The voltage transformer can be thought of as an electrical component rather than an electronic component. The basics of current transformers nk technologies. The property of induction was discovered in the 1830s by joseph henry and michael faraday. If a ct test switch is used, the switch must have a makebeforebreak contact pattern to. This voltage should be the same as was measured at the transformer secondary. The current leakage path to earth ground has been eliminated with the use of the isolation transformer. If the circuit of this secondary winding is closed, then a current will flow through it. Shunt resistors are fantastic at low currents, but dont offer isolation and get large expensive hot when higher currents are involved. 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. The basic principle of the current transformer is the same as that of the power transformer. 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 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. 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.
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. This is primarily used when a current or voltage is too high to measure directly. Instrument transformers scale the large values of voltage or current to small. According to faradays law of electromagnetic induction, there will be an emf induced in the second winding. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the same. A transformer uses the principles of electromagnetism to change one a. 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. For example, the potential transformer mentioned above having a rating of 480. Pdf current transformer ct is one of the important element of power system protection. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac. Figure 1 shows a circuit that incorporates an isolation transformer which is the preferred method.
In other words, you have to use a type of constantly reversing electricity called alternating current ac with a transformer. 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. 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. N 5 freeelectricity current transformer you can make 201120 refer to the photo below. Potential transformer pt definition the potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value.
Figure 4 works well for most instrument transformers. What is the working principle of a current transformer. The secondary is connected to something with a low impedance, often an ammeter. Electrical tutorial about current transformer basics and current transformer theory on how the current transformer works with just one secondary winding. The ratio of an instrument transformer is the relationship of its primary rating to its secondary rating. Like the power transformer, the current transformer also contains a primary and a secondary winding. Type c solid core current transformer cable profile. Normally the leakage fluxes x 1 and x 2 can be neglected. Current transformers are very useful but dont work at dc. Basics, maintenance, and diagnostics vii contents continued page 4. The current in the secondary is much smaller, and almost proportional to, the current in the primary. Current transformers, along with voltage or potential transformers, are instrument transformers.
Current transformer basics and the current transformer. It is either used to provide isolation between two circuits or to step up or step down the voltage and current. Let us use electrical symbols to help visualize this. 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. If i turn this heater on and pass one leg of its cord. The induced secondary current is then suitable for measuring instruments or processing in electronic equipment, which typically needs. Measure the ac voltage supplied to the rectifier stack f. A current transformer ct is a type of transformer that is used to reduce or multiply an. The specific performance characteristics of instrument transformers are easily determined from the equivalent circuit. Current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors.
Thus it is a good way of measuring a large current in the primary. A current transformer is an instrument transformer, used along with. Check the transformer secondary with your ac voltmeter d. For current transformers, the value of the reactance x is determined in a special way so that it represents the leakage flux. Three phase transformer winding configurations and. This is the basic working principle of a transformer. Faradays work in the 19th century showed that a changing current in a conductor e. The magnetic field around the winding is constantly in motion. 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. Transformers are used to transfer electric power from one end to another through the medium of magnetic field. 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.
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 transformer has no moving parts and is a completely. High voltage products pa 123pa 145 current transformer. 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. It can be designed to step up or step down voltages and works on the magnetic induction principle. 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. 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.
Use of an isolation transformer while performing leakage. 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. Because toroidal fields are compact, a toroidal transformer produces less magnetic interference than. Special transformers and applications transformers. How does a transformer work working principle electrical. The voltage is either stepped up or stepped down with out altering the frequency. Transformer basicsworking principle,construction,types. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering. 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. The winding which receives electrical power from the source is known as. Current transformer steps high current down to a value applicable to a conventional ammeter. Transformers do not work with direct current dc, where a steady current constantly flows.
We know that the power can be calculated by simply multiplying the voltage and current. It produces a current in its secondary which is proportional to the current in its primary. Instrument transformer basic technical information and. Therefore the current transformer operates under short circuit conditions. The balance point between coil weight and magnetic force may be adjusted to provide the desired output current.
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