Electrical Power Generation Notes

Unit 1 SOURCES OF ELECTRICAL POWER Syllabus: Wind, solar, fuel cell, tidal, geo-thermal, hydro-electric, thermal-steam, diesel, gas, nuclear power plants (block diagram approach only).Concept of co-generation. Combined heat and power distributed generation.

Discuss conventional and non conventional energy in generation. Give examples for each method.

JUNE 11, 12. 4 M

There are two types of energy sources  Conventional (non-renewable) sources  non-conventional (renewable) sources Conventional energy sources: The sources of energy which are exhaustible in nature are called conventional energy sources. The energy sources which once used cannot be recovered any more. They are depleting in nature The sources of energy which are used for the mass generation of power are called conventional energy sources. Ex:

1) Diesel 2) Gas 3) Coal 4) Nuclear

Non-conventional sources or renewable energy sources: Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

These energy sources are available abundantly in nature and they can be reused again. The energy sources which are non-exhaustible in nature are called Nonconventional sources. Ex:

1) Solar energy 2) Wind energy 3) Tidal energy 4) Geo-thermal energy 5) Biomass energy 6) Ocean thermal energy 7) Biogas energy 8) Fuel cells

Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

WIND ENERGY:  Wind flow is created as an effect of solar energy which creates low and high pressure regions on the earth due to heating.  Wind energy is inexhaustible, plentiful and pollution free source of energy.  Wind possesses energy by virtue of its motion. Any device capable of slowing down the motion of air can convert its energy into useful work.  Wind mills or wind energy converters converts wind power into electrical power. 

The typical system range from 30kW for individual units to 5 MW for combined multiple units.

Mention any three advantages and three disadvantages of wind energy conversion system. DEC 09, 6 M Advantages  It is renewable source of energy.  It can be installed any locations where topographical conditions are suitable. 

It is non-polluting in nature, so it has no adverse influence on the environment.



These plants avoid fuel provision and transport.



Cost of generation is low.

Disadvantages  Wind energy available in fluctuating in nature.  It requires large area to collect the energy.  Noisy in operation.  Wind energy requires storage capacity because of its irregularity.  Power generated is quite small. 

It is site specific. Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

Explain the working of wind energy conversion system with block diagram OR

JUNE 09, DEC 10, 6 M

With a neat sketch, explain the basic working principle of wind energy conversion system. JUNE 12, 6 M

Figure 1 : Block diagram of wind energy conversion system

 Aero turbine converts wind energy into rotary mechanical energy.  This aero turbine requires pitch control and yaw control for proper operation.  Mechanical interface consisting of a step up gear and suitable coupling to transmit the rotary mechanical energy into electrical generator.  The generator converts mechanical energy into electrical energy.  The output of the generator is connected to the load or power station.  The controller senses the wind direction, wind speed, generator output and other necessary performance quantities & generates a control signal to take proper corrective actions.


FUEL CELLS: Write a short note on fuel cell.

A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used. Fuel cells are different from batteries in that they require a constant source of fuel and oxygen to run, but they can produce electricity continually for as long as these inputs are supplied. There are many types of fuel cells, but they all consist of an anode (negative side), a cathode (positive side) and an electrolyte that allows charges to move between the two sides of the fuel cell. Electrons are drawn from the anode to the cathode through an external circuit, producing direct current electricity. As the main difference among fuel cell types is the electrolyte, fuel cells are classified by the type of electrolyte they use. Fuel cells come in a variety of sizes. Individual fuel cells produce very small amounts of electricity, about 0.7 volts, so cells are "stacked", or placed in series or parallel circuits, to increase the voltage and current output to meet an application‘s power generation Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

requirements. In addition to electricity, fuel cells produce water, heat and, depending on the fuel source, very small amounts of nitrogen dioxide and other emissions. The energy efficiency of a fuel cell is generally between 40-60%, or up to 85% efficient if waste heat is captured for use.

TIDAL ENERGY: With a neat schematic diagram, explain the working of tidal power plant. DEC 09, 4 M

What is tidal power? Tide is periodic rise and fall of the water level of the sea. Tides occur due to the attraction of seawater by the moon. These tides can be used to produce electrical power which is known as tidal power. It is another source of renewable energy. The large scale up and down movement of sea water represents an unlimited source of energy and a part of this energy can be converted into electrical energy. When the water is above the mean sea level, it is called flood tide and when the level is below the mean level, it is called ebb tide.

