Also, higher voltage levels make these devices dangerous to connect. Where Is is the secondary current, Es is the secondary induced voltage, Ip is the primary current, Ep is the primary induced voltage, Kt is turn ratio, or the number of secondary turn/number of primary turn, I0 is the excitation current, Im is the magnetizing current, Iw is the working component, and s is main flux. These current transformers have an opening where the conductor carrying the primary load is passed. Based on the function performed by the current transformer, it can be classified is follows: . 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. These transformers with low range ampere meters are used to measure the current in the high voltage circuits. 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. Current Ratio Error expressed in percent is given by the formula:Credit: https://talema.com/introduction-current-transformers/, Kn = Rated transformation ratioIp = Actual primary currentIs = Actual secondary current when Ip is flowing, under conditions of measurement. These barriers can be overcome using a CT. Current Transformers are mainly used to perform two tasks. Thus a CT must not be opened in working condition, it must always be earthed. this type of system has severe limitation in its power output which has to be amplified in order to operate relays etc. CTs used in substations are usually mounted outdoors. 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. 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. Toroidal Current Transformers: These do not include a primary winding. The current into the secondary winding depends upon the current flowing in the primary winding. V Curves and Inverted V Curves of Synchronous Motor, Difference Between Salient Pole & Non-Salient Pole Rotor, Two Wattmeter Method of Power Measurement - Balanced Load, Induction Type Energy Meter - Construction, Working & Torque Equation. 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. Wire wound Current Transformer can be used to measure currents in the range of 1A to 100A. 3). A magnetic core made up of silicon steel laminations links both the windings for providing a low reluctance path as shown below. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. 6 Types of Level Switches Technically Explained! . What are the basic requirements of a protection system used in a power network or equipment? Save my name, email, and website in this browser for the next time I comment. Construction can be one single primary turn as in Toroidal . Hence, it acts as a step-up transformer with respect to the voltage. The current transformer works to transform or change the magnitude of AC (50400 Hz) in a system, typically from a higher current value to a lower current value. Answer.1. Common value for RF is 1.5. 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. No, they are both instrument transformers, but they have different construction, applications, and functions. A variant of the . The effects of stray flux are negligible, thus making this type of winding a low-reactance design. Based on the construction, there are two types of 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. 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. The body of the CT itself provides insulation between the primary circuit and ground. Due to which an extremely high voltage appears at the secondary of the transformer which is dangerous to personnel and the CT itself. The current transformer is used as a controlling device to operate protective devices such as relays and pilot lights. Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? So the bar type transformer has only secondary windings. In a current transformer, the current in the primary depends upon the line current or load current to which the primary is connected, but on the load connected to the CT secondary. 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. Therefore, the secondary of the current transformer may never be open when the primary part is carrying the current. The current transformer is used with its primary winding connected in series with line carrying the current to be measured and, therefore, the primary current is dependant upon the load connected to the system and is not determined by the load (burden)connected on the secondary winding of the current transformer. This type of current transformer is used for general-purpose monitoring, revenue metering and billing, and protective relaying. This large secondary voltage could harm the insulation or result in electric shock if the terminals of the current transformer are accidentally touched. Table 1 Common accuracies and burden powers of CT and error limits. In short, it should be never operated at no-load condition when the current is flowing through the primary. ANSI C51.13.1978 CTs and VTs CANADIAN CSA CAN3-C13-M83 CTs and VTs AUSTRALIAN AS 1675-1986 CTs s 5 Current Transformer Construction BAR PRIMARY . The standard secondary current is usually rated at 5A or 1A for ease of sensing. The design features are described below: . . For a low voltage wound type CT, the secondary turns are wound . Home > Transformer > What is the Current Transformer? To this end, 'bar' type primaries are used, wherever practicable. 2.5.3 Core-Balance Current Transformers. Where Kt is the turn ratio, Ip is the primary current, and Is is the secondary current. Visit here to explore more about the construction of a current transformer. 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. They are also known as CTs. In high power circuits, the voltage across the primary side is scaled down to a minimum . The potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. . Cable is passing through the centre of CT and in that way forms the primary winding. Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes. 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] They are classified into four basic types: Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage type. 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. They have very similar construction to that of normal transformer. placed on panel boards can be used (Fig. The working principle of a standard current transformer is moderately different from that of an ordinary voltage transformer. Current Transformer (C.T.) HV CT are commonly installed outdoors, in AIS substations (Air Insulated Substation) Figure 2 or indoors, in GIS substations (Gas Insulated Substation) Figure 3. Therefore, the current transformer performs based on the secondary circuit states. The secondary output is commonly rated at a standard 1 A or 5 A for greater primary current ratings. The split-core type current transformer is a special case of a window-type current transformer. 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 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). 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? Thus, accurate and small instruments and monitoring devices can be applied with CTs since they are insulated away from any high-voltage energy lines. Another type of current transformer which falls into the C class is a bar-type current transformer, where the primary conductor passes through the current transformer window but there is only . Bar type current transformer. A typical connection . Typically, the single straight line considers as primary winding. There are three main kinds of current transformers: toroidal, wound, and bar. Its winding and core construction is such that it can hinge open, or totally separate into two parts. 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. Types of Current Transformers CTs are manufactured in various sizes, shapes, and ratings for a broad range of applications. The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. Bar Type Current Transformers. Advantages and Disadvantages of Autotransformer Starter. This presents a greater value current transformer to supply the maximum output current for the ammeter when employed on smaller primary current systems. For this purpose, an instrument called 'Current Transformer' is used for measuring large currents. 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