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Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
What are the electricity problems in Pakistan?
Causes Of Shortage Of Electricity In Pakistan
Introduction:
The country may plunge into energy crisis by the year 2007 due to rising electricity demand which enters into double digit figure following increasing sale of electrical and electronic appliances on lease finance, The shortage in electricity production in Pakistan is worsening day by day which is causing long break downs and load shedding as called by government. The crisis started about a year ago when all of sudden the electricity consumption increased to a point where all the electricity producing sources failed to fulfill the demand. Apparently it is a matter of supply and demand. The gap between the demand and supply resulted in routine load shedding.
Causes:
The country is facing a huge electric power crisis today. This crisis appears insurmountable in the near or even long-term future, unless proper understanding and correct implementation is undertaken on priority basis. The demand for electricity in Pakistan during the winter months actually goes down and this winter has not been an exception. The systemic issues such as the failure to build new dams and Gen. Mushraf Government's inability to add even a single megawatt of new power to the grid during 9 years of his rule, it seems that the present crisis is a result of bad management and the lack of foresight. The total installed capacity of WAPDA and KESC totals around 19,500 megawatts. Almost two third of this power comes from thermal power plants (fossil fuels), one third is generated by water and about 2% comes from nuclear power plants.
Throughout the month of December, the electricity consumption in Pakistan hovered around 11,000 MW, down from the peak levels of 17,500 MW seen in summer. This demand was well within the installed capacity of WAPDA & KESC yet they were only generating a meager one third (6500MW) of their maximum capacity during this period leaving a huge gap between supply and demand. There are two main reasons for this:
1. The water flow from all major dams was halted starting mid December to allow the annual cleaning of canals in January. This action effectively took all the hydro power off line.
2. The thermal power plants were working far below their potential due to the lack of money caused by the circular debt between various government agencies reaching a staggering 400 billion Rupees.
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Prof Zahid Ali Mangi
D J Sindh Government Science College
Karachi
How Frequency Modulation Have Higher Bandwidth then AM?
Bandwidth is defined as difference between two frequencies.
In AM only amplitude is modulated or changed to transmit the data at the given fixed frequency. In FM the frequency of the signal is changed to transmit the data. Since we will need a range of frequency to transmit the data using FM (say frequencies from f1 to f2), the bandwidth of FM signal will be higher than AM signal which can transmit at a fixed frequency.
But.....
The above answer does not address the issue of "strength of modulation", that is, modulation index.
A.M. will always have a bandwidth of twice its highest modulating frequency regardless of the strength of modulation.
For voice comms with about a 3 kHz maximum frequency, A.M. will demand (3+3) = 6 kHz of bandwidth.
Because F.M. modulates the frequency swing of the transmitter, low modulation indexes with F.M. can give a bandwidth LESS than the maximum modulating frequency. Narrow-Band F.M. (NBFM) can have a bandwidth of *less than* 3 kHz, indeed it can have a bandwidth of only a few hundred hertz, in theory.
In practice, very narrow NBFM suffers from worsening signal-to-noise ratios, and one of F.M.'s chief advantages over A.M. is the superior signal-to-noise of F.M. when it is allowed sufficient bandwidth.
What type of current is produced in a generator?
In order to generate an electric current, a magnet is moved near copper, usually copper wires. Because of the magnetic field affecting the copper, an electric current is formed due to the electrons moving in the copper.
What is the difference between a conductive and resistive load?
A resistor is used to represent any one of many different components, called loads, that convert electrical energy to other forms of energy. For example, motors, toasters, lamps, radios, televisions, microwave ovens, and electric kettles convert electrical energy to motion, heat, sound, and light.
How many lumens in an 8 watt LED bulb?
lumenicity (how much light something gives off) is not directly related to power. A 60 watt LED will give off more light than a 60 watt incandescent. You should check the manufacturers information. Light.com (first one to show up in my google search) specifies a 500 lumen 8 watt LED. the 52W incandescent "soft white" bulbs I have on many dimmers in my home put of 710 lumens as a comparison.
When was the Volt Meter invented?
Voltmeters were made possible by an 1819 discovery by Hans Oersted. The first voltmeter were made soon after that.
What colour cable usually signifies 110 volts power on site?
Brown black and ground (yellow=green). The brown and black can alco be black and blue and brown and black
Why test for polarity in welding?
Different material welds differently depending on polarity. There are also different types of welding rods, so polarity must be tested.
Input offset voltage is the equivalent voltage at the input of an operational amplifier. If an amplifier has a voltage gain of ten and an input offset voltage of 10 microvolts, a level of 100 microvolts will appear at the output with no input. Manufacturers try to design an op amp so the input offset voltage is as small as possible to minimize this error voltage at the output of the amplifier, especially for applications where small voltages are being amplified.
Can a high voltage transformer be megged with a megger meter?