The main feature of tidal cycle is the difference in the water elevations at high tide and at low tide, this differential head could be utilised in operating the


hydraulic turbine, the tidal energy converted into electrical energy by means of attached generator. A dam is constructed in such a way that a basin gets separated from the sea and a difference in the water level is obtained between the basin and sea. The constructed basin is filled during high tide and emptied during low tide passing through sluices and turbine respectively. The Potential energy of the water stored in the basin is used to drive the turbine which in turn generates electricity as it is directly coupled to an alternator.

Explain with sketches the working of single basin and double basin tidal power plant.

DEC 07, JUNE 10, 6 M

Single basin tidal plant:

It has only one basin scheme Single basin scheme can generate power intermittently. In single basin system only one basin interacting with sea The sea and basin are separated by dam or barrage or dyke. The sluice ways are located conveniently along the dam. The flow of water between sea and dam is provided by rise and fall odf tidal water level. Along with sluice gates the dam also contains low head turbine sets Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

 Double basin power plant: It requires two separate but adjacent basins. In one basin called “upper basin” (or high pool), the water level is maintained above that in the other, the low basin (or low pool). Because there is always a head between upper and lower basins, electricity can be generated continuously, although at a variable rate.

 In this system the turbines are located in between the two adjacent basins, while the sluice gates are as usual embodied in the dam across the mouths of the two basins.  At the beginning of the flood tide, the turbines are shut down, the gates of upper basin A are opened and those of the lower basin B are closed. The basin A is thus filled up while the basin B remains empty. As soon as the rising water level in A provides sufficient difference of head between the two basins, the turbines are started. The water flows from A to B through the turbines, generating power. The power generation thus continues simultaneously with the filling up the basin A.  At the end of the flood tide when A is full and the water level in it is the maximum, its sluice gates are closed. When the ebb tide level gets lower Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

than the water level in B, its sluice gates are opened whereby the water level in B, which was arising and reducing the operating head, starts falling with the ebb. This continues until the head and water level in A is sufficient to run the turbines. With the next flood tide the cycle repeats itself.

Advantages of tidal power: Inexhaustible Free from pollution These plants do not demand large area of valuable land because they are on bays or sea shore Peak demand can be effectively met when it works in combination with thermal or hydroelectric plants.

Limitations: Variable output due to variations in tidal power plant There are feasible only in certain range of tidal cycle Sea water is corrosive and it was feared that machinery may get corroded Construction is difficult High cost


GEO THERMAL POWER PLANT: With a neat sketch explain working of geo-thermal power plant DEC 10, DEC 09, 6 M OR

With a neat block diagram, explain working of geo-thermal power plant DEC 08, 6 M

The centrifugal separator removes particulate matter from the steam. The steam is admitted into the steam turbine . The steam expands in the turbine buckets producing rotary kinetic energy. The low pressure steam at the exhaust of the turbine is condensed in condenser the condensate is re injected into the earth via the reinjection wall. Cooling water for condensing the steam is circulated through the cooling tower by means of cooling water pump. The synchronous generator generate electrical power at high voltage 50 Hz A.C. The turbine and generator form one unit.Complete power plants has several units. Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

Geothermal energy in the form of dry steam is converted into mechanical energy by the turbine. The mechanical energy is converted to electrical energy by the generator.

OCEAN THERMAL ENERGY CONVERSION: Tropical oceans collect and store very large amount of solar energy. Utilization of this energy with associated temperature difference and conversion of this thermal energy into work and hence into electricity is the basis of ocean thermal energy conversion (OTEC) systems. OPEN CYCLE OTEC SYSTEM :

Open cycle’ refers to the ‘utilization of sea water as the working fluid, wherein sea water is flash evaporated under a partial vacuum. The low pressure steam is passed through a turbine, which extracts energy from it, and then the spent vapour is cooled in a condenser. This cycle drives the name ‘open’ from the fact that the condensate need not be returned to the evaporator, as in the case of the ‘closed cycle’. Instead, the condensate, can be utilized as desalinated water if a surface condenser is used, or if a spray (direct-contact) condenser is used, the condensate is mixed with the cooling water and the mixture is discharged back into the ocean. &schematic diagram of the open cycle system is shown in Fig. Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

