INDUSTRIAL TRAINING DONE AT ESKOM UGANDA LIMITED

(Nalubaale and Kiira Power Stations)

JINJA, UGANDA

PREPARED BY ORTEGA IAN

………………………………………………………………………..

SUPERVISED BY

………………………………………………………………………………

KYAMBOGO UNIVERSITY

FACULTY OF ENGINEERING

DEPARTMENT OF MECHANICAL AND PRODUCTION

PROGRAMME: BACHELOR OF ENGINEERING IN MECHANICAL AND MANUFACTURING

ENGINEERING

TOPIC: INDUSTRIAL TRAINING DONE AT ESKOM UGANDA LTD

NAME: ORTEGA IAN

REG NO: 11/U/11049/EMD/PD

A REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF BACHELOR’S DEGREE IN MECHANICAL AND

MANUFACTURING ENGINEERING AT KYAMBOGO UNIVERSITY

2014/2015

July 2nd - August 30th 2014

DECLARATION

I sincerely declare that:

1. I am the sole writer of this report

2. The details of training and experience contained in this report describe my involvement as a trainee in the field of Mechanical and Manufacturing Engineering at Eskom Uganda Limited.

3. All the information contained in this report is accurate and correct to the knowledge of the author.

Signature: ___________________________________

Name: ORTEGA IAN

Reg. No: 11/U/11049/EMD/PD

Date: 19th August 2009

For Company Supervisor: ___________________________________

For Company Human Resource Manager________________________

For University Supervisor: __________________________________

AcknowledgmentsFirst and foremost, I thank the Management and the entire staff of Eskom Uganda for according me the opportunity to train with such a remarkable company. The lifetime skills ingrained in me will never be forgotten. I thank my university Supervisor, Mr. Ssempebwa Ronald for the guidance and great service offered.

My special thanks go to my parents for the guidance and discipline instilled in me. I can’t forget to thank my mentor, Andrew Mwenda for teaching me about life. And to the Almighty God, nothing beats your love. To everyone I may have missed out, accept my appreciation.

Namaste.

Executive SummaryThe report covers the events, skills attained and lessons learned during my Industrial training at Eskom (U) Ltd. The internship program was undertaken in the Maintenance Department covering a period of two (2) months from 2nd July 2014 to 30th August 2014.

During this period, I focused on the mechanical sections (preventive and break-down) maintenance of the two power plants.

Table of ContentsDECLARATION.............................................................................................................................3

Acknowledgments...........................................................................................................................4

Executive Summary.........................................................................................................................5

Acronyms.........................................................................................................................................8

CHAPTER ONE: INTRODUCTION TO ESKOM UGANDA LTD.............................................9

Executive Summary.....................................................................................................................9

1.1 Mandate...............................................................................................................................10

1.2 Key Governing Documents.................................................................................................10

1.3 Mission, Vision and Values.................................................................................................10

1.4. Organization Structure........................................................................................................10

CHAPTER TWO: INTRODUCTION TO HYDRO-POWER......................................................13

2.1 Types of Hydro-Power Plants..............................................................................................13

2.2 Sizes of Hydro-Power Plants...............................................................................................14

2.3 Layout of Hydro-Power Plant..............................................................................................15

2.4 Advantages and Disadvantages of Hydro-Power................................................................17

CHAPTER THREE: TURBINE AND AUXILLIARIES.............................................................19

3.1 Power Generation Process...................................................................................................19

3.2 The Prime Movers...............................................................................................................20

3.3 Governing Principles...........................................................................................................25

3.4 Kaplan Turbines Continued.................................................................................................27

3.5 Auxiliary Equipment...........................................................................................................30

CHAPTER FOUR: PRACTICAL (TRAINEE) WORK DONE AT EUL....................................34

How We Carry Out Maintenance Work at EUL.......................................................................34

4.1 Generator-Transformer Work..............................................................................................35

LSL DRAIN/DEWATER (Unit Turbine).................................................................................36

MEX GOVERNOR CONTROL...............................................................................................36

FIRE PROTECTION-Auxiliary Plant.......................................................................................37

CLEANING OF SCREENS......................................................................................................38

CLEANING OF WATER STRAINERS...................................................................................38

CURING OF LEAKAGES........................................................................................................39

Packing Procedures................................................................................................................39

CHAPTER SIX: FINAL REMARKS...........................................................................................42

6.1 Challenges............................................................................................................................42

6.2 Recommendations................................................................................................................42

6.3 Conclusion...........................................................................................................................42

References......................................................................................................................................43

Acronyms CSR Corporate Social ResponsibilityDSM Demand Side ManagementEAP Employee Assistance ProgramEE Eskom EnterprisesERA Electricity Regulatory AuthorityEUL Eskom Uganda LimitedGOU Government of UgandaISO International Standards OrganisationIT Information TechnologyKPS Kiira Power StationNOSA National Occupational Safety AssociationNPS Nalubaale Power StationO&M Operate and MaintainOEM Original Equipment ManufacturerPBT Profit Before TaxPPA The Power Purchase AgreementSA The Support AgreementSHE Safety, Health and EnvironmentUEGCL Uganda Electricity Generation CompanyUETCL Uganda Electricity Transmission Company

CHAPTER ONE: INTRODUCTION TO ESKOM UGANDA LTD

Executive SummaryEskom Uganda Limited was established in 2002 through the implementation of the concession agreement between Uganda Electricity Generation Company Limited and Eskom, Eskom Uganda (Pty) Limited (EUL) has faced many challenges and achieved significant success notably:

Plant availability has been above the contractual minimum for the last 5 years. Total investments of USD $12.4m Certification in 3 international standards including ISO 9001, ISO 14001 & OSHAS Used in house skills to execute and commission projects to the value of $8.1m More than 90% compliance with new Employment Act and Occupational Safety &

Health (OSH) Act. Recognized for outstanding performance with Green award for environmental initiatives,

best utility Manager (2011) and employer of the year.

In the coming five year planning horizon EUL has identified a number of persisting trends within which they will have to build on their success. The most notable trends within which EUL will have to deliver include the following:

An increase in the demand for electricity, resulting in increased pressure for performance from existing generators in the market.

