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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
A transmission line has 30 megawatts and 40 megavars what is the megavolt amps load on the line?
By definition, MVA is equivalent to the vector sum of MW and MVAR:
MVA^2 = MW^2 + MVAR^2 = 2500
MVA = 50
What is the need of reactors at capacitor bank?
In the power system, reactors and capacitors banks are used for VAR support (basically to push up or pull down the system voltage).
In circuits, capacitors and reactors are used for isolation, filtering, coupling, biasing, oscillating, and the list goes on and on.
What is the capacitive reactance of a 1 µF capacitor at a frequency of 60 Hz?
The capacitive reactance of a 1 µF capacitor at a frequency of 60 Hz is about 2700 ohms.
There are two type of carriers in any semiconductor. For a given sample, these carriers have a specific concentration and mobility. The current flow due to the holes carriers in any semiconductor is the hole current.
Answer'Holes' are imaginary positive, mobile, charge carriers used as a model to represent the behaviour of electric current in p-type semiconducting material. A 'model' is simply a means of explaining complex behavior in terms of something we can easily understand or picture in our minds. In reality, therefore, holes do not exist, but offer a convenient way of explaining current flow in semiconductors in an understandable way.A 'hole' is simply a vacant position, formally occupied by an electron, rather than a real entity. As electrons move in one direction, relative to those electrons, these imaginary holes behave as though they move in the opposite direction (in rather the same way that scenery seems to be moving backwards when you look from a train whereas, in reality, it's the train that's moving forward!). So, as electrons move from negative to positive, holes appear as though the electrons are actually stationary and it's the holes that are moving from positive to negative.
So it's convenient to think of current flow through 'p-type' material, in particular. in terms of imaginary holes moving in the opposite direction to electron flow.
(You see a similar effect with led message boards. The message is formed by bright led dots that appear to move in one direction; but you can also argue that the message is formed by the unilluminated leds that appear to move in the opposite direction! You can think of the illuminated leds as electron flow and the unilluminated leds as hole flow.)
Diouly-dcp's answer
first lets look at what is hole
hole: is when an external voltage source of energy acquire to a piece of silicon or other,it allows the valence electrons to thermally jump from the valence bond to the conduction bond, when they moved, a vacancy is left. this vacancy is called hole
hole current: another type of current occurs at the valence level where the holes created by the free electron exist. Electrons remaining in the Valence Bond are still attached to their atoms and are not free to move randomly in the crystal structure as are the free electron, however a valence electron can move into a near by whole with little change in it's energy level thus leaving another hole where it came from. effectively the hole has more from one place to another in the crystal structure, this is called hole current.
(electrons in the valence bond are moving from one hole to another in the valence bond it self, but not to the conduction bond)
What are the application of differential compound generator?
Differential compounded generators are used in Ward Lenard motor generator loops. The shunt fields on these generators are separately excited and when the shunt field polarity is reversed by the controller the series field helps drive the generator voltage to zero thus aiding in the reversal of current.
What is the pulsating DC frequency?
When AC full wave is rectified into DC by using bridge rectifier .The DC do not actually behave like an ordinary DC and the DC has a constant value .In fact, it is in pulsating form.This is known as Pulsating DC.
Do I need tertiary winding in a auto transformer with vector YNynO?
Depends, do you need to connect auxiliaries/generator/capacitor/reactor to tertiary? If not you may consider to not to use tertiary. The 3rd harmonic current will become an issue then. The phase to ground Isc will be lower.
What is the correct name for BS 7671?
Currently;
"BS 7671 Requirements for Electrical Installations. The IEE Wiring Regulations"
With the first amendment of the 17th edition of BS 7671 due to be issued in a matter of weeks and the "IEE" being changed to "IET" on the document, what else differs is relatively unknown at present.
What is fringing in capacitor?
In conductors having sharp ages,electric field lines bulge out non uniformly.
Let me be specific with a parallel plate capacitor.Herein at the ages of plates ,pattern of field lines is different from that within the dielectric.While inside dielectric they are straight,at corners they are bent.
EFFECT: Due to bending of field lines flux is not properly linked with second plate which leads to NET DECREASE in capacitance.
