Current transformer basics and the current transformer. Types of transformer there are various types of transformer used in the electrical power system for different purposes, like generation, distribution and transmission and utilization of electrical power. In instrument transformer, the primary current is the vector sum of the excitation current i o and the current equal to the reversal secondary current i s multiplied by the ratio of 1k t. Insulation and basic impulse insulation level bil kv. In reality, however, it is not possible to neglect the excitation. In a power system, the currents and voltages are very large. Basics, maintenance, and diagnostics vi contents continued page 2. Figure 1 shows some of the most basic uses for instrument transformers. Instrument transformer theory and testing steve hudson, pe. The primary of this transformer consists of one or more turns of thick wire connected in. Introduction of instrument transformer a electrical device which help in measurement of high voltage or current.
Pdf instrument transformer basic technical information. The transformer core is used to provide a controlled path for the magnetic flux generated in the transformer by the current flowing through the windings also called coils. Instrument transformers potential transformer, current transformers for high voltage. These devices use standard transformer theory with 23 windings one primary with one or two secondary windings with a magnetic connection via an iron core. Both in the power transmission and distribution of ac network, transformer has its mandatory use. Instrument transformers are also used with protective relays for protection of power system. 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. Current transformers introduction of potential transformer introduction of potential transformer basic principle. Jan 31, 2015 introduction of instrument transformer a electrical device which help in measurement of high voltage or current. Instrument transformers are also used with protective relays for. Instrument transformer in power system, the currents and voltages are very large therefore, their direct measurements are not possible. Current transformers current and voltage transformers are responsible for scaling primary system signals. The ct ratio is the ratio of primary current input to secondary current output at full.
The maximum value of the magnetic flux density is 1. You can transform the voltage or current down with a transformer whose turns ratio is accurately known, then measuring the stepped down magnitude with a normal range instrument. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. Basics, maintenance, and diagnostics vii contents continued page 4. There are four typical types of current transformers. Instrument transformers potential transformer, current transformers for high voltage and current measurement. 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.
Ge digital energy ge e xd high voltage instrument transformers what is an instrument transformer. 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. Basic electrical engineering pdf notes bee pdf notes. Electrical tutorial about current transformer basics and current transformer theory on how the current transformer works with just one secondary winding.
Instrument transformers are high accuracy class electrical devices used to isolate or transform voltage or current levels. Analysis, size, share, business development and regional overview by 2023 transformers cover a very diverse subject area that encompasses both, small and very large components. The different types of transformer are step up and step down transformer, power transformer, distribution transformer, instrument transformer. The potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. Ppt instrument transformer powerpoint presentation. Transformer only stepup or stepdown the level of ac voltage or ac current. Determine the burden of the device connected to the ct in va or ohms impedance. Its electrical purpose is to transfer power from the primary winding to the other windings with no energy storage or loss. Transformers can be segmented on the basis of type as distribution transformer, power transformer and others, which includes instrument transformer. Instrument transformers is a generic term which refers to either current transformer ct or voltagepotential transformer vtpt as compared to power transformers. Transformers used for voltage potential measurement steps down the voltage to the level of voltmeter. Transformer cant stepup or stepdown the level of dc voltage or dc current. It is most commonly used to increase step up or decrease step down voltage levels between circuits.
Faults relays instrument transformers correlation to drawings one lines ac schematics dc schematics other types of protection coordination of relays protect personnel. The primary of this transformer consists of one or more turns of thick wire connected in series with the line. For measuring high values of current or voltage, it is desirable to use standard lowrange measuring instruments together with speciallyconstructed instrument transformers, also called accurate ratio transformers. Types of transformer different types of transformer. Basic function of instrument transformers is to step down the ac system voltage. Working principle, construction and types of transformer. It covers in detail both analogue and digital instruments, measurements errors and uncertainty, instrument transformers, bridges, amplifiers, oscilloscopes, data acquisition, sensors, instrument controls and measurement systems. Basic transformer operation can be described by two formulae relating the transformation ratio to. The basics of current transformers nk technologies. The basic principle of operation of both types of transformers is the same. Transformer operates when both circuits take effect of mutual induction. There are three basic styles used to transformer system voltages to control voltages. This is the first part of video series called as current transformer in this video i have discussed about definition of current transformer and working principle of it. The purpose of instrument transformer is to reproduce as accurately as possible the voltage of pt or current of ct in their primary circuit to their secondary circuit in order to be of any use to protection devices connected to them.
