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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
Can a 7.5 mfd capacitor be used in place of a 5 mfd capacitor?
Sometimes. The exception is when the capacitor is used as a "timing" device. But 7.5 mfd and 5 mfd are so large that one would guess that they are not being used as timing devices.
What is the demagnetizing component of armature reaction?
it is the flux which is flowing opposite to the main field flux and demaganetize it...
in order to eliminate this demagnetiszing component we have to connect the compensating winding in series with the armature winding which develop the flux in it oppose to the demagnetizing component
What happens if a lengthy cable is connected to a load?
resistance will increase because we know that resistance is directly proportional to length.
AnswerThe increase in resistance will cause an increase in the voltage drop along the cable; if this is excessive, then a cable with a greater cross-sectional area must be used to compensate. Howto choose an appropriate cable for a given length can be determined from the relevant wiring regulations for your country.
What is the difference between a slo-blo fuse and a time delay fuse?
There is no difference. Slo-Blo is just a trademarked name for a time delay fuse.
What is the reason for using 250 percent multipler for sizing motor circuit breakers in NEC?
When a motor starts the circuit breaker sees an almost dead short. Until the motor starts generating a back EMF , which opposes the current flow when rotation starts, the current is high.
If the breaker is sized to the motors full load amperage, each time the motor is started, the breaker will trip.
How do you solve earth leakage?
The best way to stop earth leakage is to make sure that the are no active circuits going to ground. This will help keep the circuit running right.
What is the relationship between root mean square voltage and DC voltage?
They are equivalent in terms of energy content or work potential. In other words, 100VAC (RMS) will do the same amount of work that 100VDC will.
What will happen if you give DC input to the primary of a transformers?
If DC voltage is applied to the primary of a transformer the flux produced in the transformer core will not vary but remain constant in magnitude therefore no emf will be induced in the secondary winding except at the time of switching on.Also there will be no self induced emf in the primary winding to oppose the applied voltage and since the resistance of the primary winding is quite low heavy current will flow through it which may result in burning out of primary winding.
Why is not impractical to power distribution in power DC?
IN DC FOR LOW VOLTAGE HIGH DENSITY OF CURRENT WILL BE THERE SO WE CAN NOT USE THIS FOR BEST PRACTICE FOR TRANSMISSION & ALSO BECOS OF HIGH CURRENT TRANSMISSION LOSSES ARE VERY HIGH ( I2XR) LOSSES, TRANSMISSIN EQUIPMENT FOR DC ARE HIGH COST
IN DC FOR LOW VOLTAGE HIGH DENSITY OF CURRENT WILL BE THERE SO WE CAN NOT USE THIS FOR BEST PRACTICE FOR TRANSMISSION & ALSO BECOS OF HIGH CURRENT TRANSMISSION LOSSES ARE VERY HIGH ( I2XR) LOSSES, TRANSMISSIN EQUIPMENT FOR DC ARE HIGH COST
AnswerThe main reason is that we cannot use transformers to easily and efficiently change the magnitude of DC voltages, and the ability to change voltages is essential for electricity distribution.However, having said that, very high-voltage transmission over exceptionally long distances is often done using DC. This is because DC losses are far lower than AC losses.
What is the difference between a flexible cord and a flexible cable?
A flexible cord is a flexible cable having a conductor cross section less than =<6mm squared providing a high degree of flexibility for non fixed wiring systems
Why is it we do not use a DC electricity service in our homes?
The transmission losses are enormous for DC. It is much more efficient to use AC.
For more information see the answers to the Related Questions shown below.
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Apart from the reasons why, instead of using direct current, alternating current is used for distributing electricity from power generation stations to consumers, it is worth considering the fact that many different types of electrical equipment are used in today's homes, offices and factories, but they don't all run at the same voltage.
For example, in North America many types of large household appliances - such as range cookers, water heaters, washing machines, clothes dryers and air conditioning units - need 240 volts.
Lights, hair dryers and other small appliances need 120 volts.
Electric razors, personal computers, flat-screen televisions, radios, hi-fi units and personal music players, etc. need low voltages such as 3, 5 or 12 volts.
If the main incoming electricity service to a building were dc (direct current) there would be only two ways in which such a wide range of voltages could be produced:
1) by using a different in-line resistor for each appliance, to drop the incoming service voltage to the correct amount that the appliance needs.
