This book explains the basic measurement techniques, instruments, and methods used in everyday practice. Instrument transformers is a generic term which refers to either current transformer ct or voltagepotential transformer vtpt as compared to power transformers. The basic principle of operation of both types of transformers is the same. Basics, maintenance, and diagnostics vii contents continued page 4. Current transformer and potential transformer are instrument transformers. To insulate the metering circuit from the primary high voltage system. A transformer consists of two electrically isolated coils and operates on faradays principal of mutual induction. Instrument transformers instrument transformers ct current transformer current scaling isolation vt voltage transformer voltage scaling isolation 1. Transformer operates when both circuits take effect of mutual induction. 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. The primary winding is connected to the voltage side to be measured and secondary to the voltmeter. The primary of this transformer consists of one or more turns of thick wire connected in. Instrument transformers reduce the line current and voltage being provided to the customers load to safe levels for input to solid state meters. Faults instrument transformers correlation to drawings.
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. Instrument transformers potential transformer, current transformers for high voltage and current measurement. To transform currents or voltages from a usually high value to a value easy to handle for relays and instruments. Electrical tutorial about current transformer basics and current transformer theory on how the current transformer works with just one secondary winding. Instrument transformers will operate successfully under many atmospheric. Figure 1 shows some of the most basic uses for instrument transformers. The primary of this transformer consists of one or more turns of thick wire connected in series with the line. The specific performance characteristics of current and voltage instrument transformers are easily determined from the equivalent circuit. Types of transformer different types of transformer. 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. Ge e xd high voltage instrument transformers what is an instrument transformer.
In order to understand the advantage and use of a transformer, lets first look at the basic transformer. Working principle, construction and types of transformer. Instrument transformers are also used with protective relays for protection of power system. 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.
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 transformer electronic. In a power system, the currents and voltages are very large. The potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. Download instrument transformer basics wmea book pdf free download link or read online here in pdf. Basic electrical engineering pdf free download links. 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. Typical nominal secondary values are 5 a and 1 a for current transformers and 110 v for voltage transformers. There are several classes of accuracy for instrument transformers defined by the ieee, csa, iec, and ansi standards. 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. Transformer basics two or more wire windings placed around a common magnetic core is the physical structure of a transformer. Current transformers introduction of potential transformer introduction of potential transformer basic principle. The ct ratio is the ratio of primary current input to secondary current output at full. Pp vp ip ps vs is this is true for an ideal transformer.
The different types of transformer are step up and step down transformer, power transformer, distribution transformer, instrument transformer. Basic transformer operation can be described by two formulae relating the transformation ratio to. What is electrical transformer transformer is an electrical machine that transfers unchanged electrical energy and frequency with a. 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. Therefore, their direct measurements are not possible. Figure 1 works well for most instrument transformers. 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. 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.
Line power manufacturing instrument transformer basics what is an instrument transformer. Typical nominal secondary values are 5 a and 1 a for. They find application in a switchgear or a controlgear assembly and a switchyard. Read online instrument transformer basics wmea book pdf free download link book now. Instrument transformers ct current transformer current scaling isolation vt voltage transformer voltage scaling isolation 1. Jan 31, 2015 introduction of instrument transformer a electrical device which help in measurement of high voltage or current. Basic electrical engineering pdf notes bee pdf notes.
Typical output levels of instrument transformers are 15 amperes and 115120 volts for cts and vts, respectively. Instrument transformers will transmit the signal to the metering and protective relaying instrumentation, with the purpose of protection of important equipment. In a shelltype shell form transformer, the steel magnetic circuit core forms a shell surrounding the windings. Basic impulse level measures the maximum voltage stresses that the transformer can handle bil. While operating principles of transformers remain the same, the challenges of maintaining and testing transformers. In reality, however, it is not possible to neglect the excitation. 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. An accurate ratio transformer does just as the name suggests. Insulation and basic impulse insulation level bil kv.
Nov 17, 2019 a transformer is a static device which transfers electrical energy from one circuit to another through the process of electromagnetic induction. Instrument transformer basic technical information and. The v p is the voltage applied to the primary terminal of the potential transformer. Instrument transformer basics wmea pdf book manual. Instrumentation and measurement in electrical engineering. Instrument transformer theory and testing steve hudson, pe. 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. Current transformer ct is a stepup transformer which steps down the current to a known ratio. Transformers used for voltage potential measurement steps down the voltage to the level of voltmeter. 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. Its electrical purpose is to transfer power from the primary winding to the other windings with no energy storage or loss. These transformers can be used for metering and protection in high voltage circuits, it is another type of instrument transformer.
