The . Secondary Rating. These are present for sensing currents from 100 A up to 5000 A, with square window forms from 25 mm to 300mm. The standard secondary current is usually rated at 5A or 1A for ease of sensing. . Generally, most of the current transformer's secondary current is rated at 5A. Bar-type Current Transformer . The basic flux is taken as a reference. 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. 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). Windings in this manner ensure optimum flux linkage and distribution. Bar type current transformers consist of a single bar as a primary winding. . There are three main kinds of current transformers: toroidal, wound, and bar. and the resistance of secondary winding is 0.5 ohm. A current transformers primary winding is often configured in series form with the main conductor. Difference between utilization categories AC-1 and AC-3, EMF equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator. The magnitude of the secondary output is based on the turns ratio of the instrument. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. Two types of CT are manufactured: "On line" (straight-through) CT (Figure 6) - bar primary type and wound primary type. Therefore, if we know the current ratio and the rating of AC ampere meter, we may determine the line current. Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes. In the shape of a doughnut, these transformers are designed without having a primary winding as part of their construction. Construction. It produces a current in its secondary which is proportional to the current in its primary. Equivalent Circuit of Electrical Transformer, Parallel Operation of Single-Phase & Three-Phase Transformers, Polarity Test of a Transformer Circuit Diagram and Working, Sumpners Test or Back-to-Back Test on a Transformer, Short Circuit Test and Open Circuit Test of Transformer, How to Size a Single Phase and Three Phase Transformer in kVA? should have an output of at. 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. Your email address will not be published. 6 Types of Electrical Switches In The Home Explained! They are constructed to supply a current in its secondary winding related . 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. [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. Why are current transformers (CT) necessary? The use of this type should be with discretion since this construction results in higher-than-normal errors. . 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. Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. Looks Like You're Using an Ad Blocker. Difference Between Single Phase and Three Phase Transformer. Bar Type CT: One that has a fixed and straight single primary winding turn passing through the magnetic circuit. One of the major differences between them is . Due to the absence of primary windings and their simplicity, they are much preferred in low voltage circuits and switchboards. A more common type of construction is the window type which is also known as a through type or donut type. The current transformer connected to a small line voltage system uses tape or varnish as insulation. Types of current transformer (CT meter) #1 - Toroidal Current Transformer. Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. Toroidal Current Transformers, Bar type Current Transformers, and . The primary winding needs to be physically connected in series to current carrying conductor. . placed on panel boards can be used (Fig. Advantages and Disadvantages of Autotransformer Starter. Wire wound Current Transformer can be used to measure currents in the range of 1A to 100A. A bar type current transformer of toroidal construction requires 400A to magnetize it, and 300 A to supply the iron loss for each volt per turn induced in the secondary winding and rated frequency. According to IEC[2] Standard 61869-2, Clause 5.201, rated primary currents of CT are: 10 12,5 15 20 25 30 40 50 60 75 A and their decimal multiples or fractions. As the name suggests in wound type current transformers both primary and secondary windings are of wound type with a suitable number of turns. 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. 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. [2] IEC: International Electrotechnical Commission. The primary of a CT typically has only one turn, which is nothing but the current-carrying conductor passed through its window. 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 . A current transformer further isolates the measuring instruments from whatever may be very high voltage in the monitored circuit. The current transformer is used in meters for sensing the current up to 100 A. 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. It is used to activate the trip coil of a circuit breaker. 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. 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. Figure 3. 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. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter Your Email Address to Subscribe to this Blog and Receive Notifications of New Posts by Email. In Protection-class CTs, burdens are displayed as the maximum allowable secondary volts when 20 times the CT rating flow through the secondary under abnormal conditions. It is used to measure current through a bus bar which is inserted through it. . When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). If you are facing with any issues or want to request any article please feel free to contact us, and also check out our privacy policy. 5, 7.5, 3C, 40. View Answer. The working principle of a standard current transformer is moderately different from that of an ordinary voltage transformer. The instruments (ammeter etc.) Difference between Power Transformers and Distribution Transformers? But if the secondary is opened, the current flow as well as the back EMF breaks. This type of current transformer is available to measure AC currents from 100A to 600A, at 50 to 400HZ. . 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 proper combination of core type and coil arrangement can greatly reduce the total reactance, thus reducing errors. Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. Required fields are marked *. This type of current transformer is used for general-purpose monitoring, revenue metering and billing, and protective relaying. A current transformer, like any other type of transformer, should satisfy the amp-turn formula. Window-type current transformers generally have a round window opening but are also available with rectangular and oval openings. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. They have separate primary and secondary winding. A. true. The split half consists of 2 finely grounded or lapped gap faces. CT are connected in series and protection devices and metering equipment are connected to the secondary of the CT in series association, as shown in Figure 1. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. 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. least 40 V. With bar primary, number of turns = 20. Basically, it is a step-down transformer (with respect to current) consisting of two windings, primary and secondary without any electrical connection between them. The symbolic symbol of the current transformer is presented in the figure below. This process is shown in fig below. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. The body of the CT itself provides insulation between the primary circuit and ground. The primary consists of a bar-type conductor with a suitable cross-section . They are directly connected to the current-carrying conductor. CT consists of three main components: a primary winding . Advantages & Application, Working Principle of Transformer: Discover the Mechanism Involved in the Operation, Difference between Power Transformer and Distribution Transformer, Easy Guide to Cooling Tower Efficiency & How To Increase it, Parts of Boiler and Their Function in the Boilers, Types of Alternator: Features, Advantages, and Vast Usage, Ball Valve Parts: An Easy-to-Understand Guide (2022 Updated). Buy Equipment or Ask for a Service. 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. Ring type CT are commonly used in cables, busbars and transformers bushings. 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