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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 digital multimeter fails to read low resistance values?
They read low resistance values very well. I measured several dead shorts today accurately with a digital voltmeter.
However, when attempting to measure LARGE amount of resistance, the current generator in a standard digital voltmeter may fail to effectively penetrate the medium being measured. It is for this reason that Meggers (Mega-Ohmmeters) are used to measure high amounts of resistance. They usually employ a hand crank to develop the current needed to effectively flow through the medium being measured.
Sometimes digital voltmeters can be very inaccurate if they are measuring something that matches the impedance of the meter (loading effects of the voltmeter), but that is another story.
What is the power dissipated in the Ohm resistor?
Power dissipated is always Volts times Amps.
W= V*I
because of ohm's law, V=I*R, you can substitute either the voltage or amperage with the other value;
W= V^2/R or
W= I^2*R.
What makes the armature in the electric motor rotate?
from Faraday's law of electromagnetic induction :
when a current carrying conductor cuts the magnetic field an E.M.F (electro motive force) is produced and it sets up in such a direction so as to oppose the cause of it.
the stator winding of a motor which produces the R.M.F (rotating magnetic field) serves as the magnetic field and the armature winding is the current carrying conductor which cuts the magnetic field , thus an EMF is induced in the armature which again produces a force to oppose the emf produced in the armature winding.
What is meant by neutral grounding reactor?
Neutral-earthing reactors or Neutral grounding reactors are connected between the neutral of a power system and earth to limit the line-to-earth current to a desired value under system earth fault conditions.
Why clippers are also called limiter?
bcoz, voltage clipping limits the voltage to a device without affecting the rest of the waveform.
Because the Power Factor is over corrected.
What happen when the polarity of transformer reversed?
You cannot 'reverse' the polarity of a transformer -it is either wound with 'additive polarity' or 'subtractive polarity', and there's not much you can do about it!
For a single transformer, its polarity doesn't really matter. But if you are going to parallel two transformers, then you must know the polarity of each transformer in order to avoid harmful circulating currents in their secondary windings.
What is the effective value of an AC sine wave current having a peak-to-peak value of 8 amperes?
The rms value of a sine wave current is 0.707 Imax. So the answer to your quesion is 0.707 x 4 = 2.83 A.
What are the effect of electrical cable joint?
A cable joint is the term used in the UK for what, in North America, is called a cable splice.
In the case of high- and medium-voltage underground cables, if they are done correctly, there is no adverse affect and joints should last as long as the cable itself. A great deal of care is taken replacing the insulation after jointing the conductors themselves, and to ensure that the cable remains waterproof and any armouring is replaced. HV and MV cable jointers are highly-skilled tradesmen who have completed an apprenticeship in cable jointing.
More_Information:">More Information:The connection of wires is typically called a splice (North American term). If the splice involves two different types of wire like copper and aluminum you would have to use special connectors made for this purpose and perhaps a compound made for the purpose. In the normal connection of two or more wires of the same type you need to make sure the ends of the wires are clean and that the connection is firm so as to reduce resistance at the joint. You also need to make the splice in a junction box for power wiring applications; and that bare wire isn't exposed which could cause shock or shorting situations. Underground splices pose yet another problem with moisture and varmints chewing on the splice.
What happens when load is removed from an operating series DC motor?
The speed will increase possibly to the point that it throws out the coils from the armature & self destructs.
Why do you use slotted armatures in dc machines?
Those slots, or areas where metal was removed serve to balance the motor's armature. This is similar to the concept of "balancing" a wheel on a car.
Metal material is 'shaved' or notched ( removed) from the side of the armature which is too heavy, ( and causes a ' wobble' as the RPM's are increased.)
However, On a car, wheel weights are added to the OPPOSITE side of the wheel's heaviest spot of imbalance, until the wheel can be spun at a high speed, with no wobble.
Answer
The slots carry the armature conductors, while minimising the air gap between the rotor and and the stator (to minimise the reluctance of the magnetic circuit)!
They have nothing to do with 'balancing' the armature.
Why rated voltage is to be applied to primary for open circuit test?
Open circuit test on a transformer is usually performed to measure the IRON losses.Iron losses are produced due to eddy current and hysteresis losses. In open circuit test, the LV side, generaly the secondary winding, is kept open and the HV side, generaly the primary winding is fed with the rated voltage and frequency. The rated voltage is applied in order to setup normal flux in the transformer, which in return further produces the normal iron losses at rated voltage. the wattmeter connected at the primary side will show the power consumed due to iron losses. this calculation further utilized for determing the efficiency of transformer.
What happens to the voltage if batteries if they are setup in a parallel and a series circuit?
Assuming all of the individual batteries are the same voltage, if arranged in a parallel circuit the voltage is the same as any one battery.
If arranged in a series circuit the voltage will be the sum (the total) of all of the batteries added together.
Can a digital circuit produce the same output voltage for different input voltage values explain?
No, value of output voltage depends upon the value of input voltage and digital can not produce the same output voltage for different input values.
For example, suppose in a digital circuit two switches are connected. A closed switch is represented by 1 and an open one by 0. If there are two switches and we say that they are in state 1, then it would mean that both of them are closed. In this circuit after connection with the battery some current would pass so we call this current as output.Depending upon the states of the switches, the current either would pass or it would not pass.In case the current is passing, we can say the value of output is 1 and it is 0 when no current is passing. Whether the value of the output would be 1 or 0, it depends upon the values of input variables( 1 and 0) which specify the state of the switches.In this example, the switches form the input variable because the value of output depends upon the state of these variables which shows that digital circuit can not produce same output voltage for different values of input voltage.
Why the no-load current of an induction motor is high compared to a transformer?
Because of the presence of the air-gap between stator and rotor in motor the magnetization current is much higher than that of a transformer in addition to the friction and windage losses due to the rotation of the rotor.
What is the minimum safe distance from a house and an electric transformer 13.8 KV?
The transformer enclosure should isolate the transformer sufficiently from the environment. I believe OSHA specifies 2 feet, 1 inch as the minimum appoach distance to 13.8kV, so I suppose a transformer could be put this close to a building and still be safe. My guess is there are codes in place in your local area that prevent this and specify some greater distance.
What are the advantages of Swinburne's test?
1. swinburne's test is economical since power required to test a large machine is very small (i.e.,)no load input power.
2.The efficiency of the machine can be predicted at any load, since constant losses are known.
3.This method enables us to determine the losses and efficiency without actually loading the machine
When the motor is found running hot to touch what happen?
A motor is always going to be hot to the touch because when it is running it is very hot and takes awhile to cool down after it is shut off. If an engine is hot to the touch, it just means it was recently running.
What is the voltage power current and resistance of an electrical heater?
The two most important ratings for an electrical heater are its rated power and its rated voltage, and these will be printed on a 'nameplate' fixed somewhere on the heater (e.g. '3 kW at 230 V').
For the heater to operate at its rated power, it must be subject to its rated voltage. In the above example, the heater will only operate at 3 kW if it is supplied with 230 V.
If you know the heater's power (P) and its voltage (U), then you can calculate the rated current (I) it will draw from the supply, using the equation: I = P/U.
You can also determine its resistance (R), using the equation R = U2/P.
Transmission power cables are designed by current carrying capacity.
The Linear Variable Differential Transformer is a type of electrical transformer used for measuring linear displacement. A counterpart to this device that is used for measuring rotary displacement is called a Rotary Variable Differential Transformer.