It might appear that the extension of range could be conveniently done by the use of shunts for currents and multiplier for voltage measurement, as in dc. These instruments transformers are of two types i current transformers ct and ii potential transformers pt. This book explains the basic measurement techniques, instruments, and methods used in everyday practice. There are several classes of accuracy for instrument transformers defined by the ieee, csa, iec, and ansi standards. Instrument transformers are designed specifically for use with electrical equipment falling into the broad category of devices commonly called instruments such as voltmeters, ammeters, wattmeters, watthour meters, protection relays, etc. To transform currents or voltages from a usually high value to a value easy to handle for relays and instruments.
Basic impulse level measures the maximum voltage stresses that the transformer can handle bil. A transformer consists of two electrically isolated coils and operates on faradays principal of mutual induction. In order to understand the advantage and use of a transformer, lets first look at the basic transformer. Instrument transformers are used in ac system for measurement of electrical quantities i. Transformers used for current measurement steps down the current to the level of ammeter. Instrument transformer basics transformer electronic. Similarly, current transformers take a high current and reduce it to typically 5 amps on the secondary winding so that it can be used with a watthour meter, ammeter. Transformer can increase or decrease the voltage with corresponding decrease or increase in current. Measure the length of the wire between the current transformer and the burden. Such specially constructed transformers with accurate turns ratio are called as instrument transformers. Current transformer sometimes called cts it is simply a device unused to measure current by producing a smaller current that is proportional to the current that is to measured.
Typical nominal secondary values are 5 a and 1 a for. A transformer changes the voltage level or current level on its input winding to another value on its output winding using a magnetic field. Instrument transformers its are designed to transform voltage or current from the high values in the transmission and distribu tion systems to the low values that can be utilized by low voltage metering devices. Instrument transformer basics wmea pdf book manual free. An introduction to instrument transformer fundamentals, a discussion on power quality, and a detailed explanation of design considerations to assist in selecting an instrument transformer. To insulate the metering circuit from the primary high voltage system. These transformers can be used for metering and protection in high voltage circuits, it is another type of instrument transformer. 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. Instrument transformer basics wmea pdf book manual. It might appear that the extension of range could be conveniently done by the use of shunts for currents and multiplier for volta. Current transformers cts and voltage transformers pts or vts are the frontline guardians of any ac power supply system. Read online instrument transformer basics wmea book pdf free download link book now. Nov 17, 2019 a transformer is a static device which transfers electrical energy from one circuit to another through the process of electromagnetic induction. Download instrument transformer basics wmea book pdf free download link or read online here in pdf.
Basics of electrical transformer instrumentation tools. 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 transformers are used to scale down the voltage or current to a standardized value when voltage or current is too large to be conveniently used by a measurement, protection, or control instrument. The original magnitude can be determined by just multiplying the result with the transformation ratio. Instrument transformer basic technical information and. What is electrical transformer transformer is an electrical machine that transfers unchanged electrical energy and frequency with a. The function of pt is to steps down the voltage to the level of voltmeter. Typical electrical drawing symbols and conventions. Transformers explaining the basics of transformers. A transformer is a static device which transfers electrical energy from one circuit to another through the process of electromagnetic induction. Nowadays, it is the transient performance of instrument transformers that has gradually become. Transformer doesnt change the the circuit frequency during operation.
