Numerical Relay - Final Report - Winston Netto

GENERATOR RELAY PANEL

AND

DESIGN AND SIMULATION OF NUMERICAL RELAY.

A PROJECT REPORT

Submitted by

WINSTON NETTO (SEE - 1697)

KARTHICK HARI (SEE - 1980)

SHAMSHEER C.K (SEE - 1989)

REJIL.C (SEE - 1987)

in partial fulfillment of the requirements for the award of degree of

BACHELOR OF TECHNOLOGY

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

SCMS SCHOOL OF ENGINEERING & TECHNOLOGY (Affiliated to M.G University)

VIDYA NAGAR, PALISSERY, KARUKUTTY

ERNAKULAM-683 582

MARCH - 2010

SCMS School of Engineering and TechnologySCMS School of Engineering and TechnologySCMS School of Engineering and TechnologySCMS School of Engineering and Technology

Karukutty, Ernakulam.Karukutty, Ernakulam.Karukutty, Ernakulam.Karukutty, Ernakulam.

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This is to certify that this is a bonafide record of the project work titled

“GeneratorGeneratorGeneratorGenerator Relay Panel Relay Panel Relay Panel Relay Panel andandandand Design and Simulation of Numerical Relay Design and Simulation of Numerical Relay Design and Simulation of Numerical Relay Design and Simulation of Numerical Relay” ” ” ” done by

Winston Winston Winston Winston NetNetNetNetto, Karthick Hari, Rejil. C and to, Karthick Hari, Rejil. C and to, Karthick Hari, Rejil. C and to, Karthick Hari, Rejil. C and Shamsheer C.K Shamsheer C.K Shamsheer C.K Shamsheer C.K during the academic

year 2009-2010 in partial fulfillment for the award of Degree of Bachelor of

Technology in Electrical and Electronics Engineering of Mahatma Gandhi

University, Kottayam.

Ashly Mary Tom

(Asst. Professor) Head of the Department

Internal Guide Electrical and Electronics Engineering

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ACKNOWLEDGEMENT

First and foremost we thank Almighty for making this venture a success.

We sincerely express our gratitude to Mrs. Sreekumari Radhakrishnan

(Human Resources - ES) RGCCPP for providing us with the necessary

facilities and guidance required to complete the project.

We also extend our gratefulness to Mr. Anil Kumar P.K (DGM), Mr.

K.S.Venkataraman (Dy. Supdt), Mr. Ashil Thomas (Engr) and Mr. Manu

George (Engr) of Electrical Maintenance Dept, RGCCPP, Kayamkulam for

their valuable technical guidance throughout this project.

We wish to thank all the staff members of Department of Electrical

Maintenance and Department of Human Resources, RGCCPP,

Kayamkulam for their kind cooperation.

We are thankful to Mrs. Deepa S, Associate Professor, Department of

Electrical and Electronics for her timely help and cooperation.

We express our sincere gratitude to our internal guide Mrs. Ashly Mary

Tom, Asst. Professor, Department of Electrical and Electronics for her

valuable guidance and cooperation.

We wish to thank all the staff members of Department of Electrical and

Electronics.

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ABSTRACT

Our modern working lives would be inconceivable without power supply systems,

instrumentation and control equipment. They have become matter-of-fact and we

realize their significance only when they breakdown. The potential scenario ranges

from a brief interruption in the work to bankruptcy. Only good protection can prevent

that.

The protection scheme is to protect the station equipments from abnormal condition.

Such a scheme should consist of protective relays and circuit breakers. Protective relays

functions as the sensing device, it sense the fault, determines its location, send a

tripping command to the breakers. The circuit breaker then disconnects the faulty

element. A number of relays are used in power protection system depending on the

kind of fault to be detected, the equipment to be protected by the relay, location etc. any

such relay plays and important role and must be reliable, efficient and fast in operation.

By clearing the fault fast with the help of fast acting protective relays and associated

circuit breakers, damage to the apparatus can be avoided or reduced by removing the

faulty section.

With growing complexity of modern power systems - faster, more accurate and

reliable protection than existing protection schemes have become essential.

Microcontroller based protective schemes are the latest development in this area.

These micro-controller based schemes generally deliver better performance at

relatively lower cost and with simpler construction because the operation of the

scheme depends largely on programming the micro-controller and little on the actual

hardware connections. In this paper the design and simulation of Impedance relay,

Under frequency relay, Reverse power relay, Field failure relay and Over voltage relay

using PIC16F72 micro-controller is described.

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CONTENTS

SL NO. INDEX PAGE NO.

Acknowledgement i

Abstract ii

Contents iii

List of notations v

List of figures vi

List of tables vii

Chapter 1 Introduction to Power Sector 1

Chapter 2 About the Company

2.1 Overview of RGCCPP

2.2 Operation in Brief

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Chapter 3

Turbines and Operation Cycles

3.1 Gas Turbine

3.2 Steam Turbine

3.3 Combined Cycle

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Chapter 4 Station Protection System

4.1 Relays

4.2 Electromechanical Relays

4.2.1 Attracted Armature Relay

4.2.2 Moving Coil Type

4.2.3 Induction Type Relay

4.3 Static Relays

4.4 Numerical Relays

4.5 Characteristics of Relay

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Chapter 5 Need for Instrument Transformer 22

Chapter 6 Tripping Mechanism

6.1 Inter Tripping

6.2 Direct Tripping

6.3 Permissive Tripping

6.4 Relay Settings

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Chapter 7 Protection Schemes

7.1 Differential Protection

7.2 Reverse Power Protection

7.3 Generator Impedance Relay

7.4 Over Voltage Protection

7.5 Abnormal Frequency Protection

7.6 Field Failure Protection

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Chapter 8 Design and Simulation of Numerical Relay.

8.1 Generator Relay Panel in NTPC

8.2 PIC Microcontroller

8.3 PIC16F72 Microcontroller

8.4 Numerical Relay Design Considerations

8.5 Software

8.6 Hardware

8.7 Component List

8.8 Advantages of Numerical Relay

8.9 Disadvantages of Numerical Relay

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Conclusion 71

References 72

Appendix

v

LIST OF NOTATIONS

1. MW Mega Watt

2. kWh Kilo Watt Hour

3. RES Renewable Energy Sources

4. WHRSG Waste Heat Recovery Steam Generator

5. GTG Gas Turbine Generator

6. STG Steam Turbine Generator

7. CT Current Transformer

8. PT Potential Transformer

9. C.B Circuit Breaker

10. UAT Unit Auxiliary Transformer

11. PSM Plug setting Multiplier

12. TSM Time Setting Multiplier

13. SLG Single – Line to Ground Fault

14. DG Diesel Generator

15. GCB Generator Circuit Breaker

16. FCB Field Circuit Breaker

17. HVCB High Voltage Circuit Breaker

18. LT Low Tension

19. HT High Tension

20. PIC Programmable Interface Controller

21. RAM Random Access Memory

22. ROM Read only Memory

23. ADC Analog to Digital Converter

24. DAC Digital to Analog Converter

25. CMOS Complementary metal oxide semiconductor

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LIST OF FIGURES

FIG NO. FIGURE NAME PAGE NO.

01 Relay 14

02 Attracted Armature Relay 16

03 Moving Coil Type 17

04 Induction Type Relays 18

05 Static Relays 20

09 Tripping mechanism 23

07 Single Line Diagram of RGCCPP 31

08 Differential protection 32

09 Differential protection - External Fault 33

10 Differential protection - Internal Fault 33

11 Generator Differential Protection 35

12 Reverse Power Protection 38

13 Generator Impedance Relay 40

14 Over Voltage Protection 42

15 Under Frequency Layers 45

16 Generator Field Failure Relay 48

17 Electromechanical Relay Panel 50

18 Typical Electromechanical Relay 51

19 Pin Diagram for PIC16F72 57

20 Flowchart for Numerical Relay Design 63

21 Input Simulator – Block Diagram 64

22 Numerical Relay – Block Diagram 64

23 Numerical Relay on PCB 65

24 Schematic Diagram – Numerical Relay 67

25 Schematic Diagram – Simulator Sheet No.1 68

26 Schematic Diagram – Simulator Sheet No.2 69

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LIST OF TABLES

TABLE NO. TABLE NAME PAGE NO.

01 Power Generated in India 1

02 Power Generated from various Resources 2

03 Capacity of Plants using various resources 4

04 Tripping Scheme for GTG. 26

05 Gas Turbine Generator – Relay settings 27

06 Components list 66

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1. INTRODUCTION TO POWER SECTOR

Power is the basic need for the economical development of any country. The availability

of electricity has been the most powerful vehicle of introducing economic development

and social changes throughout the world. The process of modernization, increase in

productivity in industry and agriculture and improvement in the standard of living of the

people basically depend on the adequate supply of the electric energy. Appropriately

programs relating to the generation, transmission and distribution of electric energy have

been the highest priority in the national planning process.

