Sample Report

STUDY AND RENOVATION OF EXCITATION AND REGULATION OF VOLTAGE SYSTEM OF EDEA II TURBO-ALTERNATORS.

WRITTEN BY NDIFON KENNETH A. Page 1

DEDICATION

This piece of work is dedicated to my family especially to my mother Mama

Nange Josephine who is of blessed memory for bringing me into this world RIP.



ACKNOWLEDGEMENT

This work successfully saw the light of day due to the ceaseless efforts and

valuable contributions of some persons. In this light I say thanks to:

Prof Tanyi Emmanuel, Dean, Faculty of Engineering and Technology and Head

of department Electrical and Electronic Engineering. For your unequivocal,

unflinching support in making industrial attachment for me a dream comes true. I

remain ever grateful to you and your staff and pray the Almighty to continue

showering His wisdom and favour on you all. Mr Ahmadou Bivoung, Director

Edea Hydro Power plant. For the warmth, enthusiastic and fatherly reception you

gave me upon arrival and throughout my stay in the plant. This kind gesture of

yours really brought light in me and gave me hope of a successful internship in

the hydro power plant. Mr Ahmadou Ndotti, Head of Maintenance Division .

For the fatherly love you showed us through out internship period in your

division, To my supervisor Mr Tuekam Gabriel head of Automatic and

Auxiliaries Department I think you for your effective follow up and comfort

you gave me through out my internship and for this work to see the lamp light.

Mr. Tchakouteu Celestine, head of service for low current equipment and

laboratory in Automation and auxillaries department who has been my eye opener

for automatic systems control with his endless effort trying to let me understand

every work we did in plant . Mr Wefonge James For his fatherly care and he

effectively follow up in the plant .Mr Mundi Eugene who provided me with

shelter through out my stay in Edea only God can fully reward you .Dr Mborong

who from time to time created time to visit us in Edea . Gratitude also goes to all

my lecturers to name a few Dr. Tsafack Pierre my programme coordinator, Mr

Fotso Raul, Mr Obenufunde. Mr Nguajep Seurge . To my brother and friend

Mr Chongwain Gilbert who has contributed enormously for this piece of work

to come to reality.

To my parents, family members, brothers and sisters, friends and well-

wishers.For the timely, unflinching all round support you gave me.



TABLE OF CONTENTS

DEDICATION ........................................................................................................i

ACKNOWLEDGEMENTS....................................................................................ii

TABLE OF CONTENTS.......................................................................................iv

GENERAL INTRODUCTION.......1

CHAPTER ONE

PRESENTATION OF AES SONEL

1)GENERALITIES ABOUT AES SONEL........3

IDENTIFICATION FORM OF AES SONEL........................................................3

1.2 HISTORICAL BACKGROUND..3

1.2 ) MISSION OF AES SONEL............................................................................4

1.3.1) PRODUCTION OF ELECTRICAL ENERGY............................................4

1.3.2) TRANSMISSION.........................................................................................5

1.3.3) DISTRIBUTION...........................................................................................5

1.5) . HYDROELECTRIC POWER PLANT EDEA .............................................8

1.5.1) LOCATION OF THE PLANT.....................................................................8

1.5.2) HISTORICAL BACKGROUND OF THE PLANT.....................................9

1.5.3) ORGANISATION OF THE PLANT........................................................10

1.5.4) OPERATION OF THE PLANT.................................................................14

1.5.5) OBJECTIVE OF THE PLANT...................................................................17

1.6) PRINCIPLE OF ELECTRICAL ENERGY PRODUCTION IN

THEPLANT..........................................................................................................19

CHAPTER TWO

DEPARTMENT OF AUTOMATION AND AUXILARIES

2.1) INTRODUCTION..................................................................................20

2.2) ROLE OF THE DEPARTMENT................................................................20



2.3) TYPES OF AUXILIARIES.......................................................................20

2.3.1) DC AUXILIARIES : ..............................................................................20

2.3.2) AC AUXILIAIRES : ...............................................................................21

2.4) AUTOMATES (PLCs) .................................................................................21

2.5 SOME OF THE JOBS THE INTERN PARTICIPATED ........................ 22

CHAPTER THREE

STUDY AND RENOVATION OF EXCITATION AND REGULATION OF

VOLTAGE SYSTEM OF EDEA II TURBO-ALTERNATORS

3.1) ABSTRACT. .............................................................................................27

3.2) INTRODUCTION...................................................................................27

3.3) DESSRIPTION OF EDEA II EXCITATION SYSTEMS:.........................28

3.4) FUNCTIONS OF GOOD A GENERATOR EXCITATION SYSTEMS.29

3.5) EXCITATION SYSTEMS ........................................................................30

3.6) TYPES OF EXCITATION SYSTEMS. ...................................................30

3.6 .1) STATIC EXCITATION SYSTEMS ...................................................31

3.6 .1.2) DRAWBACKS OF STATIC EXCITATION SYSTEM31

3.6.2) DC EXCITATION SYSTEM. ................................................................31

3.6.2.1) IT DRAWBACKS OF DC EXCITATION SYSTEM ........................32

3.6.3) AC EXCITATION SYSTEMS 33

3.6.3.1) DRAWBACKS OF AC EXCITATION SYSTEM..33

3.6.4) BRUSHLESS AC EXCITATION SYSTEMS ..33

3.7 WHY SHOULD BRUSHLESS AC EXCITATION SYSTEM BE CHOSEN

FOR EDEA II?.....................................................................................................35

I. ADVANTAGES ..35

II. RESULTS36

III .FACTS36

IV GENERAL CHARACTERISTICS:............................................................40

4) DE-EXCITATION AND OVERVOLTAGE PROTECTION OF

GENERATOR EXCITATION SYSTEM .........................................................40



4.1) REQUIREMENTS OF DE-EXCITATION.................................................41

4.2)CLASSIFICATION OF DE-EXCITATION SYSTEM ..41

4.3 PRINCIPLE OF DC DE-EXCITATION................................................... 42

4.3 DE-EXCITATION RESISTANCE............................................................42

4.4 DESIGN OF DE-EXCITATION ...............................................................43

5. AUTOMATIC VOLTAGE REGULATOR. .................................................43

5.1) REQUIREMENTS FOR AUTOMATIC VOLTAGE REGULATOR.44

5.1) CHOSING A VOLTAGE REGULATOR FOR EDEA II TURBO-

ALTERNATORS ................................................................................................45

5.2 REASONS WHY RT2DB EXCUTATION-REGULATION SYSTEM IS

CHOSEN FOR EDEA II.......................................................................................45

5.3) RT2DB EXCITATION AND VOLTAGE REGULATION SYSTEM FOR

SYNCHRONOUS GENERATORS ...................................................................45

5.3.1ADVANTAGES...........................................................45

6) DETAIL DESCRIPTION OF RT2DB EXCITATION AND VOLTAGE

REGULATION SYSTEM ...46

6.1) POWER STAGE ......46

6.2)CONFIGURATION OF THE ELECTRONICS 47

6.3) AUTOMATIC CHANNEL ...........................................................................48

6.4) HAND CHANNEL ....................................................................................49

6.4.1) CHANNEL SWITCH OVER AND FOLLOW-UP CONTROL.49

6.5) OPERATION ...............................................................................................50

6.6)INSTRUMENTATION AND OPERATION ......51

6.7) DE-EXCITATION AND OVERVOLTAGE PROTECTION 51

6.8)MECHANICAL FEATURES ......................................................................51

6.9) OPTIONAL FRAME ASSEMBLY............................................................ 52

6.10) GENERAL TECHNICAL DATA OF THE RT2DB DIGITAL

EXCITATION SYSTEM ...................................................................................55

CONCLUSION.....................................................................................................56



General Introduction

Electric power systems are real-time energy delivery systems. Real time means

that power is generated, transported, and supplied the moment you turn on a

switch. An electric power system starts with generation, by which electrical

energy is produced in the power plant and then transformed to high-voltage

electrical energy that is more suitable for efficient long-distance transportation.