Instrument transformers instrument transformers ct current transformer current scaling isolation vt voltage transformer voltage scaling isolation 1. Current and voltage instrument transformers applicaton guide for current transformers, the value of the. The primary winding is connected to the voltage side to be measured and secondary to the voltmeter. All books are in clear copy here, and all files are secure so dont worry about it. An accurate ratio transformer does just as the name suggests.
The specific performance characteristics of current and voltage instrument transformers are easily determined from the equivalent circuit. It is designed to have an accurate transformation ratio in both magnitude and phase over a range of measuring circuit impedance, it is designed to present a negligible load to the supply being measured. Current transformer and potential transformer are instrument transformers. Instrument transformers are used to scale down the voltage or current to a standardized value when voltage or current is too large to be conveniently. Current transformer ct is a stepup transformer which steps down the current to a known ratio. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high. It is most commonly used to increase step up or decrease step down. Figure 1 works well for most instrument transformers. Instrument transformers will transmit the signal to the metering and protective relaying instrumentation, with the purpose of protection of important equipment. November 17, 2019 february 24, 2012 by electrical4u. Current and voltage instrument transformers technical and.
Electrical transformer basic construction, working and. By using low range ammeter can measure high current. Ge e xd high voltage instrument transformers what is an instrument 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. Typical nominal secondary values are 5 a and 1 a for current transformers and 110 v for voltage transformers. Transformers used for voltage potential measurement. Faults instrument transformers correlation to drawings. Electrical transformer is the most used electrical machine in power system.
An introduction to instrument transformer fundamentals, a discussion on power quality, and a detailed explanation of design considerations to assist in selecting. The v p is the voltage applied to the primary terminal of the potential transformer. Instrument transformers will operate successfully under many atmospheric. Instrument transformer basic technical information and application. Power transmission and distribution author page 242 200708. Basic electrical engineering pdf free download links.
Typical output levels of instrument transformers are 15 amperes and 115120 volts for cts and vts, respectively. After studying this section, you should be able to describe. Transformer basics two or more wire windings placed around a common magnetic core is the physical structure of a transformer. Electrical transformer is a static electrical machine which transforms electrical power from one circuit to another circuit, without changing the frequency. Instrument transformers are the most common and economic way to detect a disturbance.
Potential transformers pts or voltage transformers vts pts or vts are the most common device used. Then to summarise this transformer basics tutorial. Ppt instrument transformer powerpoint presentation free. Instrumentation and measurement in electrical engineering. Line power manufacturing instrument transformer basics what is an instrument transformer. Instrument transformers its are designed to transform voltage of current from the high values in the transmission and distribution systems to the low values that can be utilized by low voltage metering devices. Current transformer, standard for steadystate performance. Instrument transformers reduce the line current and voltage being provided to the customers load to safe levels for input to solid state meters. Basic transformer theory vp primary voltage ip primary current. In a shelltype shell form transformer, the steel magnetic circuit core forms a shell surrounding the windings. While operating principles of transformers remain the same, the challenges of maintaining and testing transformers. The potential transformer is connected in parallel with the circuit. A single phase transformer has 480 turns on the primary winding and 90 turns on the secondary winding. It provide low range current and voltage to the protection system.
The most common usage of instrument transformers is to operate instruments or metering from high voltage or high current circuits, safely isolating secondary control circuity from the high voltages or currents. They find application in a switchgear or a controlgear assembly and a switchyard. Therefore, their direct measurements are not possible. Instrument transformers ct current transformer current scaling isolation vt voltage transformer voltage scaling isolation 1. A distinction has to be made between a metering class and a protection class current transformer. Pdf as the development of digital measurement and protection equipment has progressed over. By using low range voltmeter can measure high voltage. Potential transformers pts are necessary to a power system for metering and protective relaying to convert higher system voltages to lower control voltages that are more practical from an equipment, operation, and safety perspective. Potential and current transformers, ratio and phase angle errors, phasor.
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