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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 three factors affectthe size of induced emf?
If you are referring to the voltage induced into a conductor moving through a magnetic field, then the FOUR (not three) factors are (a) the flux density of the field (teslas), (b) the velocity of the conductor (metres per second), (c) the angle at which the flux is being cut, and (d) the length of the conductor within the field.
Two sine waves, one with zero crossing at 30 degrees, the other with zero crossing of 45 degrees, have a relative phase angle of 15 degrees. Simply subtract the two angles from each other.
Why rms value of ac not peak value is used?
RMS (root mean square, 1.414) voltage of an AC (alternating current) sine wave represents its actual ability to do work. What can be converted to direct current, DC. Since the sine waves voltage (and current) varies constantly as it goes from zero to a peak through out its cycle it goes from no potential to a large potential to do work. The rms represents the power time of wave. The multiplier of 0.607 times peak gives the waveforms average voltage.
What causes resistance to increase or decrease?
Voltage, if voltage is increased resistance in the circuit increases
AnswerResistance is determined by the length, cross-sectional area, and resistivity of a conductor. Resistivity is, in turn, affected by temperature -so temperature indirectly affects resistance.
These are the only factors that affect resistance. Voltage and current have no direct effect whatsoever on resistance. Current can affect resistance indirectly if it causes the conductor's temperature to increase.
For AC circuits, 'skin effect', due to frequency, causes the current to flow towards the surface of a conductor which acts to reduce the effective cross-sectional area of that conductor. So, frequency can also indirectly affect resistance.
What is difference in motor winding according duty s1 to s9?
S1Continuous duty
The motor works at a constant load for enough time to reach temperature equilibrium.
S2Short-time duty
The motor works at a constant load, but not long enough to reach temperature equilibrium. The rest periods are long enough for the motor to reach ambient temperature.
S3Intermittent periodic duty
Sequential, identical run and rest cycles with constant load. Temperature equilibrium is never reached. Starting current has little effect on temperature rise.
S4Intermittent periodic duty with starting
Sequential, identical start, run and rest cycles with constant load. Temperature equilibrium is not reached, but starting current affects temperature rise.
S5Intermittent periodic duty with electric braking
Sequential, identical cycles of starting, running at constant load and running with no load. No rest periods.
S6Continuous operation with intermittent loadSequential, identical cycles of running with constant load and running with no load. No rest periods.S7Continuous operation with electric brakingSequential identical cycles of starting, running at constant load and electric braking. No rest periods.S8Continuous operation with periodic changes in load and speedSequential, identical duty cycles run at constant load and given speed, then run at other constant loads and speeds. No rest periods
What is the difference between a motor starter and a contactor?
Motor started will have overloads the contactor connect es line voltage.
What happens when a charged capacitor is connected across an uncharged one?
When a charged capacitor is connected to an uncharged capacitor charge flows from the charged to the uncharged capacitor until there is no net force on the charge carriers. This means that both capacitors are at the same potential, because if they were not, there would be an electric fieldand hence a force on the charge carriers of magnitudeand the charge carriers would move to equalize the potentials and reduce the electric field and hence the force, eventually to zero.
Of course, as charge flows from one capacitor to the other, the total charge is conserved.
In the diagram above, when switch is closed chraged flows from the top capacitor to the bottom. When charge has stopped flowing,
Also, because the potentials are equal(1)
Suppose then that the capacitor at top left is initially charged to potential ofand that it has capacitanceand is then connected to a capacitance
Initiallystores a charge
Then (3)
From (1) (4)
Sub (4) into (1) to get
Now usefor either capacitor to findUsing it for (2) gives
from A Level Physics Notes
In Ohm law what must be greater to maintain the same current in a conductor with more resistance?
ohms law states V = I*R. If I is to remain the same, and R is increased, the voltage must also increase.
How does the process of electromagnetic induction work?
The process by which a substance, such as iron or steel, becomes magnetized by a magnetic field. The induced magnetism is produced by the force of the field radiating from the poles of a magnet.