The power plants transform other sources of energy in the process of producing

electrical energy. For example, heat, mechanical, hydraulic, chemical, solar,

wind, geothermal, nuclear, and other energy sources are used in the production of

electrical energy. High-voltage (HV) power lines in the transmission portion of

the electric power system efficiently transport electrical energy over long

distances to the consumption locations. Finally, substations transform this High

Voltage electrical energy into lower-voltage energy that is transmitted over

distribution power lines that are more suitable for the distribution of electrical

energy to its destination, where it is again transformed for residential,

commercial, and industrial consumption.

In Cameroon, electrical energy is supplied by the company AES Sonel which

depends mostly on water (hydro) for energy production.

Hydro sector in Cameroon produces 87% of all power production. The remaining

13% is produced by thermal and gaz plants built to boost up energy production in

the country. These plants go operational mostly during the dry season when the

water level is low. In Edea where this report is written energy is produced from

water. The 276MW Edea Hydroelectric projects, located on the Sanaga River is

the second largest in Cameroon. The energy production process is summarised

below: Water is held at a height and is forced to flow through a penstock to

turbines. As the water hits the turbines, they are set in to motion. The turbines are

mechanically coupled to generators through a shaft which can either be vertical or

horizontal. The hydraulic energy of the water is converted in to kinetic energy by



the turbines. This kinetic energy sets the shaft in to motion which in turn sets the

generators in to motion. As the generator rotates by virtue of this kinetic energy,

magnetic field lines are cut; flux varies, producing current hence voltage. This

voltage is then stepped up and send to the public sector and the ALUCAM

Company.



CHAPTER ONE

PRESENTATION OF AES SONEL

1) GENERALITIES ABOUT AES SONEL

1.1) IDENTIFICATION FORM OF AES SONEL

FULL NAME Socit Nationale dElectricit du Cameroun

ACRONYM AES SONEL

LOGO

ADDRESS P.O. BOX : 4077 Douala

TEL : (237) 33 42 83 09 (Grouped line)

CALL CENTRE: 77 11 77 11; 99 11 99 11; 33 42 33

33

LEGAL STATUS Parastatal

DATE OF CREATION 18th July 2001

CAPITAL 43.903.690.000 FCFA

COMMERCIAL

REGISTERED NUMBER

4624

ACTIVITIES Production, Transmission, Distribution and

Commercialization of electrical energy in Cameroon

and to some neighbouring countries

GENERAL MANAGER Jean David Bile

1.2 HISTORICAL BACKGROUND

Everything started in 1929 by Companie Coloniale de Distribution dEnergie

Electrique (CCDEE) which ensured the supply of electrical energy to Yaounde,



Douala and Nkongsamba. This gave birth to Energie Electrique du Cameroun

(ENELCAM) in 1948 which had as objective to distribute electrical energy it

produced.

On October 22nd 1962 POWERCAM was created which was in charge of

transmitting and distributing electrical energy to the Anglophone part of

Cameroon. On 15th July 1965, Electricit du Cameroun (EDC) was created which

ensured the distribution of electrical energy in the eastern part of Cameroon

except Edea which was taken care of by ENELCAM.

18th May, 1974 marked the fusion of ENELCAM and EDC to give rise to SONEL

(SOCIETE NATIONAL DELECTRICITE), and then in 1975 POWERCAM was

absorbed in order to harmonize the production, transmission and distribution of

electrical energy in Cameroon.

AES SONEL came as a result of the privatization of SONEL on 18th July, 2001

by AES-SIROCCO LIMITED, a subsidiary of AES-CORPORATION based at

Arlington in the United States of America (USA), for an amount of 23 billion

FCFA in order to possess 56% of the capital of which 51% is for AES

corporation and 5% for the AES SONEL staff and 44% for the Cameroon state.

1.2 ) MISSION OF AES SONEL

AES SONEL has as mission to produce, transmit, distribute and commercialize

electrical energy to be consumed by Cameroon .They aspired to supply the

neighbouring countries like Tchat in a nearby feature.

1.3.1) PRODUCTION OF ELECTRICAL ENERGY

AES SONEL uses two forms of electrical energy production in Cameroon:

Hydroelectric production, Thermal and Gas production. It has two types of

interconnected networks; Northern Interconnected Network (NIN) and Southern

Interconnected Network (SIN).

AES SONEL has a production capacity of about 918 MW divided as follows:

a. Southern Interconnected Network

- Hydroelectric plants: 648 MW

- Thermal plants : 171.3 MW

b. Northern Interconnected Network

- Hydroelectric plants: 72 MW

- Thermal plants : 24.15 MW

c. Isolated Thermal plants



- Installed in regions that are not covered by interconnected networks: 10.4

MW.The active power each hydroelectric power plant produces is shown in

the table below.

PLANTS ACTIVE POWER (MW)

Songloulou 384

Edea 276

Lagdo 72

Songloulou and Edea hydroelectric power plants are built on river Sanaga while

Lagdo hydroelectric power plant is built on river Benoue.

1.3.2) TRANSMISSION

For electrical energy transmission, AES SONEL, mostly uses overhead

transmission. That notwithstanding underground transmission is also used, but

mostly for short distances. The voltages that AES SONEL uses for high voltage

(HV) transmissions are 225KV, 90KV and 110KV.

1.3.3) DISTRIBUTION

The distribution of electrical energy is done using the following voltages:

Medium Voltage (MV): 30KV, 15KV and 10KV

Low Voltage (LV): 380V (phase to phase)/220V (phase to neutral)

1.1) SAFETY POLICIES AND CORE VALUES OF AES SONEL

The slogan of AES SONEL is Safety is my No 1 priority. It has two safety

policies; Environmental policy and sanitary policy.

The five core values are;

- SAFETY: We will always put safety firstfor our people, contractors and

those in the communities we serve.

- INTEGRITY: Our people are honest, trust worthy and dependable.

Integrity is at the core of all we dohow we conduct ourselves, how we

perform our jobs and how we interact with one another and all of our stake

holders. Our people can be trusted to meet our commitment and to perform.

- COMMITMENT: We have commitment to our stake holders. We want

our businesses on the whole to make a possible contribution to society.

- EXCELLENCE: We want to be best in all that we do. We will perform at

world-class levels and provide high quality and reliable services to our

customers.



- FUN: We want our people to enjoy our work, to appreciate the fun of being

part of a successful team that is making a difference. We work because

work is fun, fulfilling and exciting. And when it stops being that way, we

will change what or how we do things.

TEN SAFETY RULES

1) When in a car, fasten your seat belt.

2) When on a motorbike, wear a crash helmet.

