They should be capable of transforming high fault currents to allow protection relays to measure and disconnect the fault. Measuring current transformers are constructed to feed on other . 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. . This is the same concept used in the clamp meters. StudyElectrical.Com | Online Electrical Engineering Learning Site 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 . 2.5, 3.75. Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa? Thus a CT must not be opened in working condition, it must always be earthed. Tamper-Resistant Outlet: What is it? Based on the construction, there are two types of current transformer. 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 transformers are available in various sizes and shapes and are used as an interface between high currents and measuring/sensing devices. SAT 0 0 10 20 30 40 50 60 70 80 M s 38 CT Types s . Windings in this manner ensure optimum flux linkage and distribution. Ring type CT are commonly used in cables, busbars and transformers bushings. Here, we can also say that the current transformer has a primary and secondary turn ratio of 1:200. A current transformer is connected in series to the current-carrying conductor and an ammeter is connected to its secondary. Eaton's Power Systems Experience Center is the ideal place to learn how to prop. The working principle of a standard current transformer is moderately different from that of an ordinary voltage transformer. 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. According to the above referred IEC Standard, CT most common accuracies and burdens are: Class PX is the most accurate and is used usually for main protections. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). 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. These units are typically used by utilities in substations. The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. They are . 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. All Rights Reserved. Save my name, email, and website in this browser for the next time I comment. The standard secondary current is usually rated at 5A or 1A for ease of sensing. . A current transformer (CT) basically has a primary coil of one or more turns of heavy cross-sectional area. The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. Also important to consider in a CT is the magnetizing curve that is similar to the one shown in Figure 9. Current transformers (CT) are used in High Voltage (HV) and Medium Voltage (MV)[1] installations to give an image of electrical current to protection relays and units and metering equipment and they are designed to provide a current in its secondary proportional to the current flowing in its primary. Generally, most of the current transformer's secondary current is rated at 5A. 2.5.3 Core-Balance Current Transformers. Insulation Voltage: 3000 volts. oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. Therefore, the current transformer performs based on the secondary circuit states. placed on panel boards can be used (Fig. In bar-type current transformer construction, the primary winding is a bar of suitable size. The bar may be of rectangular or circular cross-section. The windings should be close together to reduce the secondary winding leakage reactance as the leakage reactance increases the ratio error. Current transformers are considered to be applied as proportional current instruments. These contain a copper or aluminium busbar surrounded by the secondary winding wound over the ferromagnetic core. 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. Table 1 Common accuracies and burden powers of CT and error limits. The current transformer (CT) is a type of instrument transformer designed to measure high-value current in the power system. They isolate the measurement and sensing devices from the main circuit. a) primary winding consists of a rod of suitable size and material. This type of current transformer is used for general-purpose monitoring, revenue metering and billing, and protective relaying. Thus in the case of a hollow transformers designed to measure 1000A primary current, the turns ratio will be 1000/5, which means the secondary winding has 200 turns. TRue Engineer on October 24, 2019: Protection current transformer: used to protect the circuit through protective relays.generally having class 5P10,10P10,5P20etc. 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. 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. 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. A current transformer is generally used in metering and protective relays in the electrical power industry. It is a very good information about CT for electrical knowledge. 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. The primary has few numbers of the turn of heavy wire, and the secondary of the current transformer has many turns of fine wire. 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. Good to Know: This presents a greater value current transformer to supply the maximum output current for the ammeter when employed on smaller primary current systems. . The core, if of a nickel-iron alloy or an oriented electrical steel is almost certainly of the continuously wound type. b) primary winding consists of a bar of suitable size and material. 4 Types of Current Transformer Explained With Details. The primary conductor constitutes the primary winding of the CT (one pass through the window is one turn on the primary). This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. Based on the type of construction, current transformers are classified into three types as follows: This type consists of a hollow core through which the current-carrying conductor or cable is passed. Operating Temperature: -25 to 60 C. A C.T Current Transformer is a type of instrument transformer designed to step down the current in the secondary for protection and measurement of proportional primary current. [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. Transformer Basics and working principle,Construction,Types of . For example, a current transformer has a ratio of 200:1. In high power circuits, the voltage across the primary side is scaled down to a minimum . 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. Current and voltage transformers are available in voltage classes ranging from 5 kV to 34.5 kV. Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. 2.7.4 Current transformer construction. They do not have any physical contact. and the resistance of secondary winding is 0.5 ohm. The design features are described below: . Bar-type Current Transformer . This accuracy class was retained by IEC in 1966 in the Amendment nr. Shell Type Transformer Construction. Buy Equipment or Ask for a Service. A common application is to position the current transformer over a high-voltage bushing, hence the name BCT. The distance between the two windings is kept very small to reduce flux leakage. A. true. 3. 