An increase in government scrutiny in respect of electricity prices as a result of increased cost of electricity in the country.

An increase in regulatory pressure as a function of the introduction of new producers and the commitment of the Ugandan government to ensure effective electricity regulation.

Advanced age related challenges and equipment obsolesce at the power generating stations.

An increase in the battle of skills and talent

In response to these trends and their key implications, and based on the last ten years’ experience. EUL has defined five key strategic priorities in driving the business forward in the next 5 year period.

To ensure effective cost optimization To drive excellent asset care management To enhance risk and environment management To implement effective talent and people management strategies

To ensure effective stakeholder and reputation management

1.1 MandateThe mandate of Eskom Uganda (Pty) Limited (EUL) is to operate and maintain Nalubaale and Kiira Power Stations (NPS and KPS, respectively) in compliance with the concession agreements and stakeholder objectives. This mandate may change in the next five years depending in the discussions with both the shareholder. The existing mandate has and will continue to guide EUL’s operations within the Ugandan context until a new mandate is agreed with the shareholder. The key implications of this mandate are that EUL will continue focusing on operating and maintaining the two power stations listed in agreement to the shareholder’s (Eskom enterprises) objectives and in accordance with the concession agreements.

1.2 Key Governing Documents There are four documents which detail the concession agreements that govern and guide EUL’s operations and they are;

1. The concession and Assignment Agreement between EUL and Uganda Electricity Generation Company (UEGCL).

2. The Power Purchase Agreement (PPA) between EUL and Uganda Electricity Transmission Company Limited (UETCL)

3. The License issued to Eskom Uganda Ltd by the Electricity Regulatory Authority (ERA)4. The Support Agreement (SA) between the Government of Uganda and EUL.

1.3 Mission, Vision and ValuesMission: Leading generator in Affordable and Reliable electricity for National Development.

Vision: To be the Centre of Excellence in Power Concession Management.

Values:

Integrity - We always demonstrate the quality of being honest and morally upright. Zero Harm - We set robust safety and security systems at the work place to ensure zero

harm to employees. Customer Satisfaction - We treat our customers with fairness, courtesy and sensitivity

with respect to their rights. Excellence - We set high performance standards for self and others. Innovation - We try different and novel ways to deal with work challenges,

opportunities, and organizational change.

1.4. Organization StructureThe organization structure is showed with the respective hierarchies.

Eskom Uganda comprises 6 core departments, all headed by the Managing Director. These departments include;

Finance Human Resource Risk Compliance Technical Corporate Affairs

During my two months training at Eskom Uganda, I was concerned with the Technical Department, which is headed by a Technical Director. The technical department is further sub-divided into the business systems, Maintenance and Operations.

As a mechanical engineering trainee, I was situated under the Maintenance department, headed by the Maintenance Manager and concerned with the Preventive and Corrective Maintenance roles at EUL.

The four major aims of the Maintenance Section can be outlined as the following;

Keep operating equipment in the condition to deliver full design duty (reliability),

Ensure plant and equipment run properly when it is required for operation (availability),

Correct our equipment and machines when the design duty cannot be achieved and then return them to design specification (capability), and

Maintain assets most profitably for the life of the organization. (life cycle profit).

CHAPTER TWO: INTRODUCTION TO HYDRO-POWER

Hydro means "water". So, hydropower is "water power" and hydroelectric power is electricity generated using water power. Potential energy (or the "stored" energy in a reservoir) becomes kinetic (or moving energy). This is changed to mechanical energy in a power plant, which is then turned into electrical energy. Hydroelectric power is a renewable resource.

In an impoundment facility (see below), water is stored behind a dam in a reservoir. In the dam is a water intake. This is a narrow opening to a tunnel called a penstock.

Water pressure (from the weight of the water and gravity) forces the water through the penstock and onto the blades of a turbine.

A turbine is similar to the blades of a child's pinwheel. But instead of breath making the pinwheel turn, the moving water pushes the blades and turns the turbine. The turbine spins because of the force of the water. The turbine is connected to an electrical generator inside the powerhouse. The generator produces electricity that travels over long-distance power lines to homes and businesses. The entire process is called hydroelectricity.

2.1 Types of Hydro-Power PlantsThere are three types of hydropower facilities: impoundment, diversion, and pumped storage. Some hydropower plants use dams and some do not. The images below show both types of hydropower plants.

Many dams were built for other purposes and hydropower was added later. In the United States, there are about 80,000 dams of which only 2,400 produce power. The other dams are for recreation, stock/farm ponds, flood control, water supply, and irrigation. Hydropower plants

range in size from small systems for a home or village to large projects producing electricity for utilities.

(a) ImpoundmentThe most common type of hydroelectric power plant is an impoundment facility. An impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level

(b) DiversionA diversion, sometimes called run-of-river, facility channels a portion of a river through a canal or penstock. It may not require the use of a dam.

(c) Pumped StorageWhen the demand for electricity is low, pumped storage facility stores energy by pumping water from a lower reservoir to an upper reservoir. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.Pumped storage hydro-electricity works on a very simple principle .Two reservoir at different altitudes are required. When the water is released, from the upper reservoir, energy is created by the down flow which is directed through high-pressure shafts, linked to turbines.

In turn, the turbines power the generators to create electricity. Water is pumped back to the upper reservoir by linking a pump shaft to the turbine shaft, using a motor to drive the pump.

2.2 Sizes of Hydro-Power Plants Facilities range in size from large power plants that supply many consumers with electricity to small and micro plants that individuals operate for their own energy needs or to sell power to utilities.

(a) Large hydropowerAlthough definitions vary, the U.S. Department of Energy defines large hydropower as facilities that have a capacity of more than 30 megawatts.

(b) Small hydropowerAlthough definitions vary, DOE defines small hydropower as facilities that have a capacity of 100 kilowatts to 30 megawatts.

(c) Micro hydropowerA micro hydropower plant has a capacity of up to 100 kilowatts. A small or micro hydro- electric power system can produce enough electricity for a home, farm, ranch, or village.