No. A megger's output voltage is not high enough to test the insulation of a high-voltage transformer if, by 'high-voltage transformer ', you mean a distribution transformer or power transformer. Instead, a high-voltage test set or 'pressure tester' (e.g. a 'HiPot' tester) must be used, as these produce far higher voltages.
How many contactors using in star connection of motor?
two contecter
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There are three contactors used in a Star Delta configuration.
Electromagnetic waves carry what kind of energy?
It is called electromagnetic energy! But the range of frequencies goes from the lowest which are long wave radio waves, up to the shortest which are gamma rays. On the way it includes infra-red, visible, ultra-violet, microwaves, and X-rays.
What is difference between ac and dc voltages?
AC stands for alternating current, which is an electrical current that frequently reverses direction. AC electricity is measured according to its cycles, with one complete cycle being counted each time a given current travels in one direction and then doubles back on itself. An electrical current is able to complete many cycles per second, and is then given its frequency rating based on that number; for example, the typical frequency in North America is 60 hertz (Hz), which indicates that the current is performing 60 cycles per second. AC power is the type of electricity most commonly used in homes and offices, and is extremely versatile because its voltage can be changed through a transformer to suit a variety of transmission needs.
What Is DC Power?
DC is the abbreviation for direct current, which is a type of electrical current that travels through a circuit in only one direction. Direct current is the type of electrical power that is produced by fuel cells, batteries, and generators equipped with commutators. While DC power was the first type of electricity to be commercially transmitted, it has been widely replaced by alternating current (AC) electricity, and is now used primarily in electrochemical and metal-plating applications.
Why twisted cables are in transmission line?
A twisted cable is two conductors of a single circuit that are twisted together. They are twisted together to cancel out electromagnetic interference.
Is an ammeter found on a series or parallel circuit?
Series. An ammeter is used to measure current, and is connected in series!
There are also clamp on ammeters that use a small current transformer that is placed around a wire in the current loop in question. A small amount of current will be induced on this wire which can be read by the meter. This is not exactly in series or in parallel, but it "steals" some power from the circuit to induce in the meter, and at the same time keeps the circuit intact.
How do you find total resistance with only voltage?
You can't. You need to find the information about current -- a homework question normally gives you a hint.
How you increase the efficiency of a transformer?
Cooling will impact load losses (Since the resistance of copper will increase as it's temperature increases); Core losses are a characteristic of the transformer, so there is nothing you can do about them after it has been made. Insuring you aren't overexciting the transformer (overvoltaging) may help if you periodically have high voltages.
Which relay is used to control 3 phase induction motor?
Overloads for motors are sized from the full load amperage that is taken from the motors nameplate. Depending on who the manufacturer of the motor contactor is will govern the sizing of the relay. Some contactors use bolt in heaters and others use a separate unit that connects to the contactor. No matter what method is used make sure to use the manufactures recommended overloads that are based in the motors FLA.
How do you wire a 3 phase air conditioner?
The three phase supply first has to be connected through a three phase safety disconnect switch. From the safety switch the three phase supply then connects to the terminal strip that is supplied in the air conditioner's control panel. The air conditioner unit is factory wired so that all that is needed in external connections if the power and thermostat control.
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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.
Before you do any work yourself,
on electrical circuits, equipment or appliances,
always use a test meter to ensure the circuit is, in fact, de-energized.
IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.
How do you calculate brake horsepower of pump?
BHP = Flow(GPM) X TDH(FT) x SG /3960xEFFICIENCY(%)Example: BHP = (100 GPM) x (95 Ft) x (1.0) / 3960 x .6BHP = 4.0
How can a permanent charge by induction be created?
Inductance is the field created when sending a charge through a coil of wire. It's used for shunts in systems to prevent damage from shorts. So I guess if you could neutralize the charge between two coils with large capacitors ,bouncing the current back and forth like a doubler, it may be possible.
DC voltage refers to "direct current," and it can mostly be found in batteries. It means that it flows constantly through the circuit, as opposed to AC (alternating current) which switches flow quickly. There are benefits and downsides to direct current, the benefits being that it is best suited for low-current applications and is easy to work with, the downside being that it loses energy quickly as it flows and cannot reach very high power (voltage).
AnswerIn this context, 'd.c.' is being used as an adjective to describe the nature of the voltage.
What do use to measure Resistance?
To measure resistance, you could use an ohmmeter. But ohmmeters are not particularly accurate, so other methods are preferable. These include the use of Wheatstone's Bridge (which compares the unknown resistance with known values) or a Ducter (for very low resistances).
Why does an extrinsic semiconductor behave as an intrinsic semiconductor at elevated temperature?
...It is due to the fact that at higher temperatures, the energy in the semiconductor is greater than Eg by a considerable amount, meaning that the conduction band is more full. At these high temperatures, the dopants' role on electron-hole pairs is negligible.