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. A bar-type current transformer has no primary winding. View Answer. The secondary current rates are of the order of 0.1 A, 1 A, and 5 A. Then the primary current or load current I1 is given as. Construction. 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. In a split core current transformer, the core is split, each half having two finely ground or lapped gap faces.These current transformers are assembled onto the primary conductor on site for either permanent or temporary duty. Useful information on Current Transformers, Current Transformers are widely used in electrical industries. least 40 V. With bar primary, number of turns = 20. Often only 50% of the effective magnetic path is used. Over the secondary winding, the primary winding is wound on the outer core with suitable insulation between the two windings. It uses the actual cable or bus bar of the . Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes. For a low voltage wound type CT, the secondary turns are wound . Ek = 4.44 B A f N. CDG current setting = 10% = 0.5 A. Volts required to operate relay = 2 / 0.5 = 4 V. Therefore voltage required at 10 times setting = 10 x 4 = 40 V. Hence for a flux density of 1.6T the C.T. We are specialized in offering Summation Current Transformer to our clients. . Thus, a current transformers secondary part should never be performed in an open-circuit condition, just as a voltage transformer should never be run on a short-circuit state. The busbar acts as a single turn primary winding. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. Bus Bar - In this type, the bus bar of the main circuit itself acts as the primary winding with a single turn. They are also used to step down the current at a specific ratio to insulate the instrument from the high voltage lines. Some current transformers contain a split core which permits them to be opened, installed, and closed without disconnecting the system to which they are joined. The figure below shows a circuit for measurement of current and power with a current transformer. How to Connect Automatic UPS / Inverter to the Home Supply System? Bar Type Current Transformers. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); (adsbygoogle = window.adsbygoogle || []).push({}); All Rights Reserved by Electrical Engineering Info @2023, The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. A current transformer is also called an instrument transformer with an accurate current ratio of primary and secondary windings. 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). The basic flux is taken as a reference. They may contain multiple cores and secondary coils as well as added insulation. Bar Current Transformers. Construction can be one single primary turn as in Toroidal . The primary winding needs to be physically connected in series to current carrying conductor. 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. Save my name, email, and website in this browser for the next time I comment. The accuracy class of a CT is the percent allowable error, and is associated to burden power, the apparent power, expressed in VA, that is taken up from the secondary core (secondary load), and for which the accuracy is assured. They are classified into four basic types: Hairpin tank type, Cascade/eye bolt type, Top core type and Combined current-voltage type. 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. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. The alternating current produces an alternating magnetic field in the ferromagnetic core. Uncommon current primary rates differ from 10 A to 3000 A or more. The bushing-, window-, or bar-type current transformers are of the toroidal core construction. They have very similar construction to that of normal transformer. 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. 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. Construction of a Current . One of the major differences between them is . . This bar assembly can be permanently attached or held in place with brackets. Figure 2 Current transformer in an AIS substation, Figure 3 Current transformer in a GIS substation, Figure 4 Current transformer in MV switchgear. Potential Transformer (P.T.) 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 . Rating factor of a CT is largely dependent upon ambient temperature. Difference between utilization categories AC-1 and AC-3, EMF equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator. 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. A window current transformer has an open area in the centre for a power line to be passed through as the primary . 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. Bar Type CT: One that has a fixed and straight single primary winding turn passing through the magnetic circuit. If the ammeter on the secondary winding is read 1.5 amps i.e, I2 = 1.5A. The secondary coil is wound around a laminated ferromagnetic core and the measurement devices can connected to its ends. Where Kt is the turn ratio, Ip is the primary current, and Is is the secondary current. The construction of the current transformer can be wound or bar type. Clamp meters close and open around a current transporting conductor and control its current by identifying the magnetic field around it, supplying a quick measurement reading commonly on a digital display without opening or disconnecting the circuit. 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 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. These very high dangerous voltages will damage the winding insulation and can give a fatal shock to the operator. 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. Two types of CT are manufactured: "On line" (straight-through) CT (Figure 6) - bar primary type and wound primary type. If for some reasons, the ampere meter is disconnected from the secondary windings, it is necessary to short circuit the secondary winding. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. Across the secondary terminal is connected an impedance of 2 ohm with a phase angle . 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). The maximum current up to which the transformer must maintain its current ratio is 40,000 amperes. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. Bar type current transformer. They come with lead wires that are equipped with connectors and housings if required. should have an output of at. It passes through the center of the hollow metalcore. . HV CT are commonly installed outdoors, in AIS substations (Air Insulated Substation) Figure 2 or indoors, in GIS substations (Gas Insulated Substation) Figure 3.