2.3 Layout of Hydro-Power Plant

The layout covered here correlates with the structural layout of the two power plants, both at NPS and KPS. (a) Dam

Dams are

structures built over rivers to stop the water flow and form a reservoir. The reservoir stores the water flowing down the river. This water is diverted to turbines in power

stations. The dams collect water during the rainy season and store it, thus allowing for a steady flow through the turbines throughout the year. Dams are also used for controlling floods and irrigation. The dams should be water-tight and should be able to withstand the pressure exerted by the water on it. There are different types of dams such as arch dams, gravity dams and buttress dams. The height of water in the dam is called head race.

(b) SpillwayA spillway as the name suggests could be called as a way for spilling of water from dams. It is used to provide for the release of flood water from a dam. It is used to prevent over toping of the dams which could result in damage or failure of dams. Spillways could be controlled type or uncontrolled type. The uncontrolled types start releasing water upon water rising above a particular level. But in case of the controlled type, regulation of flow is possible

(c) Penstock and TunnelPenstocks are pipes which carry water from the reservoir to the turbines inside power station. They are usually made of steel and are equipped with gate systems. Water under high pressure flows through the penstock. A tunnel serves the same purpose as a penstock. It is used when an obstruction is present between the dam and power station such as a mountain.

(d) Surge Tank

Surge tanks are tanks connected to the water conductor system. It serves the purpose of reducing water hammering in pipes which can cause damage to pipes. The sudden surges of water in penstock are taken by the surge tank, and when the water requirements increase, it supplies the collected water there by regulating water flow and pressure inside the penstock.

(e) Power StationPower station contains a turbine coupled to a generator. The water brought to the power station rotates the vanes of the turbine producing torque and rotation of turbine shaft. This rotational torque is transferred to the generator and is converted into electricity. The used water is released through the tail race. The difference between headrace and tailrace is called gross head and by subtracting the frictional losses we get the net head available to the turbine for generation of electricity.

2.4 Advantages and Disadvantages of Hydro-PowerAdvantages1. Renewable source of energy thereby saves scares fuel reserves.2. Economical source of power.3. Non-polluting and hence environment friendly.4. Reliable energy source with approximately 90% availability.5. Low generation cost compared with other energy sources.6. Indigenous, inexhaustible, perpetual and renewable energy source.7. Low operation and maintenance cost.8. Possible to build power plant of high capacity.9. Plant equipment is simple.10. Socio-economic benefits being located usually remote areas.11. Higher efficiency, 95% to 98%.12. Fuel is not burned so there is minimal pollution.13. Water to run the power plant is provided free by nature.

Disadvantages1. Susceptible to vagaries of nature such as draught.2. Longer construction period and high initial cost.3. Loss of large land due to reservoir.4. Non-availability of suitable sites for the construction of dam.

5. Displacement of large population from reservoir area and rehabilitation.6. Environmental aspect reservoirs verses river ecology.7. High cost of transmission system for remote sites.8. They use up valuable and limited natural resources.9. They can produce a lot of pollution.10. Companies have to dig up the Earth or drills wells to get the coal, oil, and gas.11. For nuclear power plants there are waste –disposal problems.

Key facts about hydro power plant1. World-wide, about 20% of all electricity is generated by hydropower.2. Hydropower is clean. It prevents the burning of billion gallons of oil or 120 million tons of coal each year.3. Hydropower does not produce greenhouse gasses or other air pollution.4. Hydropower leaves behind no waste.5. Hydropower is the most efficient way to generate electricity. Modern hydro turbines can convert as much as 90% of the available energy into electricity. The best fossil fuel plants are only about 50% efficient.6. Water is a naturally recurring domestic product and is not subject to the whims of foreign suppliers.

CHAPTER THREE: TURBINE AND AUXILLIARIES

3.1 Power Generation Process

To generate power, the machine is prepared for spinning until full speed, that is 150r.p.m after opening the intake gate first and guide vanes. Initial excitation is switched on, getting 240V D.C from the batteries through a micro-computer in the static exciter.By exciting, one is creating a rotating magnetic field which will cut the coils in the stator and an e.m.f (electromotive force) will be induced in the stator coils and will be tapped off at the generator terminals. This e.m.f is 11KV, but the output of the generator is fed to the excitation transformer which feeds the static exciter. The excitation transformer is a step down transformer. In the static exciter, there are thyristers which convert a.c to D.C. So, when the output of the excitation transformer (which receives 11KV and steps it down to 415a.c) is 240V d.c then the supply from the batteries is cut off automatically by the micro-computer and the generator becomes self-exciting. The machine is then synchronized and when the conditions of synchronizing the incoming match with the existing system then the machine can be fed to the bus bars via a circuit breaker (O.C.B).How Power is Really Generated

Energy from running water is used to drive the Kaplan water turbines which in turn drive the alternators. The water is let to flow from the water dam at a high pressure through the gate, then spiral casing and is directed to the water turbine which rotates at a speed of 150r.p.m (revolutions per minute). The voltage generated is 11000V or 11KV. The generated voltage from the alternators is supplied to step up transformer in substations which step it up to 33KV and 132KV. After stepping up voltage to either 33KV in 33KV substation or 132KV in 132KV substation, the voltages are supplied to bus bars via circuit breakers. The 33KV is fed to feeders for intermediate transmission e.g areas around Jinja, while the 132KV is transmitted to distant places like Kampala and Tororo.

