Assuming an ideal transformer and the phase angles. Back to the basics current testing valence electrical. Current transformers,voltage transformers and instrument. Industry standards have established 120 volts as the secondary rating of potential transformers having primary ratings up to 24,000 volts and 115 volts as the secondary rating of pt s having ratings above 24,000 volts. Pdf improved models for current transformers ct, potential transformers, and capacitive voltage transformers cvt for a relay software. In this lecture we will solve some tutorial problems on ct and analyse. Power transformers on other hand are used to transfer power from primary side to. Pdf improved simulation models for current and voltage. Potential transformers pt s pt s step down high voltages to the voltage needed by the meter usually 120v occasionally 67v. What is the abbreviation for current transformers, potential transformers.
Potential transformer testing ptvt i cowrote an article for the neta world magazine in 20042005 that covers several different manual techniques for potential transformer testing that explains several lowtech solutions for potential transformer testing. Offered assortment is highly acclaimed for its low maintenance, optimum performance and durability. Such specially constructed transformers with accurate turns ratio are called as instrument transformers. This is a simplest form of potential transformer definition. When electricity moves from a power plant it is put into a very high voltage to be able to travel long distances. Ctpt abbreviation stands for current transformers, potential transformers. Back to the basics current transformer ct testing as test equipment becomes more sophisticated with better features and accuracy, we risk turning our field personnel into test set operators instead of skilled field service technicians.
Some people refer to the meters that use a ct pt combination or just ct s as a current transformer meter. Current transformer simple english wikipedia, the free. Eee ct metering accuracy standard ieee ct burdens 5 amp per ieee std. S note that the order of the numbers when expressing a transformers turns ratio value is very important as the turns ratio 3. Instrument transformers scale the large values of voltage or current to small. The original magnitude can be determined by just multiplying the result with the transformation ratio. 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. Hence, it is imperative that the choice of ct is made with full knowledge of the application and the number of relays and meters which are to be connected to it.
Current transformerct, voltage transformervtalso called potential transformer are used for metering purposes specially in grids. Potential transformer testing ptvt valence electrical. Current transformers occupy a vital part in the measurement and protection scheme of any electric installation. Normally the leakage fluxes x 1 and x 2 can be neglected. While a potential transformerpt used to reduce the voltage to lower values and to provide isolation. Instrument transformer basic technical information and. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. Potential transformers used with 150 volt full scale a.
Difference between ct and pt, current transformer and potential transformer april 27, 2017 may 27, 2018 admin 0 comments. 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. Current transformers ct are a series connected type of instrument transformer. Electrical tutorial about current transformer basics and current transformer theory. This makes them the perfect choice for power supply design or for use in transformer, rectifier and filter circuits. Explain and interpret information found on transformer name plates. Unlike oil transformers, it is not protected from corrosion and other extreme weather elements that can slowly degrade its inner components, especially those made of metal. Pt potential transformer used for voltage measurement, connected in parallel, step down transformer ct current traansformer used for current measurement, connected in series, step up transformer high vol. Calculation of cts if the current transformer has primary to secondary current ratio of 100.
A current transformer ct is a transformer used to measure alternating current. Current transformers cts are instrument transformers that are used to supply a reduced value of current to meters, protective relays, and other instruments. If the current measurement is carried out via two current transformers, the overall transformer ratio of the current transformers must be programmed into the measuring device. After studying this section, you should be able to describe. A test set operator connects the leads, pushes the buttons, and records the. Whereas in the past, due to the high burden of electromechanical relays, it was the rated power of the current transformers ct and potential transformers pt. Instrument transformers are used for measurement and protective application, together with equipment such as meters and relays. There are a variety of ways to ground a generator neutral. Installation of current transformers janitza electronics. To start with, both are instrument transformers basically used for measurement and protection purpose in power systems. Current transformer ct i to measuring instrument a view of a current transformer s construction shows the wrapping of the secondary turns around the toroidal magnetic core in such a way that the secondary conductor remains parallel to the primary power conductor for good magnetic coupling. Difference between ct and pt, current transformer and. A general overview of abbs current and voltage transformers.
In the neutral grounding cubicle the grounding equipment and protective relays are located. Hospitals, physicians, and other providers billing for computed tomography ct scans and services. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac. Kuphaldt under the terms and conditions of the creative commons attribution 4.