Akshay Bisht
[NIT Jalandhar]
INDIA
What are the four essential functions of an automatic process control system?
1. to protect the plant
2. to support the plant
3. To respons to changes in the plant
4. to monitor process parameters
Can you use Diac and Triac for dc supply?
The diac conducts in both directions at approximately the same voltage, making it unsuitable in an AC to DC supply. The triac also conducts in both directions, based on a gate voltage which is slightly different in the two usable quadrants. That is why the diac is often used to trigger the triac - it makes the two conduction cycles more symmetric. In both cases, the diac/triac does not make sense for an AC to DC supply, but it works well in an AC voltage regulator, such as a lamp dimmer or motor speed controller.
What is a leakage current collector is?
I am in trade school becoming an electrician and i think what it is is simply a drain for a pool, whether it be a hydro-massage, portable, spa or hot tub and it allows extra water to drain properly. If there is any current leakage from a short circuit or anything in the water then it would be bonded because the leakage collector is bonded to the control panel. That's what i think it is .
Which term is defined as the value of a current sum of money at a specified date in the future?
It is called the 'future value' .
What are the characteristics of instrumentation amplifier?
a high common mode rejection ratio, high impedance
What is the function of radiator in power and distribution transformer?
Radiators are used in a transformer to cool the transformer oil through natural air or forced air flowing in these radiator fins. As the transformer oil temperature goes down due to cooling it goes to the transformer tank from bottom ,cool the windings and gets heated, and then returns to the radiator for next cooling .This cycle repeats as the oil flow is also natural due difference in temperature of oil on bottom and top.
In big power transformers this oil circulation is forced by oil pumps for effective cooling.
The radiator has many small fins and there are 4-10 radiator banks in a transformer depending on capacity and make of the transformer.
How do motors that do NOT use magnets work?
Motors that do not have magnets work exactly the same. The permanent magnet is replaced by a electromagnet, which is a coil of wire with a voltage applied to it. This electromagnet is what produces the magnet field necessary for a motor to operate. It is just easier and lighter to use this style of DC motor in larger applications.
What is the current time in marrakech?
This cannot be accurately answered because the "current time" depends on exactly when the question is asked. Also, the answer will be different every time someone reads it.
What is a normally open momentary push button?
A normally-open, momentary push button is a type of switch. When a path is "open," that means that no current can pass through said path. This type of switch closes the path when pressed allowing current to pass through the path only when it is being pressed down. Otherwise is it normally open as the name suggests.
Lick your own bum
Hollow conductors in transmission line used to?
To reduce skin effect.
CommentHollow conductors are not used on electricity transmission lines. Transmission-line conductors are normally manufactured of stranded aluminium conductors, wound around a steel-wire core. The steel core improves the conductor's tensile strength.
Hollow conductors are, though, used as 'wave guides' in radio-frequency circuits. However, their purpose is not to reduce skin effect (in which most of the current flows close to the surface of the conductor), but to save copper -if most of the current flows close to the surface, then there's little point in using solid copper!
AnswerHollow conductors are used on very high voltage underground cables, which are cooled by passing oil or gas through the conductors.
What are the effect if you are electrocuted to 440 system voltage?
Electrocuted is the term given to death by electric shock. You can only be Electrocuted once.
There are many factors that affect the result of contact with any voltage system.
These include duration, path of current through the body etc.
You could have a 440v shock that may only travel through one hand for example. The likely result is some electrical burns just to that hand. If however, the current path , goes from your hand, through your chest to your feet (through your heart) the risk of death is high.
The amount of current required to kill a person is very small, around 50 milliamps (50 thousandths of an amp).
As Current (Amps) is proportional to voltage, the higher the voltage the higher the current.
What is the different between ATS panel and Sychronize panel?
synchronization panel is a panel that brings two or more gensets together in one distribution system supplying the load with the adequate amount of energy supply required for the load. when the main supply is interrupted, the genset comes on and certain parameters (voltage, frequency and phase) have to align before the circuit is opened for the load to receive power supply.