Since independence, emphasis as been laid on strengthening and modernization of the

transmission and distribution system along with growth of power generation facilities. As

a result the installed generating capacity in India has increased multifold from a level of

1300MW in 1947 to 155859.23 MW . Correspondingly per capita consumption from a

level of 15.60kWh to 606.20kWh during the year 1950 to 2009. Since only 40% of house

holds have electricity, still 125000 villages have to be electrified.

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� SHP = Small Hydro Project

� BG = Biomass Gasfier

� BP = Biomass Power

� U & I = Urban & Industrial Water Power

� RES = Renewable Energy Sources.

Generation and distribution system in India is quite extensive. The country has been

divided into six regions mainly northern, western, eastern, southern, north-eastern and

islands. Each with a regional electricity board so as to promote integrated operation of the

constituent power system. Each state has a state electricity board responsible for

generation transmission and distribution of electric power in their respective states. The

central government also has control over many generating plants, transmission lines and

substations through central organizations like National Thermal Power Corporation,

National Hydro-electric Power Corporation, Nuclear Power Corporation, and Power Grid

Corporation of India Limited etc.

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2 ABOUT THE COMPANY

NTPC, India's largest power company, was set up in 1975 to accelerate power development

in India. It has emerged as an ‘Integrated Power Major’, with a significant presence in the

entire value chain of power generation business. NTPC ranked 317th

in the 2009, Forbes

Global 2000, ranking of the World’s biggest companies.

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RAJIV GHANDHI COMBINED CYCLE POWER PROJECT - KAYAMKULAM

The total installed capacity of the company is 30,644 MW with 15 coal based and 7 gas

based stations, located across the country. In addition under JVs, 3 stations are coal based

& another station uses Naphtha/LNG as fuel. By 2017, the power generation portfolio is

expected to have a diversified fuel mix with coal based capacity of around 53000 MW,

10000 MW through gas, 9000 MW through Hydro generation, about 2000 MW from

nuclear sources and around 1000 MW from Renewable Energy Sources (RES). NTPC has

adopted a multi-pronged growth strategy which includes capacity addition through green

field projects, expansion of existing stations, joint ventures, subsidiaries and takeover of

stations.

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NTPC has been operating its plants at high efficiency levels. Although the company has

18.79% of the total national capacity it contributes 28.60% of total power generation due

to its focus on high efficiency.

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Recognizing its excellent performance and vast potential, Government of the India has

identified. NTPC as one of the jewels of Public Sector 'Maharatnas'- a potential global

giant. Inspired by its glorious past and vibrant present, NTPC is well on its way to realize

its vision of being "A world class integrated power major, powering India's growth, with

increasing global presence".

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The Kayamkulam Rajiv Gandhi Combined Cycle Power Project (RGCCPP) is the first

naphtha – based plant in the country.

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The 350MW combined cycle power is executed by the NTPC Ltd in the Kayamkulam

Kayal reclaimed area in Arattupuzha village of Alappuzha backwaters is now the centre

of this gigantic project. The project has 3 units comprising of 2 gas turbines of 115MW

each and one steam turbine of 129MW. The fuel (naphtha) requirement is 1750MT per

day and 0.45million MT annually for full load operation. This is being transported from

Irimpanam, Kochi to Cheppad installations\ transit storage area by railway wagons. From

Cheppad it is being transferred through 5.5km pipelines to Kayamkulam plant site where

a storage capacity of 4 tanks each of 10000KL are provided.

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2.2 OPERATION IN BRIEF

The Gas Turbine is designed for firing multi-fuel such as naphtha and natural gas. The

directly coupled compressor of gas turbine sucks air from atmosphere through specially

designed air filter and sends to combustion chamber. The hot product of combustion is

made to expand in the turbine section where the thermal energy is converted to

mechanical energy which drives the turbine and in turn drives the coupled generator.

The temperature of the exhaust gas from the turbine is around 5530C and still has

considerable heat energy and is capable of producing power. Waste heat recovery steam

generators (WHRSG) are used to recover the valuable heat energy. In the WHRSG, DM

water is heated by the hot turbine exhaust gases to produce steam before the gases are let

out to atmosphere. Achenkovil River through a pipe line of about 8km from the river to

raw water treatment plant where it is utilized for producing steam and used for other

purposes.

A bypass stack is also provided to let the hot gases directly to atmosphere in case

WHSRG is shut down for maintenance etc. In the WHSRG steam is produced in two

levels viz. low pressure with a pressure of 6kg/cm2

and high pressure with a pressure of

80kg/cm2

which are separately piped to HP/LP cylinders of steam turbine. High pressure

steam is produced in HP turbine and low pressure steam is introduced in LP turbine along

with the exhaust from HP turbine. In turbine the thermal energy of steam is converted

into mechanical energy which drives the turbine which is coupled to the generator to

produce electricity. The steam after expansion in steam turbine is condensed in a

condenser using circulating water as a cooling medium.

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The plant also consists of two unit auxiliary transformers of 10./6.6kV connected to

6.6kV bus for station supply purpose. The plant has LT power transformers, HT and LT

motors etc for the plant operation. The plant is equipped with air compressor units,

cooling towers oil pumps etc for its operation.

The electrical power in both gas turbine generator and steam turbine generator is

generated at a voltage of 10.5kV which is stepped up to 220kV by generator transformers

to 220kV gas insulated switch gear through 220kV breakers. The power then goes to

220kV double circuit power evacuation feeder system to be finally fed into grid. The

power is evacuated through four numbers of 220kV transmission lines connected to the

Edappon, Pallom and Kundra substations.

Inspired by a glorious past of illuminating home, electrifying industries and brightening

the economy and driven by its vibrant present, NTPC is looking ahead to be among the

worlds foremost utilities. NTPCs corporate plan blends an ambitious growth strategy with

financial synergy and seeks to pursue the excellence and emerges as a power giant on the

global circuit. The corporation has committed itself to achieving the status of a

30000MW plus company by 2009 and 40000MW plus power giant by 2012.

New horizons come into view as NTPC sets its sight on covering new ground with multi-

pronged growth strategy of capacity addition through green field sites expansion of

existing stations, takeovers and join ventures with selective diversification in related

areas like hydel power non-conventional energy development. In addition, NTPC plans to

take up renovation of power stations through a joined venture company investment in

LNG terminal and investment in coal mining; setting up of power plant abroad; joint

ventures for ash-based industries; setting up of associated extra high voltage transmission

lines/inter-regional EHV transmission lines so as to ensure evacuation of power from

NTPC station.

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3. TURBINES AND OPERATION CYCLES

3.1 GAS TURBINE

INTRODUCTION

The gas turbine is a common form of heat engine working with a series of processes

consisting of compression of air from atmosphere, increase of working medium

temperature by constant pressure ignition of fuel in combustion chamber and expansion

of working medium thereby causing the turbine to rotate.

When gas turbines were first applied the electric power generation industry some 20

years back, the majority of the power generated by gas turbines was for the peaking load

service. Since then how ever, with increase in efficiency and reliability, the gas turbine is

being utilized more and more in base load generation. With current state of art gas turbine

technology, combined cycles with efficiency in the neighbourhood of 55% can be

achieved and are projected to increase to 60% within next couple of years. The useful

work developed by the turbine may be used directly as mechanical energy or may be

converted into electricity by turning a generator. An aircraft jet engine is a gas turbine

except that the useful work is produced as thrust from the exhaust of the turbine.

Today gas turbine unit’s sizes with output above 200MW at ISO conditions have been

designed and developed.

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3.2 STEAM TURBINE

INTRODUCTION

The turbine is a tandem compound with HP and LP sections. The HP section is a single

flow turbine where as the LP is double flow. The individual turbine rotors and the

generator rotor are connected by rigid couplings.

The HP turbine has been constructed for throttle control governing. The initial steam is

admitted before the blading by two combined main steam stop and control valves. The

steam from HP exhaust is led to the LP turbine through cross around pipes.

Additional steam from the LP stage is waste heat recovery generator is passed to the LP

turbine via two combined LP stop and control-valves.

HP Turbine

The HP turbine is of single flow; double shell construction horizontally split castings.

Allowance is made for thermal movement is the inner casing within the outer casing. The

main steam enters the inner casing from top and bottom. The provision of inner casing

confines high steam inlet temperature and pressure conditions to the flange of the outer

casing is subjected only to the lower pressure and temperature effective at the exhaust

from the inner casing.

LP Turbine

The casing of the double flow LP turbine is of three-shell design. The shells are of

horizontally spilt welded construction. The inner casing which carries the first rows of

stationary blades is supported on the inner-outer casing rests at four points on

longitudinal girders, independent of the outer casing. Three guide blade carries, carrying

the last guide blade rows are bolted to the inner-outer casing.

