DC Machines

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Discus the types and works of power plants used in ships, Airplanes, industries and commercial enterprises

Power Plants used in Industries:

 Power plants used in industries are known as captive power plants these are used only for industry demand. Type of power plant installed in industries depends upon the fuel feasibility for industry. Most of the industries use gas and diesel power plants. However nowadays industries are prone towards renewable sources of energy i.e. Solar and wind.   

Power Plants used in Airplanes:

Engine driven generators are used in airplane due to accessibility of air. Both AC and DC generators are used for electric components used in airplane. Aircraft electrical components operate  on many different voltages both AC and DC. The most of the aircraft systems use

-115 volts (V) AC at 400 hertz (Hz)

- 28 volts DC

DC power is generally provided by “self-exciting” generators containing electromagnets, where the power is generated by a commutator which regulates the output voltage of 28 volts DC. AC power, normally at a  phase voltage of 115 V, is generated by an alternator, generally in a three-phase system and at a frequency of 400Hz. For emergency purposes turbines called RAM AIR turbines are used- air driven turbine stowed in aircraft

ventral or nose section. Gen. Sizing varies between 5 and 15kVA.Rat is intended to furnish the crew with sufficient power while  attempting to restore primary generators.

Power plants used in Ships:

Power plants used on ships are generally diesel power plants. The Power Distributed on board a ship needs to be supplied efficiently throughout the ship. For this the power distribution system of the ship is used. Ship Generator consisting of prime mover and alternator .Main switch board which is a metal enclosure taking power from the diesel generator and supplying it to different machinery. Bus Bars which act as a carrier and allow transfer of load from one point to another. Circuit breakers which act as a switch and in unsafe condition can be tripped to avoid breakdown and accidents. Fuses as safety device for machinery. In case of the failure of the main power generation system on the ship, an emergency power system or a standby system is also present. The emergency power supply ensures that the essential machinery and system continues to operate the ship. Emergency power can be supplied by batteries or an emergency generator or even both systems can be used.

Power Plants used in commercial enterprises:

 Virtually all commercial electric energy is now produced by generators driven by steam from the burning of fossil fuels or from nuclear sources or by hydropower. A basic steam-power plant includes a furnace or reactor for raising the temperature of the water in a boiler, or steam generator, until it changes into steam, and a turbine, which drives the generator to produce electric power. The electric power produced is brought from the generating plant to the user through a network of wires called transmission and distribution lines.  Majority of enterprises use diesel generators to meet their requirements.

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What are direct energy conversion methods for producing electric power?

: There are seven fundamental methods of directly transforming other forms of energy into electrical energy:

§  Static electricity, from the physical separation and transport of charge (examples: triboelectric effect and lightning)

§  Electromagnetic Induction, where an  electrical generator, dynamo or alternator transforms             generator kinetic energy (energy of motion) into electricity. This is the most used form for generating electricity and is based on Faraday's law. It can be experimented by simply rotating a magnet within closed loop of a conducting material (e.g. copper wire)

§  Electrochemistry, the direct transformation of chemical energy into electricity, as in a battery, fuel cell or nerve impulse.

§  Photoelectric effect, the transformation of light into electrical energy, as in solar cells

§  Thermoelectric effect, the direct conversion of temperature differences to electricity, as in thermocouples, thermopiles, and thermionic converters.

§  Piezoelectric effect, from the mechanical strain of electrically anisotropic molecules or crystals. Researchers at the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a piezoelectric generator sufficient to operate a liquid crystal display using thin films of M13 bacteriophage .

§  Nuclear transformation, the creation and acceleration of charged particles (examples: betavoltaics or alpha particle emission)

§  Ocean Wave Energy Conversion,in this method electrical energy is produced from floating thing(like ball type shape) over the waves these are connected to piston,duenwhich piston moves up and down motion and cause generator to run.

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List out all energy worldwide available natural energy resources for electrical power generation.

Ans.      Energy resources are categorized in two groups conventional and non conventional. Available      resources worldwide for electrical power generation  are enlisted below:

    Conventional Sources:

• ü  Coal Energy.
• ü  Hydel Energy.
• ü  Diesel Energy.
• ü  Gas Energy.

  Non-Conventional Sources:

• ü  Solar Energy.
• ü  Wind Energy.
• ü  Biomass Energy.
• ü  Ocean Energy.
• ü  Nuclear Energy.
• ü  GeoThermal Energy.

Some  sources of energy are renewable like sun, wind, flowing water, ocean, wood, biomass etc. Some sources of energy are non renewable like coal, petroleum and natural gas.

Energy sources available in Pakistan are:

Thermal Energy

Thermal Energy is the oldest type of energy. With all known history available, Wood was always used for heating and cooking. In 2nd world war fossil fuels entered in the form of coal to get the energy, until liquid fuels were discovered and because of their convenience of transportation they took over as major contributors of the energy source.

1.COAL

Pakistan has huge reserves of coal which can be used to overcome the problem of energy crises in the country . The government of Pakistan is making hectic efforts to introduce the coal usage in the industrial sector. The machinery for these units is totally exempted from import duties and taxes. A coal based power plant of 150MW has been set up in the interior sindh.