3.2 The Prime MoversThe prime-mover in the hydraulic power plant converts the energy of water into mechanical energy and further into electrical energy. Nalubaale utilizes the Kaplan Turbines as the prime mover while Kiira utilizes the Propeller type of turbines. These two, are all types of reaction turbines.In case of reaction turbine, the water pressure combined with the velocity works on the runner. The power in this turbine is developed from the combined action of pressure and velocity of water that completely fills the runner and water passage. The casing of the reaction turbine operates under high pressure. The pressure acts on the rotor and vacuum underneath it. This is why the easing of reaction turbine is made completely leak proof.

a) Propeller Turbine The propeller runner may be considered as a development of a Francis type in which the number of blades is greatly reduced and the lower band omitted. It is axial flow turbine having a small number of blades from three to six as shown. The propeller turbine may be fixed blade type or movable blades type known as Kaplan Turbine.The fixed blade propeller

type turbine has high efficiency (88°l0); at full load but its efficiency rapidly drops

with decrease in load. The efficiency of the unit is hardly 50% at 40% of full load at part load operation. The use of propeller turbine is limited to the installations where the units run at full load conditions at all times. The use of propeller turbine is further limited to low head installations of 5 to 10 meters.

b) Kaplan Turbine The Kaplan turbine was invented by Prof. Viktor Kaplan of Austria during 1913-1922 and a great development of early 20th century. The Kaplan turbine has

some specific properties as• The Kaplan is of the propeller type, similar to an airplane propeller.• The difference between the Propeller and Kaplan turbines is that the Propeller turbine has

fixed runner blades while the Kaplan turbine has adjustable runner blades angles. • It is a pure axial flow turbine uses basic aerofoil theory.• The Kaplan’s blades are adjustable for pitch and will handle a great variation of flow

very efficiently. • They are 90% or better in efficiency and are used in place of the old (but great) Francis

types is good in many of installations. • They are very expensive and are used principally in large installations. • The Kaplan turbine, unlike all other propeller turbines, the runner's blades were movable. • The application of Kaplan turbines are from a head of 2m to 40m. • The advantage of the double regulated turbines is that they can be used in a wider field. • The double regulated Kaplan turbines can work between 15% and 100% of the maximum

design discharge.

The Generator:

In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge (usually carried by electrons) to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow (but does not create water). The source of mechanical energy water falling through a turbine or waterwheel

The two main parts of a generator or motor can be described in either mechanical or electrical terms.

Mechanical

• Rotor: The rotating part of an electrical machine

• Stator: The stationary part of an electrical machine

Electrical

• Armature: The power-producing component of an electrical machine. In a generator, alternator, or dynamo the armature windings generate the electric current. The armature can be on either the rotor or the stator.

• Field: The magnetic field component of an electrical machine. The magnetic field of the dynamo or alternator can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator.

Because power transferred into the field circuit is much less than in the armature circuit, AC generators nearly always have the field winding on the rotor and the stator as the armature winding. Only a small amount of field current must be transferred to the moving rotor, using slip rings. Direct current machines (dynamos) require a commutator on the rotating shaft to convert the alternating produced by the armature to direct current, so the armature winding is on the rotor of the machine.

Excitation

Generators require direct current to energize its magnetic field. The DC field current is obtained from a separate source called an exciter. Either rotating or static-type exciters are used for AC power generation systems. There are two types of rotating exciters: brush and brushless. The primary difference between brush and brushless exciters is the method used to transfer the DC exciting current to the generator fields.

Static excitation for the generator fields is provided in several forms including field-flash voltage from storage batteries and voltage from a system of solid-state components. DC generators are either separately excited or self-excited.

Excitation systems in current use include direct-connected or gear-connected shaft-driven DC generators, belt-driven or separate prime mover or motor-driven DC generators, and DC supplied through static rectifiers.

The brush-type exciter can be mounted on the same shaft as the AC generator armature or can be housed separately from, but adjacent to, the generator. When it is housed separately, the exciter is rotated by the AC generator through a drive belt.

The distinguishing feature of the brush-type generator is that stationary brushes are used to transfer the DC exciting current to the rotating generator field. Current transfer is made via rotating slip rings (collector rings) that are in contact with the brushes.

A rotating-rectifier exciter is one example of brushless field excitation. In rotating-rectifier exciters, the brushes and slip rings are replaced by a rotating, solid-state rectifier assembly. The exciter armature, generator rotating assembly, and rectifier assembly are mounted on a common shaft. The rectifier assembly rotates with, but is insulated from, the generator shaft as well as from each winding.

Static exciters contain no moving parts. A portion of the AC from each phase of generator output is fed back to the field windings, as DC excitations, through a system of transformers, rectifiers, and reactors. 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 or from control voltage at the switchgear.

TRANSFORMER

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through these secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is called inductive coupling.

If a load is connected to the secondary, current will flow in the secondary winding, and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp) and is given by the ratio of the number of turns in the secondary (Ns) to the number of turns in the primary (Np) as follows:

By appropriate selection of the ratio of turns, a transformer thus enables an alternating current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less than Np. The windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception.

Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate on the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high-voltage electric power transmission, which makes long-distance transmission economically practical.

Energy losses

An ideal transformer would have no energy losses, and would be 100% efficient. In practical transformers, energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 98%..Experimental transformers using superconducting windings achieve efficiencies of 99.85%. The increase in efficiency can save considerable energy, and hence money, in a large heavily loaded transformer; the trade-off is in the additional initial and running cost of the superconducting design.

Losses in transformers (excluding associated circuitry) vary with load current, and may be expressed as "no-load" or "full-load" loss. Winding resistance dominates load losses, whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The no-load loss can be significant, so that even an idle transformer constitutes a drain on the electrical supply and a running cost. Designing transformers for lower loss requires a larger core, good-quality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost so that there is a trade between initial costs and running cost. Transformer losses are divided into losses in the windings, termed copper loss, and those in the magnetic circuit, termed iron loss. Losses in the transformer arise from:

Winding resistance

Hysteresis losses

Eddy currents

Magnetostriction

Mechanical losses

Stray losses

3.3 Governing PrinciplesTurbine governors are equipment for the control and adjustment of the turbine power output and evening out deviations between power and the grid load as fast as possible. The turbine governors have to comply with two major purposes:

1. To keep the rotational speed stable and constant of the turbine-generator unit at any grid load and prevailing conditions in the water conduit.

2. At load rejections or emergency stops the turbine admission have to be closed down according to acceptable limits of the rotational speed rise of the unit and the pressure rise in the water

conduit.

Alterations of the grid load cause deviations between turbine power output and the load. For a load decrease the excess power accelerates the rotating masses of the unit according to a higher rotational speed. The following governor reduction of the turbine

admission means deceleration of the water masses in the conduit and a corresponding pressure rise.

