Mv indoor current transformer documents and downloads. 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. A potential transformer is a conventional transformer. Cable current transformers pfiffner instrument transformers ltd. Transformer inrush current, including the combined effects of transformer magnetizinginrush current. Instrument transformers potential transformer, current transformers for high voltage. We have broken them up into several different groupings. Medium voltage indoor current transformers are cast in epoxy resin and designed for insulation up to 40,5kv.
It also improves the performance of current transformers and subjects their performance to simple calculation. Some other differences between the current and the potential transformer are explained below in the the comparison chart. Current transformers could be attached to the lower voltage or even high voltage prospects of a power transformer. Available from 25 kv to 800 kv for measurement, protection and control. A potential transformer or voltage transformer is a special kind of transformer used to measure voltages higher than you would want to measure directly. As the secondary burden increases the transformer excitation. This transformer step down the voltage to a safe limit value which can be easily measured by the ordinary low voltage. 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.
For the encapsulated type current transformer, the windings are enclosed in a compact and heat resistant split cap. The errors were fairly small in the whole frequency range. Current transformer ct and potential transformer pt are instrument transformers basically used for measurement and protection purpose in power systems. Instrument transformer basic technical information and. Correct operation of mps and fps relays depends on accurate polarity. Instrument transformer theory and testing steve hudson, pe engineering manager 10737 lexington drive. Instrument transformers are also used with protective relays for protection of power system basic function of instrument transformers is to step down the ac system voltage and current. Commercially available relays and meters used for protection and metering, are designed for low voltage. Difference between current transformer ct and potential. Then to summarise this transformer basics tutorial. Current transformers, inductive voltage transformers, capacitive voltage transformers, combined current voltage transformers and station service voltage transformers are designed to transform high current and high voltage levels down to low current and low voltage. Current transformer vs voltage transformer potential transformer a transformer is a device that transfers electrical energy from one circuit to another using electromagnetic induction through inductively coupled conductors, also called the transformer.
For voltage levels greater than 230 kv, we substitute capacitivecoupled voltage transformers. 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. In the current transformer unit, the iron core is set to highvoltage potential and the secondary windings to earth potenti al. The instrument transformers like voltage transformer and current transformer are used for connecting the electrical instruments to the measuring instruments. Medium voltage instrument transformers ritz instrument. Cts current transformers pts potential transformers 5 potential transformers pts pts step down high voltages to the voltage. The preference is that all large power transformers 1.
Voltage transformers are designed so the through impedance rs,r,xp, and x is as low as possible, while current. This article keys out the main differences between current and potential transformer on the basis of several factors such as function, connection, use, primary and secondary windings, excitation current, core, types, and applications. Difference between current transformer and potential transformer. Morgan lacey in 1925, based on a series of pamphlets entitled transformer. 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. Gfuve electronics manufactures an extensive line of cast epoxy resin insulated current transformers and potential transformers across the voltage range of 5. Supreme immunity to external dc magnets application 0. All merlin gerin instrument transformers are in conformity with iec standards. Ct vs pt difference between current transformer and. Voltage transformers have only one iron core with attached secondary winding s. A current transformer ct is used to obtain reduced current signals for purpose of measurement, control and protection. Finds a wide application in protection circuits of power system ex.
What are a potential transformer and a current transformer. If the voltage is raised to 10 times its original value by the transformer, the current in the secondary coil will be reduced to onetenth the value of the current. A transformer changes the voltage level or current level on its input winding to another value on its output winding using a magnetic field. The potential transformer pt multiple windings, its magnetic core and the silicon carbide surge arrester. Instrument transformers are used for measurement and protective application, together with equipment such as meters and relays. Medium voltage indoor voltage transformers are cast in epoxy resin and designed for insulation up to 40,5kv. Iec combined current transformer and potential transformer. Difference between current transformer and voltage.
Instrument transformers are used in ac system for measurement of electrical quantities i. Difference between current transformer and potential. Combined instrument transformers pfiffner instrument. Current transformers can be used to keep an eye on. Basics, maintenance, and diagnostics vii contents continued page 4. Three phase current transformer ground fault function optional common mode choke coil other current transformer features. Instrument transformers potential transformer, current transformers for high voltage and current measurement. Some other differences between the current and the potential transformer. Conventional magnetic current and voltage transformers are still in wide use in power systems.
Ct is used for current measurement and pt is used for voltage measurement. Download documents for mv indoor current transformer indoor current transformers up to 40. Current transformers, along with voltage or potential transformers, are instrument transformers. Voltage transformer or potential transformer theory. 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. Difference between current transformer ct and potential transformer pt current transformers ct and potential transformers pt are used to measure the current and voltage.
The current in the secondary coil always changes by the inverse of the ratio by which the voltage changes. Niederspannungsmesswandler low voltage instrument transformers. 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. Current transformers ct and potential transformers pt are used to measure the current and voltage in a circuit of the order of hundreds of amperes and volts respectively. Catalogue outdoor mv instrument transformers version 4. The basics of current transformers nk technologies. Voltage transformers vt, also called potential transformers pt, are a parallel connected type of instrument transformer. You can transform the voltage or current down with a transformer whose. 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.
Instrument transformers scale the large values of voltage or current. The standard that describes voltage transformers in details is iec 186. Transformers used for voltage potential measurement steps down the voltage to the level of voltmeter. Discover how we can support you in the field of instrument transformers. 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 model jlszv35w outdoor combined current transformer and potential transformer is used in threephase systems of rated frequency of 5060hz and rated voltage. Transformer types instrument transformers instrument transformers comprise a large category of current and potential transformers for various voltage, frequency and physical size ranges. Current transformers,voltage transformers and instrument. They are designed to present negligible load to the supply being measured and have an accurate voltage. Pdf a coupling capacitor voltage transformer representation for. Transformer book is still in demand is a tribute to the publishers and to the authors who have carried the torch to light our way for 75 years. The main difference between current transformer and potential transformer is that the current transformers use a stepup transformer in order to reduce current through its.
A current transformer ct is a type of transformer that is used to measure ac current. Voltage transformers are together with current transformers known as instrument transformers. Current and voltage can be stepped down by using a transformer whose turns ratio is known and then measuring the stepped down current and voltage by a normal ammeter. 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. These instruments transformers are of two types i current transformers ct and ii potential transformers pt. Markings on current transformers ct and potential transformers pt have been.
Potential transformers consist of two separate windings on a common magnetic steel core. To start with, both are instrument transformers basically used for measurement and protection purpose in power systems. Used in ac system for the measurement of current, voltage, power and energy. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac.
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