3) Any work on a low voltage facility, which has not been locked out (short

circuited), must be done while wearing insulated gloves and using insulated

tools eye protection.

4) No one shall be authorized to directly or indirectly go close to a High

Voltage (HV) or Medium Voltage (MV) without visible grounding and

short circuit devices except for authorized AES SONEL locked up

operators or qualified persons directly under their supervision.

5) Any work outside safe platform with a risk of falling from a height of over

1.8m must be carried out with a shock absorber device or a protection in

case of fall (from 01/01/2009).

6) Nobody shall be around or lifting equipment during mechanized lifting of

handling.

7) Hazardous material shall not be discharged into the environment.

8) Entry into a confined space must always be preceded by a risk assessment

and a written authorization from a unit head.

9) Any one working around flowing water must wear a life jacket with rope

tight to a fixed point or boat.

10. For any diving operation, there must be a rope to maintain permanent

communication between the diver and the surface rescue team. Each

worker including interns in AES SONEL must have Personal Protective

Equipment (PPE) which comprises of:



- A security helmet

- Safety shoes

- overalls

Fig1 Safety wears for head, feet and body

- Gloves: The choice of gloves depends on the type of work we want to do.

Shown below are some types of gloves used by AES SONEL technicians.

a) A pair of handling gloves and a pair of MV gloves (from left to right)

respectively.



- Eye glasses

Fig 1.1 Safety wears for hands and eyes

1.5) . HYDROELECTRIC POWER PLANT EDEA

The Edea hydroelectric power plant is part of the production plants in Cameroon

and the oldest in the country. The plant has an installed active power of 276MW.

In order to produce this power, the plant needs a water flow rate of 1200m3/s.

1.5.1) LOCATION OF THE PLANT

The plant is based in the Sanaga maritime division of the Littoral region. It is

built onriver Sanaga and has a dam that permits it tooperate its 14 units. The dam

here is not a storage dam because all the water that it houses is used immediately.

River Sanaga is the longest river in Cameroon with a length of 918km. It was

chosen because it has a very high flow rate due to its high slope basin

(13500km3).

River Sanaga can not be sailed before Edea. It takes its source from the Adamawa

plateau beside Meiganga at an altitude of 1200m. In Edea, its altitude at edea is

30m.

Flow rate: During the dry season, the flow rate in Edea is 200m3/s while during

the rainy season the flow rate can rise up to 7000m3/s.

The Sanaga has three branches in Edea:

- Left bank at 5km upstream from Edea, here we have bras de la garre

- Right bank before the dam, we have the derivation du bras mort

- Le bras central on which the dam is built.



The bras de la garre and the bras mort are blocked by submersible decks.

The picture below is the top view of the edea power plant.

Fig 1.2 Top view of the Edea hydro power plant.

1.5.2) HISTORICAL BACKGROUND OF THE PLANT

The civil engineering aspect of the power plant was carried out in one session, but

the installation of complete machine sets (units) ready for energy production took

place in three phases.

Phase one saw the setting up of three machines (units 1-3) purposely

for public sector consumption between the years 1949-1953 each

with a total active power output of 11.1MW. This unit were recently

replaced by modern systems that incorporate the SCADA for

automatic control and also elevates the rated active power output to

16.4MW.

Some two years later, following a partnership agreement that was

signed between ALUCAM and SONEL, six machines (units 4-9)

with rated active power output of 20MW each were installed

between the years 1955- 1958 to mark the second phase. The output



from these machines is purposely dedicated to drive the wheels of

this company.

The third phase of installation aimed to reinforce the public sector

and the near-by company ALUCAM took place in two stages. Stage

one executed between the years 1967-1970 saw the erection of two

machines (units 10 and 11) each having a rated active power output

of 21.4MW. The outputs from these two units are adapted to either

feed the public sector of ALUCAM in an Exclusive- OR logic

manner. The second stage carried out between the years 1971-1975

marked the installation of the last machines of the power plant (units

12-14) each with rated active power output of 21.4MW purely for

public sector reinforcement.

These three phases of machine installation have been baptised with the names

Edea I, Edea II and Edea III respectively.

1.5.3) ORGANISATION OF THE PLANT

The Edea hydroelectric power plant is divided into three main divisions.

- Division of Technical and Administrative support

- Exploitation and control division

- Maintenance division



The chart below shows the organisation of the plant.

FUNCTIONS OF THE VARIOUS DIVISIONS

HSE SERVICE

The HSE service is charged with the following responsibilities:

To carry on regular checks to ensure that workers and following the safety

procedures.

Plant manager

Division of Technical and Administrative

support

Engineering and reporting

Administration and accountancy

Provision and store Service

Accounting and Budget

Exploitation Division

Exploitation team A

Exploitation team B

Exploitation team C

Study Service

Maintenance Division

Department of maintenance of turb-alternator generators

and HV-MV equipment

Department of maintenance of

auxiliaries, automatiion,

regulation, workshop, LV equipment

HSE ServiceAdministrative

support



To sensitise workers and visitors on the different risk they can get exposed

to the plant.

The supply of all security wears (helmets, safety boots etc) passes through

this office before it is channelled to the appropriate individuals.

To educate visitors and workers on what a single, double or triple siren

signal mean respectively. In case of emergency that will be signalled by

three siren sounds in succession, everybody must abandon whatever they

were doing and head straight for the muster point.

Fig 1.3 Muster point

DIVISION OF TECHNICAL AND ADMINISTRATIVE SUPPORT

This division comprises of eighteen (18) workers. It has as role to provide

technical and administrative support to agents working in all the other

divisions of the plant. It is subdivided into two; Technical support and

Administrative support.



TECHNICAL SUPPORT

The main functions of this department are:

- Support the other divisions in activities like purchase equipment for them.

- Follow up the indication of performance such as auto availability of

machines, labour and finance.

- Civil engineering: maintenance of civil engineering installations

- Take care of vegetation that grows on the dykes.

- Maintenance of air conditioners: In relay rooms and offices.

ADMINISTRATIVE SUPPORT

The administrative support is in charge of the following tasks:

o The supply chain

The supply chain is concerned with the purchase of materials needed in the plant

such as furniture, spare parts and even new machines.

There are two types of purchases; Direct and Indirect purchases

DIVISION OF MAINTENANCE

The division of maintenance as its name implies is in charge of keeping the

machines in perfect states. There are two types of maintenance:

Preventive maintenance: Preventive maintenance which is sometimes called

scheduled maintenance, is a maintenance carried out at regular intervals. This is

the type of maintenance that is done in order to prevent a fault from occurring.

Corrective maintenance: It is a reactive strategy which is usually unplanned and is

carried out after a failure has occurred. The intention is to restore an item to a

state that it can perform its required function.

The division is subdivided into two departments;

1. Department of automation and auxiliaries

2. Department of Turbo-alternators.

1. AUTOMATION AND AUXILIARIES

Automation is a process by which a system is meant to function without human

assistance. And Auxiliaries are equipment that aid in energy production but are

not directly linked to the turbo- alternators. There are two types of auxiliaries



supply sources: ac and dc auxiliaries .This department is also divided into two

services:

The electrical service that takes care of low current electrical equipments Such

as excitation systems.

The mechanical service that also takes care of mechanical equipments such as

compressors.

