In such type of transformers, we get high output voltage as compared to the applied voltage, hence the name stepup. Current transformers cts can be used for monitoring current or for transforming primary current into reduced secondary current used for meters, relays, control equipment and other instruments. Feedthrough transformers are predominantly used for mounting on bus bars. The types of transformers differ in the manner in which the primary and secondary coils are provided around the laminated steel core. A current transformer, abbreviated ct, is a type of transformer used to measure the current of a given circuit.
Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering. A transformer transfers electrical energy from one electrical circuit to another without changing its frequency. The primary of the current transformers is directly connected in series with the line conductor that carries the entire current to be measured. Using a reactance to represent the magnetizing leg of a ct, as shown in figure 1, is a useful visual concept. On the basis of the value of k, types of transformers are as follows. Since, there is no rotating or moving part, so a transformer is a static device. Current transformer white paper the basics of current transformers ratio the ct ratio is the ratio of primary current input to secondary current output at full load. Transformers can be categorized in different ways, depending upon their purpose, use, construction etc. Transformer basicsworking principle,construction,types. The minimum primary inductance required l p is a function of how accurate and linear the volts per ampere versus current transfer function of the transformer needs to be. Calculation of cts if the current transformer has primary to secondary current ratio of 100.
In coretype transformer, the windings are given to a considerable part of the core. As an example, a typical 100 to 5a current transformer has a nominal ratio of single primary turn to 20 secondary turns or 1. You will also get clear idea about importance of burden in current transformer factors which affect the errors and what is difference between wound type current transformer, window or. The various types of transformer shown in the figure above are explained in detail below. Cts provide isolation from the high voltage primary, permit. Make sure the total burden does not exceed the specified limits for the ct. Transformers explaining the basics of transformers. Polarity refers to the instantaneous direction of the primary current with respect to the secondary current and is determined by the way the transformer leads are brought out of the case. Some different types of transformers are power transformers, potential transformers, audio transformers and output transformers. Jun 02, 2015 as an example, a typical 100 to 5a current transformer has a nominal ratio of single primary turn to 20 secondary turns or 1.
A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Therefore, transformation ratio k v 2 v 1 and k e 2 e 1 n 2 n 1 i 1 i 2 also. Current transformers cts are instrument transformers that are used to supply a reduced value of current to me ters, protective relays, and other instruments. May, 2017 you will also get clear idea about importance of burden in current transformer factors which affect the errors and what is difference between wound type current transformer, window or toroidal. These transformers are used for the measurement and instrumentation purposes. Here we discuss different types of transformers are the step up and step down transformer, distribution transformer, potential transformer, power transformer, 1. 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. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load. Transformer only stepup or stepdown the level of ac voltage or ac current.
A current clamp uses a current transformer with a split core that can be easily wrapped around a conductor in a circuit. The basics of current transformers nk technologies. Transformer types instrument transformers instrument transformers comprise a large category of current and potential transformers for various voltage, frequency and physical size ranges. The transformer is an electronics device which passas the elecricity one place or ckt into another one. If the primary current of the current transformer becomes a the secondary current will still be 1. Current transformer basics and the current transformer. When secondary current vector lags the primary current vector. High and even medium voltage are quite dangerous levels for instrumentation, controls, and measurements. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the same.
In a current transformer, the loads impedance or burden on the. Note that sometimes these classifications overlap e. Types of transformer different types of transformer. Current transformers are instrument transformers intended to have its primary winding connected in series with the conductor carrying the current to be measured or controlled. A transformer is an electrical device which, by the principles of electromagnetic induction, transfers electrical energy from one electric circuit to another, without changing the frequency. The byz zerosequence indoor current transformer is used for ground fault detection and is primarily designed for zerosequence overcurrent relaying schemes. Here the important thing to remember is that there will not be any difference in primary power and secondary power. We have broken them up into several different groupings. Different types of transformers and their applications.
Current transformers, along with voltage or potential transformers, are instrument transformers. Equivalent current transformer circuit x 1 primary leakage reactance r 1 primary winding resistance x 2 secondary leakage reactance z 0 magnetizing impedance r 2 secondary winding resistance z b secondary load note. The primary winding can consist merely of the primary current conductor passing once through an aperture in the current transformer core window or bartype, or it may consist of two or more turns wound on the core together with the secondary winding wound type. Instrument transformers scale the large values of voltage or current to small. Apr 16, 2011 current transformers principle of operation of ct. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to. A highvoltage current transformer may contain several cores, each with a secondary winding, for different purposes such as metering circuits, control, or protection. Here we will cover different types of transformers used. This is a common method used in portable current measuring instruments but permanent installations use more economical types of current transformer. Read through the different types we supply below and use our. Metering toroidal current transformers traditional, window type current transformers for measuring 50400hz currents of 5a to 15000a with secondaries of 0. Transformer operates when both circuits take effect of mutual induction. Sat 0 0 10 20 30 40 50 60 70 80 m s 38 ct types s 39 current transformer function two basic groups of c. A transformer works on the principle of mutual induction.
