Capicitor Application Issues
Capacitors must be built to tolerate voltages and currents in excess of their ratings according to standards. The applicable standard for power capacitors is IEEE Std 18-2002, IEEE Standard for Shunt Power Capacitors.
Heat as one of most common cause of motor failure
This slide speaks about that how motor operation fails due to heat. how heat affect motors?
Friday, 6 June 2014
Monday, 26 May 2014
What will happen to the operation of Transformer if the frequency of operation is changed?
Change in frequency affects the operation of a transformer in the following ways:
i. Iron Loss – Increases with a decrease in frequency. A 60 Hz transformer will have nearly 11% higher losses, when worked on 50 Hz instead of 60 Hz. However, when a 25 Hz transformer is worked on 60Hz, iron losses are reduced by 25%.
ii. Cu Loss – In distribution transformer, it is independent of frequency.
iii. Efficiency- Since Cu loss is unaffected by change in frequency, a given transformer efficiency is less at a low frequency than at a higher one.
iv. Regulation – Regulation at unit power factor is not affected because IR drop is independent of frequency. Since reactive drop is affected, regulation at low power factor decreases with decrease in frequency and vice versa. For example, the regulation of a 25 Hz transformer when operated at 50 Hz and low power factor is much poorer.
v. Heating – Since total loss is greater at a lower frequency, the temperature is increased with decrease in frequency.
i. Iron Loss – Increases with a decrease in frequency. A 60 Hz transformer will have nearly 11% higher losses, when worked on 50 Hz instead of 60 Hz. However, when a 25 Hz transformer is worked on 60Hz, iron losses are reduced by 25%.
ii. Cu Loss – In distribution transformer, it is independent of frequency.
iii. Efficiency- Since Cu loss is unaffected by change in frequency, a given transformer efficiency is less at a low frequency than at a higher one.
iv. Regulation – Regulation at unit power factor is not affected because IR drop is independent of frequency. Since reactive drop is affected, regulation at low power factor decreases with decrease in frequency and vice versa. For example, the regulation of a 25 Hz transformer when operated at 50 Hz and low power factor is much poorer.
v. Heating – Since total loss is greater at a lower frequency, the temperature is increased with decrease in frequency.
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.
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.
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:
- ΓΌ Coal Energy.
- ΓΌ Hydel Energy.
- ΓΌ Diesel Energy.
- ΓΌ Gas Energy.
Non-Conventional Sources:
- ΓΌ Solar Energy.
- ΓΌ Wind Energy.
- ΓΌ Biomass Energy.
- ΓΌ Ocean Energy.
- ΓΌ Nuclear Energy.
- ΓΌ 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
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.
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.
What is Turbine's Critical Frequency and why a turbine should not be operated at its critical frequency?
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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