What are dangerous laminating machine?
a laminating machine is safe as long as you dont stick your hands in the roller
Taco generator is the one which is attached to the shaft of big rotating machine to find out its speed. It converts the the rpm in to voltage i.e. the voltage generated in the small generator is directly proportional to the speed of the shaft to which it is attached meter attached to this generator is graduated in rpm instead of volts .
The effect of resistance on the rate of charging or discharging a capacitor?
If the resistance is in series with the capacitor, the charge/discharge time is extended.
What are the disadvantages of servo motors?
Top Ten DC Servo (brush type) Disadvantages (besides higher relative cost):
1) Requires "tuning" to stabilize feedback loop.
2) Motor "runs away" when something breaks. Safety circuits required.
3) Complex. Requires encoder.
4) Brush wear limits life to 2,000 hrs. Service is then required. This system causes friction between the brush and commutator, which requires replacing and maintenance
5) Peak torque is limited to a 1% duty cycle.
6) Motor can be damaged by sustained overload.
7) Bewildering choice of motors, encoders, servo drives.
8) Power supply current 10 times average to use peak torque. See (5).
9) Motor develops peak power at higher speeds. Gearing often required.
10) Poor motor cooling. Ventilated motors are easily contaminated.
What does KVR mean in electrical?
I think you probably mean 'kvar' (lower case), and stands for 'reactive kilovolt amperes'. This is the traditional unit used to measure the reactive power of an a.c. load. Reactive volt amperes are used to measure the rate at which energy is continually supplied, stored in the circuit's magnetic or electric field and, then, returned to the supply, every quarter-cycle. Some books refer to it as 'wattless power' or 'imaginary power' -although, in this sense, 'imaginary' is a mathematical term for 'quadtrature' or being 'at right angles' to true power measured in watts.
How do you draw phasor diagram of maxwell bridge?
Because current is common throughout a series circuit, current is taken as the phasor of reference for series AC circuits. So, we start by drawing a current phasor at 0o. Since the voltage across a purely resistive component (VR) is in phase with the current, we next draw VR in phase with the reference phasor. Since the voltage across a purely inductive component (VL) leads the current by 90o, we draw VL at 90o. We vectorially add phasors VR and VL to give V, the supply voltage. The angle between V and the reference phasor, I, is the phase angle. To create an impedance diagram, divide each voltage by the reference. To create a power diagram, multiply each voltage by the reference.
For Parallel Circuits (example for R-L circuit)Because voltage is common across each branch of a parallel circuit, voltage is taken as the phasor of reference for parallel AC circuits. So, we start by drawing a voltage phasor at 0o. Since the current through a purely resistive branch (IR) is in phase with the voltage, we next draw IR in phase with the reference phasor. Since the current through a purely inductive branch (IL) lags the current by 90o, we draw IL at -90o. We vectorially add phasors IR and IL to give I, the load current. The angle between I and the reference phasor, V, is the phase angle. To create an admittance diagram, divide each current by the reference. To create a power diagram, multiply each current by the reference.
Application of a common - collector amplifier circuit?
Common collector amplifier can be used as a voltage buffer and in impedance matching
What is the nominal supply voltage?
The term, 'nominal', simply means 'named'. For example, the nominal supply voltage for a residence in the UK is 230 V. But this doesn't mean that the actual supply voltage is 230 V, because the supply voltage is allowed to vary by -6% and +10% of the nominal voltage. In other words, the actual voltage could be anywhere within the range of 216.2 V to 253 V. In fact, during periods of heavy load, the actual voltage would tend towards the lower end of this range, whereas during periods of higher load, the actual voltage would vary towards the upper end.
What is disadvantage to lay power cable in the duct?
If you lay a power cable in a duct, and it overheats due to a short or overload, the smoke from the cable burning will fill the duct and be transported by the duct to places it should not be.
If the cable is not balanced, i.e. not paired up with its neutral return, current in the cable will induce a current in the duct via electromagnetic induction, causing heat, loss of power, and potentially fire, even if the original circuit was operating normally.
The latter effect is why penetrations for single cables in distribution panels must be slotted, so as to break the electromagnetic field.
Why droop ct used in generators?
Droop CT is used to control load sharing of the reactive power b/w paralleled generators.
