In most case, the secondary current of a current transformer shall be 5A. Difference between utilization categories AC-1 and AC-3, EMF equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator. 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. Plz, give the potential transformer theory, construction and working. A current transformer is a device that is used for the transformation of current from a higher value to a lower value. The maximum current up to which the transformer must maintain its current ratio is 40,000 amperes. The current carrying conductor or feeder acts as a single turn primary while the secondary winding is connected across the standard ampere-meter. 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. The current transformer is employed for sensing the high-voltage current due to the difficulty of insufficient insulation in the meter itself. Indoor and Outdoor Current Transformers Overview - Specifications. Types of current transformer based on construction. 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. A bar-type current transformer has no primary winding. 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. The secondary and primary produced voltages are lagging behind the basic flux by 90. Various primary bar arrangements can be supplied to suite most applications. Buy Equipment or Ask for a Service. 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. Circuit, Working & Phasor Diagram, Transformers Fire Protection System Causes, Types & Requirements, Efficiency of Transformer All Day Efficiency & Maximum Efficiency, Transformer Phasing: The Dot Notation and Dot Convention, Transformer Losses Types of Energy Losses in a Transformer. Figure 1 Schematic connection of a current transformer. 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. Bar Type Current Transformers. The insulation of Bar Type Rectangular Current Transformer provides an enhanced safety. This presents a greater value current transformer to supply the maximum output current for the ammeter when employed on smaller primary current systems. Most CT have rating factors for 35 C and 55 C. Common value for RF is 1.5. The ammeter is required to give a full scale deflection when the primary current is 800 Amps. It is also being introduced as the series transformer. The current transformer is used as a controlling device to operate protective devices such as relays and pilot lights. These pressboards, in addition to acting as an insulating medium, must also protect the secondary winding conductor from mechanical damage due to sharp comers.The secondary winding conductor is put on the core by a toroidal winding machine although hand winding is still frequently adopted if the number of secondary winding turns is small. Now here we have learnt Current Transformer Working, Types & Construction.You can download this article as pdf, ppt. Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. Based on the type of construction, current transformers are classified into three types as follows: Window CT or toroidal CT; Bar CT; Wound CT The Mumetal or Permalloy is used for making cores to obtain a high degree of accuracy. Base on the absence of the counter ampere rolls of the secondary section, the unopposed primary MMF (Magnetomotive Force) will set up an uncommonly great flux in the system. 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. This flux will generate core waste with subsequent heating, and a great voltage will be stimulated through the secondary terminal. For this purpose, an instrument called 'Current Transformer' is used for measuring large currents. So measured readings are obtained at high accuracy. Thus if the secondary is opened, there is no counter MMF in the secondary winding to oppose the primary MMF. The auxiliary CT is a wound type used in secondary circuits for totalizing, summation, phase shifting, isolation, or changing ratio. This is a common construction for HV and EHV current transformers. 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. (1 to over 12). These current transformers have an opening where the conductor carrying the primary load is passed. Also, consider that the number of rolls and the current in the secondary and primary windings are related by an inverse ratio. Unlike the structure of a power or voltage transformer, the current transformer includes only one or very few turns as its primary section. These transformers with low range ampere meters are used to measure the current in the high voltage circuits. The 100 to 5 and 20 to 1 types are the most common forms of current transform existence in the market. Let us see the construction of the current transformer. Eaton's Power Systems Experience Center is the ideal place to learn how to prop. Difference Between Ideal and Real or Practical Transformer, Transformer, Construction, Working, Types Application & Limitations, What is an Ideal Transformer? Notify me of follow-up comments by email. The following are different types of current transformers: A current transformer having a primary winding of more than one full turn wound on core. Now, the whole primary current acts as a magnetizing current and induces large voltages in the secondary. 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. In the case of a large number of secondary winding turns, requiring more than one winding layer, the frequently adopted technique is to sectionalize the secondary winding so as to considerably reduce the peak voltage between layers. Exciting Current) can . Frequency Range: 0.0480 to 0.0620 kHz. D. 5. The design features are described below: . Nearly all window-type current transformers manufactured today are rated 600 V class. Keeping the rated burden of the measuring devices close to the rated burden of the CT. For metering CTs, Mumetal may be used for achieving magnetizing current and low knee point voltage. 5A ammeter). Tamper-Resistant Outlet: What is it? 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? 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. They are also known as CTs. They isolate the measurement and sensing devices from the main circuit. This bar assembly can be permanently attached or held in place with brackets. It is used to measure current through a bus bar which is inserted through it. Construction of Current Transformers. 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. Common value for RF is 1.5. It uses the actual cable or bus bar of the . Therefore, the secondary of the current transformer may never be open when the primary part is carrying the current. Ring type CT are commonly used in cables, busbars and transformers bushings. If the ammeter on the secondary winding is read 1.5 amps i.e, I2 = 1.5A. The secondary section will provide a current into a resistive load or into either a short circuit, in the form of an ammeter until the voltage generated in the secondary is heavy enough to saturate the core or result in a failure from additional voltage breakdown. The primary consists of a bar-type conductor with a suitable cross-section. The instruments (ammeter etc.) Why is a Transformer Rated in kVA, but Not in kW? [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. Operating Temperature: -25 to 60 C. B. false. We are specialized in offering Summation Current Transformer to our clients. Since the leakage flux is negligible, the excitation characteristics (see Section I. 