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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 is meaning of apparent power in transformer?
Apparent power is the product of voltage and current in an a.c. system, and is expressed in volt amperes. The rated apparent power of a transformer is the product of its rated secondary current and rated secondary voltage.
Why neutral is not required for vacuum circuit breaker?
Air-blast circuit breakers are used to disconnect high-voltage transmission or distribution circuits in the event of a fault. One circuit breaker is required for each of the three line conductors; there is not normally a neutral conductor in high-voltage three-phase transmission/distribution lines.
How do you calculate the electric field inside a conductor?
A spherical conductor with a radius of 14.0 cm and charge of 26.0 microcoulombs. Calculate the electric field at (a)r=10.0cm and (b)r=20.0cm and (c)r=14.0 from the center.
How do you convert percent impedance of transformer to impedance value?
The apparent impedance looking into a transformer from one side will not be the same as looking in it from the other, which is why percent impedance is used.
If you are looking from the high voltage winding (I'm labeling #1) to the low voltage winding (#2), you must scale the percent impedance as follows:
(% impedance) x (Winding #1 nominal voltage)^2 / (transformer base VA)
Are electric motors easier to maintain than gasoline motors?
Electric motors are generally easier and less expensive to maintain than gasoline motors for cars. Electric motors are more efficient and cleaner. There is a battery that needs to be replaced every three years, but there are no other spare parts.
tantalum,mica,paper,cermic
How 3 phase unbalanced current flow through neutral?
Kirchoff's Current Law states that the signed sum of the currents entering a node is zero. If the neutral point is the node, then, in a balanced system, hot matches the other two hots, resulting in no current through neutral. Any imbalance, either due to neutral to hot current flow that is not balanced by the other two neutral to hot current flows, or due to ground fault, will result in a current flow on neutral, so that the sum of zero is maintained.
When you think about this, remember that the law said "signed" and "entering". When you analyze a circuit, simply be consistent in your usage. For instance, in a balanced system, current entering the neutral node from one hot side is considered positive, and the current entering the neutral node from the other hot side is considered negative, i.e. it is leaving, not entering.
This gets more complicated in three phase power, because now you have to consider phase angle, but the concept is exactly the same...
If you are connected in wye, with a neutral, then the neutral conductor will have zero current on it only if the three phase hots have the same current on each. If you do vector analysis on this, adding up sin(x), sin(x+120), and sin(x+240), you get zero.
The same thing happens when you are delta connected, without a neutral, but then the imbalance occurs out in the distribution system, beyond the service transformers, because the distribution system is generally a wye system.
Ground fault will, of course, "change the rules", because you no longer have only four paths to that neutral point node. In fact, that is how ground fault current interrupters (GFCI's) work - they measure outbound current and compare it to inbound current - they must be equal and opposite, i.e. they cancel each other out - otherwise there is another path - a ground fault - and the device trips.
What is the firing angle of silicon controlled rectifier?
The SCR turns on based on gate voltage. The firing angle will depend on the point in the AC cycle where the gate voltage is where you want it, so the firing angle is a function of circuit design, not of the SCR.
How does a phase converter work?
A phase converter takes single phase electrical power and turns it into multiphase electrical power. It is very difficult to explain how exactly it does this, but it involves routing power to different capacitors and sequencing them to work together.
Can an ac motor generate electricity?
An ac motor cannot generate electricity but its shaft can be coupled to that of certain devices like an alternator to in order to generate electricity.
What happen if you reduced the number of devices on each parallel circuit?
The overall current will decrease by subtracting the current used by each device.
How capacitor is connected in a table fan?
The Capacitor with running winding is connected in parallel with main winding.
Ohm's Law: Current is voltage divided by resistance
110 volts divided by 25 ohms is 4.4 amperes. This is also 440 watts, which sounds low in today's design of hair dryers, leading one to think that the 25 ohms is incorrect or was measured incorrectly.
When did the United States stop using DC power in your homes?
We never did, that battle was lost before electrical transmissions lines where anywhere near common.
What happens if ends of rotor conductor of squirrel cage induction motor are kept open?
may be it don't get started as there will be no COMPLETE PATH for induced current due to stator supply..
I.M. starts due to this completed path of current in the rotor conductor...
What component cause a generator to produce direct current rather than alternating current?
it depends on the design whether the generator produces AC or DC
generally reffered AC--- Alternator DC----- generator
to produce AC supply a simple design change in generator (DC) will do it
in the place of split rings/ commutators (as in DC generators) place a slip rings it'l produce AC
coz there wont be any change in polarinty even though armature rotates as output conductors stick to the same slip ring throuh carbon brushes and produces a polarity change called ac
Answer
Modern generators are 'alternators', that is a.c. generators. Vehicle alternators, for example, are three-phase a.c. machines whose output is converted to d.c. using semiconductor devices called 'rectifiers'.
How do you calculate DG set current from kva?
Rating for DG set and any of electrical machines is calculated in KVA. KVA is calculated as KW/pf. One can calculate the required KVA for DG set with this formulation: (KW/pf)/load rate. For example KW=110, pf=0.8 and one loads the DG at 75%, so KVA= (110/0.8)/0.75=185 KVA.
voltage is pressure and kWh is energy... therefore pressure is energy...
FET AS A VOLTAGE -VARIABLE RESISTOR (VVR):
FET is operated in the constant current portion of its output characteristics for the linear applications .In the region before pinch off , where Vds is small the drain to source resistance rd can be controlled by the bias voltage Vgs.The FET is useful as a voltage variable resistor (VVR) or Voltage Dependent resistor.
In JFET the drain source conductance gd = Id/Vds for small values of Vds which may be expressed as gd = gdo [ 1-( VgsVp)1/2 ] where gdo is the value of drain conductance when the bias voltage Vgs is zero.
The variation of the rd with vgs can be closely approximated by rd = ro / 1- KVgs ro - drain resistance at zero gate bias and K constant dependent upon FET type.
Small signal FET drain resistance rd varies with applied gate voltage Vgs and FET act like a VARIABLE PASSIVE RESISTOR.
Advantagesof JFET
Very high input impedance order of 100 ohm
Operation of JFET depends on the bulk material current carriers that do not cross junctions
Negative temperature coefficients
Very high power gain
Smaller size longer life and high efficiency
Ac drain resistance rd it is the ratio of change in drain - source voltage to the change in drain current at constant gate source voltage
Transconductance it is the ratio of change in drain current to the change in gate source voltageat constant drain source voltage
Amplification factor it is the ratio of change in drain source voltage to the change in gate source voltage at constant drain current.
Can you run a 460v 60hz motor to a 400v supply?
yes can run but motor only delivers 90%rated power because v/f less by 10%
Why do you use single phase in house wiring?
bcoz we dont require too much voltage when working in home so in home generally 220v is preferred & in industries 3phase connection is used for heavy loads (440v)
