The insulation medium used whether polymeric, oil or even air-in conjunction with its rated voltage class dictates the core and coil construction. Current-Transformer.ppt - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. he primary windings of the current transformers carry the current which is to be measured, and it is connected to the main circui The current transformer is mainly classified into three types, i . Bar type. In the shape of a doughnut, these transformers are designed without having a primary winding as part of their construction. The bar type CT is fully insulated to the switchgear voltage. 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. 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. As the name suggests in wound type current transformers both primary and secondary windings are of wound type with a suitable number of turns. 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. There are several core types used, from low-reactance toroid to high-reactance cut . A window current transformer has an open area in the centre for a power line to be passed through as the primary . If there is current flow in the primary of the current transformer and its secondary winding is kept closed, the current flowing through the secondary builds up a back EMF and counters the primary magnetizing force. 3. 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. For this CT to operate satisfactorily at maximum fault currents, it must operate on the linear part of the magnetizing curve, i.e., below the point at which saturation occurs, which is known as the knee point. Thus, accurate and small instruments and monitoring devices can be applied with CTs since they are insulated away from any high-voltage energy lines. Wound type current transformer. 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. Typically, the single straight line considers as primary winding. RITZ is one of the world's leading specialists in the field of Instrument Transformers, cast resin insulated Bus Bar Systems, cast resin insulated Power Transformers as well as cast resin parts according to customer specifications. Tamper-Resistant Outlet: What is it? Their structure can be one single primary turn as in Doughnut, Toroidal, or Bar forms, or a few wound primary turns, commonly for low current applications. In short, it should be never operated at no-load condition when the current is flowing through the primary. By using Grain-oriented cold-rolled silicon steel. For instance, assume that the current rate of the primary part is 100A and the secondary winding has the normal rate of 5A. For low and medium voltage applications, there are three main classifications based on construction; window, bar, and wound. It uses the actual cable or bus bar of the . it opens the core of the instrument transformer. This bar is connected in series with the circuit conductor. and the resistance of secondary winding is 0.5 ohm. The laminated core is designed in such a way where its trigger can be opened by pressing lightly i.e. Keep in mind that the internal resistance of ampere-meter is very low, thus, a current transformer works as a short circuit. 4. The potential transformer is connected in parallel with the circuit. In the shell type construction of the transformer, the magnetic core consists of three vertical lags and two horizontal sections. The working principle of a current transformer is especially different from the power transformer. Windings in this manner ensure optimum flux linkage and distribution. The windings should be close together to reduce the secondary winding leakage reactance as the leakage reactance increases the ratio error. The use of this type should be with discretion since this construction results in higher-than-normal errors. 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). 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. . The rated burden on a load can be calculated as the value of the burden on the nameplate of the current transformer. placed on panel boards can be used (Fig. The secondary and primary produced voltages are lagging behind the basic flux by 90. In bar-type core construction, the primary has no turns wound. 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. Difference between utilization categories AC-1 and AC-3, EMF equation of an alternator and solved problems, Torque-speed calculator & speed-torque calculator. 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. Hence, it acts as a step-up transformer with respect to the voltage. It is also being introduced as the series transformer. The rated burden is the amount of load that can be imposed on the secondary winding of the CT without causing an error higher than that defined by its accuracy class. This accuracy class was retained by IEC in 1966 in the Amendment nr. These CT's include the laminated core and a secondary winding. For this reason, the secondary of a current transformer should always be short-circuited before removing the device connected to its secondary. Cable is passing through the centre of CT and in that way forms the primary winding. It produces a current in its secondary which is proportional to the current in its primary. What is the bar type current transformer? 