UNIVERSITY OF PETROLEUM & ENERGY STUDIES

CENTRE FOR CONTINUING EDUCATION

EXECUTIVE MBA

(POWER MANAGEMENT)

SEMESTER IV

YEAR: 2014 SESSION: JULY

ASSIGNMENT – 1

FOR

Power Station Management

(MDSP 831D)

(TO BE FILLED BY THE STUDENT)

NAME: MARRAPU UDAYA BHANU NAIDU

SAP NO/REGN. NO: 500024907

Section A (20 Marks)

Write short notes on any four of the following

1. Electrical Substation: A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages. The word substation comes from the days before the distribution system became a grid. As central generation stations became larger, smaller generating plants were converted to distribution stations, receiving their energy supply from a larger plant instead of using their own generators. The first substations were connected to only one power station, where the generators were housed, and were subsidiaries of that power station.

Substations generally have switching, protection and control equipment, and transformers. In a large substation, circuit breakers are used to interrupt any short circuits or overload currents that may occur on the network. Smaller distribution stations may use recloser circuit breakers or fuses for protection of distribution circuits. Substations themselves do not usually have generators, although a power plant may have a substation nearby. Other devices such as capacitors and voltage regulators may also be located at a substation.

Substations may be on the surface in fenced enclosures, underground, or located in special-purpose buildings. High-rise buildings may have several indoor substations. Indoor substations are usually found in urban areas to reduce the noise from the transformers, for reasons of appearance, or to protect switchgear from extreme climate or pollution conditions.

Where a substation has a metallic fence, it must be properly  grounded to protect people from high voltages that may occur during a fault in the network. Earth faults at a substation can cause a ground potential rise. Currents flowing in the Earth's surface during a fault can cause metal objects to have a significantly different voltage than the ground under a person's feet; this touch potential presents a hazard of electrocution.

2. Thermal Power Station: A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fossil fuel resources generally used to heat the water. Some prefer to use the

term energy center because such facilities convert forms of heat energy into electrical energy. Certain thermal power plants also are designed to produce heat energy for industrial purposes of district heating, or desalination of water, in addition to generating electrical power. Globally, fossil fueled thermal power plants produce a large part of man-made CO2 emissions to the atmosphere, and efforts to reduce these are varied and widespread.

Almost all coal, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well as many natural gas power plants are thermal. Natural gas is frequently combusted in gas turbines as well as boilers. The waste heat from a gas turbine can be used to raise steam, in a combined cycle plant that improves overall efficiency. Power plants burning coal, fuel oil, or natural gas are often called fossil-fuel power plants. Some biomass-fueled thermal power plants have appeared also. Non-nuclear thermal power plants, particularly fossil-fueled plants, which do not use co-generation are sometimes referred to as conventional power plants.

Commercial electric utility power stations are usually constructed on a large scale and designed for continuous operation. Electric power plants typically use three-phase electrical generators to produce alternating current (AC) electric power at a frequency of 50 Hz or 60 Hz. Large companies or institutions may have their own power plants to supply heating or electricity to their facilities, especially if steam is created anyway for other purposes. Steam-driven power plants have been used in various large ships, but are now usually used in large naval ships. Shipboard power plants usually directly couple the turbine to the ship's propellers through gearboxes. Power plants in such ships also provide steam to smaller turbines driving electric generators to supply electricity. Shipboard steam power plants can be either fossil fuel or nuclear. Nuclear marine propulsion is, with few exceptions, used only in naval vessels. There have been perhaps about a dozen turbo-electric ships in which a steam-driven turbine drives an electric generator which powers an electric motor for propulsion.

3. Solar Power Plants: Solar power is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP). Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaics convert light into electric current using the photovoltaic effect.

Photovoltaics were initially, and still are, used to power small and medium-sized applications, from the calculator powered by a single solar cell to off-grid homes powered by a photovoltaic array. They are an important and relatively inexpensive source of electrical energy where grid power is inconvenient, unreasonably expensive to connect, or simply unavailable. However, as the cost of solar electricity is falling, solar

power is also increasingly being used even in grid-connected situations as a way to feed low-carbon energy into the grid

Commercial concentrated solar power plants were first developed in the 1980s. The 392 MW ISEGS CSP installation is the largest solar power plant in the world, located in the Mojave Desert of California. Other large CSP plants include the SEGS(354 MW) in the Mojave Desert of California, the Solnova Solar Power Station (150 MW) and the Andasol solar power station(150 MW), both in Spain. The 290 MW Agua Caliente Solar Project in the United States, and the 221 MW Charanka Solar Park in India, are the world’s largest photovoltaic power stations.

4. Method of Boiler Efficiency Calculation-495. Grid Connection

Section B (30 marks)

(Attempt any three)1. Give an overview of the business benefits of power station management.2. Define thermal station. Describe the classification of thermal stations.3. Write short notes on:

a. Electromagnetic Generatorsb. Electrostatic Generator.