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3.3 COMBINED CYCLE

Two gas turbines and one steam turbine put together is called a combined cycle block.

Combined cycle power plant integrates two power conversion cycles, Brayton cycle (gas

turbine) and Rankine cycle (steam turbine) with the principle objective of increasing

overall plant efficiency.

Brayton cycle

Gas turbine plants operate on this cycle in which air is compressed. The compressed air is

heated in the combustor by burning fuel, a part of the compressed air is used for

combustion and the flue gases produced are allowed to expand in the turbine which is

coupled with the generator. The temperature of exhaust is in the range of 500-550 C.

Rankine cycle

The conversion of heat energy to mechanical energy with the aid of steam is based on this

thermo dynamic cycle. In its simplest way cycle works as follows.

The initial state of the working fluid is water which at a certain temperature is pressurized

by a pump and fed to boiler. In the boiler the pressurized water is heated at constant

pressure. Super heated steam is expanded in the turbine which is coupled with a

generator. Modern steam power plants have steam temperature in the range of 5000C-

5500C at the inlet of the turbine.

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COMBINING TWO CYCLES TO IMPROVE EFFICIENCY

The gas turbine’s exhaust heat can be recovered using waste heat recovery boiler to run a

steam turbine on Rankine cycle. If the efficiency of Gas turbine cycle is 30% and the

efficiency of Rankine cycle is 35% then overall efficiency becomes 45%. Conventional

fossil fuel fired boiler of the steam power plant is replaced with a heat recovery steam

generator-HRSG. The exhaust gases from the gas turbine is led to the HRSG where heat

of exhaust gases utilized to produce steam at desired parameters as required by the steam

turbine.

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4. STATION PROTECTION SYSTEM

INTRODUCTION TO POWER PLANT PROTECTION

Our modern working lives would be inconceivable without power supply systems,

instrumentation and control equipment, IT networks and much more besides. They have

become matter-of-fact and we realize their significance only when they breakdown. The

potential scenario ranges from a brief interruption in the work to bankruptcy. Only good

protection can prevent that.

Modern power systems are complex systems growing fast with more generators,

transformers and large network. For system operation a high degree of reliability is

required. In order to protect the system from damage due to undue currents or abnormal

voltage caused by faults, the need of reliable protective devices such as relays and circuit

breakers arises. Such a protective mechanism would enable the electricity supply

company deliver power to consumers continuously with in specified limit of voltage and

frequency.

The protection scheme is to protect the station equipments from abnormal condition.

Such a scheme should consist of protective relays and circuit breakers. Protective relays

functions as the sensing device, it sense the fault, determines its location, send a tripping

command to the breakers. The circuit breaker then disconnects the faulty element. A

number of relays are used in power protection system depending on the kind of fault to be

detected, the equipment to be protected by the relay, location etc. any such relay plays

and important role and must be reliable, efficient and fast in operation. By clearing the

fault fast with the help of fast acting protective relays and associated circuit breakers,

damage to the apparatus can be avoided or reduced by removing the faulty section.

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The purpose of protection systems are

� Minimise damage

� Leave unaffected equipments in service

� Maintain equipment operating limits

� Maintain electrical system stability

4.1 RELAYS

Relays are devices by means of which an electric circuit can be controlled

(opened/closed) by the change in the same circuit or the other circuit. The protective

systems are necessary with almost every electric plant. The power systems comprise

many diverse items of equipments which are very expensive, so the complete power

system represents a very large capital investment. No matter how well designed, faults

will occur on a power system and these faults may represent a risk of life and property.

The provision of adequate protection to detect and disconnect the elements of power

system in the event of fault is therefore an integral part of power system design. In order

to fulfil the requirements of protection with optimum speed for the many different

configurations, operating conditions and construction feature of the power system, it has

been necessary to develop many types of relays that respond to various functions if the

power system quantities.

Figure: 1

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Relays may be classified according to the technology used

� Electromechanical

� Static

� Numerical

4.2 ELECTRO-MECHANICAL RELAYS

Electromechanical relays are the conventional relays having movable sub assemblies.

The operation of such relays depending upon the electromagnetic attraction or

electromagnetic induction effects of electric current. The protection system if the plant is

implemented by using electro mechanical relays, except a fewer number of static relays.

Electro mechanical relays can be classified to several different types:

� Attracting armature type

� Polarised attracted armature relay

� Moving coil

� Induction type

� Thermal

� Motor operated

� Mechanical

Principles of operation commonly used in relays are discussed below:

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4.2.1 ATTRACTED ARMATURE RELAY

These are the simplest class and most extensively used relays. The operation principle is

as follows. Current or voltage applied to the coils produce flux, which attracts the

armature or the plunger against a restraining spring. They are fast acting and are suitable

for use as instantaneous over current and over voltage relays and also for auxiliary

functions. In actual execution, they come with a range of settings accomplished by taps to

change number of turns or by changing spring tension. The formal is a step change and

the continuous variation. The operational force is proportional to the square of current in

the coil. Relays tend to chatter, which is reduced by slugging. Operating time can be

delayed by slugging.

Figure: 2

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4.2.2 MOVING COIL TYPE

The motor action of current carrying conductor in a magnetic field produces a moving

system, which is the basis for moving coil indicating instruments and relays. The core

inside the coil is a permanent magnet. The magnetic circuit is completed by concentric

mild steel tube giving an annular gap in which swings the moving coil. The coil is wound

on aluminium former. The induced eddy current in this provides necessary damping

effect. With power permanent magnet, very low energy input produces adequate torque

and hence very sensitive relays are possible.

Figure: 3

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4.2.3 INDUCTION TYPE RELAYS

The next class of relays are induction type relays, which are again subdivided into

induction disk type, induction cup type etc. Induction relays are most widely used for

protective relaying. In principle, it is a split phase induction motor. Alternating current or

voltage applied to main coil produces magnetic flux most of which passes through the

disk. The shortest turns of lag coil on one of the legs cause a time and phase shift in the

flux through leg into the disk. The main and this phase shifted flux (�1, �2) inducing

eddy currents (i1, and i2) in this disk. The current induced by one flux reacts with other

flux to produce forces that act on the bottom.

The net force F2 – F1 � I�2sin�

Figure: 4

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where � is the angle by which one flux leads other. The net torque produces force is

uniform at all instance of the cycle. For single quantity, the torque is proportional to the

square of the quantity. The spiral spring provides for the reset of contacts on removal of

operating quantity. The contact closing time depends on the magnitude of the operating

quantity. Hence an inverse time characteristics result. The current setting is by taps on

the coil and time dial setting is by adjustment of spacing between the contacts. The relay

overshot results because of inherent inertia of the moving system. Because of the heavy

moving components, the relay operation is not fast.

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4.3 STATIC RELAYS

A static relay referred to the relay, which has no armature or other moving elements. The

measurement is carried out by stationary electronics circuits. The solid state components

used are transistors, resistors, capacitors and so on. The response is developed by

electronic, magnetic, optical or other components without mechanical motion. Static

relays have quick response, long life, shock proof, fewer problems of maintenance, high

reliability and high degree of accuracy.

Figure: 5

4.4 NUMERICAL RELAYS

Conventional electromechanical and static relays are hard wired relays. Their wiring is

fixed, only their setting can be manually changed. Numeric relays are programmable

relays. The characteristics and behaviour of the relay are can be programmed. They have

numerous advantages. They have small burden on CT’s and PT’s. They can process and

display the signals efficiently, accurately and fast as possible manner.

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4.5 CHARACTERISTICS OF RELAY

SELECTIVITY

When a fault occurs, the protection scheme is trip only that circuit breaker. This

operation is required to isolate the fault, and then this property of selecting tripping is

also called discrimination and is achieved by two general methods which are time

grading and unit system. Protection systems in successive zones are arranged to operate

in times that are graded through the sequence of equipments so that upon the occurrence

of a fault, although a number of protection equipments response, only these relevant to

the fault zone complete the tripping function. It is possible to design protection system

that responds only to fault condition occurring within a clearly defined zone. This type of

protection system is called unit protection.

STABILITY

The term stability is usually associated with unit protection scheme and refers to the

ability of the protection system to remain unaffected by conditions external to the

protection zone.

SPEED

The function of protection system is to isolate fault of the power system as rapidly as

possible. The main objective is to safe guard continuity of the supply by removing each

disturbance before it leaves to wide spread loss of synchronism and consequent collapse

of the power system.

SENSITIVITY

The sensitivity is a term frequently used when referring to the minimum operating level

(current, voltage, power etc.) of relays or complete protection schemes. The relay or

scheme is said to be sensitive if the primary operating parameters are low.

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5. NEED OF INSTRUMENT TRANSFORMERS

Whenever the value of voltage or current in power circuit is too high to permit

convenient direct connection of measuring instruments or relays, coupling is made

through transformers. Such measuring transformers are required to produce a scale down

replica of the input quantity to the accuracy expected for the particular measurement.