Celsa current transformers fulfil the specifications of the accuracy classes. A current transformer can be modeled as a constant current source where ratio current is injected into a magnetizing impedance in parallel with the burdens shown in figure 1. A current transformer ct is a type of transformer that is used to reduce or multiply an. The transformation ratio of the transformer may be defined as the ratio of the secondary voltage to the primary voltage of the transformer. The ct ratio is the ratio of primary current input to secondary current output at full load. Electrical power transformer definition and types of. Voltage transformers is also called as potential transformers this is a parallel connected type of instrument transformer. Apr 18, 2020 suppose, you have one current transformer with current ratio 4001 a and its protection core is situated at 500 a. Like the power transformer, the current transformer also contains a primary and a secondary winding. If necessary, the choice of the cable section, the ct or meter should be modified to fit the requirement. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac. The current transformer is designed to connect in series with the line to transform the line current to the standard 5 amperes suitable for the.
Coupled with an ammeter, cts are used to protect the main lines of the power grid, by measuring highvoltage electrical current and preventing damage to sensitive equipment. A current transformer is a device which produces an alternating current in its secondary which is proportional to the alternating current in its primary. According to the design, transformers can be classified into two. Transformers either decrease or increase ac voltage. The energy transfer usually takes place with a change of voltage and current. Except for relatively lowaccuracy industrial types, current transformers are. Current transformer design guide an effective design of a ring type c. Current transformers ratio polarity types educypedia.
A transformer is a static machine used for transforming power from one circuit to another without changing frequency. These are widely used transformer types for all the applications. A phase imbalance produces a secondary current in the byz. The classification of protection current transformers follows the following. Current transformers have a primary winding to which the current to be measured is fed.
Current transformer is used for the measurement of electric current flowing through a circuit. We have covered about transformers construction and operation in detail in previous tutorial. Relaying cts have several different letter designations. These are the most commonly used transformer types for all the applications.
They are designed to present negligible load to the supply being measured and have an accurate voltage ratio and phase relat. Current transformers perform the following functions. If a ct test switch is used, the switch must have a makebeforebreak contact pattern to. Nov 15, 2019 the basic principle of the current transformer is the same as that of the power transformer. Current transformer construction types janitza electronics. The phase to be measured conductor rail or line is fed through the ct window and forms the primary circuit for the current transformer. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an ac. Transformer cant stepup or stepdown the level of dc voltage or dc current. Cts current transformers pts potential transformers. It is an electromagnetic device which follows the basic principle of electromagnetism discovered by michael faraday. Construction features the ringtype core is fully insulated and toroidally wound. However, the concept of knee point voltage is very pertinent to protection current transformers, since they are necessarily exposed to currents of 20 or.
Bartype cts have primary connections that boltup directly to the substation bus bars. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the. A current transformer is an instrument transformer, used along with measuring or protective devices, in which the secondary current is proportional to the primary current under normal conditions of operation and differs from it by an angle that is approximately zero. Where v 1, e 1, n 1 are the supply voltage, induced emf, winding turns of the primary winding respectively. A current transformer is defined as as an instrument transformer in which the secondary current is substantially proportional to the primary current under normal conditions of operation and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections. Chapter 16 current transformer design university of north. This fact ascertains that the current will not increase to an abrupt value. Current transformers schneider electric documentsdownloads. It produces a current in its secondary which is proportional to the current in its primary. The kneepoint 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. From the above equation, by knowing secondary ammeter current and current ratios, we can easily determine the current flowing through the primary which is connected to the main line.
A transformer is a widely used device in the electrical and electronics domain. This type of transformer is categorized on the basis of a number of turns in the primary and secondary windings and the induced emf. Hightest proportion for different ratios of main c. The current transformer function is different than that of a voltage transformer. There are four typical types of current transformers. The fundamentals of current sense transformer design patrick a. If the primary current changes the secondary current output will change accordingly. So that amount of current will flow across the inductor which can induce the same amount of the applied voltage. The working principle of the current transformer is slightly different from the power transformer. Whenever an alternating current flows through the primary winding, alternating magnetic flux is produced, which then induces alternating current in the. A neutral current transformer is used as earth fault protection to measure any fault current flowing through the neutral line from the wye neutral point of a transformer. Current and voltage transformers may be freestanding devices, or they may be built inside the bushing of some power apparatus such as a circuit breaker or a power transformer with a grounded tank. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle.
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