2. DEPARTMENT OFTURBO-ALTERNATOR

This department is in charge of the turbo-alternators and high voltage equipment

.it subdivided into two services: the electrical service that takes care of electrical

equipment such as power transformers (10/90KV).And the mechanical service

that takes care of mechanical equipment of the alternator such as the turbine and

the shaft

DIVISION OF EXPLOITATION

This division is made up of seventeen (17) workers. They perform the following

tasks:

- Decide when to start a machine.

- Watch over the equipment

- Adjust the equipments parameters such as stator voltages

- Carry out the lotto operation (lock out/tag out)

- Control the supply of energy as demand requires

- They are in contact with the Grid dispatch

- They are in charge of giving report of the plant

The division of exploitation has a supervisor and a team of four.

1) A team of four comprises of:

- A head of shift

- Two machine controllers

- An intervention operator

1.5.4) OPERATION OF THE PLANT

Being a hydroelectric power plant, the primary source of energy is water. The

dam in Edea is not a storage dam because all the water that gets into the dam is

used immediately. During the dry season, the flow rate of the river Sanaga drops

right down to 200m3/s compared to 7000m3/s in the rainy season. For nominal

production, the flow rate of water required is 1200m3/s. To solve the problem of



drastic drop during the dry season, storage dams have been put in place to remedy

the situation of water shortage. These dams include;

Bamendjin

Mbakaou

Map

Fig 1.4 Process of water flow

As mentioned earlier, Edea power plant is divided into three production stations;

Edea I, Edea II and Edea III. The units produce 10.3KV. Each of these stations

has alternators of the same characteristics.



EDEA I: The characteristics of the units are:

The 10.3 KV produced by these alternators is stepped up to 90KV and sent to the

substation

- EDEA II: Alternators characteristics:

Six (6) blade propeller turbine

Rated head : 24m

Rated output: 20MW

Rated speed: 166.7rpm

The 10.3 KV produced by these alternators is sent to ALUCAM

untransformed.

Fig 1.5 ALUCAM 10.3KV evacuation lines

Six (6) blade propeller turbine

Rated head : 24m

Rated output: 16.4MW

Maximum discharge rate: 74.6m3/s




- EDEA III: Alternators characteristics:

Six (6) adjustable blade turbine

Rated head : 24m

Rated output: 21.4MW


The 10.3 KV produced by unit 10 is sent to ALUCAM untransformed

while that produced by the other units is stepped up to 90KV and sent to

the substation. In case unit 10 is faulty and is stopped, unit 11 does the

work of unit 10.

The plant has the following feeders/supply means to supply its consumers:

- Eight10.3KV feeders that goes to ALUCAM. Six from Edea II, the

exchange line connected to the transformer (90KV/10.3KV) of generator

10 and the outputs of either generator 10 or 11 .

- A 15KV feeder that links the plant and ALUCAM. This feeder is the

emergency Feeder. This is normally open. It is used when either the plant

or ALUCAM is in total black out.

- Four 90KV dispatch from the Edea III switch yard: Two goes to

Mangombe (mangombe I and II), one to ALUCAM and the other goes to

Yaounde.

- Two15KV supplies that alternatively supply the town of Edea.

- A 15KV/30KV substation that supply Kribi.

1.5.5) OBJECTIVE OF THE PLANT

The plant has as primary objective to supply ALUCAM/SOCATRAL and the

public sector.

Edea hydroelectric power plant is one of the sources of electrical energy supply to

the SIN.

Below is the single line diagram of the SIN.



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(1.6 ) PRINCIPLE OF ELECTRICAL ENERGY PRODUCTION IN THEPLANT

The plant has a reservoir that can hold water up to 34m above sea level. The used

water head is 24m. The accumulation of water in this reservoir forms the primary

source of energy. The inlet to the penstock is covered with a trash rack. An intake

gate is readily available for the closing of the penstock when need arises. Water

from the reservoir goes into the penstock. The penstock has a circumference of

5m. From the penstock, the water passes through the spiral case, the wicket gate,

impacts the turbine blades and sets the turbine into rotation. The rotating turbine

produces mechanical energy. A shaft mechanically links the turbine to the

alternator. The rotating shaft translates motion from the turbine to the rotor of the

alternator and those of the exciters. The rotor of the alternator is excited with a

direct current called the field current to produce a constant magnetic field in the

rotor. The rotation of the rotor induces a voltage on the stator windings of the

alternator thus electrical energy is produced.



CHAPTER TWO

DEPARTMENT OF AUTOMATION AND AUXILARIES

2.1) INTRODUCTION

This department of automation and auxiliaries as earlier mention is found in the

maintenance division and is in charge of control, protect and maintain all the

automatic and auxiliary equipments.

2.2) ROLE OF THE DEPARTMENT

- It carryout two types of maintenance: preventive and curative maintenance.

Preventive maintenance is done on long term and on short term .long term

annually and short term such as monthly and weekly routines for auxiliary

equipment.

- Curative maintenance is intervention in case of malfunctioning of automatic or

auxiliary equipment.

- Request for materials needed for auxiliary maintenance.

- In charge of industrial automation and regulation.

- In charge of relay stations. Each generator unit is made up of a relay station

- In charge of alternator excitation and de-excitation systems, monitoring system.

- Responsible for all low voltage equipment in the plant such as Computers,

converters, illumination systems, electronic equipment.

2.3) TYPES OF AUXILIARIES

There are two types of auxiliaries supply sources: a.c. and dc.

(2.3.1 ) DC AUXILIARIES :

When ac to dc is performed, we have batteries to store the dc energy. We

have 6V, 300Ah batteries that are connected in series to obtain 120Vdc.And

24v DC.

Role of these auxiliaries:

- Power the PCR (Poste de Commande du Rseaux) Grid dispatch

- Telecommunication systems

- Electronic components of the factory

- Electric protection systems



2.3.2) AC AUXILIAIRES :

- Two auxiliary transformers TA and TB of 90KV/15KV.

- 15KV/220V ; BTA, BTB and BTC

These supply, control and protect the following equipment;

Oil pumping stations

Wicket gate pumping station

Generator oil regulation pumping station

Drainage pit command system

Compressors

Spill way

Lighting system

Cranes

Machine tools found in the mechanical and electrical workshop.

2.4) AUTOMATES (PLCs)

These are components that manage an industrial process without human

assistance.

The various types of automate we have are;

- Voltage regulators: It makes sure that the voltage at the output of the

generator is equal to its rated voltage no matter the disturbance on the

network. The components we can find here are;

A mother board which has a SIM card( for a SARN 3 voltage

regulator)

A supply source

Three thyristors with circuits to command their gates

Fault fuses to protect the thyristors

TSX21 Telemechanique (programming language PL7)

PMA (It is used when we have a problem with the numeric

system)manual

Elements for input and outputs

PID (Proportional Integral Differentiator)

Circuit breakers

Current transformers

Sockets for testing

Power transformers (400/380 V)



Relays

Power contactors

Siren

sensors

Shunts

protective relays

Control relays Regulators

Speed governors: It maintains the frequency of the alternator constant.

