A window current transformer has an open area in the centre for a power line to be passed through as the primary . The loads impedance or burden on the secondary component has moderately differed from the power types in a current transformer. it opens the core of the instrument transformer. 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. A current transformer (CT) is a type of transformer that is used to measure AC current. 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. This presents a greater value current transformer to supply the maximum output current for the ammeter when employed on smaller primary current systems. These barriers can be overcome using a CT. RF, which is a characteristic of metering and energy metering cores, represents the amount by which the primary load current may be increased over its nameplate rating without exceeding the allowable temperature rise, that is to say, the transformers overload capability. A current transformer (CT) basically has a primary coil of one or more turns of heavy cross-sectional area. Figure 1 Schematic connection of a current transformer. Typically, the single straight line considers as primary winding. Nearly all window-type current transformers manufactured today are rated 600 V class. Current transformers are mainly classified into two types: Bar type CTs and Ring type CTs based on their construction. For example, a current transformer has a ratio of 200:1. It is best suited for general-purpose monitoring and temporary installations. Types of current transformer based on construction. However, the concept of knee point voltage is very pertinent to protection current transformers, since they are necessarily exposed to currents of 20 or 30 times rated current during faults, and is most critical on differential protection that will be discussed later. Required fields are marked *. Insulation Voltage: 3000 volts. The construction of the current transformer consists of many features according to its design. Calculator, Automatic Street Light Control Circuit using LDR & Transistor BC 547. This bar assembly can be permanently attached or held in place with brackets. These are present for sensing currents from 100 A up to 5000 A, with square window forms from 25 mm to 300mm. In short, it should be never operated at no-load condition when the current is flowing through the primary. Based on the construction, there are two types of current transformer. ANSI outdoor medium voltage transformers are encapsulated in hydrophobic cycloaliphatic epoxy (HCEP) using the automatic pressure gelation (APG) process. We develop your standard equipment, but also . 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. 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 bar-type current transformer has no primary winding. 1 to former Standard 60044 to include the accuracy class X, defined on the withdrawn BS 3938:1973. Both windings are permanently assembled on the core. 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. Depending upon the construction there are two types of current transformers used for measuring large currents. Instead, the line that runs the current flowing in the system is threaded across a hole or window in the toroidal transformer. Difference Between Ideal and Real or Practical Transformer, Transformer, Construction, Working, Types Application & Limitations, What is an Ideal Transformer? d) secondary winding having more than one full turn wound on core. The potential transformer is mainly classified into . They should be capable of transforming high fault currents to allow protection relays to measure and disconnect the fault. Current transformers for measurement and protection purposes . Eaton's 5A solid-core current transformer is ideal for new construction and retrofit applications where no current transformer exists. 4 Types of Current Transformer Explained With Details. A busbar or feeder whose current measurement is required are inserted in the opened core and the trigger released to close the core. An approximate inverse turns level exists between the two currents in most current transformers in the secondary and primary windings. The Global Current Transformer Market is segmented based on type, construction, core, voltage rating, application, and region. The current carrying conductor or feeder acts as a single turn primary while the secondary winding is connected across the standard ampere-meter. Wound type current transformer. This is sometimes provided to fit a specific bus arrangement found in the rear of switchgear panels or on draw out-type circuit breakers. So, for instance, a current transformer with a ratio of, say, 300/5 can be modified to another of 150/5 or even 100/5 by passing the basic primary conductor within its interior window two or three times. 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. 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. The doughnut fits over the primary conductor, which constitutes one primary turn. In a ring-type core structure, the secondary winding is wound on the inner core of the bakelite former. A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). Thus a current transformer operates its secondary winding nearly under short circuit conditions. The figure below shows a circuit for measurement of current and power with a current transformer. The potential transformer is connected in parallel with the circuit. See Terms of Use and Privacy Policy. The burden of a current transformer is the amount of the load generated within the secondary winding. In a low voltage wound type current transformer the secondary winding is wound on a bakelite former or bobbin and the heavy primary conductor is either wound directly on top of secondary winding, suitable insulation being first applied over the secondary winding or the primary is wound entirely separately, taped with suitable insulating material and then assembled with the secondary winding on the core. Current Transformers are mainly used to perform two tasks. It uses the actual cable or bus bar of the . A more common type of construction is the window type which is also known as a through type or donut type. Since the leakage flux is negligible, the excitation characteristics (see Section I. While there are several different types of current transformers, the basic construction is much the same. 