While , A window type or ring type CT has the incoming or outgo. It is helpful for engineering life. 1 to former Standard 60044 to include the accuracy class X, defined on the withdrawn BS 3938:1973. SUPERBUTE Product Overview: Current Transformers. Visit here to explore more about the construction of a current transformer. There are several core types used, from low-reactance toroid to high-reactance cut . C. 4. 3. Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. The knee point is defined as the point at which a 10% increase in voltage produces a 50% increase in magnetizing current. 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. The current transformer includes two problematic errors that are ratio error and a phase angle error. Its secondary section then supplies a much decreased current which can be utilized for sensing undercurrent, overcurrent, peak current, or average current situations. The point on the magnetizing curve at which the CT operates is dependent upon the resistance of the CT secondary circuit. Construction - It consist of a primary winding & secondary winding. The uses are the same as the window type. EE-Tools, Instruments, Devices, Components & Measurements, What is Potential Transformer (PT)? The basic flux is taken as a reference. it opens the core of the instrument transformer. Generally, most of the current transformer's secondary current is rated at 5A. 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. Current Transformers (600 Volt, Indoor Bar Type) Specifications File Reference: Title: Publish Date: Format: JCM-3/4/5: Models JCM-3/JCM-4/JCM-5: 2017-11-08 [417k] The figure below shows a circuit for measurement of current and power with a current transformer. Then the primary current or load current I1 is given as. As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. 3). This accuracy class was retained by IEC in 1966 in the Amendment nr. The potential transformer is connected in parallel with the circuit. Current transformer are used for measuring current in a bus bar without disconnecting it by means of ammeter.There are three types 1.bar type current transformer 2.toroidal current transformer 3 . What are the basic requirements of a protection system used in a power network or equipment? 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. They have separate primary and secondary winding. The ammeter is connected in the secondary. 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. The secondary output can be created much lower than the current in the primary winding by increasing the number of secondary windings, Ns, being sensed because as Ns rises, Is (Current of secondary part) reduces by a related amount. Therefore, the secondary of the current transformer may never be open when the primary part is carrying the current. Medium voltage CTs come with our without mounting bracket. So measured readings are obtained at high accuracy. One of the major differences between them is . In other words, the secondary of the current transformer should be never left open under any circumstances. It is used to measure current through a bus bar which is inserted through it. They are constructed to supply a current in its secondary winding related . 5. 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. Fig. These barriers can be overcome using a CT. Also, the voltage in the secondary winding will be 200 times the primary voltage. A current transformer is generally used in metering and protective relays in the electrical power industry. Thus a CT must not be opened in working condition, it must always be earthed. They are also known as CTs. 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. There are several core types used, from low-reactance toroid to high-reactance cut cores and laminations. Potential Transformer (P.T.) The secondary winding is fully distributed around the periphery of the core. The instruments (ammeter etc.) The auxiliary CT is a wound type used in secondary circuits for totalizing, summation, phase shifting, isolation, or changing ratio. It is presented as the output in V.A (volt-amperes). Outdoor wound-type current transformers (CTs) are available 5-69 kV, 60-350 kV BIL, up to 1200 A. Wound-type units are available in two distinct . 5A ammeter). Depending upon the construction there are two types of current transformers used for measuring large currents. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. Some CT has special primary coils that allow a double ratio, when an increase of the installation is foreseen (example: 200-400/1 A) see Figure 8. 3: Bar Type CT. Precautions in the use of C.T. 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. Your email address will not be published. Your email address will not be published. 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. In both types, the core and windings are enclosed in a porcelain structure. 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 current transformer (CT) is a type of instrument transformer designed to measure high-value current in the power system. CTs used in substations are usually mounted outdoors. Shell Type Transformer Construction. In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. Where Kt is the turn ratio, Ip is the primary current, and Is is the secondary current. 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. We Rely on Advertising to Help Fund Our Site and Provide Free Information. The ratio of a CT is the relation between the values of the primary and the secondary currents; the usual secondary values are 1 A and 5 A. The manner in which the windings are arranged on the core affects the reactance since it is a geometric function. This bar is connected in series with the circuit conductor. This causes excessive core losses and produces excessive heat. The construction of the current transformer can be wound or bar type. 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. The . A current transformer is also called an instrument transformer with an accurate current ratio of primary and secondary windings. B. false. The primary winding may be a conductor, strip etc whose current is to be reduced. Working Principle of a Current Transformer, Effect of Open Secondary Windings of a Current Transformer, Current Transformer Types and Applications, Types of Transformer: An Article About How Transformers Differ in Construction and Design, working principle of transformer: discover the mechanism involved in the operation, Top Transformers Manufacturers and Suppliers in the USA and Worldwide, What is Auto Transformer? Instrument transformers are of two types - Current Transformer (C.T.) Typically, the single straight line considers as primary winding. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. There are two type of current transformer. 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. In bar-type core construction, the primary has no turns wound. The secondary winding is wound on this core. However, because of this cut, the winding is not fully distributed. If for some reasons, the ampere meter is disconnected from the secondary windings, it is necessary to short circuit the secondary winding. Rating factor of a CT is largely dependent upon ambient temperature. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. c) secondary winding having one full turn wound on core. These very high dangerous voltages will damage the winding insulation and can give a fatal shock to the operator. In some, the bar carrying high current may act as a primary. Current transformers are used with ammeters, kWh meters, power factor meters and energy meters for current measurements. The primary winding in most cases is a single conductor centrally located in the window. Figure 1 Schematic connection of a current transformer. A window type CT is rated at 600 volts and has the incoming or outgoing insulated/shielded cables pulled through it. The secondary windings of the transformer carry the current proportional to the current to be measured, and it is connected to the current windings of the meters or the instruments. B. 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. These CTs are connected such as hallow nature. 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. Over the secondary winding, the primary winding is wound on the outer core with suitable insulation between the two windings. It is used to activate the trip coil of a circuit breaker. They are . 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. The construction of the current transformer consists of many features according to its design. Based on the function performed by the current transformer, it can be classified is follows: . Wound type CT is similar to the two winding conventional transformer. In a ring-type core structure, the secondary winding is wound on the inner core of the bakelite former. Calculator, Automatic Street Light Control Circuit using LDR & Transistor BC 547. oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. It transforms the primary current to a proportional secondary value in terms of magnitude and phase. Common value for RF is 1.5. [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. How Does it Work? This presents a greater value current transformer to supply the maximum output current for the ammeter when employed on smaller primary current systems. It is also being introduced as the series transformer. 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. . Current transformers are used extensively in metering and circuit protection. Thus if the secondary is opened, there is no counter MMF in the secondary winding to oppose the primary MMF. So the bar type transformer has only secondary windings. This bar assembly can be permanently attached or held in place with brackets. The transformers are designed and manufactured in conformity with following standards: IEC, VDE, ANSI, BS,GOST and CSN. 2 Explanation: The current transformer are generally classified in two types. The bus bar type MV CTs construction usually have resin cast CT with bur bar built into the construction. The primary of a CT typically has only one turn, which is nothing but the current-carrying conductor passed through its window. 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. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. 6 Types of Electrical Switches In The Home Explained! CT may have one or more cores; typical applications of these cores are: The use of more than one core for protection is justified when the installation have two protections sets main and backup. This transformer as a low leakage reactance for which the knowledge of the transformers secondary excitation characteristics, secondary winding resistance, secondary burden resistance and turns ratio is sufficient to assess its performance in relation to the protective relay system with which it is to be used. The primary consists of a bar-type conductor with a suitable cross-section. These small currents in the secondary winding are then measured by the low-range ammeter connected across it. Why are current transformers (CT) necessary? Let us see the construction of the current 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. The core of the current transformer is built up with lamination of silicon steel. 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. 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. Figure 2 Current transformer in an AIS substation, Figure 3 Current transformer in a GIS substation, Figure 4 Current transformer in MV switchgear. 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. Burden in VA. 1. The current transformer is used as a controlling device to operate protective devices such as relays and pilot lights. 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. CT consists of three main components: a primary winding . These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. Bar type current transformers - A bar type current transformer doesn't have a primary winding of its own. Advantages and Disadvantages of Autotransformer Starter. 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 Resolution: A bar type CT is an in-line CT, much more costly and is mounted in line with the bus bars (bolted on both sides). 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. The Specification of CT 1 . . If the ammeter on the secondary winding is read 1.5 amps i.e, I2 = 1.5A. 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. . The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. 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. The secondary output lags behinds the secondary stimulated voltage by a particular angle (). 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. A current transformer further isolates the measuring instruments from whatever may be very high voltage in the monitored circuit. 6 Types of Level Switches Technically Explained! The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. 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. A Clampon (also known as Clipon) is a type of amperemeter based on current transformer. A magnetic core made up of silicon steel laminations links both the windings for providing a low reluctance path as shown below. A current transformer (CT) basically has a primary coil of one or more turns of heavy cross-sectional area. [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. 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. Current-Transformer.ppt - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. In the shape of a doughnut, these transformers are designed without having a primary winding as part of their construction. Toroidal Current Transformers, Bar type Current Transformers, and . The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. Current Transformers are mainly used to perform two tasks. 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. With wound primary current transformers this particular problem is rarely met but it is of importance to try to obtain good relative positioning of primary and secondary winding coils, thus minimizing the axial forces on both coils caused by primary winding short circuit currents. 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. (1 to over 12). 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