Protective relays are actuated by current and voltage supplied by current and voltage

transformers. These transformers provide insulation against the high voltage of the power

circuit, and also supply the relays with quantities proportional to those of the power

circuit, but sufficiently reduced in magnitude so that the relays can be made relatively

small and inexpensive. The proper application of current and voltage transformers

involves the consideration of several requirements such as: mechanical construction, type

of insulation (dry or liquid), ratio in terms of primary and secondary currents or voltages,

service conditions, accuracy, and connections. Protective relays in power systems are

connected to the secondary circuit of current transformer and potential transformers. The

design and use of these transformers are quite different from that of well-known power

transformers. Both current transformers and potential transformers come under the type

instrument transformers.

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6. TRIPPING MECHANISM

Figure: 6

The operation of relay depends on whether operating torque/force is greater than

restraining torque or force i.e. the relay operates if the net force F is positive or net torque

T is positive.

F = FO − Fr

F� Net force

FO� Operating force

Fr� Restraining force

OR

T = To− Tr, T� Net torque

To� Operating torque, Tr� Restraining torque

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The figure shows the basic connection of the CB control for the opening operation. The

circuit to be protected is shown by the thick line. When a fault occurs in the protective

circuit the current and voltage in the secondary of the associated CT and PT varies which

will activate the relay and the relay operates. We say the relay has picked up. The relay

pick up is due to anyone of the basic principle such as electromagnetic, thermal etc.

Hence when a relay picks up, closes the relay contact, completes the tripping circuit,

which in turn energizes the CB, which will operate and isolate the faulty section from the

healthy one.

Auxiliary relays assist protective relays. They may be instantaneous or may have a time

delay. They relieve the protective relays from duties like sounding an alarm.

6.1 INTER TRIPPING

Inter tripping is the controlled tripping of a circuit breaker so as to complete the isolation

of the circuit or piece of apparatus associated with the tripping of other circuit breakers.

The main use of such a scheme is to ensure that protection at both end of a faulted circuit

will operate to isolate equipment concerned.

6.2 DIRECT TRIPPING

In direct tripping applications, inter trip signals are sending directly to the master trip

relay. The method of the command circuit causes circuit breaker operation. The method

of communication must be reliable, because any signal detected at the receiving end will

cause a trip of the circuit at that end. The connection system designed must be such that

on the communication circuit does not cause spurious trips should a spurious trip occurs,

considerable unnecessary isolation of the primary system might result, which is at best

undesirable and at worst quiet unacceptable.

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6.3 PERMISSIVE TRIPPING

Permissive trip commands are always monitored by a protection relay. The circuit

breaker is tripped when receipt of commands coincides with operation of protection relay

at the receiving end responding to a system fault. Requirement for the communication

channel are less than for direct tripping schemes, since receipt of an incorrect signal must

coincide with operation of the receiving end operation for a trip operation to take place.

The intentions of these schemes are to speed up tripping for faults occurring within the

protected zone.

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TRIPPING SCHEME OF GAS TURBINE GENERATOR UNITS (GTG 1 & GTG 2)

MASTER RELAY

EQUIPMENTS/BREAKERS TRIPPED

186A1

Gas turbine, Generator circuit breaker, Field circuit breaker,

High voltage circuit breaker, Unit auxiliary transformer

breaker

186A2 Gas turbine, Generator circuit breaker, Field circuit breaker.

186D2 Generator circuit breaker, Field circuit breaker

186C High voltage circuit breaker

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6.4 RELAY SETTINGS

GAS TURBINE GENERATOR

DEVICE DESCRIPTION RANGE SET VALUES

59 G1 Generator over voltage

relay

105−170%;0−5sec 120%

59 G2 Generator over voltage

relay

105−170%;0−5sec Definite time:

110%; 2 sec

Instantaneous: 145%

64 G1 Generator stator earth

fault relay

5.4− 20 V PSM: 5.4 V

TSM: 0.1

64 G2 Generator stator earth

fault relay

2−14 MA;

0.1−6.4 sec

PSM: 5.4 V

TSM: 0.1

64 GIT Generator inter turn

fault relay

5.4− 20 V PSM: 5.4 V

TSM: 0.1

64 GT Earth fault relay 5.4− 20 V PSM: 5.4 V

TSM: 0.1

80 G1 Group 1 DC supply

supervision relay

25− 60% 60%

80 G2 Group 2 DC supply

supervision relay

25− 60% 60%

81 G1 Under frequency relay 10.001− 500 Hz;

0.1− 21 sec

F1 47.4 Hz

T1: 0.21sec;

T2: 0.22 sec

81 G2 Under frequency relay 10.001Hz;

0.1− 21 sec

F1 47.4 Hz

T1: 0.21sec; T2:

0.22 sec

87 G1 Generator differential

relay

5− 20%

PMS: 0.25 A

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87 G2 Generator differential

relay

5− 20% PSM: 0.25 A

99 G Generator over flux

relay

Inverse: 1−1.25

High set: 1− 1.5

K1: 1.15; K2: 1.3

99 GT Generator transformer

over fluxing relay

Inverse: 1−1.25

High set: 1−1.5

K1: 1.15 K2: 1.3

2/99GT Time delay relay for

99 GT.

0.1− 1 sec 0.2 sec

51 G Generator definite time

over load relay

50− 200%;

2.5− 25 sec

4.32A; 25 sec

21 GRY

21 GYB

21 GBR

Generator back up

impedance relay

3− 12 ohm K1: 12 ; K2: 0.5

2A/21 G Time delay for 21 G 0.5− 5 sec 1 sec

32 G1 Generator reverse

power relay

0.5− 5%;

0.5− 5 sec

Power: 0.5%

Time: 5 sec

32 G2 Generator reverse

power relay

0.5− 5%; 0.5− 5

sec

Power: 0.5%

Time: 5 sec

40 G Generator field failure

relay

5− 50 ohm;

0.5− 4 ohm

K1: 0.855, K2: 2ohm

K3: 0 ohm, K4:2ohm

K5: 36 ohm

2A/40G Time delay relay for

40G

1− 10 sec 2 sec

2B/40G Time delay for 40 G 2.5− 25 sec 3 sec

27 G Under voltage relay for

40 G

30− 90% 30%

46 G Generator negative

sequence relay

12s: 7.5− 30%,

12s: 10%

K1: 10

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SINGLE LINE DIAGRAM – RGCCPP KAYAMKULAM

220kV BUS

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7. PROTECTION SCHEMES

7.1 DIFFERENTIAL PROTECTION

To respond quickly to a phase fault with damaging heavy current, sensitive, high speed

protection is normally applied to generators rated in excess of 1 MVA. In generators the

occurrence of phase to phase and three phase faults are rare and less common than phase

to earth faults. When they occur they are match more severe in intensity and require high

speed clearance, if considerable damage to both the stator and rotor is to be avoided.

Differential relays take a variety of forms, depending on the equipment they protect. The

definition of such a relay is “one that operates when the vector difference of two or more

similar electrical quantities exceeds a predetermined amount.” Most differential-relay

applications are of the current-differential type. The dashed portion of the circuit of

Figure: 10 represent the system element that is protected by the differential relay. This

system element might be a length of circuit, a winding of a generator, a portion of a bus,

etc. The secondaries of the CT’s are interconnected, and the coil of an over current relays

connected across the CT secondary circuit.

Figure: 8

Now, suppose that current flows through the primary circuit either to a load or to a short

circuit located at X. The conditions will be as in Figure 10. If the two current

transformers have the same ratio, and are properly connected, their secondary currents

will merely circulate between the two CT’s as shown by the arrows, and no current will

flow through the differential relay.

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Figure: 9

But, should a short circuit develop anywhere between the two CT’s, the conditions of

Figure: 12 will then exist. If current flows to the short circuit from both sides as shown,

the sum of the CT secondary currents will flow through the differential relay. It is not

necessary that short-circuit current flow to the fault from both sides to cause secondary

current to flow through the differential relay. A flow on one side only, or even some

current flowing out of one side while a larger current enters the other side, will cause a

differential current. In other words, the differential-relay current will be proportional to

the vector difference between the currents entering and leaving the protected circuit; and,

if the differential current exceeds the relay’s pickup value, the relay will operate.

Figure: 10

The differential protection is one which responds to the vector difference between two or

more similar electrical quantities. In generator protection, the current transformers are

provided at each end of the generator armature windings. When there is no fault in the

windings and for through faults, the currents in the pilot wires fed from CT connections

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are equal. The differential current I1s−I2s is zero. When fault occurs inside the protected

winding, the balance is disturbed and the differential current I1s−I2s flows through the

operating coil of relays causing relay operation. Thereby the generator circuit breaker is

tripped. The field is disconnected and discharged through suitable impedance.

