In a ring-type core structure, the secondary winding is wound on the inner core of the bakelite former. Ring type CT are commonly used in cables, busbars and transformers bushings. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work , use of current tran. 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. How to Check Whether a Multimeter is Working or Not! Wound-type current transformers, T-type classification, are . The construction of a Current Transformer is very similar to a normal transformer. Switched Reluctance Motor Drive: Definition and Function. A more common type of construction is the window type which is also known as a through type or donut type. Assume that a bar primary type 2000/5A (CROSS core) current transformer having a core csa area of 20 square cm's is available with a secondary resistance of 0 31 ohm. Current transformers are available in various sizes and shapes and are used as an interface between high currents and measuring/sensing devices. 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 bus bar type MV CTs construction usually have resin cast CT with bur bar built into the construction. Types of Instrument Transformers. No, they are both instrument transformers, but they have different construction, applications, and functions. The design features are described below: . A typical connection . Large alternating currents that cannot be measured directly by normal ammeters or by wattmeters current coil to measure power can be done by using a current transformer. Both the primary and secondary windings are wound on the central limb and the two outer limbs provide the low reluctance flux path (see the figure). 1 A, 5A. How to Connect Automatic UPS / Inverter to the Home Supply System? Your email address will not be published. CT consists of three main components: a primary winding . The secondary current rates are of the order of 0.1 A, 1 A, and 5 A. 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 alternating current produces an alternating magnetic field in the ferromagnetic core. Also, higher voltage levels make these devices dangerous to connect. A common and portable kind that can be employed to detect the circuit loading is introduced as clamp meters or Handheld type, as shown. . 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. 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. 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. 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 point on the magnetizing curve at which the CT operates is dependent upon the resistance of the CT secondary circuit. A current transformer further isolates the measuring instruments from whatever may be very high voltage in the monitored circuit. Figure 8 Schematic connection of primary CT windings with double ratio. This type of current transformer is available to measure AC currents from 100A to 600A, at 50 to 400HZ. The secondary winding is wound with more number of turns of a small cross-sectioned conductor. This bar assembly can be permanently attached or held in place with brackets. 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. 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). Usually HV CT use oil or gas (SF6) as insulation medium and MV CT use synthetic resins. Bar-type Current Transformer . 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. Bar type current transformers consist of a single bar as a primary winding. The high voltage . Save my name, email, and website in this browser for the next time I comment. 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 commonly used shapes i.e., stadium, circular and rectangular orifices. Based on the construction, there are two types of current transformer. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). Insulation Voltage: 3000 volts. The paper insulation is kept on the bar i.e., between the primary and secondary. c) secondary winding having one full turn wound on core. 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. It uses the actual cable or bus bar of the . CT secondary circuit must be grounded, and grounded at one point only. The transformer is fundamentally a step-down transformer (with respect to current), consisting of primary and secondary windings without any electrical connection between them. 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. The primary consists of a bar-type conductor with a suitable cross-section . It passes through the center of the hollow metalcore. . Nearly all window-type current transformers manufactured today are rated 600 V class. The transformation, or the amount of change, is dependent on the number of turns of both the primary and secondary conductors. Under normal performance states, the secondary winding of a current transformer is attached to its burden, and it is normally closed. The 100 to 5 and 20 to 1 types are the most common forms of current transform existence in the market. 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. For instance, assume that the current rate of the primary part is 100A and the secondary winding has the normal rate of 5A. Tamper-Resistant Outlet: What is it? Based on the function performed by the current transformer, it can be classified is follows: . Essentially, C relaying accuracy class applies to a current transformer of the toroidal, bushing or window type, commonly called donut-type transformers. The primary of a CT typically has only one turn, which is nothing but the current-carrying conductor passed through its window. The primary winding may be a conductor, strip etc whose current is to be reduced. By using Grain-oriented cold-rolled silicon steel. 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 phasor diagram of the current transformer is illustrated in the figure below. These CTs are connected such as hallow nature. Bar-type Current Transformers: This form of current transformers employs the actual wire or bus-bar of the main circuit as the primary section, which is identical to a single turn. 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. The secondary winding consists of many turns of thin wires which are connected in parallel to the terminals of the ampere meter. In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. 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. They have very similar construction to that of normal transformer. The rated burden of the system is of the voltage and current on the secondary winding when the CT supports the relay or instrument with its maximum rated amount of the current. 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. 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. The potential transformer is mainly classified into . The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. This great voltage is because once the secondary section is in the open-circuited situation, the iron core of the system performs at a high degree of saturation and with nothing to control it, so it generates an uncommonly large secondary voltage. Bar-type Current Transformers: This form of current transformers employs the actual wire or bus-bar of the main circuit as the primary section, which is identical to a single turn. One is Live Tank CT and another one is Dead Tank CT. Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. While there are several different types of current transformers, the basic construction is much the same. Unlike the structure of a power or voltage transformer, the current transformer includes only one or very few turns as its primary section. Construction - It consist of a primary winding & secondary winding. They are typically 600 V class since they are used in the low-voltage circuit. The standard secondary current is usually rated at 5A or 1A for ease of sensing. Such use may be seen in isolated-phase bus compartments. #2 - Wound Current Transformer One of the major differences between them is . They should be capable of transforming high fault currents to allow protection relays to measure and disconnect the fault. Save my name, email, and website in this browser for the next time I comment. The window-type current transformer is the simplest form of instrument transformer. All Rights Reserved. Construction. Bus Bar - In this type, the bus bar of the main circuit itself acts as the primary winding with a single turn. Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. The potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). For low and medium voltage applications, there are three main classifications based on construction; window, bar, and wound. The primary current and secondary output of the current transformers are related to each other. Fig. Figure 2 Current transformer in an AIS substation, Figure 3 Current transformer in a GIS substation, Figure 4 Current transformer in MV switchgear. The windings must be designed to withstand, without damage, the large short circuit forces that are caused when a short circuit takes place on the system in which the current transformer is connected. The current transformer is employed for sensing the high-voltage current due to the difficulty of insufficient insulation in the meter itself. Depending upon the construction there are two types of current transformers used for measuring large currents. 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. The knee-point voltage is less applicable for metering current transformers as their accuracy is generally much tighter but constrained within a very small bandwidth of the current transformer rating, typically 1.2 to 1.5 times rated current. While , A window type or ring type CT has the incoming or outgo. A variant of the . For this purpose, an instrument called 'Current Transformer' is used for measuring large currents. They have separate primary and secondary winding. The secondary current replaces the primary side by reversing the secondary output and multiply by the turn rate. Ek = 4.44 B A f N. 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