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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
Why coupling capacitor block DC in amplifier?
capacitors at input block dc and allows ac only. so absolute none of the dc enters the circuit. They are called decoupling capacitors or blocking caps.
-DANNY S
Why do several 40watt and 220volt lamps not light to full brilliance when in series?
To get full brightness, the rated voltage has to be applied across the bulb. When several bulbs are connected in series, the voltage gets devided among these sevral bulbs and correct rated voltage will not be applied acros each bulb, hence the brightness reduces.
Can you apply thevenin's theorem in circuits having multisource?
yes. its trickier but it works fine.
Why rotating magnetic field is not produced in a transformer?
Even an emf is induced in the rotor also, with similar synchronous speed, but owing to large inertia of rotor, it cannot attain synchronous speed and stays standstill.
In case of transformer, the three-phase windings are wound on three limbs - on each limb LV winding is wound on the core and then HV winding is wound over the LV winding (for increased efficiency of transformer). Due to this constructional arrangement, a rotating magnetic field is not visualized in transformer, rather mutual inductance comes in to picture.
What size generator do you need to move a 30 hp electric motor?
A 5 kW generator would turn it over but if the full 30 hp of mechanical power is needed, that would require about 30 kW of electric power from the generator.
24VACRMS * 1.414 = 33.94VACPEAK
The unloaded filtered DC voltage is 33.94V
The unloaded unfiltered voltage will be a single polllarity AC voltage with a peak of 33.94V
What is the condition of maximium power transfer of circuit?
Maximum power transfer happens in a circuit when the resistance of the circuit equals the reactance.
Impedance Z = R + jX. At R=X, maximum power transfer happens.
How do you reverse a direction of a slip ring motor?
It is very simple. Just interchange any two phase wires.
i.e.
Y and B
( or )
R and B
( or )
R and Y
for example Stop the supply. keep R phase wire as it is and disconnect B phase wire and Y phase wire. Connect B phase wire to the Y phase motor stud and Y phase wire to the B phase motor stud. Now give the supply, now motor revolves in opposite direction to the earlier.
Why superposition theorem is not valid for power?
we cant consider two source at a time in superposition theorem....but power =v*i.so we cant calculate power.
Mutual (not 'matual') induction occurs when a changing current in one circuit induces a voltage into a second circuit. An example of mutual induction is a transformer.
Why wattmeter shows negative reading during no load condition of 3phase ac induction motor?
no load means the motor is acting like a coil
What is voltage drop in an electrical circuit?
When a current flow on a conductor , or load or resistor, some voltage will drop across that load or resistor.
AnswerA voltage drop is the potential difference appearing across individual components in a circuit, necessary to drive current through those components. The sum of the individual voltage drops around a series circuit will equal the supply voltage applied to that circuit.
Is a transformer load inductive or capacitive?
A transformer is fundamentally a set of coils; therefore, a transformer is an inductive load. However, by "transformer load", you seem to mean "the load that is connected to a transformer". Whether that load is inductive or capacitive depends mostly on what is hooked up to the transformer.
Divide VA rating with the Voltage and get Amp rating.
So say you have a transformer that delivers 26V, 80VA, that means a maximum current of 80/26=3.07A for a resistive load.
Why sf6 circuit breaker is mostly used in substations rather than other?
Rather than where? Circuit breakers are always located in substations.
What is mean by auto re-closer in high voltage breaker?
Many high-voltage overhead line faults are temporary in nature -e.g. a branch hitting a line conductor during a storm. An 'autorecloser' mechanism is designed to automatically reclose a circuit breaker after it has tripped. If the fault has cleared itself, then the circuit breaker will remain closed; if not, the autorecloser mechanism can be set to reclose the circuit breaker several times (typically 3) before, finally, locking the circuit breaker open. Autoreclosers are often used in conjuction with 'sectionalisers'; these are non-load breaking switches which will disconnect sections of line towards the end of a feeder, in the hope that any fault has existed beyond that point and will be cleared before the autorecloser recloses the circuit breaker.
What is internal gain of amplifier?
The internal gain of an amplifier is the gain or the amplification factor of the transistor used in it....................it is internal because it is fixed for transistors while manufacturing..................
Why it is connected tap changer on primary side?
This isn't necessarily the case. Tap changers are normally located on the high-voltage side of the transformer, regardless of whether it is a step up or a step down type. This is because the current is lower on the h.v. side, enabling smaller contacts, etc., to be utilised.
Is oil in transformer use for lubrication?
Transformer oil is for cooling.
Transformer oil has heat conductive properties, along with its insulating properties, that take the heat build up from the windings to the outer case of the transformer. The transformer tank is used as a heat sink to allow the outside ambient temperature to cool it down. On big kVA transformers there are heat tubes on the outside of the tank. On even bigger transformers there are fins that the oil travels through. This provides a bigger surface area to dissipate the heat. The tubes and fins also allow thermal siphon of the oil through the tubes by drawing in the cooler oil at the bottom of the tank and moving it to the top of the tank where the hotter oil is. This circulation greatly increases the cooling ability of the oil to keep the transformer with in its allowable temperature rate of rise zone.
Additional AnswerThe second function of transformer oil is insulation. Oil has a far greater dielectric strength than air, so it enables internal components at different potentials to be located far closer together -thus significantly reducing the 'footprint' of a transformer.
Why is armature connected to a sprinngy steel strip?
In an electric bell, a flat steel spring brings the armature back to its original position.
What are the physical significance of self inductance?
According to lenz law , "effect opposes the cause "
now due to flux cutting action emf induce in coil opposes the flux by which this emf is induced . So this opposition by induced current of staring current is called inductance .
Would a DC motor turn if only the armature were supplied DC voltage?
if there are magnets on the stator
and the commutator is phased properly
this is known as a permanent magnet dc motor
the starting torque is dependent on armature current and the strength of the magnet
the speed is directly proportional to the armature voltage
a shunt motor needs the field energized for starting.
more field more starting torque
pcc is the power control center, in which all distribution switches are installed and operated here