Differential relay provides fast protection to stator winding against to phase faults and

phase to ground fault. Differential relay is recommended for generators above 2 MVA.

Differential relay does not respond to through fault and overload.

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GENERATOR DIFFERENTIAL PROTECTION (87G1)

Generator differential protection is connected across generator terminals through two

current transformers CT 1 and CT 9. This is a single zone protection which protects the

generator from three phase, phase to phase and phase to earth fault. Once the set value

exceeds, 87G1 is picked up, it will actuate an auxiliary relay 87G1X, which in turn

actuates the master relay 186A2. The master relay 186A2 sends tripping command to trip

circuits of gas turbine, generator circuit breaker, field breaker. Another generator

differential 87G2 is also employed as a backup to 87G1.

Figure: 11

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7.2 REVERSE POWER PROTECTION (32G1)

For generators operating in parallel with a mains or another generator, it is imperative to

supervise the power direction. If for example the prime mover fails the alternator

operates as a motor and drives the prime mover (diesel or turbine). The reverse power

relay detects the reverse of the power direction and in case of this error switches off the

alternator. This way, power losses and damages of the prime mover are avoided. The

failure of prime mover of a generating set will keep the set running as a synchronous

motor, taking the necessary active power from the network and could be detrimental to

the safety of the set, if maintained for any length of time. The amount of power taken

will depend on the type of prime mover involved and typical values are:

Diesel generator 15 to 25% of rated power

Gas turbines 10 to 15% of rated power

Steam turbine 5 to 7.5% of rated power

These values refer to the condition when power input to the prime mover is completely

cut off. The reverse power relay essentially has two electromagnets. The upper magnet is

coupled with voltage coil energized by a potential transformer. The lower magnet has

current coil energized by a CT. The flux �1 produced by voltage coil lags voltage by 90

degree. Current through current coil lags voltage by an angle � and flux produced by the

current coil is almost in phase with current. Driving torque,

T � �1�2sin�

T � VI sin (90−�)

T � VI cos�

T � power

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If the phase angle � becomes more than 90 degree, torque reverses and relay trips the

circuit. When power flows in the normal direction, the relay will be rendered inoperative.

However, power flows in the reverse direction, the flux set up by the actuating quantities

and the two winding develop positive operating torque and relay contact will be closed.

The figure shows the scheme employed for reverse power protection. The relay 32G1 has

a voltage winding energized from VT3 and a current winding energized from CT3. The

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32G1 picks up for reverse power , then it activates the master relay 186D2. . The relay

32G2 is a back up to 32G1 with same tripping time.

Figure: 12

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7.3 GENERATOR IMPEDANCE RELAY (21G)

Impedance relays are used to cover the protection against phase to phase fault, phase to

earth fault, double phase to earth fault and three phase fault. Impedance relay works on

the principle of impedance of a circuit. In an impedance relay, the torque produced by a

current element is balanced against the torque of a voltage element. The current element

produces positive (pick up) torque, where as the voltage element produces (reset) torque.

In impedance relay two torques created by the electromagnetic action of the voltage and

current and these two quantities are mechanically coupled. The solenoid B is voltage

excited from the secondary of PT. The clockwise torque Tb is developed by the solenoid

B which pulls the plunger P2 downward and tends to rotate the balance arm in the

clockwise direction. The spring acts as a restraining force and sets up mechanical torque

in clockwise direction as shown. Another solenoid A, which is current excited from

secondary of CT connected to the line to be protected and produces torque Ta in anti-

clockwise direction which tends to pull the plunger P2 downwards. Under ordinary

circumstances when there is no fault and equilibrium prevails, then the balance arm

remains horizontal and relay contacts are open. However when fault occur, the current in

current transformer goes up and increases the torque Ta. Also added to this effect the

magnitude of the torque Tb decreases since the voltage drops with the fault.

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On the implementation scheme current coil of impedance relay 21G is energized by CT4,

voltage coil is energized by VT2. 21G activates at an impedance of 5 ohm. The relay

21G in turn energizes a set of timer relays 2A/21G with a set value of 1 sec, 2A/21G

activates auxiliary relay 2A/21GX,2A/21GX then activates 2B/21G. Also the relay

2A/21G energizes 186C. The 2A/21GX energizes the master relay 286C. 2B/21G in turn

activates 186A1 the tripping time of 2B/21G is 0.2 sec.

Figure: 13

7.4 OVER VOLTAGE PROTECTION (59G1, 59G2)

The field excitation system of generators is usually arranged so that over voltage

conditions at normal running speed cannot possibly occur. The conditions where over

voltage other than transient over voltage, do occur is when the prime mover speed

increases due to a sudden loss of load. The control governors of industrial prime movers

are inherently very sensitive to speed change and resulting increase from any sudden loss

of load is normally checked before any dangerous overload conditions can arise. Over

voltage protection is generally recommended for all hydro-electric or gas-turbine

generators they are subjected to over speed and consequent over voltage and loss of load.

Over voltage on a generator may also occur due to transient surges on the network, or

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prolonged power frequency over voltages may arise from a variety of condition. Surge

arresters may be required to protect against transient over voltages, built relay protection

may be used to protect against power frequency over voltages.

A sustained over voltage condition should not occur for a machine with healthy voltage

regulator, but it may be caused by the following contingencies.

a. Defective operation of the automatic voltage regulator on the machine is in isolated

operation.

b. Operation under manual control with the voltage regulator out of service. A sudden

variation of the load, in particular the reactive power component, will give rise to a

substantial change in voltage because of the large voltage regulation inherent in a

typical alternator.

c. Sudden loss of load may cause a sudden rise in terminal voltage due to the trapped

field flux and/or over speed.

The overload relay has two electromagnets. The upper electromagnet has two windings;

one of these is primary and is connected to the secondary of voltage transformer. A plug

setting bridge is normally provided for adjusting the number of primary windings so that

the desired voltage setting can be achieved. The secondary winding is energized by

induction from primary, and is connected in series with winding on the lower magnet. By

this arrangement, leakage fluxes of upper and lower electromagnets are sufficiently

displaced in space to set up a rotational torque on the aluminium disk. This torque

opposes the restraining force provided by the spring. Under normal operating condition,

the restraining torque is greater than the driving torque produced by the relay voltage.

However if the voltage exceeds the preset value the driving torque become greater than

restraining torque. Consequently the disk rotates and moving contact bridges the fixed

contacts when the disk rotated through a preset angle.

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On the implementation scheme the generator unit has two over voltage relays named

59G1 and 59G2. Both energized by VT2. The relay 59G1 activates at 120% of rated

voltage. 59G1 in turn activates the master relay 186D2. The relay 59G2 activates

auxiliary relay 59G2X. This in turn activates 186D2 and 286D2. 59G2 activates at 110%

of rated value of voltage. If the voltage is 145% of rated value, the acts instantaneously.

Figure: 14

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7.5 ABNORMAL FREQUENCY PROTECTION RELAY

Generator is limited in the degree of abnormal frequency operation that can be tolerated.

At reduced frequencies there will be a reduction in the output capability of generator.

Also there will be an increase in vibratory stresses which may cause cracking of some

parts of the blade structure. Primary under frequency protection for turbine generators is

provided by the implementation of automatic load shedding programs on the power

system. These load shedding programs are designed to:

a) Shed enough loads to relieve the overloading on connected generation.

b) Minimize the risk of damage to the generating plant.

c) Quickly restore system frequency to near normal.�

Two types of abnormal frequency conditions can occur on a power system.

Under Frequency condition due to sudden reduction in input power through the loss of

generator importing power.

Over frequency condition due to sudden loss of load or exporting power.

Under Frequency Condition:

During an under frequency operation f the unit it is almost certain to be accompanied by

high value of load current drawn from the generator. This could result in exceeding the

short time thermal capability of the generator. The limitations on generators operating in

an under frequency condition are less restrictive than those placed on the turbine.

However when generator protection is required it has been industry practice to provide

over current protection.

Over Frequency Condition:

Over frequency is usually a result of sudden reduction in load and therefore is usually

associated with light load or no load operation. During over frequency operation machine

ventilation is improved and the flux densities for a given terminal voltage are reduced. If

the generator voltage regulator is left in service at significantly reduced frequencies the

volts per hertz limitation of a generator could be exceeded.

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UNDER FREQUENCY RELAYS

Under frequency relays are commonly associated with gas turbines and are used to

prevent the possibility of over loading the generator in the event of severe loss of

generating capacity on failure of governor speed control system.