4. Highlight the features of single-phase and three-phase electric power.

Section C (50 marks)

(Attempt all questions. Every question carries 10 marks)

Read the case “Performance Analysis of Thermal Power Station: Case Study of Egbin Power Station, Nigeria” and answer the following questions:

Case Study: Performance Analysis of Thermal Power Station:

Case Study of Egbin Power Station, Nigeria

Egbin Thermal Plant

Egbin thermal plant is located at the suburb of Lagos State, Ijede area of Ikorodu. The plant was

commissioned in 1985 and consists of 6 units of 220 (6X220) MW (Reheat – Regenerative).

They are dual fired (gas and heavy oil) system with modern control equipment, single reheat; six

stages regenerative feed heating. The plant was constructed under joint Japanese/ French

financing on a turnkey contract basis and most of the equipment were Japanese supplied. The

overall cost of the plant was US $ 1 billion with an expected life of 25 years. The estimate was

based on the fact that the plant should run mainly on natural gas which does not give the serious

boiler slag and ash problem characteristic of coal fuel. Natural gas is supplied to the plant

directly from the Nigerian Gas Company (NGC). Lagos operations department is the annexed to

Egbin gas station of the thermal plant. Since Egbin thermal plant is located on the shores of the

lagoon cooling water for the plant’s condensers is pumped from the lagoon into the water

treatment plant en route to the condensers.

Major Plant Components

The Boiler, Turbine and Generator (collectively known as the B-T-G system) are the most

crucial equipment required for the generation of electricity in steam power plants. All other

equipments in the station are termed auxiliaries and are needed for the smooth running of the

boiler, turbine and generator of the units in the station. According to Egbin Design Manuals the

functions and operating conditions of these plant components are x-rayed as follow:

Boiler: The Boiler is designed to produce flow of main steam at temperature of 5410C and

pressure of 12,500kPa and also to reheat steam from the turbine high pressure stages, from the

combustion of heavy fuel oil or natural gas.

Turbine: The Turbine is the impulse type, tandem-compound, double flow reheat, condensing

tube, with maximum continuous rating of 220MW, speed 3000rpm, initial steam pressure

12.5MPa, initial steam temperature 538oC, exhaust steam pressure 8.5kPa, twenty-four (24)

stages (eight (8) high, six (6) intermediate and 10 (5*2) low pressure stages) and with three (3)

low pressure heaters, two (2) high pressure heaters and one (1) de-aerator, which receives dry

steam from the boiler and rotates a shaft coupled to the rotor of the generator to generate power.

Generator: The Generator is the radiant type, 3-phase, 2-pole, hydrogen-cooled, with output

voltage of 16kV, power of 245.8MVA (221.22MW), speed 3000rpm, 0.9 power factor, exciting

voltage of 440V, 50Hz frequency, armature current of 8870A and field current of 2781A,

ambient temperature of 45oC, armature temperature rise of 55oC, field temperature rise of 65oC,

and with natural circulation with single reheat and duct firing.

Performance of Steam Power Plants

The choice of a steam turbine power plant depends on its performance, which depends on five

factors:

Capacity of plant

Plant’s load factor and capacity factor

Thermal (and overall) efficiency

Reliability

Availability of water for condensate.

Efficiency

The thermal efficiency of steam power plants, defined as the ratio of heat equivalent of

mechanical energy transmitted to the turbine shaft is quite low (about 30%). The thermal

efficiency of a power plant depends on three (3) factors which include, the pressure of steam

entering turbine, the temperature of steam entering turbine and the pressure in the condenser. It

increases by increasing the temperature and pressure of the steam entering the turbine,

decreasing the pressure in the condenser, re-heating steam between turbine stages and by

bleeding steam along the heating lines. In order to increase the efficiency of steam power plants,

heat/loss saving devices such as reheaters, superheaters, economizers, preheaters among others

are incorporated in the design.

Overall efficiency of the plant, defined as the ratio of heat equivalent of electrical output to the

heat of combustion is about 29%. In case of most modern super-criticalpressure steam plants

employing many heat saving devices, the plant overall efficiency may reach the value of 50%

(i.e. with a supercritical temperature of about 600oC, overall efficiency could be just over 40%

while with ultra supercritical temperature of around 700oC, efficiency may be improved to

around 50%). The overall efficiency of steam power station is low mainly due a large amount of

heat (over 50%) that lost in condensers and secondly heat that wasted in other parts of the plant

(boiler, alternator etc). The heat loss in the condenser is unavoidable since heat energy cannot be

converted into mechanical energy without temperature difference. The greater the temperature

difference, the greater is the heat energy converted into mechanical energy. This necessitates

keeping the temperature of the condenser to a minimum value. But the greater the temperature

difference, the greater the amount of heat lost. This explains the low efficiency of steam plants.

Reliability

Reliability is the probability that a device or system will operate for a given period of time

without failure, and under given operating conditions. Reliability of a system is the characteristic

of the system that it will perform its required function under stated conditions for a specified

period of time. The concept of reliability is associated, in qualitative terms, with good design,

endurance, consistent quality, maintainability and dependability. With adequate maintenance, the

reliability of a power plant may approach 1 (that is, 100%).

Constraints and Limiting Factors

Irregularities in figures for some data obtained from the plant.