Incepted in the year 2009 at ghaziabad up, india, we electro mech industries are a renowned firm engrossed in manufacturing high quality array of ctpt unit, current transformer, instrument transformer, ltct panel, material cubicle and voltage transformer. Current and voltages are very high in the substation, cts and pts step down the current and voltage respectively, to a level on which it can be measured. Current transformers are often constructed by passing a single primary turn either. It can be used in a classroom learning situation, as a selfstudy textbook, or as a reference book on advanced transformer wiring connections and applications. Many people want to know what is a current transformer and potential transformer. What is the difference between ct,vt,and power transformer. Modular electronics learning model project v1 1 0 dc 12 v2 2 1 dc 15 r1 2 3 4700 r2 3 0 7100. But in this post you will learn about how to install the current transformers for three phase. Current transformers, along with voltage or potential transformers, are instrument transformers. Voltage transformer or potential transformer theory. Selecting ansi class metering current transformers 142 h b0. They come in various power ratings expressed in va.
Potential transformer or voltage transformer gets used in electrical power system for stepping down the system voltage to a safe value which can be fed to low ratings meters and relays. As you know that always we need ct coil and ampere meter in main panel board for measuring amperes load and one thing more that in this post i will show you the image of three current transformer installation in main power panel board. A current transformer also has very few, or even a single turn on primary and many on secondary. Transformers transformers on the electrical grid lets look at the electricity that comes to your home. Current transformer and potential transformer hindi. Cts, or current transformers, and pts, or potential transformers are used in metering to step down current and voltage to safer and more manageable levels. Current transformer installation for three phase power. They come in many shapes and sizes for different applications they work exactly as you would expect them to. The transformation ratio of the current transformer is always remained high, whereas for the potential transformer its remains low. Basics, maintenance, and diagnostics vii contents continued page 4. When cts and pts are used in a metering installation, the installation is known as being transformer rated.
Per medicares national coverage determination ncd, ncd 220. Cts provide isolation from the high voltage primary, permit grounding of the secondary for safety, and step down the magnitude of the measured current to a value that can be. In part 1a of the series, we shall explain the important parameters of a current transformer, when it comes to its equivalent circuit model, and we go through this in much greater detail. Identify transformer polarity using dot and conventional labeling. The equivalent circuit model and its important parameters were briefly discussed in the previous video series called the brief introduction to current. It produces a current in its secondary which is proportional to the current in its primary. Ct is used to measure current in a circuit when the current magnitude is too high to be measured safely. Transformer rated services run in parallel with the service. Current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. Low voltage pt used to measure the voltage of 120 vac systems with 5 volt full scale a. As a layman view, sld is nothing but consisting of various components of the electrical system like, transformer, dg. Ring core cts are available for measuring currents from 50 to 5000 amps, with windows power conductor opening size from 1 to 8. Therefore, it is necessary to step down the voltage and also to insulate the protective equipment from the primary circuit.
Ideal ct p1 i m s1 n 1 2 u z m 2 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. An instrumentcurrent transformer ct requires good accuracy around the nominal current value. The normal range of the current transformer for measuring the current is 5a or 1a whereas the standard voltage at the secondary winding of the potential transformer is up to 110v. As with other dry transformers, a core type transformer is not good for outdoor use. Piezoelectric transformers pt or solid state transformers sst are made from hard piezoelectric ceramics and can be made very small and light, while being at a comparable cost to conventional transformers, when manufactured in large quantities. Their role in electrical systems is of primary importance as they are a means of stepping down the current or voltage of a system to measurable values, such as 5a or 1a in the case of a current transformers or 110v or 100v in the case of a voltage transformer. These instruments transformers are of two types i current transformers ct and ii potential transformers pt. They are designed to present negligible load to the supply being measured and have an accurate current ratio and phase relationship to enable accurate secondary connected metering. Commercially available relays and meters used for protection and metering, are designed for low voltage. Both current transformers have a transformer ratio of 1,0005a. Transformer principles and applications atp learning. It is very versatile and comprehensive because it can depict very simple dc circuits, or a very complicated threephase system.
97 784 1169 420 85 1023 845 848 1061 57 1392 879 245 339 791 203 1015 1181 427 576 1547 289 997 1618 1179 470 1228 424 1566 1472 1344 727 638 1105 642 163 697 1462 374 633 1306