Over loading a generators perhaps due to loss of system generation and insufficient load

shedding can lead to prolonged operation of the generator at reduced frequencies. This

can cause particular problems for gas and steam generators which are susceptible to

damage from operation outside of the normal frequency band. The turbines are usually

considered to be more restrictive than the generator at reduced frequencies because of

possible mechanical resonance in the many stages of the turbine blades. If the generator

peed is close to the natural frequency of any of these blades, there will be an increase in

vibration. Cumulative damage to these blades due to vibration can lead to cracking of the

blade structure. While load shedding is the primary protection against generator

overloading, under frequency relay should be used to provide additional protection.

Modern switch gear systems use digital technique for the measurement of frequency. The

reference value of frequency is supplied by a built-in high precision quartz crystal

oscillator of 100 KHz. The oscillations of the oscillator are counted during one cycle of

the system under supervision. If the number of oscillations counted during one cycle

exceeds the set number, means that the measured frequency is lower than the set value

for the time of measurement.

Two under frequency relays 81G1 and 81G2 in implemented in gas turbine generator

units. Both are connected to the secondary of voltage transformer VT2. 81G1 picks up,

when frequency falls below 47.4 Hz, it activates the master relay 186C and 81G2 in turn

activates 286A1. The master relays then send trip commends to corresponding breakers.

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Figure: 15

7.6 FIELD FAILURE PROTECTION

Partial or total loss of field on a synchronous generator is detrimental to both the

generator and the power system (to which it is connected. The condition must be quickly

detected and the generator isolated from the system to avoid generator damage. A loss of

field condition which is not detected can also have a devastating impact on the power

system by causing both a loss of reactive power support as well as creating a substantial

reactive power drain. On large generators this condition can contribute to or trigger an

area wide system voltage collapse. This section of the tutorial discusses the generator

loss of field characteristics and schemes to protect the generator from loss of field

conditions.

A synchronous generator requires adequate dc voltage and current in its field winding to

maintain synchronism with a power system. There are many types of exciters which are

used in the industry including rotating dc exciters with conventional commutators

rotating brushless rectifier sets and static exciters.

Normally the generator field is adjusted so that reactive power as well as real power is

delivered to the power system. If the excitation system is reduced or lost, the generator

absorbs reactive power from the power system rather than supplies it. Generators have

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low or reduced stability in this area. If a total loss of field occurs and the system can

supply sufficient reactive power without a large terminal voltage drop, the generator may

run as an induction generator, otherwise: synchronism will be lost. Die change from

normal overexcited operation to under excited operation upon loss of field is not

instantaneous but occurs over a time period depending on the generators output level and

connected system capability. Complete loss of excitation occurs when the direct current

source of the machine field is interrupted. The loss of excitation can be caused by such

incidents as field open circuit, field short circuit, accidental tripping of the field breaker,

regulator control system failure, loss of field to the main exciter, loss of an ac supply to

the excitation system.

When a synchronous generator loses its excitation it will run at higher than synchronous

speed and operate as an induction generator delivering real power to the system but at the

same lime obtains its excitation from the system becoming a large reactive drain on the

system. This large reactive drain cayses problem for the generator, adjacent machines

and the power system. The system impact of loss of field to a generator depends on

stiffness of the connected system, load on the generator prior to the loss of field�and the

size of the generator.�

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GENERATOR FIELD FAILURE RELAY (40G)

When a synchronous generator losses excitation, it operates as an induction generator,

running above synchronous speed. Round-rotor generators are not suited to such

operation because they do not have amortisseur windings that can carry the induced rotor

currents. Consequently, a steam-turbine-generator’s rotor will over heat rather quickly

from the induced currents flowing in the rotor iron, particularly at the ends of the rotor

where the currents flow across the slots through the wedges and the retaining ring, if

used. The length of time to reach dangerous rotor over heating depends on the rate of

slip, and it may be as short as 2 or 3 minutes. Salient-pole generators invariably have

amorttisseur windings, and, therefore, they are not subject to such overheating. The stator

of any type of synchronous generator may overheat, owing to over current in the stator

windings, while the machine is running as an induction generator. The stator current may

be as high as 2 to 4 times rated. Such overheating is not apt to occur as quickly as rotor

overheating. The relay recommended for field failure protection is an impedance relay. It

works on the principle of ratio of voltage and current. In impedance relay two torques

created by the electromagnetic action of the voltage and current and these two quantities

are mechanically coupled. The clockwise torque Tb is developed by the solenoid B

which pulls the plunger P2 downward and tends to rotate the balance arm in the

clockwise direction. The spring acts as a restraining force and sets up mechanical torque

in clockwise direction as shown. Another solenoid A, which is current excited from

secondary of CT connected to the line to be protected and produces torque Ta in anti-

clockwise direction which tends to pull the plunger P1 downwards. Under ordinary

circumstances when there is no fault and equilibrium prevails, then the balance arm

remains horizontal and relay contacts are open. However when fault occur, the current in

current transformer goes up and increases the torque Ta. Also added to this effect the

magnitude of the torque Tb decreases since the voltage drops with the fault.

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Figure: 16

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8. DESIGN AND SIMULATION

OF NUMERICAL RELAY

USING PIC16F72.

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8.1 Generator Relay Panel in NTPC

Presently the relay system used in NTPC-RGCCPP is of electromechanical type, mainly

induction type and differential type relays. Relay protection has been divided into various

schemes based on the type of device to be protected. The electromechanical relay devices

occupy large amount of space in the panel board. Although accuracy is maintained at a

better level it can be improved by the use of numerical relays. Traditional

electromechanical and static protection relays offers single-function and single

characteristics. Range of operation of electromechanical relays is narrow as compared to

numerical relay.

Figure: 17

Electromechanical Relay makes use of mechanical comparison devices, which cause the

main reason for the bulky size of relays. It uses a flag system for the indication purpose

whether the relay has been activated or not. Electromechanical relay do not have the

ability to detect whether the normal condition has been attained once it is activated thus

auto resetting is not possible and it has to be done by the operating personnel.

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Figure: 18

The disadvantages of a conventional electromechanical relay are overcome by using

microcontroller for realizing the operation of the relays. Microcontroller based relays

perform very well and their cost is relatively low.

Numerical relays are highly compact devices, characterized with fast operation, high

sensitivity, self monitoring and low maintenance. First generation numerical relays were

mainly designed to meet the static relay protection characteristic, whereas modern

numeric protection devices are capable of providing complete protection with added

functions like control and monitoring. Numerical protection devices offer several

advantages in terms of protection, reliability, and trouble shooting and fault information.

Numerical protection devices are available for generation, transmission and distribution

systems.

Modern power system protection devices are built with integrated functions. Multi-

functions like protection, control, monitoring and measuring are available today in

numeric power system protection devices. Also, the communication capability of these

devices facilitates remote control, monitoring and data transfer.

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Modern numeric protection offers multi-function and multiple characteristics. Some

protections also offer adaptable characteristics, which dynamically change the protection

characteristic under different system conditions by monitoring the input parameters.

The measuring principles and techniques of conventional relays (electromechanical and

static) are fewer than those of the numerical technique, which can differ in many aspects

like the type of protection algorithm used, sampling, signal processing, hardware

selection, software discipline, etc.

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8.2 PIC MICROCONTROLLER

PIC is a family of Harvard architecture microcontrollers made by Microchip Technology.

The name PIC initially referred to “Programmable Interface Controller”.

PICs are popular with both industrial developers due to their low cost, wide availability,

large user base, extensive collection of application notes, availability of low cost or free

development tools, and serial programming (and re-programming with flash memory)

capability.

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The PIC architecture is distinctively minimalist. It is characterized by the following

features:

• Separate code and data spaces (Harvard architecture)

• A small number of fixed length instructions

• Most instructions are single cycle execution (4 clock cycles).

• A single accumulator (W), the use of which (as source operand) is implied (i.e. is not

encoded in the opcode)

• All RAM locations function as registers as both source and/or destination of math and

other functions.

• A hardware stack for storing return addresses.

• Data space mapped CPU, port, and peripheral registers.

• The program counter is also mapped into the data space and writable (this is used to

implement indirect jumps).

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Unlike most other CPUs, there is no distinction between memory space and register space

because the RAM serves the job of both memory and registers, and the RAM is usually

just referred to as the register file or simply as the registers.

Data space (RAM)

PICs have a set of registers that function as general purpose RAM. Special purpose

control registers for on-chip hardware resources are also mapped into the data space. The

addressability of memory varies depending on device series, and all PIC devices have

some banking mechanism to extend the addressing to additional memory.

Code space

All PICs feature Harvard architecture, so the code space and the data space are separate.

PIC code space is generally implemented as EPROM, ROM, or flash ROM. In general,

external code memory is not directly addressable due to the lack of an external memory

interface.

Word size

All PICs handle data in 8-bits, so they should be called 8-bit microcontrollers. However,

the unit of addressability of the code space is not generally the same as the data space.

Stacks

PICs have a hardware call stack, which is used to save return addresses. The hardware

stack is not software accessible on earlier devices, but this changed with the 18 series

devices.