These have the following components;

Tachometer controller. A speed detector is on the shaft that measures

the frequency of the alternator

Unit processor (Digital controller)

Two petitioners (turbine wheel and wicket gate)

Regulator of the water level upstream

Generator monitoring system

2.5 SOME OF THE JOBS THE INTERN PARTICIPATED

The intern was integrated in this department and as the days go by, the intern

assisted in so many operations as accounted below: The very first activity carried

out was the cleaning and putting in place all the machines of the mechanical



workshop. This activity of equipment arrangement is

Fig 2.1 Mechanical workshop

The second job that the intern participated in was on the intervention on the

drainage well pump automatic control system, after the pump stop functioning

when verifications where made it was discovered that the circuit breaker of the

automatic system was faulty and it was replaced.The picture of the pump

automatic control system is found below and the box at the upper left end of the

automatic control system casing is circuit breaker .



Fig 2.2 Pump automatic control system.

As the units stay on in production, there is bound to vibration inside the power

plant and consequently dust particles are raised. In the voltage cellules, these dust

particles tend to settle on the conductors that are placed following standardised

distances apart and with respect to the mass. If this process continues and no

cleaning is carried out, it is possible that a phase conductor links the neutral

through these particles. So the high voltage team has as tradition to clean all the

high voltage cellules of the plant once a year sequentially. The very first cleaning

routine that the intern was involved in, was the one carried out on the 10.3KV cell

of generator 7. While there, the intern had the chance to see and touch instrument

transformers, high current rating fuses, line and ground isolator switches and

circuit breaker as well as the opportunity to carry out resistance tests on the

terminals of the circuit breaker using a device called the mega ohm meter to

determine if the device was still functional. The resistance test is carried out at

1000/volt, hence the best resistance values are in the order of Giga and Mega;

kilo ohm resistance values are not acceptable. Following ohm/volt theory above,

it is safe to conclude that for this 10KV voltage cell, the minimum acceptable



resistance value is 10M. Anything less than this threshold value implies the

circuit breaker needs to be replaced.



Fig 2. 3,2.4,2.5,2.6 and 2.7 respectively: Isolator, instrument transformers, fuses

and mega ohm meter

The two Edea town lines powered from the 15KV bus bar was isolated in

order to clean its cellule and to carry out the resistance test on the circuit

breakers to see if it was still functional. The intern was a part of the team

that was charged with this cleaning routine and learned and witnessed the

procedures that leads to the isolation of a line. In order to isolate the town,

the exploitation team began by opening the circuit breaker that connects the

town to the bus bar. Secondly, they pulled down the line isolators to isolate

our area of work from the bus bar and then the ground isolators whose

function is to link all the three supply lines in short circuit to the main earth

of the installation as the first security measure. To add a second safety

measure, the operator uses the virtual voltage detector to test if the isolated

lines still have any charges flowing through them using the active bus bar

as reference. If this test proves negative, the team proceeds to put the

ground jumpers which again links the three conductors to the ground in

short circuit and with this final step completed, the maintenance is cleared

to work.

The new excitation system of unit 10 that uses the programmable logic

controller(PIC) to control the excitation and automatic voltage regulator

process witnessed an excitation voltage failure due to loss of the part of

PLC indicated by the automate. An auxiliary team set out to solve this

problem and the intern was incorporated into the team. After three days of

countless attempts to restore the memory of this system without success,

the team finally decided to bypass it with the aid of a relay whose only

constrain was that all the excitation control will be carried out locally the

relay, which it was later on replaced.



Fig 2.8 Memory of the PLC microcomputer excitation device

The intern with one the technician were assigned to install level sensors at the

turbo-alternator unit five to detect the opening and closing of wicket gates that

varies the flow of water into the turbine.The picture below is the arm of the

wicket gate and the equipment attached to it with the black cable is the level

sensor that was installed.



Fig 2.9 Wicket gate.

The intern also participated with auxiliary team putting on and off some the

groups ( turbo-alternator units) , maintaining the relays, low voltage circuit

breakers, contactors ,signalling systems kilow-wattmeters and connection of the

batteries for dc auxiliaries.



CHAPTER THREE

STUDY AND RENOVATION OF EXCITATION AND REGULATION OF

VOLTAGE SYSTEM OF EDEA II TURBO-ALTERNATORS

3.1) ABSTRACT .

An integral part of generator is excitation systems and new technology of

excitation system has been developed utilizing a power source. The most

important portion of electric power system is synchronous generator due to it

is the source of electrical energy transformation is possible only when generator

excitations exists .the generator excitations systems work when generators

excitation operate a dc charge to the generator heads to energize the magnetic

field around them to enable the electricity that should be generated .There are

brushless and brush-type exciters and generators are build in exciters or charge

can be established from any external source. This chapter present the control

and configuration of a synchronous generator excitation system as a current

mainstream technology which is widely designed for feeding of turbo-generator

excitation winding with auto-regulated DC in generator operation, normal

control and emergency modes. In this chapter we shall discuss appended on the

old excitation system of Edea 2 and the various excitation system models of

synchronous generators and emphasis on drawbacks, different, de-excitation

systems ,possibilities to regulate generator excitation and also append short

descriptions of functions ,compositions, structure and working principle of

generator excitation system and chose the best excitation sytem and automatic

voltage regulator to be implemented in Edea 2 because the present excitation

systems in Edea 2 are old and as a result present frequent faults that makes

them less reliable .This Edea 2 automatic voltage regulator is bad so it does not

have an automatic voltage regulation system, it has but a manual voltage

regulated system which is unreliable and tedious to handle .

3.2) INTRODUCTION

Synchronous generation excitation system is a part of the electrical energy

production system. The excitation system excites the alternator which enables it



to generate electrical energy. As a result high priority is assigned to the reliability

and availability of excitation equipment when choosing an excitation system and

automatic voltage regulator to maintain a constant voltage at generator

terminal for satisfactory main supply.

3.3) DESSRIPTION OF EDEA II EXCITATION SYSTEMS:

The edea 2 excitation system consist of a pilot exciter, the main exciter .The pilot

exciter is connected to the potentiometer and the output of the potentiometer

is connected to the main exciter which is a DC generator ,the field of the main

synchronous generator is fed from this dc generator, called the main exciter

since the field of the synchronous generator is in the rotor, the required dc field

current is supplied to it through slip rings and brushes with the help of a

contactor called the principal excitation contactor. The DC generator is driven

from the same turbine shaft as generator itself. The voltage regulation hear is

done manually through the potentiometer by varying its resistance hence the

excitation current which produces a constant magnetic field in the rotor ,the

rotation of the rotor induces a voltage on the stator windings of the alternator

corresponding to the output voltage. This type of DC excitation system has a

slow response: normally for 10MVA synchronous generator, the exciter power

rating should be 20 to35KW for which we required a huge DC generator. For this

reason, DC excitation systems are gradually disappearing mainly because they

are unreliable.



Figure 3 : Excitation system of Edea II alternators



3.4) FUNCTIONS OF GOOD A GENERATOR EXCITATION SYSTEMS.

The function of generator excitation system contributes stable operation of

power system which is included in three mainstream steps.

1. First is maintaining the voltage of generator to another control points

reference value.

2. Second is control the reasonable distribution of reactive power of parallel

operation unit.

3. It improves the stability of power system.

The first step ensures the safety of operating equipment of power system.

Ensure the economical operation of generator and the equipment for

improvement of capability of maintenance generator voltage consistent

with that for improvement of power system stability in many aspects.