To keep the rise of the rotational speed below a prescribed limit at load rejections, the admission closing rate must be equal to or higher than a certain value. For the pressure rise in the water conduit the condition is opposite, e.g., the closing rate of the admission must be equal to or lower than a certain value to keep the pressure rise as low as prescribed.

For power plants where these two demands are not fulfilled by one single control, the governors are provided with dual control functions, one for controlling the rotational speed rise and the other for controlling the pressure rise.

A complete turbine governor system may be divided in three main components:

- The controller. This is the unit for execution of control processes. The unit may be of mechanical-hydraulic or electrohydraulic construction.

- Servo system. The servo system is an amplifier that executes the admission changes determined by the controller.

- The pressure oil supply system. The principal duty for this system is at any time to supply sufficient quantities of pressure oil to the servo system.

3.4 Kaplan Turbines Continued

Part list of Kaplan Turbine drawing

1a Runner cone 10 Turbine guide bearing

1e Runner hub 11 Guide vane servomotor

1f Runner blades 12 Servomotor connecting rod

3 Top & bottom plates 13 Guide vane regulating ring

4 Spiral case 14 Guide vane link

5 Stay vane 15 Guide vane arm

6 Guide vane 16 Shaft seal

7 Draft tube 17 Head cover

8 Discharge ring 18 Runner blade servomotor

9 Turbine shaft

Scroll casing

The scroll casings for lower heads 25 - 30 meters are made of concrete. To make these type of scroll casings with the required accuracy, wooden models are used against which the concrete is poured.

The manufacturer of the turbine determines the shape and makes the drawings of these models. The quality of a water tight and even surfaces of the scroll casings is required to be the same as for draft tube bends of concrete.

The guide vane cascade

The guide vane cascade of Kaplan turbines are constructed in the same way as for Francis turbines. In the sense of operation a regulating ring rotates the guide vanes through the same angles simultaneously when adjustments follow changes of the turbine load. The vanes are manufactured of steel plate material and the trunnions are welded to them. The vane design is purposely to obtain optimal hydraulic flow conditions, and they are given a smooth surface finish.

Runner

The runner in a Kaplan turbine is a very challenging part to design. The details for adjusting the blades can be designed in different ways. Increasing blade number for increasing head may create problems because of lack of space and consequently high stresses in some details of the construction. It is not however, only the head that determines the number of blades. The blade length and shape as well as the specific blade loading and location in relation to the downstream water level, are factors which must be considered. As a general guideline four blades can be used up to heads of 25 - 30 meters, five blades up to 40 meters, six blades up to 50 meters and seven blades up to heads of 60 - 70 meters. Kaplan turbines have also been designed with 8 blades for heads even higher than 70 meters. This increases the hub diameter and the shape of the hub becomes more complicated, and the efficiency may suffer.

The outside of the hub is spherically shaped. This is done to keep a small clearance gap between the adjustable blade ends and the hub for all operating conditions. With increasing head the hub diameter is increasing from approximately 40% to 65 - 70 % of the runner diameter.

The torque of the runner is transferred to the turbine shaft through either a pure friction joint connection or through a combined shear bolt and friction joint. The bolts joining the turbine shaft flange and the runner are pre-stressed by means of heat for the largest bolt dimensions.

Runner blade servomotor

The servomotor for the rotary motion of the runner blades is either a construction part of the turbine shaft or located inside the hub. There are however, good reasons for localizing the servomotor inside the hub, and the details of such a construction are dealt with in the chapter of bulb turbines. This servomotor may consist of a moving cylinder and a fixed piston integrated with the hub. The conversion from axial piston movement to rotating blade movement is carried out by a link and lever construction.

The hub is completely filled with oil to provide reliable lubrication of moving parts. The oil pressure inside the hub is kept higher than the outside water pressure to prevent water penetration into the oil.

Regulating mechanism of the runner blades

The slope of the runner blades are adjusted by the rotary motion activated by the force from the piston through the rod. The cylindrical extension of the upper end of the turbine shaft (9) serves as a servomotor cylinder whereas the lower flange of the generator shaft serves as cover. The rod moves in the two bearings.

The oil supply to the servomotor is entered at the upper end of the generator shaft. The oil is conveyed to the respective sides of the servomotor through two coaxial pipes inside the hollow generator shaft. The inner tube conveys oil to and from the lower side of the piston, whereas the annular opening between the pipes and conveys oil to and from the piston top side. The oil is supplied through the entrance arrangement with the two chambers and at the top of the unit.

Cooperation of regulating the guide vanes and the runner blades

The turbine governor operates directly on servomotor which executes the movement of the guide vanes. The movement of the servomotor thriggs and controls the slope adjustment of the runner vanes. This is carried out by a rod and lever transfer from the servomotor to the cam which is turned according to the movement of the servomotor piston. In this way the spool valve is moved out of the neutral position and the servomotor piston is then put to movement by the oil pressure supply. The spool valve receives pressure oil either directly from the oil pump or from the accumulator which is energized by an oil pump.

Runner chamber

The clearance gap between the outer blade ends and the chamber wall is essential to keep as small as possible for all blade inclinations. Therefore the runner chamber is made spherical below the rotation Centre line of the blade trunnions.

Ideally the spherical shape should have been maintained above the blade rotation Centre as well. However, on account of installation and dismantling aspects, this part is being made cylindrical. The gap between the runner blade ends and the runner chamber wall is approximately 0.1% of the runner diameter.

Cavitation erosion on the runner chamber may occur during the running time of the turbine. To reduce the magnitude of such erosion attacks and to ease the subsequent repair, the runner chamber is normally made of cast or welded stainless chromium nickel steel with higher cavitation resistance than carbon steel. Existing erosions may then be repaired by welding on site. The runner chamber is reinforced by external ribs. The runner chamber is normally completely or partly embedded in concrete.