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Instruction set

PICs instructions vary from about 35 instructions for the low-end PICs to over 80

instructions for the high-end PICs. The instruction set includes instructions to perform a

variety of operations on registers directly, the accumulator and a literal constant or the

accumulator and a register, as well as for conditional execution, and program branching.

Some operations, such as bit setting and testing, can be performed on any numbered

register, but bi-operand arithmetic operations always involve W; writing the result back

to either W or the other operand register. To load a constant, it is necessary to load it into

W before it can be moved into another register.

Limitations

The PIC architectures have several limitations:

• Only a single accumulator

• A small instruction set

• Memory must be directly referenced in arithmetic and logic operations, although

indirect addressing is available via 2 additional registers

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8.3 PIC 16F72 MICROCONTROLLER

PIC16F62 is a 28-pin, 8-bit CMOS Flash drive with A/D converter. Features of

PIC16F72 are:

� ��Only 35 single word instructions to learn

�� All single cycle instructions except for program�branches, which are two-cycle

�� Operating speed!��DC – 20 MHz clock input

� � ��DC – 200 ns instruction cycle

� ��2K x 14 words of Program Memory,�128 x 8 bytes of Data Memory (RAM)

�� Interrupt capability

�� Eight-level deep hardware stack

�� Direct, Indirect and Relative Addressing modes�

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Peripheral Features

1. High sink/source current: 25mA

2. Timer0: 8-bit timer



5. 8-bit, 5 channel analog-to-digital converter

6. Synchronous serial port

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CMOS Technology

1. Low power, high speed CMOS FLASH technology

2. Wide operating range : 2.0V to 5.5V

3. Industrial Temperature Range.

4. Low power consumption.

Special Microcontroller Features

1. 1000 erase/write cycle FLASH program memory.

2. Programmable code protection.

3. Power saving sleep mode.

4. Processor read access to program Memory

Pin Diagram

Figure: 19

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8.4 Numerical Relay Deign Considerations

Mainly five relays viz. Impedance relay, Under Frequency relay, Over-voltage relay,

Field Failure relay and Reverse power relay have been designed and simulated using

microcontroller . The design considerations are given below:

Impedance Relay

Set value Z = 5 ohm

Normal Operating Condition

Original Voltage V = 10.5 kV

Original Current I = 7440 A

Display Voltage (Output of P.T) V = 110V

Display Current (Output of C.T) I = 5A

Z value under normal operating condition = V/I = 110/5 = 22 ohm which is greater than 5

ohm and the relay should not act.

When Fault Occurs

Original Voltage V = 9.058 kV

Original Current I = 28420 A

Display Voltage V = 94.9V

Display Current I = 19.1 A

Under this condition Z1 = 4.9 ohm

Thus Z1 < Z therefore the relay closes.

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Under Frequency Relay

Normal Operating frequency 50Hz

Range of Frequency 47.4 Hz to 52.6 Hz

Condition to be checked: a. Unsynchronized

b. Synchronized

In unsynchronized condition, if frequency falls below 47.4Hz the relay should not act.

In synchronized condition if frequency falls below 47.4 Hz the relay should act.

Over Voltage Relay

When the prime mover speed increases due to a sudden loss of load over voltage may

occur��Over voltage protection is generally recommended for all hydro-electric or gas-

turbine generators they are subjected to over speed and consequent over voltage.�Over

voltage on a generator may also occur due to transient surges on the network, or�

prolonged power frequency over voltages.� Surge arresters may be required to protect

against transient over voltages, built relay protection may be used to protect against

power frequency over voltages.�

Normal voltage = 10.5 kV

If Voltage rises to 120% of normal voltage relay should act.

120% of Normal Voltage = (120*10.5kV)/100 = 12.6 kV

Display Value = 132 V; i.e. if V >= 132V relay should close.

Reverse Power Relay

Normal speed of operation = 3000 RPM

Frequency f = (N * P)/ 120

When speed decreases to 2843 RPM; frequency also decreases to 47.3Hz, which is under

frequency condition and the under frequency relay should act.

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E.M.F generated by generator is proportional to frequency, therefore when frequency

decreases, generated voltage also decreases this may cause reversal of power and the

generator under consideration may draw power from other parallel operated generators

and may work as motor in order to prevent this Reverse Power Relay should act.

Field Failure Relay

If excitation system is connected relay should not act.

If excitation system is disconnected relay should act.

When Impedance or Reverse Power or Over Voltage relay acts correspondingly the

master relays 186A1, 186D2 and 186A2 will act. Since these master relays get activated,

contacts of Field Circuit Breaker opens up i.e. field system will get disconnected from the

generator and this should actuate the field failure relay.

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8.5 SOFTWARE

PIC16F72 has been programmed using Basic language for the relay operation. The

programming has been done in Proton – IDE software which is then converted to HEX

format using the conversion software PICkit – 2 and the HEX converted program is

written into the flash memory of PIC16F72. Program has been written based on the

following flowchart.

Screenshot for Proton – IDE

Screenshot for PICkit - 2

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FLOWCHART

B A

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B A

Figure: 20

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8.6 HARDWARE

Hardware for the Numerical relay simulation circuit mainly consists of two sections:

a. Input Simulator

b. Numerical Relay with microcontroller

Input Simulator

For the simulation of relay the fault conditions are generated using an input simulator

which generates the normal working conditions of the generating plant such as voltage,

current, frequency, speed of turbine and excitation condition. By varying the values of

these quantities fault conditions can be generated for making the relay to act.

Figure: 21

Numerical Relay

Numerical relay is designed with the help of PIC16F72 microcontroller, which compares

various inputs with the set values. When a fault condition is generated using input

simulator, the input to microcontroller violates the relay set conditions which cause the

controller to send trip signal to relay devices and thus the relay acts.

Figure: 22

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Figure: 23

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8.7 COMPONENT LIST

COMPONENTS SPECIFICATION QUANTITY

IC

PIC16F72

74HC595

MC7805

2

4

1

LCD DISPLAY LCD 16 x 2 1

DIODE IN4007 8

CAPACITOR

15pF

1000�F

100�F

0.1�F

10�F

4

1

1

8

3

RESISTOR

1K

10K

470K

1M

2.2K

560�

180 �

5

14

23

29

5

5

2

TRANSISTOR BC547 5

LED 8

RELAY 61-121CE 5

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SCHEMATIC DIAGRAM FOR NUMERICAL RELAY USING PIC16F72

Figure: 24

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SCHEMATIC DIAGRAM FOR NUMERICAL RELAY SIMULATOR (SHEET NO. 1)

Figure: 25

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SCHEMATIC DIAGRAM FOR NUMERICAL RELAY SIMULATOR (SHEET NO. 2)

Figure: 26

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8.8 ADVANTAGES OF NUMERICAL RELAY

1. Multiple functions can be achieved using numerical relay.

2. The size of numerical relay panel is small as compared to electromechanical relay panel.

3. Time and date of fault occurrence can be automatically recorded.

4. Cost can be reduced significantly.

5. Auto resetting can be achieved

6. Better accuracy of operation.

7. Can be reprogrammed as per the working requirement

8. Installation time required is very less as connections required are small.

8.9 DISADVATAGES OF NUMERICAL RELAY

1. Operating life of numerical relay is only about 20 years.

2. It requires continuous power supply for its operation.

3. Any error in the software may cause severe damage to devices associated with it.

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CONCLUSION

Accommodating different functions in the same case enables significant saving in space,

and in auxiliary cabling. With numerical relays there are no more requirements for

spacious control and relay rooms, numerous cables in and between cubicles, which

reduces the installation time. Combining several functions enables manufacturers to

produce one uniform design of a protection for different applications comparing with a

wide range of electromechanical relays particularly designed for generator, transmission,

distribution or industrial protection.

Numerical relays are environmentally friendly because of very small amount of raw

material used for their manufacturing, easy dismantling and the good component rate of

recovery and recycling.

The future scope for numerical relay system is the online remote data exchange between

numerical relays and remotely located devices offers remote relay settings applications,

data processing for network operations and maintenance, or remotely analyzing recorded

fault data.