SOLAR POWER: With a neat schematic diagram, explain the working of a solar power plant. What is the importance of this plant in the present energy crises in the world? DEC 10, JUNE 08 10 M

The basic components of solar power plant are also exactly identical to thermal power plant except boiler is replaced by a flat plate solar collector. The energy from solar radiation is collected and utilized to generate a steam to run steam turbines. For obtaining reasonably high efficiency, concentration type of collectors are used when steam is used as working fluid. The cost of concentrating collector is more than flat plate collector. Therefore, new working fluid whose saturation temperature is lower than that of water at considerably high pressures are normally used in this type of power plant. But the thermal efficiency of the plant will be low due to low temperature range. This is more suitable in rural areas for house lighting and water pumping for irrigation purpose. 1) Solar radiation does not disturb ecological balance. 2) It is available freely in nature. 3) It is non-depleting source. 4) It is easily available all over the wind.


NUCLEAR POWER PLANT:

Nuclear reactor. It is an apparatus in which nuclear fuel (U235) is subjected to nuclear fission. It controls the chain reaction* that starts once the fission is done. If the chain reaction is not controlled, the result will be an explosion due to the fast increase in the energy released. A nuclear reactor is a cylindrical stout pressure vessel and houses fuel rods of Uranium, moderator and control rods. The fuel rods constitute the fission material and release huge amount of energy when bombarded with slow moving neutrons. The moderator consists of graphite rods which enclose the fuel rods. The moderator slows down the neutrons before they bombard the fuel rods. The control rods are of cadmium and are inserted into the reactor. Cadmium is strong neutron absorber and thus regulates the supply of neutrons for fission. When the control rods are pushed in deep enough, they absorb most of fission neutrons and hence few are available for chain reaction which, therefore, stops. However, as they are being withdrawn, more and more of these fission neutrons cause fission and hence the intensity of chain reaction (or heat produced) is increased. Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

Therefore, by pulling out the control rods, power of the nuclear reactor is increased, whereas by pushing them in, it is reduced. In actual practice, the lowering or raising of control rods is accomplished automatically according to the requirement of load. The heat produced in the reactor is removed by the coolant, generally a sodium metal. The coolant carries the heat to the heat exchanger. Heat exchanger. The coolant gives up heat to the heat exchanger which is utilised in raising the steam. After giving up heat, the coolant is again fed to the reactor. Steam turbine. The steam produced in the heat exchanger is led to the steam turbine through a valve. After doing a useful work in the turbine, the steam is exhausted to condenser. The condenser condenses the steam which is fed to the heat exchanger through feed water pump. (iv) Alternator. The steam turbine drives the alternator which converts mechanical energy into electrical energy. The output from the alternator is delivered to the busbars through transformer, circuit breakers and isolators

GAS TURBINE POWER PLANTS:

(i)

Compressor: The compressor used in the plant is generally of rotatory type. The air at atmospheric pressure is drawn by the compressor via the filter


which removes the dust from air. The rotatory blades of the compressor push the air between stationary blades to raise its pressure. Thus air at high pressure is available at the output of the compressor.

(ii)

Combustion chamber: The air at high pressure from the compressor is led to the combustion chamber via the regenerator. In the combustion chamber, heat is added to the air by burning oil. The oil is injected through the burner into the chamber at high pressure to ensure atomization of oil and its thorough mixing with air. The result is that the chamber attains a very high temperature (about 3000 0F). The combustion gases are suitably cooled to 1300 0F to 1500 0F and then delivered to the gas turbine.

(iii)

Gas turbine: The products of combustion consisting of a mixture of gases at high temperature and pressure are passed to the gas turbine. These gases in passing over the turbine blades expand and thus do the mechanical work. The temperature of the exhaust gases from the turbine is about 900 0F.

(iv)

Alternator OR generator: The gas turbine is coupled to the alternator. The alternator converts mechanical energy of the turbine into electrical energy. The output from the alternator is given to the bus-bars through transformer, circuit breakers and isolators.


COGENERATION: What is co-generation? Explain the necessary block diagram of concept of cogeneration. DEC 11, 8 M Write the concept of co-generation plant with neat block diagram. JUNE 09, 6 M

Explain the concept of co-generation & discuss its benefits. JUNE 12, 6 M

Discuss the benefits of co-generation.