3.5 Auxiliary EquipmentThe auxiliary equipment for the mechanical systems in water power plants comprises

- Oil pressure system

- Air pressure supply system

The oil pressure system has to supply pressurised oil energy for the turbine governor system. Different types and sizes of these systems are in use and they exist for pressures between 25 and 40 bar. The pressure tank which is designated accumulator is of the oil-air type for pressures of these levels.

The main components can be summarized as follows:

- oil sump tank

- check valves

- switches and indicators

- main oil valve

- accumulator, e.g., oil pressure tank - relief valve

- oil pump units - oil cooler

- unloader valve

The accumulator is filled with oil and air under pressure. This energy storage allows a short time high oil consumption which is much higher than the capacity of the oil pumps. The energy storage is also sufficient for the oil consumption during a stop sequence of the turbine unit without the oil pumps in operation.

Oil sump tank

The oil sump tank is designed with a volume sufficient for the amount of oil in the system. The tank has inspection openings to give access for service and routine inspections. The oil sump tank contains a special arrangement with strainers to ensure deaeration of the oil. The separation of air entrapped in the oil prevents rapid oxidation and ensures long service life of the oil and also of the components in the system.

Accumulator

The accumulator is mounted on the top of the oil sump tank. A man hole gives access for inspection and service. The oil level in the tank is controlled by refilling of compressed air. Correct oil level is important to obtain necessary energy storage and necessary amount of oil. Refilling of air is necessary because that pressurised oil absorbs air linearly dependent on the pressure. The absorbed air releases from the oil during the passage of the oil sump tank.

Oil pump unit

The oil pressure system is equipped with two equal oil pump units.

Each pump unit consists of a screw pump, flexible shaft coupling, distance piece, tube/fittings and an electric motor. It can be removed as a separate unit for overhaul. One pump unit may even be dismantled for service and overhaul when the turbine is operating.

The pump is of the self-priming positive displacement type. The main parts in the pump are the three rotating screws, e.g., one power rotor and two idler rotors. The power rotor is the only driven element and the idler rotors turn due to the action of the driven rotor. Their thread surfaces are shaped to form a tight seal both in relation to each other and the surrounding rotor housing. The fluid is transported axially and quite uniformly according to the screw rotation.

The pump units are equipped with a fluid trap on the suction side to ensure that the pump remains filled with oil in the standby mode. This fluid trap shall be filled with oil before the pump is started after overhaul. The oil pump units are driven by alternating current (AC) motors.

An oil pressure system with two pump units has one pump running continuously while the other pump is in standby. The standby pump will start automatically at low pressure in the accumulator.

The control of the oil pump units permits the selection of either pump as the preferred unit.

As an option a direct current (DC) motor driven oil pump can be supplied. A DC motor driven pump is operating only if the AC supply fails. The pump will then start and stop via a pressure switch control which keeps the pressure below but close to the normal oil pressure.

Due to the pump start and stop automatic control the DC motor driven pump unit has no unloader valve system.

Unloader valve

The unloader valve is installed to prevent a fast degradation of the oil quality. A relatively fast degradation will happen if the relief valve, is in continuous operation and thereby cause unwanted oxidation and cavitation.

The unloader valve is installed in the pipeline between the oil pump unit and the inlet check valve of the accumulator. At low pressure in the accumulator, the oil is fed from the pump to the accumulator. As soon as the oil pressure has reached the upper set point, the pressure switch activates the unloader valve. The pressure on the top of the unloader valve piston is then decreased, the piston moves upwards and the oil flow is led to the oil sump tank.

Check valves

Between each oil pump unit and the accumulator a check valve is installed .These valves prevent pressure oil to flow back to the oil sump tank through the oil pump. The valve piston is spring loaded to ensure that the valve is closed during pressurizing the oil pressure system. The oil pump unit, the oil pipe and other equipment between the pump and check valve may be dismantled without de-pressurizing the accumulator.

Main oil valve

The main valve, is the shut off valve between the accumulator and the main oil piping system. Opening and closing of the main oil valve is controlled by the pilot valve. This valve drains or pressurizes respectively the piston chamber. This opening and closing sequence can be done by remotely controlled solenoid valves.

Relief valve

The relief valve protects the accumulator against unintended high pressure. The relief valve shall not open before the pressure in the accumulator exceeds normal working pressure.

The oil begins to flow through the valve when the oil pressure on the lower side of the valve piston balances against the spring pressure. The design of the valve with a long coil spring and a large valve piston gives a very accurate flow - pressure characteristic. The valve is adjusted by turning the top cover.

Air Supply System

The air pressure system serves to refill the accumulator in the oil pressure system with air. The air in the accumulator is in direct contact with the oil. With pressurised accumulator, the oil absorbs air linearly with the pressure. In the sump tank the absorbed air releases again during the pressure relief to atmospheric pressure. This process however, takes some seconds to be fulfilled, but the passage time for the oil flow through the sump tank is longer than for the air release process.

The main components are:

- one or two AC powered high pressure air compressors with inlet filter

- relief valve mounted on the compressor

- air cooled aftercooler with condensate trap

- valves

CHAPTER FOUR: PRACTICAL (TRAINEE) WORK DONE AT EUL My major training role was in the field of maintenance and as such, most of my practical training was in the area of condition control. Condition control of water turbines and additional mechanical equipment is the primary basis for organizing and carrying out

- Preventive maintenance - a continuous process which is taking place with certain time intervals and at planned dates.

- Overhauls - being performed to improve the operation conditions, rectify wear and leakages on the plant according to plans adapting to the plant operation.

Maintenance activities fall into three general categories:

• Routine Maintenance: Activities that are conducted while equipment and systems are in service. These activities are predictable and can be scheduled and budgeted. Generally, these are the activities scheduled on a time-based or meter-based schedule derived from preventive or predictive maintenance strategies. Some examples are visual inspections, cleaning, functional tests, and measurement of operating quantities, lubrication, oil tests, and governor maintenance.

• Maintenance Testing: Activities that involve using test equipment to assess condition in an offline state. These activities are predictable and can be scheduled and budgeted. They may be scheduled on a time or meter basis but may be planned to coincide with scheduled equipment outages. Since these activities are predictable, some offices consider them “routine maintenance” or “preventive maintenance.” Some examples are governor alignments and balanced and unbalanced gate testing.