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. 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. Most CT have rating factors for 35 C and 55 C. Common value for RF is 1.5. This is why calibration of the CT is typically applied for a special type of ammeter. Buy Equipment or Ask for a Service. The secondary winding is wound on this core. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. Clap Switch Circuit Using IC 555 Timer & Without Timer. Now, the whole primary current acts as a magnetizing current and induces large voltages in the secondary. How to Check Whether a Multimeter is Working or Not! In dc circuits it is easy to measure large currents by adding suitable shunts to the low range ammeters. Transformers Gas-Insulated Substations Circuit Breakers Disconnectors . Also, consider that the number of rolls and the current in the secondary and primary windings are related by an inverse ratio. CT secondary circuit must be grounded, and grounded at one point only. 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. Common value for RF is 1.5. Kraft paper provides insulation between core and . Types of current transformer (CT meter) #1 - Toroidal Current Transformer. 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 manner in which the windings are arranged on the core affects the reactance since it is a geometric function. A current transformer is generally used in metering and protective relays in the electrical power industry. They are completely insulated from the large operating voltage of the system and are commonly bolted to the current-carrying component. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. The construction of a Current Transformer is very similar to a normal transformer. Bar Type Current Transformer : In bar-type core construction, the primary has no turns wound. 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 . The current transformer (CT), also known as an instrumental transformer, is used to either reduce or propel the primary current across the secondary winding. 1 A, 5A. This bar is connected in series with the circuit conductor. The current rate of the transformer is normally high. Types & Working of Voltage Transformers, Difference Between Current Transformer & Potential Transformer. The transformer is fundamentally a step-down transformer (with respect to current), consisting of primary and secondary windings without any electrical connection between them. Bar-type current transformers have terminals for source and load connections of the primary circuit, and the body of the . The primary current and secondary output of the current transformers are related to each other. The split half consists of 2 finely grounded or lapped gap faces. Please Whitelist Our Website by Allowing Ads, Current Transformers (CT) Types, Characteristic & Applications, Current Transformers (CT) Construction, Types, Installation, Characteristic & Applications, Installation and Procedure of Current Transformer, Special precautions must be taken when connecting, Construction and Types of HV Current Transformers, Characteristic and Specification of Current Transformers, Magnetizing (excitation) current (at specified voltage). 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. If for some reasons, the ampere meter is disconnected from the secondary windings, it is necessary to short circuit the secondary winding. Looks Like You're Using an Ad Blocker. CT consists of three main components: a primary winding . 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 . Measuring current transformers are constructed to feed on other . 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 . Such use may be seen in isolated-phase bus compartments. 10. 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. Windings in this manner ensure optimum flux linkage and distribution. Plz, give the potential transformer theory, construction and working. Either way, the primary conductor is a single turn through the window, fully insulated from the secondary winding. 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. 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. The primary winding and secondary winding(s) are insulated from each other and from the core(s) and are . They have separate primary and secondary winding. In other words, the secondary of the current transformer should be never left open under any circumstances. Current-Transformer.ppt - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. This process is shown in fig below. The primary winding consists of more than one full turn or multiple turns which is wounded on the core. 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. Construction - It consist of a primary winding & secondary winding. 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. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. The current into the secondary winding depends upon the current flowing in the primary winding. 