1.      NATURAL OIL

Oil is one of the most important sources of energy throughout the
world and its importance is increasing day by day. many wars are
being fought just tov get the reserves of the oil..the government of
Pakistan is making sincere efforts to find out new oil fields in the
country .the policy is to attain self sufficiency in oil because oil as a
source of energy is expensive if it is imported from other countries and
it greatly increases the import bills of the country, at present the
generation capacity of electricity through oil is 12340MW

2.     Natural Gas

Natural gas   is          also a precious gift of Allah to our country. huge deposits
of natural gas has been discovered in many parts of Baluchistan and
sindh. Natural gas is a cheap sources of energy in comparison to oil
and it can also play a great role in the industrial sector because it is
used as a raw material in many industries like fertilizers cement and
plastics etc.

Hydel Energy:

In Pakistan hydel energy is usually generated through waterfalls (dams).there are many dams in the country which play a great role in the generation of electricity for household, business and industrial sector. since independence huge amounts have been allocated for the development of hydel energy as it is a main source of electricity generation in the country as a result of this the generation of electric power through hydel energy has been increased from 68MW  to 6555MW .

Nuclear Energy:

The importance of nuclear energy as a source of electricity generation is increasing very rapidly throughout the world as many developed as well as developing countries are making use of nuclear enery to generate electricity. the main fuel which is required to run the nuclear reactor is called uranium.with the grace of all mighty uranium is found in excess in Pakistan. at present there are two nuclear electric power generation plants in Pakistan namely Karachi nuclear power plant and chasma nuclear power plant.

Bio Gas

It is produced from animal and plant wastes although it is a very cheap source of energy but it can not be used on the large scale like the solar and wind energy. However it can be utilized very well in the rural areas as 72% of our population live in villages they make the best use of this source of energy .

Wind Energy:

Wind energy is a very cheap source of generating power in windy areas, the windmills can be used for supplying electricity on a small scale the windmill can be used for pumping water for crops, grinding corn, crushing sugar cane, thrashing, cutting of wood etc. at present there are four mechanical wind pumpers and one wind power generation system has been set up. Wind energy in Pakistan is in its developing stage. 500MW wind mill has been established near jhampir side (windy area  in Pakistan). Majority of Pakistanis are prone towards this type of the source in order to get electricity from an ample source available in nature.

Solar Energy:

The sun provides 170000MW of power to earth on daily basis the sunshine can also be used a cheap source of energy many developed countries as well as developing countries are now making use of the solar energy in order to fulfill their energy demand as it is a very cheap and easily available source of energy. Many steps have been  taken to boost solar energy in Pakistan by installing solar panels at various public places and institutes.

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What is Turbine's Critical Frequency and why a turbine should not be operated at its critical frequency?

Answer:

Turbine shaft material has its own natural frequency, when turbine rotates on such a speed that frequency of shaft become close to its natural frequency, machine causes noise & high vibrations because of resonance due to matching of frequency. Running of Steam "TURBINE" on this speed is avoided & this is called Critical speed. A turbine may have more then one critical speed, which may depend upon number of couplings. 
A second critical speed is when the Turbine blade tips approach the speed of sound. This effectively limits the speed of a turbine and explains why power plants tend to have turbines of the same capacity.


Critical speed of the turbine is the rotor speed at which natural frequency of the assembled rotor (rotor shaft with discs, blades, shrouding strips etc in assembled condition) becomes equal to the operating speed. This is usually a expressed as a range (critical speed range).

There are multiple critical speeds. However, the operating speed of the turbine may be above or below the first / lowest critical speed. Accordingly it is called as a flexible or a rigid rotor.

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Why efficiency in Thermal Power Plant is Low?

Almost 50% of the heat generated is lost at the condenser as heat rejection. It is unavoidable as with out heat rejection it is not possible to convert heat energy into mechanical energy and drive the turbine without drop in temperature. Therefore majority of the loss takes place in the condenser. Thus efficiency of the thermal power plant is between 30-35%.

On What Cycle does Thermal Power Plant operate?

Thermal Power plant works on the principle of Rankine cycle

Why Generation Voltage in Thermal Power Plant is between 11kV to 33kV?

The current carrying conductor cross section depends upon the magnitude of the current it is carrying and insulation strength of the conductor depends on the maximum voltage it can withstand. Therefore while designing the generator an optimum value is chosen between the amount of the current and voltage conductor can withstand.

What are the different circuits in Thermal Power Plant?

Some of the major circuits in the thermal power plant are:

·         Coal and Ash circuit

·         Air and gas circuit

·         Cooling water circuit

·         Feed water and steam flow circuit

How efficiency of Thermal Plant can be improved?

Some of the methods by which the efficiency of the thermal plant can be improved are:

·         By increasing the temperature and pressure of the steam entering the turbine

·         By reducing the pressure in the condenser

·         By reheating the steam between different stages between the turbine

Advantages and Disadvantages of Thermal Power Plant?

Advantages:

·         Thermal Power Plants can be operated near the load centers unlike hydro and nuclear plants

·         Requires less space compared to hydro plants and cost of construction is less

·         Running or operating costs are less compared to diesel or gas plants

·         Can able to handle over load for certain period of time

Disadvantages:

·         Emits green house gases and causes pollution

·         Coal and Ash handling requires large area

·         Efficiency is low

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Electronics Fundametals Chapter 8

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