Second step is the drop /voltage drop compensation, drop expressed as

percentage of rated generator voltage when the reactive current of

generator changes to Rated value from zero under such conditions that

voltage-drop compensation unit is switch on, the drop of voltage is

calculated as follows, (D%)=[(Ugo-Ug/Ug]x100%

Where

Ugovoltage at no load.

Ug. Load Voltage.

3.5) EXCITATION SYSTEMS

The basic function of an excitation system is to provide necessary direct current

to the field winding of the synchronous generator. The excitation system must

be able to automatically adjust the field current and maintain the required

terminal voltage. The dc field current is obtained from a separate source called

the Exciter. The excitation systems have taken many forms over the years their

evolution and we are going to discuss the various types of excitation systems.



3.6) TYPES OF EXCITATION SYSTEMS.

The following are the different types of excitation systems:

I. STATIC EXCITATION SYSTEMS

II . DC EXCITATION SYSTEMS

III.AC EXCITATION SYSYTEMS

IV.BRUSHLESS AC EXCITATION SYSYTEMS

3.6 .1) STATIC EXCITATION SYSTEMS

Static excitation system, a portion of the AC from each phase of synchronous

generator output is fed back to the field windings, as excitations, through a

system of transformers, rectifiers, and actors. An external source of DC is

necessary for initial excitation of the field windings. On engine driven

generators, the initial excitation may be obtained from the storage batteries

used to start the engine

( 3.6 .1.2) DRAWBACKS OF STATIC EXCITATION SYSTEM

Difficult to maintain in areas of high vibrations.

Less reliable.

Greatly disappearing from the market.

Slow response

(3.6.2) DC EXCITATION SYSTEM.

DC generator, called exciter since the field of the synchronous generator is in the

rotor, the required field current is supplied to it through slip rings and brushes.

The DC generator is driven from the same turbine shaft as generator itself. One

form of a simple DC Excitation system is shown in figure 1: we required a

hurge DC generator to excite a large synchronous generator. For this reasoned

dc excitation systems are gradually disappearing.



( 3.6.2.1) IT DRAWBACKS OF DC EXCITATION SYSTEM

* There is carbon dust contamination at the end of dc generator.

* The brushes wear out due to the electric arc occurring between the brushes

and the commutate

*The brushes consumed electric energy as it produces sparks

* It increase replacement of parts such as brushes

* DC excitation system has slow responds

* Readily not available



Expensive .To improves the slow response we required a larger dc

generator which makes it more expensive.

3.6.3) AC EXCITATION SYSTEMS .

In AC excitation system, the DC generator is replaced by an alternator of

sufficient rating, so that it can supply the required field current to the field of the

main synchronous generator. In this scheme, three phase alternator voltage is

rectified and the necessary DC supplied is obtained .Generally, two sets of slip

rings, one to feed the rotating field of the alternator and the other to supply the

field of the synchronous generator are required.

The basic block of AC excitation systems are showed in figure in 2.

3.6.3.1) DRAWBACKS OF AC EXCITATION SYSTEM

Difficult to maintain.

Expensive.

Unreliable.

3.6.4) BRUSHLESS AC EXCITATION SYSTEMS

Old type AC excitation system has been replaced by brushless AC excitation

system wherein, inverted alternator (with field at the stator and armature at the

rotor) is used as exciter. A full wave rectifier converts the exciter AC voltage to

DC voltage. The armature of the exciter, the full wave rectifier and the field of

the synchronous generator form the rotating components. The rotating

components are mounted on a common shaft. This kind of brushless AC

excitation system is shown in Fig. 3.



Figure 3:

In this arrangement, the exciter consists of an inverted three phase

alternator which has its three phase armature on the rotor and its field on the

stator. Its AC armature voltage is rectified in diodes mounted on the rotating

shaft and then fed directly into the field of the main synchronous generator.



3.7 WHY SHOULD BRUSHLESS AC EXCITATION SYSTEM BE CHOSEN

FOR EDEA II?.

After studing the four excitation system enumereted above BRUSHLESS AC

EXCTATION SYSTEM has been seen as the best excitation system and should be

chosen for edea ii because of the folowing reasons:

I. ADVANTAGES

* It has Sufficient speed of respnse.

* It has an adequate power capacity in the low range for large alternators

* No carbon dust contamination

* No wear (no electrical no mechanical contacts)

* No consumable parts (brushes)

* No circuit breaker and no field breaker incase of static exciter.

II. RESULTS

Reduced maintenance(from each 3\4months to 5\6 years).

Reduced outage time.

Improve the system by reducing the replaced parts .



III .FACTS

_Made in Switzerland.

_Over 200 delivered brushless exciters.

_Over 45 years of experience

_operating world wide

_For generator from 5 to 250MW.

IV GENERAL CHARACTERISTICS:

Rotor external diameter in mm(330 to 1900mm).

Mounting.



*Horizontal or vertical is possible .

SPEED:

*1800---88 rpm.The fact that the old rotor is rated 187.5rpm implis that

this rotor can convinienly be fitted into the system.

Retrofits

*Modification / re-use of existing parts.

Any Brand

This rotorsfields and excitersfields are produced by ABB company but are not

limited only to ABB motor and generators.



BRUSHLESS EXCITATION ROTOR.

Figure 7,8 are brushless excitation rotors.

Customization:

*Internal fixation (adjustted diameter,old or new exciter shalfcan be coupled)

*Connection to rotor,through the shalf ,external are rigid and flexible.

*Sealed and taped end -winding .

*longer operational life.



INSULATION.

*Vacuum impregnated (VPI Micadure compact) winding.

* CLASS F

*Selected over tested diodes .

*Electrical :forward voltage drop ,endurance.

*Mechenical :Acceleration, storage temperaturewel taken of.

*Easy to replace.

BRUSHLESS EXCITATION STATOR.

Figure 9:

*Customization .

*External housing:

*Re-use or design a new housing.

*Sealing .

*Splitted stator frame.



CLASS F.

*Enamelled copper wire.

* Vacuum impregnated.

*Servce friendly .

* Individual poles.

4) DE-EXCITATION AND OVERVOLTAGE PROTECTION OF GENERATOR

EXCITATION SYSTEM

The safe and reliable de-excitation of synchronous generator not only concerns

to self-safety of excitation system, but also has a direct concern on the safe

operation of whole power system. When generator stops normally: invert de-

excitation. When generator stops due to accident: de-excitation due to accident

stop when there are faults inside generator, the relay protection activates to cut

off main circuit breaker. In this case, quick de-excitation is required to be carried

out; when electrical accident happens in generator, the de-excitation system

quickly cuts off excitation circuit of generator and consumes the energy of

magnetic field stored in excitation winding rapidly in de-excitation circuit.

4.1) REQUIREMENTS OF DE-EXCITATION

The requirements of de-excitation are involved:

The Time for De-excitation shall be as short as possible.

The inverse voltage of De-excitation should not exceed the specified multiple.

The circuit and structure of de-excitation device shall be simple and reliable.

The field circuit breaker shall have sufficient capacity to break the current of

generator rotor .

The de-excitation system shall have enough capacity.

4.2)CLASSIFICATION OF DE-EXCITATION SYSTEM

I. Classification as per breaker function:

Energy-consumed de-excitation: the field circuit breaker consumes energy of

magnetic field.



Energy-transferred de-excitation: the field circuit breaker doesnt consume

energy of magnetic field.