• Diagnostic Testing – Activities that involve using test equipment to assess the condition of equipment after unusual events, such as equipment failure/ repair/replacement or when equipment deterioration is suspected. These activities are not predictable and cannot be scheduled because they are required after a forced outage.

How We Carry Out Maintenance Work at EUL Much of the maintenance at Eskom Uganda is Preventive Maintenance with routine checks after 1-6 months on given units, and outages on specific units for complete maintenance. Even when the maintenance is a breakdown, the appropriate person must raise a notification which is sent to the planning authority. The procedure is as follows:

1. Planning Department receives notifications about procedures to be carried out

2. Planning Engineer issues work-packages detailing the process to be carried out on specific components and units with technicians in charge.

3. Technician who receives a work package then applies for a work-permit through the Operations office, with risk assessment of work to be carried out.

4. All staff at maintenance site fills in their names in the worker’s register to show that they are working at the specific site. As the norm is, my colleagues and I would always note down our names in the workers’ register plus the time during which we commenced work and append our signatures to it.

5. After work, the appropriate person signs off the work-package and returns it to the planning authority to show completion of work.

4.1 Generator-Transformer Work Here, we carried out the Generator Transformer Cooler Cleaning. Some of the safety precautions taken included; isolation of the unit, wearing of industrial boots and ensuring no work was carried out during rain.Tools and Equipment

2 off 11/16 inch W combination Spanners 1 off mallet 2 off rodding sticks fitted with 9/16 inch rodding brushes on Metal scrapper 2 off 2mm and 25mm combination spanners Thin metal wedges 20Ib hammer

Spares and Materials Gasket material Gasket Sealant

Procedure Before opening up, we checked if there were traces of oil in the water I then, switched off oil circulation pump and closed valves We closed off the water supply valve using the electric valve motor We opened the cooler and cover nuts and jack the covers to enable complete removal I then, cleaned the tube ends and using rodding sticks, cleaning each tube at a time. We cleaned the dirt from the end covers Flushed the cooler with water Inspected the tube ends for damage and record Then bolted back the end covers replacing the gaskets where necessary We normalized the oil circulation and water supply The activity was repeated for the second cooler We cleaned all trash from the area

LSL DRAIN/DEWATER (Unit Turbine)We were required to Remove and Inspect Top Cover Drain Pump. Tools and equipment used included 1 tool box normal to a technician and a wire brush.

Procedure The pump was isolated electrically and removed from the turbine pit and placed in a

convenient working place. We cleaned the tin can strainer with wire brush We opened the oil plug to check state of oil, whether the oil was milky, then removed the

pump completely from the pit for fuller inspection and repair according to WP LSL UNPS MW P0044A.

Where the oil was not milky, we placed the pump back into working position and normalized electrical system.

In cases where unit was on load and there was adequate water, then I was told to switch on the pump and record the time it takes to complete the water.

We put the pump on auto and recorded whether it cuts in normally and cuts out after completing the water.

MEX GOVERNOR CONTROLOur main area of concern here was to Inspect/Clean filters, Check Unloading valve locknut. Some of the safety precautions taken included; not trying to clean governor oil filters when the unit is on load and making sure that the isolation valves are closed before opening any filter.Spares and Materials

Spare filters Gasket Materials

Pre-Conditions Unit had to be shut down and at a stand still Governor pump was switched off before we commenced any work

ProcedureUnloading Valve Filter

Starting with the pressure vessel filter, we closed the isolation valve. Opened the two bolts securing the filter cover onto the filter housing Withdrew the filter and washed with paraffin and blew with compressed air. Returned the filter and replaced the cover with a new gasket

Actuator Filter Closed the filter isolation valve Opened the access window Using the King Dick spanner, opened the filter, washed in paraffin, inspected and blew

clean with compressed air, Where the mesh was damaged, we replace the filter Returned the filter and tightened properly Cleaned the drain filter at the actuator base

Closed the access window.Pressure Supply to five way Valve Filter

We closed the HP and LP isolation valves I was told to open the bolts securing the filter covers Then, removed, cleaned and inspected the filter Where the filter mesh was damaged, we replaced it. Returned the filter and used new gaskets for the cover plate Opened the isolation valves

Unloading Valve Lock Nut Removed the glass cover Checked if the knurled lock nut was loose With the unit on load, we took note of the Min and Max Pressure We loosened or tighten the bottom nut to adjust the pressure range to required level (265-

285psi) Where the range was normal, we tightened the locknut Finally, we replaced the glass cover

FIRE PROTECTION-Auxiliary PlantHere, we were required to clean and inspect Fire Engine Pump. Among the other things, we had to obtain a permit to inspect and test the fire-water system, watch out for slippery floor, clean work area before and after inspection and testing.

This is a no-smoking area; the engine can’t be started when there is evidence of fuel fumes. No attempt is made to work, when engine is running, no fuel is spilt on engine and the area should be well ventilated.

Tools and Equipment:

-Technician Tool Box

-Allen Key set

Spares and Materials:

-Gasket Kit, Sealing materials

-Petrol Engine Oil

Procedure:

Closed water inlet valves to the pump from pit1 and 2. Closed water discharge valves from pump Switched off charging system Disconnected one battery lead

Removed air inlet filters, inspect, cleaned and refit Drained crankcase oil, clean and filled with new oil Replaced compressor oil filter and ensured lubricant level was correct for the pump and

engine Checked for any oil, water, fuel leaks and cured Checked for exhaust gas leaks and cured Checked water level and topped up Checked fuel level and topped up

CLEANING OF SCREENS This was at the intake during one of the outages on one of the ten units at NPS. The screens at the intake are of the mesh type.

Using a gantry crane of tonnage capacity correlating to that of the mesh, we lifted out the screens from the spaces that house the bulkheads.

The cleaning process here was a manual one and as such, we employed hand-gloves to protect our hands from getting soiled. The screens always come in pairs, and as such, we cleaned one, then another in the same time period before later inserting them into the under-water compartments housing them.

