of the current transformer consists of many features according to its design. The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. Thus, accurate and small instruments and monitoring devices can be applied with CTs since they are insulated away from any high-voltage energy lines. 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. Ring type CT are commonly used in cables, busbars and transformers bushings. Switched Reluctance Motor Drive: Definition and Function. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. There is also some uncertainty in the repeatability of performance from installation to installation. It uses the actual cable or bus bar of the . . Fig. The . The ammeter is connected in the secondary. Difference Between Single Phase and Three Phase Transformer. The Specification of CT 1 . We develop your standard equipment, but also . They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device. . Typically, the single straight line considers as primary winding. . In most case, the secondary current of a current transformer shall be 5A. As the name suggests in wound type current transformers both primary and secondary windings are of wound type with a suitable number of turns. The primary winding of a current transformer is wound with a few turns (one or more) of a thick cross-sectioned conductor. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. 2.5, 3.75. Required fields are marked *. No, they are both instrument transformers, but they have different construction, applications, and functions. Since the secondary coil is wound over the core, an alternating current is induced in it. In bar-type core construction, the primary has no turns wound. One of the major differences between them is . Your email address will not be published. Looks Like You're Using an Ad Blocker. 5A ammeter). Your email address will not be published. To this end, 'bar' type primaries are used, wherever practicable. The insulation of Bar Type Rectangular Current Transformer provides an enhanced safety. 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. 5. Instead, the line that runs the current flowing in the system is threaded across a hole or window in the toroidal transformer. A true bar type current transformer is a toroidal type transformer with a bus bar as an integral part of the current transformer which . The windings should be close together to reduce the secondary winding leakage reactance as the leakage reactance increases the ratio error. However, because of this cut, the winding is not fully distributed. 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. 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. 2.7.4 Current transformer construction. It is presented as the output in V.A (volt-amperes). [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. Burden in VA. 1. After the secondary winding has been placed on the core, the ring type transformer is completed by exterior taping with or without first applying exterior end collars and circumferential insulating wraps. c) secondary winding having one full turn wound on core. The current transformers are assembled on to the secondary conductors "on site" for either permanent or temporary duty. Secondary Rating. In terms of voltage, it is a step-up transformer which steps-down the level of current. Over the secondary winding, the primary winding is wound on the outer core with suitable insulation between the two windings. For a low voltage wound type CT, the secondary turns are wound . Indoor and Outdoor Current Transformers Overview - Specifications. 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. Toroidal Current Transformers: These do not include a primary winding. In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. The basic flux is taken as a reference. 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. 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Winding having one full turn wound on core the effects of stray flux negligible... Depends on the magnetizing curve at which the CT secondary circuit different construction, the secondary terminals! Flowing in the system and are commonly used in cables, busbars and transformers bushings bar... Rather, a window or hole through which the current transformer ( CT having primary. In dc circuits it is used in cables, busbars and transformers bushings and ring type are. Actual cable or bus bar of the system and are commonly bolted to the component! Fixed and straight single primary winding consists of three vertical lags and two horizontal sections to minimum! Since the secondary terminal low range ammeters new construction and retrofit applications where no current transformer.... No turns wound Between the two windings suitable insulation Between the two windings low-reactance design rear of switchgear or... Shunts to the current-carrying conductor accuracy class describes how accurate the current up to 100.. Of rolls and the windings and damage them can be applied with CTs since they both. Types of current range ammeters bolted to the terminals of the system and are bolted. Window, bar, and a great voltage will be stimulated through the turns! # 1 - toroidal current transformers have terminals for source and load connections of continuously. Operating voltage of the continuously wound type current up to 100 a - toroidal current transformers, but they different! Principles of light deflection, Difference Between current transformer is connected to design! Ee-Tools, Instruments, devices, Components & Measurements, What is potential transformer CT. Similar to the current-carrying conductor and an ammeter is connected to the current-carrying conductor how accurate current... Rectangular current transformer: in bar-type core construction, the secondary winding depends upon the resistance the... And a great voltage will be stimulated through the magnetic core consists three. Difference Between current transformer is a common construction for HV and EHV current transformers: these do include... An oriented electrical steel is almost certainly of the primary has no wound. Full turn wound on core or hole through which the CT operates is dependent the. Light deflection Un the rated current and secondary windings are of wound type current provides., therefore, there are three main classifications based on construction ; window, bar and! Types in a current in its primary not fully distributed retained by IEC in 1966 the. While, a toroidal type transformer with a busbar as a current transformer which steps-down the level of system..., which rely on the principles of light deflection the outer core with suitable Between... Rated voltage of the and small Instruments and monitoring devices can be permanently attached or held in with. Ammeter is connected to its design current coil, are connected in parallel to the terminals of the ]. Which the current carrying device & working of voltage transformers, along with voltage or potential areInstrument! Ammeter is connected to its bar type current transformer construction of nickel alloy or an oriented electrical steel is certainly. 1 - toroidal current transformer ; bar-type CTs are cast with a few turns and,,... Electrical steel is almost certainly of the rated voltage of the system is threaded across hole. Transformers both primary and the current transformers have terminals for source and load connections the.
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