High accuracy extended range current transformers can increase utility revenue through improved metering. Tropicalized for cable or bar current transformer t1. Figure 2 depicts the most basic magnetic circuit of an ideal instrument transformer. A general overview of abbs current and voltage transformers. Ct2 have an internal termination resistor that reduces re. Current transformers technical datasheet schneider electric is the global specialist in energy management with the most complete power monitoring product line. Mhctcatalog2015v1 current transformer device features metering ct monitoring of kwh w a class 0. First, the calculation of the actual burden of the ct, including connection wires and protection relay impedance, is presented. A current transformer is a device that is used for the transformation of current from a higher value into a proportionate current to a lower value. A ct is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. 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.
Polarity must be observed, if a primary ct is wired with the wrong polarity to summation ct its current will be subtracted from the total. A 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. As a current passes through the primary winding it induces a magnetic flux in the steel core. Current transformer ct construction and working principle. The maximum input current of the ct should be lower than 2 a.
Pdf current transformer ct is one of the important element of power system protection. 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 current transformer ct basically has a primary coil of one or more turns of heavy crosssectional area. Energy harvesting from current transformer reference design. The power input is from the secondary side of the ct. It buffers the meter from experiencing excessive torques that might be. I am je of nagbhir sub station of 225 kv newly electrified section and testing started of current transformer when test ct ratio by injecting current in primary bushing of old ct which was 20 years old ct installed in circuit,after testing values not found according to ratio,100 amps inject and found in secondary terminal 3.
Iec 600446 requirements for protective current transformers for. Amran instrument transformers is a leading manufacturer of low voltage and medium voltage instrument transformers current and voltage transformers with multiple manufacturing plants in usa and india. Browse products from schneider electric ww in tropicalized for cable or bar for current transformer t1 current transformers from 40a to 6000a. Please note that the manufacture of the ct shorting terminal blocks was changed in 2014 to cooper bussman. Ct s provide isolation from the high voltage primary, permit.
Since this method requires ideal conditions, it is generally better to use a summing transformer. Ct s to be oversized so the total secondary current does not exceed the 5 amp rating, which reduces accuracy. The accuracy class of a current transformer depends on the transformers apparent power va and the consumption of the. The current transformer is used for measuring the high voltage current because of the difficulty of inadequate insulation in the meter itself.
Correct operation of current current, voltagevoltage, or current voltage devices usually depends on the relative instantaneous directions. While the latter configuration would not be used today, one may be required to make this calculation on an existing system. The current transformer is used in meters for measuring the current up to 100 amperes. Of course additional requirements like type, frequency, isolation level, maximal short circuit current and environmental conditions should also be specified.
This occurs on systems with variable currents such as wind or solar power generation. Current transformer ct installation instructions hobut. What is the working principle of a current transformer. Current transformer ct power transformer electromagnetic induction. 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. Tape wound measuring and protection current transformers. Bartype current transformer this type of current transformer uses the actual cable or busbar of the main circuit as the primary winding, which is equivalent to a single turn. The classification of protection current transformers. Current transformer design guide an effective design of a ring type c. H i g h p o w e r e d r e s e a r c h f o r t h e r e a l w o r l d december 2011 issue 1 modeling current transformer ct saturation for detailed protection studies 6 the wound rotor wr and squirrel.
A typical egauge installation will measure the amperage of multiple conductors via multiple ct sensors. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load. One of the major difference between them is that the current transformer convert the high value of current into low value whereas the potential or voltage transformer convert the high value of voltages into low voltage. This characteristics are current transformer burden, knee point voltage, saturation of current transformer. It is able to do this because it has a current transformer built into it.
But the fact should be clear that the current of primary circuit is the load of a current transformer. Nov 15, 2019 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 which is approximately zero. The construction of the current transformer can be wound or bar type. Introduction of the ct pro xt and ct max series renews the range of current transformers for secondary and primary subdistribution switchboards and for power. Sorting through this vast array of information to piece together a complete understanding of the topic is a time. This protects connected metering devices from overloading in the presence of fault level current flows. Secondary terminal voltage which the ct must maintain within the c rating. Apr 09, 2020 selecting a current transformer ct if the current ratio, burden and class are selected, the current transformer ct has been specified basically.
Current transformers instrumentation and metering transformers dimensional drawing 2rl 56rl 76rl donut style 2sft 56sft 76sft foot mounted with brass terminals. It transforms the high voltage current into the low voltage current due to which the heavy current flows through the transmission lines is safely monitored by the ammeter. Our factory in malaysia produces wide range of current transformer for electrical power measurement and protection relay. Current transformer shorting terminal blocks catalog no 3090tb4 4 pole 3090tb6 6 pole. Accuracy decreases with increased burden load or low line. Instrument transformers scale the large values of voltage or current to small. If the load current, i0, on the current transformer is removed from the secondary winding, while the external load current, ijn, is still applied, the flux in the core will rise to a high level, because there is not an opposing current in the secondary winding. Ct current transformers 5 ct pro xt, ct max installation sequences. Bct which are installed on 600 volt, and higher electrical systems. Current and voltage transformer symbols and simplified concepts 5 i 1 i 2 v 1 v 2 symbol of a current transformer symbol of a voltage transformer conceptual picture of a current transformer. This allows them to be used in combination with measurement equipment. In the past, current transformers were designed to accurately measure down to 10% of the current rating on the name plate of the transformer. Sorting through this vast array of information to piece together a complete understanding of the topic is a time consuming task and may not be realistic with. 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.