The major reason why we cleaned the screens was to increase the water intake, and the velocity, since these are the two major reasons that determine the capacity of an individual turbine unit. Cut out the pressure, and velocity, and you will witness a downfall in capacity.

Overall, the act of cleaning the mesh screens was in due accordance with the best practices of maintenance of trash-rack/intake gate filters for hydro-power plants.

Raising and lowering fish guidance equipment, such as submerged traveling screens or submerged bar screens and vertical barrier screens, is a major task for intake gantry cranes at the powerhouse.

CLEANING OF WATER STRAINERSHere, we based on the differential pressure gauge to determine which strainer to work on, and whether it was appropriate to really work on it. This is based on the principle that each strainer has an operational pressure below which is indicative of clogs which would require need for cleaning.

Some of the tools and equipment used included;

Eyebolts Combination spanners Clogging spanners Hammers

Pipe Wood packings Wire Ropes

We started off by closing the valves that supplied water to these strainers. Then, we opened the bolts on the individual covers. We removed the wheel on the cover, inserted the eyebolts and henceforth used a rope and pipe to carry out the cover.

The wheel was then inserted back on the shaft that is joined to the wheel, so as to pull out the strainer. When strainer was pulled out, compressor was switched off, to supply the compressed air which was to be used to clean the strainer/filters.

After blowing, strainer was inserted back into its housing, grease was applied on the sealant aka gland packing, and the cover replaced. New differential pressure is noted on the gauge to confirm that the strainer is now operating perfectly.

The strainers are of the duplex type, for one major reason-to enable one to be in service and another on stand-by.

CURING OF LEAKAGES In curing leakages in piping systems, our main concern was about cutting new gasket from appropriate materials, and replacing them where needed. In other areas, we had to cut new gland packing and replace them where called for.

However, for some situations, for example those that involved flanges, we concerned ourselves with tightening the bolts, since in some cases, and leakages were as a result of a few loose bolts.

Packing ProceduresThe most common method of controlling leakage past a pump, turbine, or wicket gate shaft is by using compression packing. The standard packing or stuffing box will contain several rings of packing with a packing gland to hold the packing in place and maintain the desired compression. Some leakage past the packing is necessary to cool and lubricate the packing and shaft. If additional lubrication or cooling is required, a lantern ring also may be installed along with an external packing water source.

Over time, the packing gland had to be tightened to control leakage.

To prevent burning the packing or scoring the shaft when these adjustments are made, most compression packing contains a lubricant. As the packing is tightened, the lubricant is released to lubricate the shaft until leakage past the packing is reestablished. Eventually, the packing can be compressed to a point where no lubricant remains and

replacement is required. Continued operation with packing in this condition can severely damage the shaft.

When packing replacement was necessary, we removed all of the old packing. Where the packing box was equipped with a lantern ring, this was also removed along with all of the packing below it. With the packing removed, special attention had to be given to cleaning and inspecting the packing box bore and the shaft or shaft sleeve.

To provide an adequate sealing surface for the new packing, a severely worn shaft or shaft sleeve was repaired or replaced. Likewise, severe pitting in the packing box bore was repaired. For the packing to seal against a rough packing box bore requires excessive compression of the packing. This over compression of the packing always led to premature wear of the shaft or shaft sleeve.

On small pumps, the shaft runout at the packing box was checked by manually rotating the shaft and measuring the runout with a dial indicator. In most cases, total indicated runout should not exceed 0.003 inch. If the runout is excessive, the cause had to be found and corrected. Bent shafts should be replaced and misalignment corrected.

There is a number of different types of packing available; so when choosing new packing, we ensured that it is the correct size and type for the intended application.

All of the relevant conditions that the packing will operate under, such as shaft size and rotational speed, had to be considered. Installing the wrong packing can result in excessive leakage, reduced service life, and damage to the shaft or sleeve.

The new packing should be installed with the joints staggered 90 degrees apart. It is sometimes helpful to lubricate the packing prior to installation. The packing manufacturer should be consulted for recommendations of a lubricant and for any special instructions that may be required for the type of packing being used. With all of the packing and the lantern ring in place, the packing gland should be installed finger tight.

There should be generous leakage upon the initial startup after installing new packing. The packing gland should be tightened evenly and in small steps until the leakage is reduced sufficiently. The gland should be tightened at 15- to 30-minute intervals to allow the packing time to break-in. The temperature of the water leaking from the packing should be cool or lukewarm, never hot. If the water is hot, we backed off the packing gland.

CHAPTER SIX: FINAL REMARKS

6.1 Challenges1. Undetailed machine and equipment manuals concerning the power plant machinery.

2. Presence of monitor lizards in some areas of the power plant, and lack of information about their dangers.

3. Accommodation constraints as far as locating good and cheap places of housing in Jinja

4. Difficulty in accessing the document Centre, locating right material, and impossibility of borrowing the books.

6.2 Recommendations1. Eskom Uganda should carry out an arrangement with one of the guest houses in Jinja so as to make the process of landing accommodation easy for trainees.

2. Resource Centre should be easily assessed by trainees.

3. A clear program as far as sections to handle during specific periods of training should be devised and given to every trainee.

4. The Training should be holistic in form, that is, exposure to a wide range of areas as far as the operation of the power plant, and the management is concerned

6.3 ConclusionThe two months training at Eskom Uganda was worth it. It allowed us an opportunity to get an exposure of the practical implementation of theoretical fundamentals. To summarize the gains:

1. Hands-on practical experience as far as mechanical and manufacturing systems are concerned.

2. Better Time Management skills and on-job etiquette

3. Confidence gained as far as operations are concerned and a wide range of holistic kills that a mechanical and manufacturing engineer would ever acquire during training.

References1. Electro-Mechanical Works –Operation and Maintenance of Small Hydropower Station (Indian Institute of Technology Roorkee)

2. http://www.eere.energy.gov/basics/renewable_energy/hydropower.html

3. Power Plant Engineering By P.K.Nag

4. Power Plant Engineering By A.K Raj, Amit Prakash and Manish Dwivedi

5. Serek Heat Exchanger Manuals