Instrument transformers are the most common and economic way to detect a disturbance. 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. By using low range ammeter can measure high current. Faults relays instrument transformers correlation to drawings one lines ac schematics dc schematics other types of protection coordination of relays protect personnel. By using low range voltmeter can measure high voltage. Typical electrical drawing symbols and conventions. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. Basics of electrical transformer instrumentation tools. Introduction of instrument transformer a electrical device which help in measurement of high voltage or current. Current and voltage instrument transformers technical and.
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. Pdf as the development of digital measurement and protection equipment has progressed over. Then to summarise this transformer basics tutorial. Measure the length of the wire between the current transformer and the burden. The function of pt is to steps down the voltage to the level of voltmeter. 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.
Potential transformers pts or voltage transformers vts pts or vts are the most common device used. 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. After studying this section, you should be able to describe. Ge digital energy ge e xd high voltage instrument transformers what is an instrument transformer. Current transformer, standard for steadystate performance. Transformer can increase or decrease the voltage with corresponding decrease or increase in current. Ppt instrument transformer powerpoint presentation free. Transformer doesnt change the the circuit frequency during operation. Instrument transformers are used in ac system for measurement of electrical quantities i. 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. Such specially constructed transformers with accurate turns ratio are called as instrument transformers.
Basic transformer theory vp primary voltage ip primary current. Instrument transformers are high accuracy class electrical devices used to isolate or transform voltage or current levels. Current and voltage instrument transformers applicaton guide for current transformers, the value of the. 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. 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. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high. Instrument transformers potential transformer, current transformers for high voltage. Electrical transformer basic construction, working and. Current transformers cts and voltage transformers pts or vts are the frontline guardians of any ac power supply system. All books are in clear copy here, and all files are secure so dont worry about it. 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. A single phase transformer has 480 turns on the primary winding and 90 turns on the secondary winding. Power transmission and distribution author page 242 200708. Ppt instrument transformer powerpoint presentation.
An introduction to instrument transformer fundamentals, a discussion on power quality, and a detailed explanation of design considerations to assist in selecting. There are three basic styles used to transformer system voltages to control voltages. 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. Pdf instrument transformer basic technical information. Determine the burden of the device connected to the ct in va or ohms impedance. Transformer only stepup or stepdown the level of ac voltage or ac current. It provide low range current and voltage to the protection system. Transformers used for current measurement steps down the current to the level of ammeter.
A distinction has to be made between a metering class and a protection class current transformer. Electrical transformer is the most used electrical machine in power system. 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. Transformer cant stepup or stepdown the level of dc voltage or dc current. Electrical transformer is a static electrical machine which transforms electrical power from one circuit to another circuit, without changing the frequency. Instrument transformers are also used with protective relays for. 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 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. The maximum value of the magnetic flux density is 1. A transformer changes the voltage level or current level on its input winding to another value on its output winding using a magnetic field. Current transformer basics and the current transformer. Instrument transformer basic technical information and application. Both in the power transmission and distribution of ac network, transformer has its mandatory use. 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.
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. 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. Basic function of instrument transformers is to step down the ac system voltage. The original magnitude can be determined by just multiplying the result with the transformation ratio. It might appear that the extension of range could be conveniently done by the use of shunts for currents and multiplier for volta. November 17, 2019 february 24, 2012 by electrical4u. The potential transformer is connected in parallel with the circuit.
It is most commonly used to increase step up or decrease step down. It is most commonly used to increase step up or decrease step down voltage levels between circuits. Transformers used for voltage potential measurement. Transformers can be segmented on the basis of type as distribution transformer, power transformer and others, which includes instrument transformer. Instrument transformer basics wmea pdf book manual free. The basics of current transformers nk technologies. These instruments transformers are of two types i current transformers ct and ii potential transformers pt. Potential and current transformers, ratio and phase angle errors, phasor. Instrument transformer in power system, the currents and voltages are very large therefore, their direct measurements are not possible. Nowadays, it is the transient performance of instrument transformers that has gradually become.
966 1373 1033 458 1407 207 1365 1178 1262 306 784 1222 286 1165 411 636 794 795 588 570 924 1273 1372 972 497 876 911 524 65 893 858 1171 656 1366 1194 1431 15 1298