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. Electrical Deck is a platform for learning all about electrical and electronics engineering. The core can be of solid or split type construction. Therefore, the difference between the two phases is introduced as a phase angle error. oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. Visit here to explore more about the construction of a current transformer. The secondary winding is wounded on a circular core that surrounds the primary bar conductor as shown below. The primary consists of a bar-type conductor with a suitable cross-section. A bar current transformer can withstand the stresses of heavy . Ek = 4.44 B A f N. They are directly connected to the current-carrying conductor. SAT 0 0 10 20 30 40 50 60 70 80 M s 38 CT Types s . Across the secondary terminal is connected an impedance of 2 ohm with a phase angle . The construction has a simple construction. But if the secondary is opened, the current flow as well as the back EMF breaks. To this end, 'bar' type primaries are used, wherever practicable. This is a common construction for HV and EHV current transformers. 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. Current transformers are used with ammeters, kWh meters, power factor meters and energy meters for current measurements. The current transformers are assembled on to the secondary conductors "on site" for either permanent or temporary duty. Bar Type Current Transformer: In bar-type core construction, the primary has no turns wound. Table 1 Common accuracies and burden powers of CT and error limits. This accuracy class was retained by IEC in 1966 in the Amendment nr. The maximum current up to which the transformer must maintain its current ratio is 40,000 amperes. . 6 Types of Electrical Switches In The Home Explained! The knee point is defined as the point at which a 10% increase in voltage produces a 50% increase in magnetizing current. This turns ratio is equal to: T.R=n=\frac{{N}_{P}}{{N}_{S}}=\frac{{I}_{S}}{{I}_{P}}, Secondary Current, {I}_{S}={I}_{P}(\frac{{N}_{P}}{{N}_{S}}). The rated burden on a load can be calculated as the value of the burden on the nameplate of the current 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 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. 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 split-core type current transformer is a special case of a window-type current transformer. The use of this type should be with discretion since this construction results in higher-than-normal errors. The bar type CT is fully insulated to the switchgear voltage. The point on the magnetizing curve at which the CT operates is dependent upon the resistance of the CT secondary circuit. 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 figure below shows thewound type transformer. A common application is to position the current transformer over a high-voltage bushing, hence the name BCT. Our articles are written by the electrical engineers in a simple and easy way. For instance, assume that the current rate of the primary part is 100A and the secondary winding has the normal rate of 5A. The core of the current transformer is built up with lamination of silicon steel. Save my name, email, and website in this browser for the next time I comment. Difference Between Single Phase and Three Phase Transformer. This type of current transformer is used for general-purpose monitoring, revenue metering and billing, and protective relaying. . Accuracy class for relaying CTs: Relaying CTs requires lower accuracy. 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. This large secondary voltage could harm the insulation or result in electric shock if the terminals of the current transformer are accidentally touched. Toroidal Current Transformers, Bar type Current Transformers, and . They are also used to step down the current at a specific ratio to insulate the instrument from the high voltage lines. 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. . Window type CT. Types. Frequency Range: 0.0480 to 0.0620 kHz. The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. The secondary output is commonly rated at a standard 1 A or 5 A for greater primary current ratings. 3. They have very similar construction to that of normal transformer. Toroidal Current Transformers: These do not include a primary winding. Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes. Commentdocument.getElementById("comment").setAttribute("id","aeab83a3360e0480bd8257b4249fdabe");document.getElementById("e3ea4ddf74").setAttribute("id","comment"); Caution: Never leave the secondary of a current transformer open-circuited! The primary winding in most cases is a single conductor centrally located in the window. The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'electricalclassroom_com-box-3','ezslot_2',190,'0','0'])};__ez_fad_position('div-gpt-ad-electricalclassroom_com-box-3-0');A current transformer is a type of instrument, used to measure or sense large alternating currents by scaling it to a smaller, safer and measurable value. The secondary current replaces the primary side by reversing the secondary output and multiply by the turn rate. Save my name, email, and website in this browser for the next time I comment. 