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REFERENCES

1. AREVA – Relay Operating Manual.

2. www.areva-td.com 3. www.microchip.com

4. A Course in Power Systems – J.B Gupta

5. en.wikipedia.org

6. www.ntpc.co.in 7. Journal on Numerical Relays – Jalica Polimac, Aziz Rahim

i

APPENDIX

Appendix – I

Coding for PIC16F72

Numerical Relay

Include "numrly.inc"

Declare ADIN_RES 8 ' 10-bit result required

Declare ADIN_TAD FRC ' RC OSC chosen

Declare ADIN_STIME 50 ' Allow 50us sample time

Symbol VOLT_IN PORTA.0

Symbol CURRENT_IN PORTA.1

Symbol FREQ_IN PORTC.2

Symbol SYNC_IN PORTC.1

Symbol FIELD_VOLT_IN PORTC.0

Symbol IMP_RELAY PORTB.0

Symbol FREQ_RELAY PORTB.1

Symbol CUR_REV_RELAY PORTB.2

Symbol OVER_VOLT_RELAY PORTB.3

Symbol FIELDFAIL_RELAY PORTB.4

Low PORTA

Low PORTB

Low PORTC

' |76543210|

TRISA = %11111111

TRISB = %00000000

TRISC = %11111111

ADCON1 = %00000000 ' Set analogue input on PORTA.0

Dim VOLT As Word

Dim CURRENT As Word

Dim FREQ As Word

Dim RPM As Word

Dim RPMVal As Float

Dim Err As Byte

Dim CntVal As Byte

Low PORTB

DelayMS 3000

Err = 0

Loop:

VOLT = ADIn 0

ii

CURRENT = ADIn 1

RPM = ADIn 2

If CntVal <= 1 Or CntVal = 4 Then

FREQ = Counter FREQ_IN, 1000

End If

VOLT = VOLT * 10

CURRENT = CURRENT * 10 / 5

RPMVal = RPM * 16.123

If (VOLT / CURRENT) < 5 Then

FIELDFAIL_RELAY = 1

IMP_RELAY = 1

Err 0# = 1

Else

IMP_RELAY = 0

Err 0# = 0

End If

If SYNC_IN = 1 And FREQ < 475 Then

FIELDFAIL_RELAY = 1

FREQ_RELAY = 1

Err 0.1 = 1

Else

FREQ_RELAY = 0

Err 0.1 = 0

End If

If VOLT > 1300 Then

FIELDFAIL_RELAY = 1

OVER_VOLT_RELAY = 1

Err 0.2 = 1

Else

OVER_VOLT_RELAY = 0

Err 0.2 = 0

End If

If RPMVal < 2844 Then ' < 1768 Then 'rpm = 2844 relative volt = 3.43v

FIELDFAIL_RELAY = 1

CUR_REV_RELAY = 1

Err 0.3 = 1

Else

CUR_REV_RELAY = 0

Err 0.3 = 0

End If

If FIELD_VOLT_IN = 0 Or Err > 0 Then

If CntVal >= 1 Then

FIELDFAIL_RELAY = 1

If CntVal < 4 Then

CntVal = CntVal + 1

End If

Else

CntVal = CntVal + 1

End If

Else

FIELDFAIL_RELAY = 0

CntVal = 0

End If

GoTo LOOP

End

iii

Appendix – II

VISUAL BASIC – SCREENSHOTS.

SCREENSHOT - SHEET NO.1

SCREENSHOT - SHEET NO.2

iv

SCREENSHOT – SHEET NO.3

SCREENSHOT SHEET NO.4

v

VB Coding

Private Sub END_Click()

End

End Sub

Private Sub FEILDFAILURE_Click()

RELAYSH4.FF40G.BackColor = &HC000&

RELAYSH4.FF40GX.BackColor = &HC000&

RELAYSH4.FFA40GY.BackColor = &HC000&

RELAYSH4.FFT40GZ.BackColor = &HC000&

RELAYSH3.FF40GZ.BackColor = &HC000&

RELAYSH3.M186D2.BackColor = &HC000&

If RELAYSH3.M186D2.BackColor = &HC000& Then

RELAYSH2.GCB.BackColor = &HFF&

RELAYSH1.FCB.BackColor = &HFF&

End If

End Sub

Private Sub OVERFLUXING_Click()

RELAYSH4.OVF99G.BackColor = &HC000&

RELAYSH3.OV99G.BackColor = &HC000&

RELAYSH3.M186A1.BackColor = &HC000&

If RELAYSH3.M186A1.BackColor = &HC000& Then


RELAYSH2.HVCB.BackColor = &HFF&

RELAYSH2.CB.BackColor = &HFF&


RELAYSH1.GASTURBINE.BackColor = &HFF&

End If

End Sub

Private Sub OVERVOLTAGE_Click()

RELAYSH4.OV59G2.BackColor = &HC000&

RELAYSH4.OV59G2X.BackColor = &HC000&

RELAYSH3.OV59G2X.BackColor = &HC000&

RELAYSH3.M186D2.BackColor = &HFF&




End If










End If

End Sub

Private Sub PHASETOEARHTFAULT_Click()

RELAYSH4.IM2A21G.BackColor = &HC000&

vi

RELAYSH4.IM2A21GX.BackColor = &HC000&

RELAYSH4.IM2B21GX.BackColor = &HC000&

RELAYSH3.IM2A21G.BackColor = &HC000&

RELAYSH3.IM2B21G.BackColor = &HC000&


RELAYSH3.M186C.BackColor = &HC000&




RELAYSH2.CB.BackColor = &HFF&



End If

If RELAYSH3.M186C.BackColor = &HC000& Then


End If

End Sub

Private Sub PHASETOPHASEFAULT_Click()

RELAYSH4.D87G1.BackColor = &HC000&

RELAYSH4.D87G1X.BackColor = &HC000&

RELAYSH3.D87G1X.BackColor = &HC000&






End If

End Sub

Private Sub REVERSEPOWER_Click()

RELAYSH4.RP32G1.BackColor = &HC000&

RELAYSH4.RP32G1X.BackColor = &HC000&

RELAYSH3.RP32G1X.BackColor = &HC000&





End If










End If

End Sub

Private Sub STATOREARTHFAULT_Click()

RELAYSH4.SEF64G1.BackColor = &HC000&

RELAYSH4.SEF64G1X.BackColor = &HC000&

RELAYSH3.SEF64G1X.BackColor = &HC000&



vii












End If

End Sub

Private Sub UNDERFREQUENCY_Click()

If BFSYNCH.Value = True Then

UF81G1.BackColor = &HFFFFFF

UF52HX.BackColor = &HFFFFFF

ElseIf AFSYNCH.Value = True Then

UF81G1.BackColor = &HC000&

UF52HX.BackColor = &HC000&

RELAYSH3.UF52HX.BackColor = &HC000&

RELAYSH3.M186C.BackColor = &HC000&


End If

End Sub

Private Sub RESET_Click()

RELAYSH4.FF40G.BackColor = &HFFFFFF

RELAYSH4.FF40GX.BackColor = &HFFFFFF

RELAYSH4.FFA40GY.BackColor = &HFFFFFF

RELAYSH4.FFT40GZ.BackColor = &HFFFFFF

RELAYSH3.FF40GZ.BackColor = &HFFFFFF

RELAYSH3.M186D2.BackColor = &HFFFFFF

RELAYSH4.OV59G2.BackColor = &HFFFFFF

RELAYSH4.OV59G2X.BackColor = &HFFFFFF

RELAYSH3.OV59G2X.BackColor = &HFFFFFF


RELAYSH4.RP32G1.BackColor = &HFFFFFF

RELAYSH4.RP32G1X.BackColor = &HFFFFFF

RELAYSH3.RP32G1X.BackColor = &HFFFFFF


RELAYSH4.SEF64G1.BackColor = &HFFFFFF

RELAYSH4.SEF64G1X.BackColor = &HFFFFFF

RELAYSH3.SEF64G1X.BackColor = &HFFFFFF

RELAYSH3.M186A2.BackColor = &HFFFFFF

RELAYSH4.UF81G1.BackColor = &HFFFFFF

RELAYSH4.UF52HX.BackColor = &HFFFFFF

RELAYSH3.UF52HX.BackColor = &HFFFFFF

RELAYSH3.M186C.BackColor = &HFFFFFF

RELAYSH4.D87G1.BackColor = &HFFFFFF

RELAYSH4.D87G1X.BackColor = &HFFFFFF

RELAYSH3.D87G1X.BackColor = &HFFFFFF


RELAYSH4.IM2A21G.BackColor = &HFFFFFF

RELAYSH4.IM2A21GX.BackColor = &HFFFFFF

viii

RELAYSH4.IM2B21GX.BackColor = &HFFFFFF

RELAYSH3.IM2A21G.BackColor = &HFFFFFF

RELAYSH3.IM2B21G.BackColor = &HFFFFFF


RELAYSH3.M186C.BackColor = &HFFFFFF

RELAYSH1.FF40G.BackColor = &HFFFFFF

RELAYSH4.OVF99G.BackColor = &HFFFFFF

RELAYSH3.OV99G.BackColor = &HFFFFFF


End Sub

ix

Appendix – III

PCB DESIGN

INPUT SIMULATOR

x

NUMERICAL RELAY

xi

APPENDIX - IV

1. DATA SHEET – PIC16F72

2. DATA SHEET – 74HC595

Date post:	27-Apr-2015
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Numerical Relay - Final Report - Winston Netto

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