ATS which stands for automatic transfer switching, helps to bridge the gap of time loss between the time the main supply is interrupted and the time it takes to start up the backup supply or genset by automatically switching to genset immediately when there is no power supply or fault with the main power supply.
The Line Tester or Neon Screwdriver is tools specified for electrical works, though we can use it as Screwdriver in special case. The Line Tester is one of the important tools of electrician. The Line Tester should be a tool of home ‘Tool Box’.
Before we learn about the Line Tester we must learn about some common terms and get some basic knowledge of electricity.
All Electrical device and appliance use maximum three wires and minimum two wires for electric supply. These wires differ from one another and denoted by specific names
o
Phase Wire:
This wire is also called as “Live Wire” or “Hot Wire”.
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Neutral Wire:
This wire is also called as “Cold Wire”
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Earth Wire:
This wire is used for safety purpose.
The Phase Wire in alternating current supply is very important and dangerous. This wire is also called Live or Hot because it has higher potential difference from Neutral or Earth wire. When two different potential wires come in contact current flows in the circuit.
The potential difference between two wires or terminals is called ‘Voltage’. In India the potential difference between Phase and Neutral is specified as 220 Volt. While the difference between Neutral and Earth is about 5Volt.
Construction of Line Tester or Neon Screwdriver:
The Line Tester is tool used to identify the Phase or Live Wire. The main parts of a Line Tester are shown in diagram.
1.
Metallic Rod:
This cylindrical metallic rod is designed as Flat Screwdriver on one end while the other end and major portion of rod remains covered inside the Insulated Transparent Body.
2.
Resistance:
The Resistance is a device which prevents the flow of electric current through it. The resistance of Line Tester reduces the flow of current through it. This resistance makes the tester a safe tool.
One end of resistance gets connected with cylindrical metallic rod and another gets connected with the neon lamp.
3.
Neon Lamp:
The Neon lamp is most important part of Line Tester; due to the neon lamp the line tester is also called Neon Screwdriver. The neon lamp is very similar to torch lamp or bulb. One terminal of neon lamp gets connected with Resistance and another terminal gets connected with metallic spring.
4.
Metallic Spring:
The Metallic Spring is used to make connection between Neon lamp and metallic touch screw.
5.
Metallic Touch Screw:
The metallic touch screw is a part of Line Tester which is used to tight all the above components inside the Insulated transparent plastic body and contact with metallic spring connected with Neon Lamp.
The outer body of Line tester is made of transparent hard Plastic.
Working of Line Tester:
When the Screwdriver end of Line Tester comes in contact with the Live/ Hot wire and we touches the rear metallic touch screw a circuit gets completed and the current moves through metallic rod.
The metallic rod is connected with a resistance the electric current passes through the resistance. Due to the resistance the great amount of electric current drops and a small amount of electric current passes through it to the next component, viz Neon Lamp and reaches till the metallic touch screw which is in contact of our finger.
A small current passes through our body to earth and complete the circuit. As the circuit gets completed a current starts flowing and the filament of Neon lamp starts glowing. This indicates that the Phase of electric supply is present in the touched wire.
It is advice to work with electricity only in presence of adult; who has good knowledge to deal with electricity; and take all necessary measures for safe handling of electricity. Never! Never try to work on electricity without proper guidance and care.
Precautions:
When ever you use a line tester take some precautions
- Ensure that the tester is working properly.
- Ensure that the tester is not broken.
- Don’t touches the open wire even tester shows absence of phase or hot supply.
How line voltage is equal to root three phase voltage for star connected load?
Let's start with the correct terminology. The three energised, or 'hot', conductors are called 'line' conductors (not 'phase') conductors. which (surprise, surprise!) is why the voltages across them are called 'line voltages'.
In the case of a star (wye) connected, three-phase, four-wire, system each phase is connected between a line and the neutral. And, yes, the line voltage is indeed root-3 (or 1.732) times the phase voltage.
If the lines are labelled a, b, c, and the neutral is labelled N, then line voltage Vab is equal to the phasor (vector) sum of phase voltage Van and phase voltage Vnb, which are displaced from each other by 60 electrical degrees. The length of the resulting phasor is 1.732 times either of these phase voltage.