II. Classification as per breaker position:

De-excitation of DC field circuit breaker: the field circuit breaker is installed

at DC side.

De-excitation of AC field circuit breaker: the field circuit breaker is installed

at AC side.

III . De-excitation of crowbar: use crowbar rather than field circuit breaker

IV Classification as per type of de-excitation resistance:

De-excitation of zinc oxide nonlinear resistance

De-excitation of silicon carbide nonlinear resistance

De-excitation of linear resistance.

4.3 PRINCIPLE OF DC DE-EXCITATION

Principle for de-excitation of DC breaker: trip DC breaker at the time of de-

excitation. Electric arc is produced at the break of DC breaker. The arc voltage

plus SCR output voltage of rectifier equals to rotor induction against

potential. The induction against potential is added to both ends of de-

excitation resistance at the same time. When UR(regulated voltage) is more

than the break-over voltage of de-excitation resistance, the de-excitation

resistance circuit is conductive, which consumes energy of magnetic field for

the purpose of de-excitation .

UR=UK-USCR.

In De-excitation conditions of DC breaker: It is necessary to ensure that the

sum of arc voltage at switch break and voltage

output by rectifier exceeds the break-over voltage of de-excitation resistance

when carrying out de-excitation in all operating conditions of generator.

Advantage:

External logic cooperation is not required for de-excitation, ensuring simple

operation.

Disadvantage:

high requirement for arc voltage at break of DC breaker, resulting to

difficult breaker manufacturing.



4.3 DE-EXCITATION RESISTANCE

The resistance for de-excitation can be linear resistance, nonlinear zinc

oxide resistance or nonlinear silicon carbide resistance. For de-excitation

of turbo generator, the solid generator rotor has strong damping effect.

Although the current in excitation winding is rapidly reduced to zero, fast

voltage attenuation of generator cannot be realized as the current in

damping winding cannot be reduced quickly. And the current in

damping winding is uncontrollable. Therefore, most generator units with

strong damping effect use linear resistance for de-excitation and ones with

weak damping effect use nonlinear resistance for de-excitation. For de-

excitation of hydro generator, the generator rotor is not solid and its

damping effect is also not strong. Besides, the generator voltage will raise a

lot in failure conditions. Therefore, it is recommended to use nonlinear

resistance for de-excitation, so as to effectively prevent accident

expansion. The nonlinear resistance is classified into zinc oxide and silicon

carbide. Edea II groupes uses de-excitation resistance mode.

de-excitation resistace mode for edea II

4.4 DESIGN OF DE-EXCITATION

According to the stipulation of excitation national standard, the designed

multiple of de-excitation voltage shall not exceed 5 times of rated excitation

voltage and is usually 3-5 times .According to the stipulation of excitation

national standard, the design multiple of overvoltage shall not exceed 7



times of rated excitation voltage and is usually 5-7 times. Problems taken into

considerations for design of excitation system

1. Calculation of de-excitation capacity

2. Selection of de-excitation valve plate

3. Residual voltage and chargeability of de-excitation resistance

4. Average energy and current of nonlinear resistance.

5. AUTOMATIC VOLTAGE REGULATOR.

A voltage regulator is defined as a device for varying the voltage of a circuit or

for automatically maintaining it at or near a prescribed value. From this, it would

appear that the term automatic voltage regulator covers the apparatus used

in the methods of obtaining a constant voltage. By the control of the output

voltage of a generator. One can only express the performance in terms of

the whole equipment as this is determined by the characteristics of the

generator exciter. When referring to the performance which is used by the

term automatic voltage regulators will imply the whole equipment and not

just that part which controls the field current. In alternating voltage the

frequency is also under control, and it may be necessary to use some type

of frequency stabilizer for varying of frequency with different load and input

conditions. A constant voltage at the generator output is essential for

satistfactory main supply. The terminal output can be affected by various

disturbing factors such as speed ,load, power factor,and temperature rise,so

that special regulating equipment is required to keep the voltage constant ,even

when the affected by these disturbing factors . How ever both active and

reactive power demands are never steady and they continually change with

rising or falling trends.The water input in to the hydro-generators must be

continously regulated to match the active demand,failing which the machine

speed will vary with consequent change in frequency which may be highly

undesirable.The voltage regulator may also manually controlled like that of edea

2 .The manual voltage regulaor may not always be feasible due to varius factors

and accuracy,which can be obtained,depending on the instruments and giving

much better performance so far as stability.

5.1) REQUIREMENTS FOR AUTOMATIC VOLTAGE REGULATOR

Voltage regulators for synchronous generators must satisfy the following

conditions:



(1) Regulation to counter disturbances must take place as rapidly as possible

(high-speed regulators).

(2) There should, as far as possible, be no derivation from the set voltage

in stationary installations.

(3) In the event of the generator terminals being short-

circuited the excitation must be controlled, so that the generator relay can

act satisfactorily to prevent any continuous feed into the short circuit.

(4) The revolving field must be protected against overload by a limit device

in the regulator.

(5) The rated voltage must be easily adjustable on the regulator

(6) Proper sharing of reactive load must be assured where several generators are

connected in parallel.

The design of the regulator most depend on;

(1) The characteristics of the driving source since changes in speed cause

variations of voltage

(2) The maximum and minimum load on the generator

(3) In the case of alternating current, the power factor of the load, since this,

in conjunction with (2), will determine the range of field current required

(4) The characteristics of the excit

5.1) CHOSING A VOLTAGE REGULATOR FOR EDEA II TURBO-ALTERNATORS

In this section, the automatic voltage regulator is chosen which uses

electronic control circuit and a programable logic controller technology. In the

specification for an automatic voltage regulator of a good type it is

necessary to bring in the characteristics of the machine which we have

taken into consideration and the requirements before chosing RT2DB excitation

auto- voltage regulation system produced by siemens for synchronous

generators to be impelmented in edea II .

5.2 REASONS WHY RT2DB EXCUTATION-REGULATION SYSTEM IS CHOSEN

FOR EDEA II

1)It meet the requirement of the edeaII turbo-alternator charecteristic



(1) To have better system voltage regulation,

(2) To improve stability and

(3) To reduce over-voltage on loss of load.

5.3) RT2DB EXCITATION AND VOLTAGE REGULATION SYSTEM FOR

SYNCHRONOUS GENERATORS

5.3.1ADVANTAGES

* Fully digital.

* Parameter settings done by software.

* Self monitoring routines.

*Maintenance free.

*High reliability.

*Excellent dynamic performance.

*Strong construction.

Several communication protocols available.

6) DETAIL DESCRIPTION OF RT2DB EXCITATION AND VOLTAGE

REGULATION SYSTEM

The RT2DB excitation system was developed for excitation and voltage

regulation of synchronous generators equipped with rotating exciters (brushless

or DC exciters).

In the case of brushless exciters it will result in a maintenance free power

generation system. The system can be used in new projects or as an excellent

alternative for refurbishment of old regulators such those of this edea II. The

RT2DB excitation system can take the necessary energy either from the

terminals of thegenerator being excited,through a three-phase dry type

excitation transformer in this case or from a permanent magnet exciter (PMG)

The voltage regulation is achieved by actuating on the field winding of the

exciter machine. For the field flashing auxiliary energy is taken from the auxiliary

power supply (DC or AC). The voltage and current regulation, the setpoint

generation, the actual value measuring, the control of the field flashing and

shutdown processes, as well as the excitation system monitoring are fully digital.