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. Such use may be seen in isolated-phase bus compartments. This component has a large cross-sectional region so that the magnetic flux density produced is low, employing a much smaller cross-sectional zone wire, depending upon how much the current should be stepped down as it wants to create a constant current, unrelated to the connected load. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. 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. 4. Protection current transformer: used to protect the circuit through protective relays.generally having class 5P10,10P10,5P20etc. 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. 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. 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. All Rights Reserved. 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 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. . Answer: Hello A bar type or primary wound type CT is an in-line CT, much more costly and is mounted in line with the bus bars Or cables or any conductor carrying current. A common application is to position the current transformer over a high-voltage bushing, hence the name BCT. Difference between Power Transformers and Distribution Transformers? A bar current transformer can withstand the stresses of heavy . Toroidal Current Transformer [wp_ad_camp_1] Bar-type Current Transformer: The primary of the current transformers is considered as the line or cable or busbar of the load circuit. This is why calibration of the CT is typically applied for a special type of ammeter. 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. There are several metering cases and usages for current transformers, such as with power factor meters, Wattmeters, protective relays, watt-hour meters, or as trip coils in MCBs or magnetic circuit breakers. Your email address will not be published. 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. . 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. When using bar type primary, the external diameter of the tube must be large enough to keep the voltage gradient, in the dielectric at its surface, to an acceptable value in order to avoid corona effect. . The transformers are designed and manufactured in conformity with following standards: IEC, VDE, ANSI, BS,GOST and CSN. The ammeter, or wattmeter current coil, are connected directly across the secondary winding terminals. Window type CT. Types. SUPERBUTE Product Overview: Current Transformers. The current transformers are assembled on to the secondary conductors "on site" for either permanent or temporary duty. The basic flux is taken as a reference. The symbolic symbol of the current transformer is presented in the figure below. We Rely on Advertising to Help Fund Our Site and Provide Free Information. These CT's include the laminated core and a secondary winding. Types of Instrument Transformers. a) primary winding consists of a rod of suitable size and material. The primary winding has very few windings, with some transformers only using one. Wire wound Current Transformer can be used to measure currents in the range of 1A to 100A. Burden: 2 to 30 VA. The primary winding and secondary winding(s) are insulated from each other and from the core(s) and are . A window current transformer has an open area in the centre for a power line to be passed through as the primary . The . . The core material can be in the shape of a rectangle or ring made up of nickel alloy or steel as shown below. It must be considered, however, that a current transformer introduced as 100/5 is not identical to one expressed as 20/1 or subdivisions of 100/5. 2.7.4 Current transformer construction. A more common type of construction is the window type which is also known as a through type or donut type. [1] Being Un the rated voltage of the network: HV Un 60 kV; MV 1 kV < Un 49.5 kV. 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. [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. There is also some uncertainty in the repeatability of performance from installation to installation. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. . 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. The ammeter is connected in the secondary. There are several core types used, from low-reactance toroid to high-reactance cut . The knee point is defined as the point at which a 10% increase in voltage produces a 50% increase in magnetizing current. 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 figure below shows a circuit for measurement of current and power with a current transformer. 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. 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. For core-type transformers, the windings encircle the core, while in shell-type transformers, the core encircles the windings. 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. The secondary of the transformer has many turns depending on the magnitude of the current to be stepped down. Construction and Types of HV Current Transformers. Calculator, Automatic Street Light Control Circuit using LDR & Transistor BC 547. A typical connection . The secondary winding consists of many turns of thin wires which are connected in parallel to the terminals of the ampere meter. 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 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. There are different types of design and construction of current transformers which will be explained later, whose performance can be calculated or must be tested to determine. A common and portable kind that can be employed to detect the circuit loading is introduced as clamp meters or Handheld type, as shown. 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. It produces a current in its secondary which is proportional to the current in its primary. Our articles are written by the electrical engineers in a simple and easy way. The current transformer (CT) is a type of instrument transformer designed to measure high-value current in the power system. How to Connect Automatic UPS / Inverter to the Home Supply System? This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. 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. Secondary and primary produced voltages are lagging behind the basic flux by 90 categories AC-1 and,! ] Being Un the rated voltage of the transformer must maintain its current ratio is amperes. 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