The percent ratio error is positive if mary current or voltage is equal to the formers in terms. As an example, a typical 100 to 5a current transformer has a nominal ratio of single primary turn to 20 secondary turns or 1. Jul 24, 2015 the primary of voltage transformer is connected to power circuit between phase and ground. Current transformer is used to step down the current of power system to a lower level to make it feasible to be measured by small rating ammeter i. Difference between current transformer and potential. The differences between current transformer ct and potential transformer pt are given below. Cts current transformers pts potential transformers. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the same. The primary winding of the transformer is connected to the high voltage or high current circuit, and the meter or relay is connected to the secondary circuit. Apr 19, 2017 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 secondary coils whereas the potential transformers use a stepdown transformer in order to reduce the potential difference across its secondary coil.
Instrument transformers may also be used as an isolation transformer so that secondary quantities may be used in phase shifting without affecting other primary connected devices. Instrument transformer basic technical information and. What are the difference between power transformer and. The basic principle of the current transformer is the same as that of the power transformer. Like the power transformer, the current transformer also contains a primary and a secondary winding. Difference between current transformer,voltage transformer. Whenever an alternating current flows through the primary winding, alternating magnetic flux is produced, which then induces alternating current in the. At the other hand, the distribution transformers generally pole mounted are those installed nearby the load terminals city and villages to provide utilization voltage at the consumer terminals mostly step down. What is the difference between voltage transformer and. Pdf on jan 1, 2014, michael stanbury and others published the impact of currenttransformer saturation on transformerdifferential protection find, read and cite all the research you need on. A current transformer, abbreviated ct, is a type of transformer used to measure the current of a given circuit. The terminal of the transformer should be designed so that the variation of the voltage ratio with load is minimum and the phase shift between the input and output voltage is also minimum. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to.
Difference between current transformer and potential transformer 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. The potential transformer is made with highquality core operating at low flux density so that the magnetising current is small. Difference between core type and shell type transformer 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. A constant k is able to be calculated based on load resistor and turns ratio such that iin vout x k. In brief, those transformers installed at the ending or receiving point of long and high voltage transmission lines are the power transformers mostly step up. The basics of current transformers nk technologies. A ct has large number of turns on its secondary winding, but very few turns on its primary winding.
Coupled with an ammeter, cts are used to protect the main lines of the power grid, by measuring highvoltage electrical current and preventing damage to sensitive equipment. Commercially available relays and meters used for protection and metering, are designed for low voltage. Apr 26, 2012 one important difference between a current and voltage transformer is that if the secondary of a current transformer is unterminated, or terminated in too high a resistance, the transformer core can be saturated voltseconds too high, leading to a highly nonlineear response. Current transformers are commonly used in metering and protective relays in the electrical power industry. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering.
A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. The current transformers reduce the level of current to the instrument or relay operating range, whereas potential transformers transforms the high voltage to a circuit operating low voltage. In this article differences between power transformer and instrument transformer are discussed. At the other hand, the distribution transformers generally pole mounted are those installed nearby the load terminals city and villages to provide utilization. Hence potential transformer is that type transformer which protect from over voltage and also in earth fault protection. Apr 07, 2018 the differences between current transformer ct and potential transformer pt are given below. While a potential transformer pt used to reduce the voltage to lower values and to provide isolation between high voltage power network and the relays and the other instruments that are connected to their secondary. What is the difference between ctcurrent transformer and. The power transformer is used to convert voltage using the number of windings in the two coils as ratio, while the current transformer is just an. Working of potential transformer the electrical portal.
Current transformer basics and the current transformer. Another distinguishing feature is the difference between indoor and outdoor. It is connected in parallel with the power circuit. Difference between current transformers and power transformers.
Mar 10, 2016 to start with, both are instrument transformers basically used for measurement and protection purpose in power systems. Differences between instrument and power transformers. This is a simplest form of potential transformer definition. T can be open circuited without any damage being caused either to the operator or the 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. Some other differences between the current and the potential transformer are explained below in the comparison chart. The current transformer can reduce the high current to low current, while the potential transformer steps down the high voltage to low voltage for. 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. Nov 15, 2019 the basic principle of the current transformer is the same as that of the power transformer. 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. In the nature potential transformer are not possible to exist. Current transformer ct and potential transformer pt are instrument transformers basically used for measurement and protection purpose.
Main difference between power transformer and distribution transformer. Iec combined current transformer and potential transformer. This model jlszv35w outdoor combined current transformer and potential transformer is used in threephase systems of rated frequency of 5060hz and rated voltage of 35kv. Jan 08, 2019 while a potential transformer pt used to reduce the voltage to lower values and to provide isolation between high voltage power network and the relays and the other instruments that are connected to their secondary. It works on law mutual induction as in simple transformer. Daelim provides reliable current, current transformer and potential transformer for metering and protective relays. Instrument transformers are used for measurement and protective application, together with equipment such as meters and relays. Key differences between current transformer and voltage transformer. Ct is used for current measurement and pt is used for voltage measurement. To start with, both are instrument transformers basically used for measurement and protection purpose in power systems.