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. In most case, the secondary current of a current transformer shall be 5A. Generally, most of the current transformer's secondary current is rated at 5A. Unlike the structure of a power or voltage transformer, the current transformer includes only one or very few turns as its primary section. A bar-type current transformer has no primary winding. All Rights Reserved. The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. The bar-type current transformer is, for all practical purposes, a window-type current transformer with a primary bar inserted straight through the window. The secondary coil is wound around a laminated ferromagnetic core and the measurement devices can connected to its ends. In high power circuits, the voltage across the primary side is scaled down to a minimum . Two principal types of transformer construction embody the requirements of economics, ease of manufacture, insulation, mechanical strength, and ventilation: core-type and shell-type. In other words, the secondary of the current transformer should be never left open under any circumstances. Required fields are marked *. The wound-type current transformer is a special type of CT that has a primary winding that is fully insulated from the secondary winding. 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. Your email address will not be published. In high line voltage systems oil-immersed current transformers are used. 2.7.4 Current transformer construction. They are directly connected to the current-carrying conductor. The specification of a PX accuracy CT is: Common accuracies and burden powers, as well as error limits, according to IEC Standard 61869 are indicated in Table 1. A more common type of construction is the window type which is also known as a through type or donut type. 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 . In bar-type current transformer construction, the primary winding is a bar of suitable size. The secondary winding is wound on this core. A window type CT is rated at 600 volts and has the incoming or outgoing insulated/shielded cables pulled through it. Bar type current transformer. . The potential transformer is mainly classified into . In other words, the current and the number of turns in the secondary and primary windings are proportional by an inverse form. It is best suited for general-purpose monitoring and temporary installations. 1 to former Standard 60044 to include the accuracy class X, defined on the withdrawn BS 3938:1973. Bar type current transformers consist of a single bar as a primary winding. The proper combination of core type and coil arrangement can greatly reduce the total reactance, thus reducing errors. They are also known as CTs. The primary of a CT is connected in series to the current-carrying conductor and measurement devices are connected to its secondary. When large currents pass through the primary winding, it induces small currents in the secondary winding (depending upon the turns ratio). The construction has a simple construction. Accuracy class describes how accurate the current transformation of a current transformer would be within when the burden within the allowable limits. Current transformers decrease the high-voltage values to a much lower current and supply a convenient method of safely measuring the actual electrical current moving in an AC transmission line applying a standard ammeter. The design features are described below: . 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. 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. An alternating current is passed to the primary of the transformer and the measurement/sensing/protection device is connected to its secondary. The core can be of solid or split type construction. . The ammeter is arranged to give a full deflection with either 5A or 1A depending on the turns ratio of the CT. Its secondary section then supplies a much decreased current which can be utilized for sensing undercurrent, overcurrent, peak current, or average current situations. 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. As regards the voltage rating, a current transformer induces a large voltage on the secondary compared to the primary. Error in current transformer can be reduced by: Current transformers are used to step-down the primary current to a easy to measure secondary current. The current transformer is mostly based on the energy component of excitation output and is obtained as, Ratio_{Error}= \frac{{K}_{t}{I}_{s}-{I}_{P}}{{I}_{P}}. The TTR transformers with bar primary conductor are constructed to be used as a bushing. Accuracy classes for metering CTs: Metering devices such as ammeters, wattmeters, energy meters, kVar and kVarh meters requires high accuracy and has a low burden. 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. Visit here to explore more about the construction of a current transformer. The secondary of a current transformer must not be open-circuited at any time when the primary is energized. Why are current transformers (CT) necessary? 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. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Linquipis a Professional Network for Equipment manufacturers, industrial customers, and service providers, Copyright 2022 Linquip Company. "Ring type" (doughnut) CT (Figure 7) "Ring type" CT is constructed of an iron toroid, which forms the core of the transformer, and is wound with secondary turns. StudyElectrical.Com | Online Electrical Engineering Learning Site Now, the whole primary current acts as a magnetizing current and induces large voltages in the secondary. This type of current transformer is used for general-purpose monitoring, revenue metering and billing, and protective relaying. 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). A CT consists of one or a very few primary turns and can have several hundreds of secondary turns. Essentially, C relaying accuracy class applies to a current transformer of the toroidal, bushing or window type, commonly called donut-type transformers. 4 Types of Current Transformer Explained With Details. 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. 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.