JUNE 10, 6 M

Discuss the concept of co-generation, its merits & demerits

DEC 09, 8 M

 Cogeneration is a process capturing waste heat from manufacturing, industrial process or heating systems and using it to generate electric power  

Cogeneration is the concept of producing two forms of energy from one fuel. One of the forms of energy must always be heat and the other may be electricity or mechanical energy.


i)Topping Cycle  The input is first used to produce power and the exhaust heat from the power producing prime mover is used to generate steam or used directly in heating process. 

Thermal energy is a byproduct used in this process.

 This is most popular method of cogeneration.

ii) Bottoming Cycle  It is the reverse of topping cycle, utilizes waste heat from heating process such as an industrial furnace, to produce electricity.  Primary fuel produces high temperature thermal energy.  Rejected heat is used to generate power  Suitable for manufacturing processes  The potential for cogeneration primarily in sugar, distilleries, petrochemicals ,rice industries steel, cement, fertilizers, paper industries etc.

Operational advantages: 1. Base load electrical supply 2. Security of supply 3. Increased diversity on heating and hot water 4. Steam raising capabilities 5. Tri-generation, using absorption/mechanical chillers for cooling

Financial advantages: 1. Reduced primary energy cost 2. Stabilized electricity cost over a fixed period Vinayaka BG, Asst.Professor, Dept of E&E, BIET, Davanagere

3. Flexible procurement solutions 4. Reduced investment in surrounding plants eg. Boilers

Environmental advantages: 1. Improved fuel efficiency 2. Reduced CO2 emissions 3. No transmission losses

DISTRIBUTED GENERATION: When small generators of capacities around 2 - 50 MW output are installed at typical points in the area such that each of these generators supply power to a small number of consumers nearby then it is called distributed generation. The generators may be operated through renewable energy sources such as solar, wind or gas turbines, small hydro or micro turbines as these are most economical choices. Dispersed generation is use of still smaller generating units of less than 500 kW and use for individual houses or small business. The distributed or dispersed generators may be standalone or grid connected depending on the requirement. Distributed generation proves to be economical as it requires to transmission network and reduced need of distribution equipments. Another advantage is this generation is portable or compact as compared to big power stations located far away from consumers. Also they are modular and relocatable. The fuel cells and micro gas turbines are two new types of techniques evolved in distributed generation. The main challenge is to upgrade existing technology and to promote development, demonstration of new and upcoming technologies for widespread adaptation of distributed generation.


Co-generation is defined as the sequential generation of two forms of useful energy from a single primary energy source; typical two forms of energies are mechanical energy and thermal energy. Mechanical energy may be used may be used to either to drive an alternator to produce electricity or rotate an equipments like motor, compressor, pump or fans etc., for delivering different services. Thermal energy may be used directly for the process for heating purpose or indirectly to produce the steam generation, hot water or hot air for dryer and chilled water generation for process cooling. Generation of three different forms of energy from the single primary energy source is called as Tri-generation, i.e., generation of Electricity, Steam or Hot water and Chilled water from single source of primary fuel. Above both systems is also called as ―Total Energy System‖ Thermal power plants are major sources of electricity supply in India. The conventional method of power generation and supply to the customer is wasteful in the sense that only about a third of the primary energy fed into the power plant is actually made to available to the user in the form of electricity (Figure 1). In conventional power plant, efficiency is only 33% and remaining 65% of energy is lost. The major loss in the conversion process is the heat rejected to surrounding water or air due to the inherent constraints of the different thermodynamic cycles employed in power generation. Also of further losses of around 1015% are associated with the transmission and distribution of electricity in the electrical grid. Through the utilization of the heat, the efficiency of the co-generation plant can reach 90% or more. In addition, the electricity generated by the co-generation plant is normally used locally, and then transmission and distribution losses will be negligible. Co -generation therefore offers energy savings ranging between 15-40% when compared against the supply of electricity and heat from the power stations and boilers.


With a neat schematic diagram, explain the working of a solar power plant. What is the importance of this plant in the present energy crises in the world? DEC 10, JUNE 08 10 M

Figure : Schematic diagram of solar plant

THERMAL POWER PLANT:


Electrical Power Generation Notes

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