Difference between current and voltage transformer. Power transformers are used to transfer large amount of power form 1 voltage level to other voltage level for obvious reasons and are used at p. The primary winding has very few turns while secondary winding has more turns. In its most basic form, the device consists of three parts. Difference between ct and pt the electrical portal.
Current transformers need to have a large number of windings in. Difference between power transformer and distribution transformer definition of power transformer and distribution transformer as voltage is produced in lower voltage ranges, but the transmission in that range has greater energy losses, the voltage levels need to be increased. Difference between current transformer ct and potential transformer pt, what is current transformer, what is potential transformer, what are difference between current transformer and potential transformer, why current transformer is used, why potential transformer is used, what is ct and what is pt, cs electrical and electronics, the swipe up. The current transformer is designed to connect in series with the line to transform the line current to the standard 5 amperes suitable for the. Unlike a voltage transformer, the primary current of a current transformer is not dependent of the secondary load current but instead is controlled by an external. This means that when 480 volts is applied to the primary winding, 120 volts will be induced on the secondary. 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. Voltage transformers and current transformers are mainly used in instrumentation hence collectively known as instrument transformers.
Difference between current transformer and potential transformer. 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. 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. Major differences between the current transformer ct and potential transformer pt are listed below. Voltage transformer or potential transformer theory. Jan 16, 2012 the primary is typically the main power line conductor, which passes directly through the toroidal core. A current transformer is always operated with a defined load resistor. Difference between current transformer and voltage. Overall working of both the transformers is same, they both differ only in application point of view. One of the major difference between them is that the current transformer converts the high value of current into low value whereas the potential or voltage transformer converts the high value of voltages into low voltage. Current transformer and potential transformers come under instrument transformers. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load.
Some other differences between the current and the potential transformer are explained below in the the comparison chart. Current transformer vs potential transformer current transformers and potential transformers are devices that allow us to measure large. Voltage transformers vts are essentially step down transformers. The voltampere rating of potential transformer is less than power transformer. 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. We have broken them up into several different groupings. The key operation of the current transformer is absolutely no different from those of a regular transformer. In current transformer current and density vary over a wide range but in potential or voltage transformer it varies over a small range. 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. Sep 20, 2012 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 transformers coils. Transformer types instrument transformers instrument transformers comprise a large category of current and potential transformers for various voltage, frequency and physical size ranges.
The current transformer function is different than that of a voltage transformer. These are connected across or parallel to the line which is to be monitored. 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 secondary coils whereas the potential transformers use a stepdown transformer in order to reduce the potential difference across its secondary coil. Apr 24, 2016 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.
The instrument is directly connected across the secondary winding. 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. Current transformers,voltage transformers and instrument. If a ct test switch is used, the switch must have a makebeforebreak contact pattern to. Current transformers ct are broadly employed in order to measure high magnitude currents. A typical connection diagram of a current transformer is shown in figure below. This type of transformer is specifically for the purpose of measuring current values, and the secondary windings cannot be left opencircuited, or a large voltage will be produce, resulting in dielectric failure and often an explosion. One important difference between a current and voltage transformer is that if the secondary of a current transformer is unterminated, or terminated in too high a resistance, the transformer core can be saturated voltseconds too high, leading to a highly nonlineear response. Difference between current transformer and potential transformer use.
The primary winding is connected in series with the load so that it carries full load current. Gfuve electronics manufactures an extensive line of cast epoxy resin insulated current transformers and potential transformers across the voltage range of 5. Depending on the significant output in the secondary coil current voltage, the transformer is called a voltage potential transformer or current transformer. T can not be open circuited on any circumstance when it is under service. Current transformer vs potential transformer difference. Current transformer and potential transformer photos and features model illustration 105 potential transformer current transformer rated current. Difference between current transformer ct and potential. 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.
Ct vs pt difference between current transformer and potential. Primary winding of a current transformer is connected in series with load. What is the difference between ctcurrent transformer and pt. Jun 01, 2015 potential transformer is a voltage stepdown transformer which reduces the voltage of a high voltage circuit to a lower level for the purpose of measurement. Main difference between power transformer and distribution. Difference between power transformer and distribution. 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. 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. The primary is typically the main power line conductor, which passes directly through the toroidal core. Difference between current and voltage transformer physics. In this article we are going to discuss in detail about the potential transformers. Pdf the impact of currenttransformer saturation on.
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