These functions are carried out by a 32 bit processor module, which is plugged in

a three-phase fully controlled converter of the series Simoreg DC Master.

6.1) POWER STAGE

The current rectification is carried out by the self cooled Simoreg DC Master

unit. The thyristors are protected by monitored ultra-fast fuses. The Simoreg

converter is designed taking into account the most severe overload conditions of

the generator. In the cases where the excitation system takes its supply voltage

from the generator terminals it may be necessary to sustain the excitation

current during a short circuit on the generator terminals in order to guarantee

the actuation of protection relays or protection selectivity. For that reason the

RT2DB excitation system can also include a special circuitry for sustaining

thestator current of the generator at a certain level in the case of near short

circuit.

Fig. 11: The Simoreg DC Master converter unit.

6.2)CONFIGURATION OF THE ELECTRONICS

The voltage regulation, the control and the monitoring functions of the

excitation system are carried out by the processor module T400plugged in

the Simoregconverter. The thyristorgating and monitoring are

implemented by theconverter itself. Thepower supply for the electronics



is taken in a redundant way fromthe excitation transformer and from the

station battery.

Fig. 12: The generator voltage regulation is carried out by the T400

technological board,

which is plugged in the Simoreg unit.

There are two regulating channels: AUTOMATIC (automatic voltage regulator)

and HAND (field current regulation). Both regulating channels (AUTOMATICand

HAND) act on the same power stage. The bumpless channel change-over is

carried out by software.



Fig. 13 : By means of the Drive Monitor parametering software it is also

possible to record oscillograms of analogical signals.

6.3) AUTOMATIC CHANNEL

The automatic channel corresponds to the automatic voltage regulator

(AVR), which compares the generator voltage actual value with the

reference value (voltage setpoint) adjusted by the power plant operator.

The actual values of the active and reactive power are measured directly

on the generator

terminals through 3 potential transformers with secondary voltages of

110, 115 or 120V as well as 2 current transformers with with secondary

current of 1 or 5 A.

The generator voltage setpoint is digitally generated and can be adjusted

in the range

90% to 110% of the rated generator voltage During the operation of the

synchronous

generator attention must be paid to its capability diagram. For this reason

there following limiters act on the AVR:

1. Quick acting excitation current limiter (field forcing limiter)

2. Overexcitation limiter

3. Underexcitation limiter

4. Volt/Herz limiter

5. Stator current limiter

The AVR possesses an underordinated excitation current regulator. This

configuration ensures the system an excellent dynamic behavior and

simultaneously allows limiting the excitation current at its maximum

values regulator . This configuration ensures

the system an excellent dynamic behavior and simultaneously allows

limiting the excitation current at its maximum values. A power factor (or

reactive power) regulator is also included. This additional regulator allows

the generator to operate at

any desired power factor regarding its capability diagram. The setpoint

value is digitally generated by the T400 module.

6.4) HAND CHANNEL

from zero to 110 This control channel corresponds to the excitation

current regulator. It is extremely useful when performing tests on the



generator. In addition the hand channel works as a stand-by regulator

allowing continuing of the operation even at failures in the AVR. The

setpoint of the excitation current ranges from about 10% up to 110% of

the rated excitation current of the exciter. By taking an independent

power supply for the excitation system the setpoint range stretches %

6.4.1) CHANNEL SWITCH OVER AND FOLLOW-UP CONTROL.

A bumpless channel change-over from AVR to excitation current regulator and

vice-versa can occur at any time. This is possible thanks to the follow-up routine,

which ensures that the selected control channel follows up the settings of the

other channel. This way both channels outputs always the same firing angle for

the thyristors, what guarantees a bumpless channel change-over at any time.

Certain failures involving the AVR cause an automatic change-oveto the hand

channel. A trip signal is released if failures occur in the hand channel being

selected the hand channe

l

Fig. 14: The regulation and control software is user friendly, what makes the

programming and understanding very easy.

6.5) OPERATION

The excitation cubicle is delivered with provisions both for local control (from

the cubicle door) and for remote control (from a central control room). In the

standard version of this cubicle the local operation is carried out by means of

push buttons on the cubicle door. Alarms and status indications are made by LED

signalizations. A man-machine interface (MMI) is optionally available to make

the operation of the system easier. This optional device is equipped with

keyboard and display (LCD). Through this device commands can be entered and



actual system parameters (excitation current and voltage, generator active and

reactive power, generator voltage, setpoints etc) can be read out.

Fig. 15: In order to make die operation easier a man-machine interface can be

additionally ordered. The figure shows one of the available models (OP17).

There are two standardized types of MMI: a simple one (OP1S) and a more

comfortable one, which can display alarm messages of the excitation system in

clear text with indication of the time in which the alarm occurred. The RT2DB

cubicle can be connected to the superordinatedcontrol system by means of

normal cabling because all of the input and output signals are available on

terminal strips as potential-free contacts.

6.6)INSTRUMENTATION AND OPERATION

In the standard version of the system the following instruments are

installed on the cubicle door: reset push-button, signaling LEDs to indicate

operational statuses and grouped alarms and push-buttons to enter

commands for the local operation. In the case the optional MMI is

ordered neither push-buttons nor signaling LEDs are supplied.

6.7) DE-EXCITATION AND OVERVOLTAGE PROTECTION

At normal conditions de-excitation is carried out by forcing the thyristor bridge

to operate as inverter. The field polarity inversion causes thus a very quick

reduction of the excitation current towards zero. About 5 s after introducing

inverter operation the controller opens the field contactor. Since the excitation

current at this time will have already reached zero, the main contacts of the field

contactor open at no load condition, what increases the lifetime of the device.

Additionally the RT2DB excitation cubicle is also equipped with a linear field

discharge resistor. It is used to dissipate the stored energy of the exciter field



winding in emergency situations, where inverter operation cannot be ensured

any more. The RT2DB excitation system has a suppressor device in to its DC

output, in order to protect the thyristors and the field winding against induced

overvoltages.

6.8)MECHANICAL FEATURES

The excitation cubicle has the following approximate dimensions: Width:

600mm

Depth: 800 mm

Height: 2200 mm

The cubicle has only front door. Cables inlet and outlet are made

from the bottom.

The cubicle is constructed with 1.9 mdick steel sheets.

The supporting frames are made of 2.5 mm dick steel sheets.

The cubicle wiring uses self extinguishing copper conductors insulated for

750V. All conductors haven identification rings at both ends. Each one of

the devices ha identification tags with the device symbol according to the

electrical diagrams. Each device can be easily accessed.

6.9) OPTIONAL FRAME ASSEMBLY

As an economical alternative all the low voltage parts of the RT2DB

excitation system can be supplied assembled on a steel sheet (frame)

sized 800 x 1200 mm (see Fig. 8). This way the system can be installed in a

clientsexisting cubicle saving thus the costs o an additional cubicle.

monitoring the fully controlled three phase rectifier bridge. for controlling Fig.

16: The Simoreg DC Master converter includes the electronics and



Fig. 17: As an economical solution the RT2DB excitation system can also be

supplied on a steel sheet to be housed in a clients existing cubicle



6. 8) General technical data of the RT2DB digital excitation system

CONCLUSION

In this report t

Sample Report

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