CURRENT TRANSFORMERS AND VOLTAGE TRANSFORMERS

Slides:



Advertisements
Similar presentations
TO CURRENT TRANSFORMER PERFORMANCE ANALYSIS
Advertisements

Digital Current Transformer Reporter
Chapter 12 Transformers. Chapter 12 Transformers.
ENERGY CONVERSION ONE (Course 25741)
SMAW Equipment (Shielded Metal Arc Welding- commonly called “stick welding”, or “arc welding”)
CHAPTER 3 PERFORMANCES OF DC GENERATOR 1. OPEN-CIRCUIT (NO-LOAD) CHARACTERISTICS Conditions: No-load characteristic : No-load characteristic is essentially.
Power System Analysis/ Power System 1 EEE 4113/ EEE 3131
Al Penney VO1NO Inductance.
PHY2049: Chapter 31 Transformers Purpose: to change alternating (AC) voltage to a bigger (or smaller) value input AC voltage in the primary produces a.
TRANSFORMERS. TRANSFORMER PARAMETERS Turns Ratio (n) It is defined as the ratio of the number of turns in the secondary winding (N sec ) to the number.
TESTING AND COMMISIONING
Combined Selective Systems :-
Generator Protection. Amount of Protection Rated power of the generator Ratio of its capacity to the total capacity of the system Configuration of the.
Unit Transformer Unit transformer are step up transformer which is connected to generating house & step up voltage from 15kV voltage to 132 voltage level.
Transformer.
Substations. Substations Chapter 4 Substations Major types of equipment found in most transmission and distribution substations with their purpose,
Chapter 9 Ideal Transformer
Main article: Leakage inductance
Unit 27 Transformers. Objectives –After completing this chapter, the student should be able to: Describe how a transformer operates. Explain how transformers.
BENE 1113 PRINCIPLES OF ELECTRICAL AND ELECTRONICS
Single Phase Transformer
Instrument Transformers
Radian Research, Inc. Radian Research, Inc. an employee owned company Power and Energy Measurement Specialists 3852 Fortune Drive.
Connections of a CT and a PT to supply, load and relay.
Section 3 Basic Electricity and Magnetism
Announcements For lectures 8 to 10 please be reading Chapter 3
Announcements Please read Chapter 3 H4 is 4.34, 4.41, 5.2, 5.7, 5.16
By J DAVID MANOHAR (08A31A0232). NECESSITY OF SUPERCONDUSTOR  Damage from short circuit is constant threat in power systems  All the power systems components.
POWER CIRCUIT & ELECTROMAGNETICS
Chapter 13 Principles of Electric Circuits, Conventional Flow, 9 th ed. Floyd © 2010 Pearson Higher Education, Upper Saddle River, NJ All Rights.
Today Course overview and information 09/16/2010 © 2010 NTUST.
EET 103 Transformer Chapter 5 1. A transformer is a device that changes ac electric energy at one voltage level to ac electric energy at another voltage.
Protection of Microgrids Using Differential Relays
Magnetic field due to an electric current
POWER SYSTEM PROTECTION AND SWITCHGEARS
Lecture 04Electro Mechanical System1 Ideal Transformer  An ideal transformer  Transformer has no losses and core is infinitely permeable  All fluxes.
ELECTRICAL MACHINE DET 204/3 JIMIRAFIZI BIN JAMIL Transformer CHAPTER 1.
POWER CIRCUIT & ELECTROMAGNETICS EET 221 Transformer.
Protection of Power Systems
SMJE 2103 Electrical Power System 3- Ph Power Apparatus.
MAHATMA GANDI INST. OF TECHNICAL EDUCATION & RESEARCH CENTRE, NAVSARI.
Instrument Transformer Electrical Measuring Instruments & Instrumentation 3rd SEMESTER ELECTRICAL ENGG.
D.C. Machine & Transformer Topic: Instrument Transformer Electrical:-1 presented by: Jill Chauhan ( ) Chirag Agarawal ( )
1 :. Introduction These are special type of transformers used for the measurement of voltage, current, power and energy. As the name suggests, these transformers.
Transformer A Presentation on. Transformer2 Coil 1 i 1 (t)i 2 (t) Coil 2 M e 1 (t)e 2 (t) S1S1 S2S2 i 1 (t) i 2 (t) The Transformer (Primary has N 1 turns)
DC Machine & Transformer
True-False Questions. A magnetic core material may exhibit hysteresis or saturation but not both.
Part Three – Relay Input Sources
1. 2 Magnetization Current in a Real transformer Although the output of the transformer is open circuit, there will still be current flow in the primary.
Current Transformer Testing
Auto Transformer Current Flow. Principles of Auto Transformers H X H0/X0.
DCMT PRESENTATION DEVANSH KHARE ( )
SYNCHRONOUS GENERATOR
Lesson 8: Ideal Transformer Theory and Operation
True-False Questions.
Chapter 18 Transformers.
CHAPTER 6 SPECIAL TRANSFORMERS Electrical Machines.
BACK EMF When the coil L is connected in series with the cell V it produces an increasing magnetic field as the current through the coil rises. This induces.
Electric Machine Transformers
Transformer -Types & Applications
ELE 2103 Dept . of E & E, MIT Manipal
Electromechanical Systems
Associated Hazards and Safety Practices
Transformer Impedance
EE216 Electrical Engineering
EET 503 Power System Protection (Instrument transformer )
Prof.mrs najma siddiqui
Instruments & Electrical Measurements Lecture 10
Unit-1 Transformer.
Electric Machine Design Course
Presentation transcript:

CURRENT TRANSFORMERS AND VOLTAGE TRANSFORMERS

INTRODUCTION Function of the protection relays Information to the protection relays have to be accurate and reliable Currents and voltages How to overcome this difficulty

WHAT DOES CURRENT AND VOLTAGE TRANSFORMERS DO… Insulate secondary circuits from primary Provide currents/voltages proportional to the primary

ROLE OF CT, PT IN POWER SYSTEM PROTECTION Protection systems depend heavily on information provided CTs and PTs a constituting part of the protection system No great difference between a measuring voltage transformer and a protective voltage transformer However, Current transformer is different

BASIC PRINCIPLES OF OPERATION Transformer can be operated in Shunt mode Series mode

SHUNT MODE Voltage applied across the primary terminals When secondary is on open circuit, Induces an EMF equal to the voltage applied Current flowing will be that required to excite the core When secondary is loaded Ampere turns of the primary winding will exceed that of secondary Difference is the flux needed to excite the core.

SERIES MODE Primary winding is connected in series with a circuit. Its current is determined by the sources and loads. Its current is determined by its sources/load conditions A component of this current is used to excite the core sufficient to induce an EMF to drive a current in the secondary

COMPARISON-SHUNT MODE AND SERIES MODE Voltage applied across the primary terminals When secondary is on open circuit, Induces an EMF equal to the voltage applied Current flowing will be that required to excite the core When secondary is loaded Ampere turns of the primary winding will exceed that of secondary – Difference is the flux needed to excite the core Series mode Primary winding is connected in series Its current is determined by its sources/load conditions A component of this current is used to excite the core sufficient to induce an EMF to drive a current in the secondary

STEADY STATE THEORY OF CTS

CT ACCURACY If the CT is ideal Primary AT = Secondary AT Secondary current ∞ Primary current Every CT requires a certain AT to induce in it the magnetic flux With secondary impedance fixed exciting AT form a larger proportion at smaller primary currents Exciting current required to magnetize the core is the cause for th errors in CTs

AC PERFORMANCE OF A CT ES = 4.44 f A B 10-8 Volts ES = Secondary induced volts f = Frequency in cycles/second N = Secondary number of turns A = Core cross sectional area in sq.cm B = Flux density in lines per sqcm. ES = Is( Zb + Zs + Zl)

CT MAGNETIZATION CURVE Exciting current is the source of errors Value of exciting current depends on the core material and the amount of flux. Ankle point and knee point,

CT EQUIVALENT CIRCUIT

OPEN CIRCUITING OF CT If the secondary of a CT is kept open with a current flowing in the primary, then No secondary current No MMF to oppose the flux Core driven to saturation High rate of change of flux High voltages

CT ERRORS Phase angle error Composite error Ratio error (KnI s ‑ Ip ) x 100/ Ip Kn = Nominal ratio I s = Actual secondary current Ip = Actual primary current Phase angle error Angle by which the secondary current vector when reversed differs from the primary current. Composite error r.m.s. value of the difference between the ideal secondary current and the actual secondary current. Includes the current and phase angle errors

LIMITS OF ERRORS Metering CTs Protection CTs

CT RATINGS Accuracy limits Limit up to which the specified accuracy could be retained. Accuracy Limit Factor Rated short time current r.m.s. value of the a.c. component of the current which a CT is capable of carrying for the rated time without being damaged by thermal or dynamic effects CT Burden the load applied to the secondary of the CT. Normal practice is to express the burden in terms of VA and power factor, the VA being what would be consumed in the burden impedance at rated secondary current

CHOICE OF CT RATIO Secondary current 5 Amps or 1 Amp Primary current to be equal to or greater than the normal full load current of the protected circuit Maximum ratio of a CT is made about 3000/1 and secondary CTs of 20/1 are used.

TRANSIENT RESPONSE OF CT Transient conditions, prevail within the first few cycles of a fault. System conditions are very different to that under steady state conditions. Power systems expansions increases fault currents and time constants of dc transient components. It is mandatory for the protective equipment/circuit breakers to clear the faults within few cycles This makes CT duties more onerous Hence, behaviour of CTs during transient conditions is of great importance.

TRANSIENT CONDITIONS IN A POWER SYSTEM Sudden application of a sinusoidal voltage to a series R/L circuit will cause a current to flow in the circuit. This is equivalent to a fault condition of a power system,

Equivalent circuit