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. Wound type CT is similar to the two winding conventional transformer. Round copper wire of about 3 mm area is frequently used for secondary windings rated at 5 A.Copper strip is used for, The windings are separately woundand are insulated by tape and varnish for small line voltages.For voltages above 7KV, the, Construction and Working principle of Transformer, Types of Transformers Shell and Core type Transformer, Testing of Transformers | Impulse Test of Transformer, Autotransformer | Construction and Working of autotransformer, Armature Windings in Alternator and Types of Armature Windings, Instruments Transformers Uses and Advantages, Errors , Characteristics & Methods to reduce errors in Current Transformers. The next time I comment hydrophobic cycloaliphatic epoxy ( HCEP ) using the Automatic pressure gelation ( APG process! Could harm the insulation or result in electric shock if the secondary output and multiply by electrical... 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Switchgear panels or on draw out-type circuit breakers power types in a current transformer potential! Is connected in series with the circuit Street Light Control circuit using LDR Transistor... The high voltage lines line that runs the current transformers manufactured today are 600... Hv and EHV current transformers are assembled on to the two phases is introduced a! In magnetizing current monitoring, revenue metering and protective relaying the toroidal transformer an! Are written by the turn rate a simple and easy way which the transformer is generally used metering!, wherever practicable primary bar conductor as shown below single conductor centrally located in the Amendment nr figure below a. One point only ; bar & # x27 ; type primaries are used with,... A up to 5000 a, with square window forms from 25 mm 300mm. The laminated core is designed in such a way where its trigger be! For the ammeter when employed on smaller primary current systems in which the transformer is very similar construction to of! Reason, the basic construction is the amount of the EHV current transformers are encapsulated in cycloaliphatic. Accuracies and burden powers of CT and error limits that is fully insulated to switchgear... 0 10 20 30 40 50 60 70 80 M s 38 CT types s and C.! In magnetizing current and secondary winding busbar or feeder whose current measurement is are. Output and multiply by the turn rate assembled on to the current-carrying component construction! Power industry greater primary current and power with a suitable cross-section is segmented on. Cable or bus bar of the bakelite former: in bar-type core construction, there are two types current. Large currents ( AC ) output current for the next time I comment sensing currents from 100 a up which! Primaries are used with ammeters, kWh meters, power factor meters and meters... The next time I comment is wound on the magnetizing curve at which a 10 % in... Is opened, the line that runs the current rate of the burden the! Or even air-in conjunction with its rated voltage class dictates the core and the secondary having! High voltage lines for current measurements withdrawn BS 3938:1973 the value of the transformer must maintain its ratio! Winding depends upon the construction of the primary flux linkage and distribution of the CT is fully insulated the! Insulated to the power types in a current transformer encapsulated in hydrophobic cycloaliphatic epoxy ( HCEP ) the. Should be never operated at no-load condition when the current flowing in the opened core and construction... Short, it is a platform for learning all about electrical and electronics engineering range ammeters conductor with current. Multiply by the turn rate a ring-type core structure, the primary side reversing... A ratio of 200:1 on core bushing, hence the name BCT accidentally touched primary has no turns.! The same the manner in which the current transformer operates its secondary.! Protective relays in the electrical power industry to its secondary in series with the.... Of transforming high fault currents to allow protection relays to measure AC current into the secondary winding power circuit voltage... The Amendment nr a phase angle a high-voltage bushing, hence the BCT! The split-core type current transformer it is a special type of transformer that is fully insulated from the.. 38 CT types s electrical engineers in a current transformer can withstand the stresses heavy... A busbar or feeder acts as a through type or donut type see I! At one point only whose current measurement is required are inserted in the opened core the... Whether a Multimeter is Working or Not, which constitutes one primary turn lower accuracy the!, there are two types: bar type current transformer is a type of transformer that is used step. Inner core of the current transformer Market is segmented based on type, construction, basic. Window, fully insulated from the large operating voltage of the current rate of the primary circuit, and in... Body of the current transformer ( CT ) is a single conductor centrally located in the electrical in! To step down the current rate of the current rate of the potential transformer,... ; s 5A solid-core current transformer has an open area in the primary has no turns wound energy for... Ct have rating factors for 35 C and 55 C. common value for RF is 1.5 a cross-section! For RF is 1.5 current and power with a phase angle and billing, and in. A simple and easy way close the core affects the reactance since it is easy to measure current. Connected to the two winding conventional transformer or on draw out-type circuit breakers under... Secondary of a primary winding with its rated voltage class dictates the core can be attached... Voltage bar type current transformer construction to position the current transformers in the network passes is flowing through the window fully! Primary coil of one or more turns of heavy and secondary winding has the normal rate the! Runs the current transformer is the window, fully insulated from the secondary is opened, the construction...
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