For low and medium voltage applications, there are three main classifications based on construction; window, bar, and wound. 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. Measuring current transformers are constructed to feed on other . 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 paper insulation is kept on the bar i.e., between the primary and secondary. The bus bar type MV CTs construction usually have resin cast CT with bur bar built into the construction. It is best suited for general-purpose monitoring and temporary installations. In general, current transformers and ammeters are employed together as a particular pair in which the model of the instrument is such as to supply a maximum secondary current controlled by a full-scale deflection on the ammeter. 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? Documentary information about C.T. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. The current transformer has easy maintenance and installation. 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 current transformer (CT) is a type of instrument transformer designed to measure high-value current in the power system. The current transformer connected to a small line voltage system uses tape or varnish as insulation. The busbar acts as a single turn primary winding. The magnitude of the primary and secondary voltages depends on the number of rolls on the windings. The turns ratio of a current transformer is made such that the full load current in its primary give a secondary current of either 5A or 1A. 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 . Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. TRue Engineer on October 24, 2019: Thus a current transformer operates its secondary winding nearly under short circuit conditions. The current transformer has high electrical isolation. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. The construction of a current transformer is similar to that of a conventional transformer. The auxiliary CT is a wound type used in secondary circuits for totalizing, summation, phase shifting, isolation, or changing ratio. Current-Transformer.ppt - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. Toroidal Current Transformers: These do not include a primary winding. 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}}. The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. By using Linquip RFQ Service, you can expectto receive quotations from various suppliers across multiple industries and regions. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. The bar type CT is fully insulated to the switchgear voltage. The primary section of the current transformers carries the current which should be measured, and it is attached to the main circuit. The current transformer is used as a controlling device to operate protective devices such as relays and pilot lights. But in a practical current transformer, there is a phase difference between the secondary and the primary current since the primary output has also supplied the portion of the exciting current. The doughnut fits over the primary conductor, which constitutes one primary turn. 3. The construction of the current transformer consists of many features according to its design. In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. 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 primary winding of a current transformer is wound with a few turns (one or more) of a thick cross-sectioned conductor. The working or operation of a current transformer is similar to that of a normal two-winding transformer. If the ammeter on the secondary winding is read 1.5 amps i.e, I2 = 1.5A. 5A ammeter). Your email address will not be published. Figure 1 Schematic connection of a current transformer. 2.5, 3.75. 3: Bar Type CT. Precautions in the use of C.T. They have very similar construction to that of normal transformer. 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. Thus, accurate and small instruments and monitoring devices can be applied with CTs since they are insulated away from any high-voltage energy lines. In bar-type core construction, the primary has no turns wound. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. HV CT are commonly installed outdoors, in AIS substations (Air Insulated Substation) Figure 2 or indoors, in GIS substations (Gas Insulated Substation) Figure 3. Why are Air-Conditioners (AC) Rated in Tons, Not in kW or kVA? This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. 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. 5. Current Transformers are mainly used to perform two tasks. Difference between Power Transformers and Distribution Transformers? Below are the types of current transformers in the manner of construction and applications. Eaton's 5A solid-core current transformer is ideal for new construction and retrofit applications where no current transformer exists. This bar assembly can be permanently attached or held in place with brackets. They are typically 600 V class since they are used in the low-voltage circuit. . The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. 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. Wound-type current transformers, T-type classification, are . 3). . 5, 7.5, 3C, 40. 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 primary consists of a bar-type conductor with a suitable cross-section. Figure 2 Current transformer in an AIS substation, Figure 3 Current transformer in a GIS substation, Figure 4 Current transformer in MV switchgear. This process is shown in fig below. 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. These transformers with low range ampere meters are used to measure the current in the high voltage circuits. 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 typical connection . While there are several different types of current transformers, the basic construction is much the same. This voltage resulted in the breakdown of the insulation, and also the waste of accuracy in the future can occur since the additional MMF leaves the residual magnetism in the system. 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. B. false. The ammeters scale is adjusted according to the turns ratio. They are . The current rate will determine the turn ratio, and as the primary winding commonly includes one or two turns, whereas the secondary winding can include several hundred turns, the rate between the primary and secondary can be relatively large. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. Depending upon the construction there are two types of current transformers used for measuring large currents. Current transformers are available in various sizes and shapes and are used as an interface between high currents and measuring/sensing devices. 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 the AC device, meters, or monitoring apparatus where the current to be sensed is of such magnitude that the instrument coil or meter cannot conveniently be created from adequate current carrying capacity. 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. Advantages and Disadvantages of Microgrids. If for some reasons, the ampere meter is disconnected from the secondary windings, it is necessary to short circuit the secondary winding. The windings are separately woundand are insulated by tape and varnish for small line voltages.For voltages above 7KV, the transformers are oil immersed or compound filled. A current transformer is generally used in metering and protective relays in the electrical power industry. Construction. Current transformers for measurement and protection purposes . Thus if the secondary is opened, there is no counter MMF in the secondary winding to oppose the primary MMF. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. Buy Equipment or Ask for a Service. They are also known as bar-primary CTs. Good to Know: Types of current transformer (CT meter) #1 - Toroidal Current Transformer. They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device. 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). The alternating current produces an alternating magnetic field in the ferromagnetic core. The type of wire used as the main current carrying conductor in a transformer winding is either copper or aluminium. Typically, the single straight line considers as primary winding. Medium voltage CTs come with our without mounting bracket. Why are current transformers (CT) necessary? One is Live Tank CT and another one is Dead Tank CT. Calculator, Automatic Street Light Control Circuit using LDR & Transistor BC 547. 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. It is helpful for engineering life. The 100 to 5 and 20 to 1 types are the most common forms of current transform existence in the market. Plz, give the potential transformer theory, construction and working. 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. Most CT have rating factors for 35 C and 55 C. Common value for RF is 1.5. The point on the magnetizing curve at which the CT operates is dependent upon the resistance of the CT secondary circuit. Generally, most of the current transformer's secondary current is rated at 5A. . Shell Type Transformer Construction. 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. Common value for RF is 1.5. The insulation medium used whether polymeric, oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. The primary has few numbers of the turn of heavy wire, and the secondary of the current transformer has many turns of fine wire. However, because of this cut, the winding is not fully distributed. Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Go back to contents . The level of the primary and the secondary output is introduced as a current transformer rate of the system. This is the same concept used in the clamp meters. For core-type transformers, the windings encircle the core, while in shell-type transformers, the core encircles the windings. C. 4. Bar-type Current Transformer ; Bar-type CTs are cast with a busbar as a single turn primary winding. Also, higher voltage levels make these devices dangerous to connect. 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. In high line voltage systems oil-immersed current transformers are used. The ammeter is arranged to give a full deflection with either 5A or 1A depending on the turns ratio of the CT. A Clampon (also known as Clipon) is a type of amperemeter based on current transformer. 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. The secondary winding of the current transformer has a larger number of turns, the exact number being determined by the turns ratio. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. 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. A current transformer is connected in series to the current-carrying conductor and an ammeter is connected to its secondary. 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Ct have rating factors for 35 C and 55 C. common value for RF 1.5... Bar-Type current transformer is wound with a primary bar inserted straight through the window,,.
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