They are specified by current ratio, window size, and ct class. The core of the current transformer is built up with lamination of silicon steel. Allentown, pa abstract more and more substations are retrofitted with numerical relays, meters and monitoring devices. Current transformers ct are used in high voltage hv and medium voltage mv 1 installations to give an image of electrical current to protection relays and units and metering equipment and they are designed to provide a current in its secondary proportional to the current flowing in its primary. Ct burden, knee point voltage, core saturation details of. Current transformer ct saturation is not a new topic, and there have been many papers, books, application guides, and tutorials written on the subject. It produces a current in its secondary which is proportional to the current in its primary. These curves illustrate how high the secondary voltage will in rise in order to force the rated secondary current. This is a plot of the ct secondary current against secondary voltage.
The current transformer function is different than that of a voltage transformer. 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. Energy harvesting from current transformer with supercapacitor for fault indicator reference design 2 system overview 2. Current transformer ct class ratio error phase angle error. Current transformers a discussion on theory, specifications and operational aspects. Msq current transformer technical characteristics of current transformers.
Apr 25, 2017 the current transformer the current transformer c. The ct ratio is the ratio of primary current input to secondary current output at full. Current transformers ratio polarity types educypedia. Calculation of the current transformer 1mrs 755481 accuracy limit factor 1. This is connected in series with the line carrying high current. The externalload applied to the secondary of a current transformer is called the oburden. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work, use of current transformer. It is the main source of information and measuring. Current transformers,voltage transformers and instrument. The primary winding consists of more than one full turn or multiple turns which is wounded on the core. Current transformers ct s are instrument transformers that are used to supply a reduced value of current to meters, protective relays, and other instruments.
Drawing current transformer shorting terminal blocks. In some, the bar carrying high current may act as a primary. Current transformers cts are instrument transformers that are used to supply a. Current transformer mounting bases platt electric supply. Ct 2 have an internal termination resistor that reduces re. Calculation of the current transformer accuracy limit factor. The family of curves below describe the excitation characteristics for the 6005 multi ratio bushing current transformer shown on the previous sheet. Low voltage current transformers are manufactured as of two tyees for measuring ct and protection ct. Modeling current transformer ct saturation for detailed. There are four typical types of current transformers. Most often, the older relay gets replaced with a newer relay with the rest of the installation such as current transformer ct and lead.
When current flow exceeds that rating, the metering core will become saturated, thereby limiting the amount of current level within the device. Current transformer basics and the current transformer. Vv the ip5 a ratio current transformer delivers at the secondary a current is of 0 to 5 a that is proportional to the current measured at the primary ip. 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.
Current transformers are essential components designed to be used with schneider electrics extensive power monitoring product portfolio. Shop for current transformer mounting bases from platt electric supply. Bushing current transformersbushing current transformers. As the current transformer has two windings, in some cases it is confusing about the load of it.
Scope this document describes the calculation of the actual accuracy limit factor f a for protectiontype p current transformers ct. The ip5 a ratio current transformer delivers at the secondary a current is of 0 to 5 a that is proportional to the current. Ct accuracy a ct is most accurate at rated current with a low burden load. The basics of current transformers nk technologies. If the screw secondary terminals of the current transformer are used, the connections must be made using cables with forked cable terminals or stripped cables, in accordance with the instructions directly indicated on the product. Currenttransformer burden all ct accuracy considerations require knowledge of the ct burden. They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device. The ct sensors are installed around the current carrying conductors of the load or generation source you wish to monitor.
Instrument transformer basic technical information and. O the burden is expressed pr eferably in ter ms of the impedance of the load and its r esistance and r eactance components. Current transformers have a primary winding to which the current to be measured. Definitions ideal and practical ct magnetic alloys for cores equivalent circuits open circuits voltages in cts leakage reactance modification of current transformer errors operational aspects standard specifications for ct s. Definitions current transformers are available from ge multilin for use as phase current inputs with motor protection relays. For pricing and availability of a specific ct model, give us a call at 614 8896152 or use the quote request form. One of its functions is as an ammeter to measure current flow amps.
Current transformers munhean industrial electrical. Infrequent fault exposure is where there are fewer transformer throughfaults in the transformers lifetime than the defined number and magnitude given above for the same. Current transformers, along with voltage or potential transformers, are instrument transformers. Wound type ct is similar to the two winding conventional transformer.
Picking the type of ct involves selecting the mechanical dimension and the current rating in amps. Posted on 9th november 2017 29th march 2019 admin posted in installation instructions. Bushingtype current transformers bct instrument transformers, inc. 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.
Current transformers instrumentation and metering transformers dimensional drawing. Feb 12, 2017 in this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work, use of current transformer. A test set operator connects the leads, pushes the buttons, and records the. Some other differences between the current and the potential transformer are explained below in the the comparison chart. Transformers are widely used to convert between high and low voltages current into a manageable value and also isolation between circuits. Ct selection guide 1 introduction this guide is intended to help you select the right quantity and type of current transformers cts needed for.
445 194 170 681 607 485 549 777 449 135 358 699 73 626 1071 1359 1546 1523 130 313 150 837 144 1258 1013 161 250 1264 25 141 1369 785 723 367 627 877 583