Constant fluctuation and irregularity of plant loading due to constant

fluctuations in the transmission efficiency of the national grid as controlled by

the National Control Centre (NCC), Oshogbo.

Unavailability of some records for some of the period under review (2000 -

2004) as the Performance Management Department of the Plant was only set up

in 2005.

Breakdown of equipment, as some of the units were out of service during the

period under review.

Conclusion

Performance analysis of Egbin Thermal Plant has been carried out with specific emphasis on the

Efficiency and Reliability of the plant. For the eleven (11) years under review (2000-2010), the

study revealed that the average overall efficiency was 34.67% (30.30% minimum; 36.60

maximum) as against expected values of 40-45%. The average reliability of the plant, for the

period under review, was 80.92% (69.47 minimum; 79.73 maximum) as against best

practices/target of 98-100%. A number of reasons were adduced to be responsible for this

shortfall in performance. These include: low plant availability due to breakdowns/failures,

overdue overhaul of units, obsolete technology, instability of the national grid system, aging

plant components, disruption in gas supply among others. Measures to improve the performance

indices (efficiency and reliability) of the plant have been suggested and this include: overhaul

maintenance of due plant equipment/units, training and re-training of operation and maintenance

(O&M) personnel, upgrading obsolete technology, ensuring security of gas supply and

rehabilitation of failed equipment.

Questions:

1. Highlight the features of the Thermal power plants.

2. Throw light on the Egbin Power Plant.Egbin thermal plant is located at the suburb of Lagos State, Ijede area of Ikorodu. The

plant was commissioned in 1985 and consists of 6 units of 220 (6X220) MW (Reheat –

Regenerative). They are dual fired (gas and heavy oil) system with modern control

equipment, single reheat; six stages regenerative feed heating. The plant was constructed

under joint Japanese/ French financing on a turnkey contract basis and most of the

equipment were Japanese supplied. The overall cost of the plant was US $ 1 billion with

an expected life of 25 years. The estimate was based on the fact that the plant should run

mainly on natural gas which does not give the serious boiler slag and ash problem

characteristic of coal fuel. Natural gas is supplied to the plant directly from the Nigerian

Gas Company (NGC). Lagos operations department is the annexed to Egbin gas station

of the thermal plant. Since Egbin thermal plant is located on the shores of the lagoon

cooling water for the plant’s condensers is pumped from the lagoon into the water

treatment plant en route to the condensers.

3. What are the factors that affect the performance of Thermal Power plant?

The following five factors are affected the performance of Thermal Power Plant Capacity of plant

Plant’s load factor and capacity factor

Thermal (and overall) efficiency

Reliability

Availability of water for condensate.

4. Comment on the constraints and the limiting factors mentioned in the above case.Constraints and Limiting Factors:

Irregularities in figures for some data obtained from the plant.

Constant fluctuation and irregularity of plant loading due to constant

fluctuations in the transmission efficiency of the national grid as controlled by

the National Control Centre (NCC), Oshogbo.

Unavailability of some records for some of the period under review (2000 -

2004) as the Performance Management Department of the Plant was only set

up

in 2005.

Breakdown of equipment, as some of the units were out of service during the

period under review.

Comments: Due to deficiency in record keeping/filing systems, there were some records that could not be readily available. Though the utility was commissioned in 1985, the records of the running hours, gross energy generated total fuel energy consumed etc could not be found and so were not used for our analysis. It is very difficult to review or make the analysis.

5. Describe the major plant components. The Boiler, Turbine and Generator (collectively known as the B-T-G system) are

the most crucial equipment required for the generation of electricity in steam power

plants. All other equipments in the station are termed auxiliaries and are needed for the

smooth running of the boiler, turbine and generator of the units in the station. According

to Egbin Design Manuals the functions and operating conditions of these plant

components are x-rayed as follow:

1. Boiler: The Boiler is designed to produce flow of main steam at temperature of

5410C and pressure of 12,500kPa and also to reheat steam from the turbine high

pressure stages, from the combustion of heavy fuel oil or natural gas.

2. Turbine: The Turbine is the impulse type, tandem-compound, double flow reheat,

condensing tube, with maximum continuous rating of 220MW, speed 3000rpm, initial

steam pressure 12.5MPa, initial steam temperature 538oC, exhaust steam pressure

8.5kPa, twenty-four (24) stages (eight (8) high, six (6) intermediate and 10 (5*2) low

pressure stages) and with three (3) low pressure heaters, two (2) high pressure heaters

and one (1) de-aerator, which receives dry steam from the boiler and rotates a shaft

coupled to the rotor of the generator to generate power.

3. Generator: The Generator is the radiant type, 3-phase, 2-pole, hydrogen-cooled, with

output voltage of 16kV, power of 245.8MVA (221.22MW), speed 3000rpm, 0.9

power factor, exciting voltage of 440V, 50Hz frequency, armature current of 8870A

and field current of 2781A, ambient temperature of 45oC, armature temperature rise

of 55oC, field temperature rise of 65oC, and with natural circulation with single

reheat and duct firing.