What is the working principle of a current transformer. Current transformer steps high current down to a value applicable to a conventional ammeter. The current leakage path to earth ground has been eliminated with the use of the isolation transformer. The voltage is either stepped up or stepped down with out altering the frequency. Normally the leakage fluxes x 1 and x 2 can be neglected. As an example, a typical 100 to 5a current transformer has a nominal ratio of single primary turn to 20 secondary turns or 1. This is the basic working principle of a transformer. If i turn this heater on and pass one leg of its cord. Whenever an alternating current flows through the primary winding, alternating magnetic flux is produced, which then induces alternating current in the. Transformers do not work with direct current dc, where a steady current constantly flows. Figure 4 works well for most instrument transformers. High voltage products pa 123pa 145 current transformer. Current transformer basics and the current transformer. The voltage transformer can be thought of as an electrical component rather than an electronic component.
Thus it is a good way of measuring a large current in the primary. Let v p be the voltage at the primary, i p be the current at the primary and p p be the power at the primary side of the transformer. Pdf current transformer ct is one of the important element of power system protection. In this video well be looking at how a transformer works covering the basics with transformer working animations and explanations to understanding the working principle. A current transformer ct is a type of transformer that is used to reduce or multiply an. 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. Like the power transformer, the current transformer also contains a primary and a secondary winding. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the same. The secondary is connected to something with a low impedance, often an ammeter. Type c solid core current transformer cable profile. It is either used to provide isolation between two circuits or to step up or step down the voltage and current. Instrument transformer basic technical information and. A current transformer is an instrument transformer, used along with.
A transformer has no moving parts and is a completely. The current in the secondary is much smaller, and almost proportional to, the current in the primary. The specific performance characteristics of instrument transformers are easily determined from the equivalent circuit. A transformer uses the principles of electromagnetism to change one a. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering. We know that the power can be calculated by simply multiplying the voltage and current. Current transformers are very useful but dont work at dc. This voltage should be the same as was measured at the transformer secondary. Instrument transformers scale the large values of voltage or current to small. Measure the ac voltage supplied to the rectifier stack f. A current transformer is a device used to produce an alternating current in its secondary, which is proportional to the ac current in its primary.
Use of an isolation transformer while performing leakage. A transformer is an electrical device used to convert the voltage of one magnitude to voltage of another magnitude without changing the frequency. Figure 144 shows the magnetic field during one cycle. For example, many cell phones, laptops, video games, and power tools and small appliances have a transformer built into their plugin unit like that in figure 1 that changes 120 v or 240 v ac. If the circuit of this secondary winding is closed, then a current will flow through it. A toroidal transformer is donutshaped, with primary and secondary coils that are wound around a ferromagnetic core and often layered on top of one another. A transformer basically is very simple static or stationary electromagnetic passive electrical device that works on the principle of faradays law of induction by converting electrical energy from one value to another. The basic principle of the current transformer is the same as that of the power transformer. For example, the potential transformer mentioned above having a rating of 480. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work, use of current transformer. This is primarily used when a current or voltage is too high to measure directly.
Once the transformer fabricated you can use either way as your application transformer named step up or step down bat carful apply the correct voltage to as you desired winding say if you want input 12 volt and get out put 230 apply 12 volt twelve volt winding vice visa the transformer works. 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. Because toroidal fields are compact, a toroidal transformer produces less magnetic interference than. The constantcurrent transformer, usually called a regulator, has a movable secondary winding that automatically changes position to provide constant current for any load within its fullload rating. 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 balance point between coil weight and magnetic force may be adjusted to provide the desired output current. Current transformers, along with voltage or potential transformers, are instrument transformers. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac. The magnetic field around the winding is constantly in motion. Therefore the current transformer operates under short circuit conditions. In other words, you have to use a type of constantly reversing electricity called alternating current ac with a transformer. The dc current transformer dcct is a type of dccapable current transformer, which produces an output current proportional to the input current all the way down to dc.
It produces a current in its secondary which is proportional to the current in its primary. The induced secondary current is then suitable for measuring instruments or processing in electronic equipment, which typically needs. 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. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. Since the diode onresistance is manufactured more uniformly, using separate forward diodes is a better solution for current sharing. The winding which receives electrical power from the source is known as. The property of induction was discovered in the 1830s by joseph henry and michael faraday.
This may cause an insulation breakdown of the secondary winding and results in burnout. Shunt resistors are fantastic at low currents, but dont offer isolation and get large expensive hot when higher currents are involved. Check the transformer secondary with your ac voltmeter d. Let us use electrical symbols to help visualize this.
The basics of current transformers nk technologies. Figure 1 shows a circuit that incorporates an isolation transformer which is the preferred method. Faradays work in the 19th century showed that a changing current in a conductor e. Transformers do what their name impliesthey transform voltages from one value to another the term voltage is used rather than emf, because transformers have internal resistance. Note that while the pt is a stepdown device, the current transformer or ct is a stepup device with respect to voltage, which is what is needed to step down the power line current. It can be designed to step up or step down voltages and works on the magnetic induction principle. Current and voltage relation in step down transformer. The ratio of an instrument transformer is the relationship of its primary rating to its secondary rating.
Transformers are used to transfer electric power from one end to another through the medium of magnetic field. Transformer basicsworking principle,construction,types. This transformer step down the voltage to a safe limit value which can be easily measured by the ordinary low voltage instrument like a voltmeter, wattmeter and watthour meters, etc. Special transformers and applications transformers. Three phase transformer winding configurations and. Current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. How does a transformer work working principle electrical. If a ct test switch is used, the switch must have a makebeforebreak contact pattern to. Electrical tutorial about current transformer basics and current transformer theory on how the current transformer works with just one secondary winding. According to faradays law of electromagnetic induction, there will be an emf induced in the second winding. 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.
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