Doing that would produce a lot of heat from all the various in-line resistors and that heat would just be an expensive way of heating the surrounding air in the room...
(In the 1940's and '50s, after World War II, that system was actually used for ac appliances as a way to allow US-made 120 volt ac radios, etc. to be used in Europe and other countries where the incoming service voltage was around 240 volts ac. Those voltage-drop resistors were commonly known as "line cords".)
or
2) by using lots of electronic voltage regulator units - but that method was totally impossible at the time the first electric power distribution services and networks were invented in the 19th century because, to be able to build those units you need lots of cheap semiconductors, but such semiconductors were not actually invented until around the middle of the 20th century!
So it's quite a clever idea to use ac (alternating current) for the incoming main service because it is then very easy and efficient - and relatively inexpensive - to produce the actual voltages that are required by each different appliance. All you need for each appliance is an appropriately-sized "power supply unit" which includes a small transformer and rectifier to produce dc.
Ever since low-cost semiconductors were invented, power supply units have been made in very small sizes by using miniature transformers and/or electronic voltage regulators and invertors.
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Most places in North America use AC at 120v which has been transformed down from a much higher voltage using transformers. Transformers do not work with DC.
However solar panels put out DC which is converted to AC at the house.
For more information see the answers to the Related Questions shown below.
AnswerIn fact, DC transmission losses are significantly lowerthan AC transmission losses. Which is one of the reasons that DC is often used for long-distance overhead transmission lines. For underground cables, the closeness of the cable's cores make them highly capacitive, which means that an AC cable will draw far more current than a DC cable -for this reason, undersea cables are often DC.
The pole tip which is met first during rotation by armature conductors is known as leading pole tip
A: Only if the current is very small and the scaling very large. Like trying to measure micro amps on amp meter
What happens to its resistance when an electrical device is heated?
That will depend on the temperature coefficient of resistance of the device, which could be positive (i.e. resistance increases with increasing temperature), negative (i.e. resistance decreases with increasing temperature), or zero (i.e. resistance is unaffected by temperature changes).
Is there a demand for Electrical Engineers in the future?
yes, very much so espaicaly after the economy gets worse
Why is used just 2 or 4 poles in non salient pole rotor?
to force the generation machines ( generator in power plant) to work on constant speed which mean constant frequency for any power network
n= 120 F / p
What are the differences between inductance capacitance and resistance in tabular form?
R x(l) x(c)
1 1 1
2 2 2
5 5 5
What are the advantages of weee?
According to the EU WEEE Directive: "The objectives of the Community's environment policy are, in particular, to preserve, protect and improve the quality of the environment, protect human health and utilise natural resources prudently and rationally. That policy is based on the precautionary principle and principles that preventive action should be taken, that environmental damage should as a priority be rectified at source and that the polluter should pay... the achievement of sustainable development calls for significant changes in current patterns of development, production, consumption and behaviour and advocates, inter alia, the reduction of wasteful consumption of natural resources and the prevention of pollution. It mentions waste electrical and electronic equipment (WEEE) as one of the target areas to be regulated, in
view of the application of the principles of prevention, recovery and safe disposal of waste."
So as an overview the advantages of WEEE, as described by the European Parliament and Council, is to reduce the pollution and damage to living creatures and the environment caused by waste electronics and electricals by placing the responsibility for safe disposal on the producers of electronic and electrical goods.
What are the advantages and disadvantages of parallel change over?
advantage
1. Effective in Recognition and correction of errors.
How do you measure the volt ampere rating of a transformer?
Your transformer should have a namplate on it that states how many amps or fractions of amps it can produce. You would then multiply that number by your secondary voltage to get your VA rating. sec. voltage 12v X .05 amp = 12 X .05= .6va
What is starting capacitor and run capacitor?
A starting cap is placed in circuit of the start windings only when the motor is starting and is normally of a higher capacitance than a running cap, in the region of 70 - 120 mf, where a running cap stay connected with the start windings of the motor and is normally an 8 mf cap.
How do you change a bad capacitor in an air conditioner?
Locate the defective capacitor, short the terminals to ground to release any stored energy and prevent shock, remove the old capacitor then install the new capacitor wired as the old one was and secure it in the bracket that held the old one - done.
