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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
How much energy does a nightlight use compared to a 100 watt bulb?
An incandescent nightlight bulb is either 4 watt or 7 watt.
A 4 watt bulb uses 1/25th (0.04) the power of a 100 watt bulb.
A 7 watt bulb uses 7/100th (0.07) the power of a 100 watt bulb.
There are LED and other types of nightlights that use much less power than this.
To find the energy total used multiply the power (in watts) by the total time the light is on (in hours) to get energy (in Wh). If you want kWh divide this by 1000 as a watt is 1/1000th of a kW.
The device is known as a "motor".
When single core cables laid in trefoil formation what clamping materials should be used?
I am assuming you are referring to high voltage cables. These clamps must be designed to withstand the large electromagnetic forces that result during a short circuit. This is their main purpose. The electromagnetic forces can be simplified as an impulse. The impulse (of duration ~0.2s I believe) causes the core of a cable to accelerate within the elastic region of the clamp and insulation material until these materials are stretched sufficiently to provide an equal and opposite reaction force. Upon reaching this "equilibrium" position, the core and insulation will have acquired a certain amount of kinetic energy such that in the absence of any damping effects they will continue to move within the elastic regionof the clamp and insulation until a reaction force equal to twice the magnitude of the impulse is reached.
So we need a material with a high yield strength to resist this large force without plastic deformation.
In short, materials that have been proven suitable for this use are: Aluminium alloy LM25 which offers a good level of corrosion resistance. In situations where exceptional corrosion resistance is needed, Polyamide 6/66 with glass reinforcement (30% fibre should be acceptable) and PET with glass reinforcement (30%) have had proven success. Note that with its higher yield strength the polyamide is the better choice of the two composite materials. Polyamide in general is vulnerable to UV light, this problem can be solved by either coating the clamps or using a UV resistant blend.
VA Rating stands for Volt-Ampere Rating, It is the basic unit of Alternator or Transformer.
This is so because in AC System Power(P) is the product of Voltage(V),Current(I)and Power Factor.
Power(P) = Voltage(V) * Current(C) * Power Factor
But power factor of the load is never constant and depends on the type of load. So to resolve this problem power ratings of the above mentioned machine is always rated in VA or KVA and its the product of voltage and current.
Why do you use resistors and capacitors in a circuit?
resistors and capacitors are used in order to create a path for the current , for the resistivity of the current , for the storage of the current.
AnswerResistors don't just 'resist' electric current, they create a predictable change in voltage (electric potential) from one side to the other, so they can be used to adjust the expected voltage level at each point in a circuit.
In an electric circuit with an unchanging current and voltage, capacitors simply store current and wait for something to change.
In the more common electronic case of a circuit with voltage fluctuations, each capacitor is effectively a high-pass filter -- it permits quickly-fluctuating voltages to pass through, but reduces or stops slowly-fluctuating voltages.
Why synchronous motor is not a self starting motor?
As per the operating principle of the Synchronous motor, due to continuous & rapid rotation of stator poles,the rotor is subjected to a torque which is rapidly reversing i.e. in quick succession,the rotor is subjected to torque which tends to move it first in one direction & then in the opposite direction.Owing to its large inertia,the rotor cannot instataneously respond to such quickly-reversing torque,with the result that it remains stationary or in other words it is not self starting.
Causes for a brand new AC capacitor start motor to overheat and shut off?
Two reasons could be that the motor was wired incorrectly or the load that the motor is driving is too heavy for the HP of the motor.
What is series - parallel connection?
In series connection current will be same. in parrel connection voltage will be same and current wil be varying
How can you test the vector group DYn11 and vector diagram?
connect the neutral point of the star (secondary) to u phase of primary, and now apply voltage to primary and measure the voltage between V&R, W&B, V&Y and V&B. when you measure voltage b/w
1. V&R the voltage must be maximum,
2. W&B Should be minimum and
3. voltage between V&Y and V&B should be same
U.V&W are primary (Delta)
R,Y&B are secondary (Star)
What 4 colour bands represent a resistor with resistance of 270 k ohms and a tolerance of 5 percent?
red-violet-yellow-gold
Why current a fundamental quantity though it is flow of charge per unit time?
Ampere = Coloumb / second is the same as saying that Coloumb = Ampere x second. Any of the two electrical units can be derived from the other one.
Ampere is NOT a "fundamental quantity"; it is an SI base unit. The base units are not necessarily those that are somehow considered more "fundamental" than others; instead, the base units are those that can be measured with a great accuracy. In the case of current vs. charge, it seems that measuring a current can be done with greater accuracy than measuring a charge directly; therefore, the current is the base unit, and the current is derived. However, this doesn't make current any more "fundamental" than charge.
What is the approximative power factor of an incandescent lamp?
Incandescent lamps are nearly pure resistive loads with a power factor of 1
Why armature is static and field is rotating in alternator?
It is a more convenient arrangement because it does not need a commutator. The rotor is fed with DC through slip-rings and the brushes last much longer. The main current is generated in the static winding enclosing the rotor.
Why power remains the same in transformer from primary to secondary?
Because of the law of conservation of energy. Neglecting minor losses from imperfect efficiency, eddy losses, heating, etc., a transformer's output power is always the same as its input power. If the voltage, for instance, is stepped down by a factor of 10, then its current will be stepped up by a factor of 10. Since power is voltage times current, power is preserved.
In reality, looking at the big picture, there are no losses. Whatever is "apparently" lost is made up in heat and electromagnetic radiation. Power In minus Power "Lost" equals Power Out. Always.
The current of one bulb (two bulbs shorted) would be about1 three times the current of three bulbs.
1 I say "about" because resistance is a function of temperature, and running three times the current through one bulb will make that one bulb much hotter, increasing its resistance. It might also burn out the bulb.
How can measure the voltage only seeing the insulators in a high voltage transmission lines?
i think 11kv per insulator
What does OL indicate in a digital multimeter?
It usually stands for open loop, another way of saying there isn't continuity.
Original answer: it means OVER-LIMIT
beyond the limits of the meter to register, such as "infinity" on a resistance scale
Can you run a AC generator with help of a DC motor if yes how if no why not?
Yes, but the power you get out will be much less than the power you put into the motor.
There is no "slam dunk" answer for calculating the derating of a motor operated beyond its manufacturer's rated temperature. There is a very good reason for this. The "curve" of a motor's performance with regard to temperature isn't linear. In fact, it's far from it. And it will vary a great deal depending on a number of characteristics associated with a given machine. These will include its rating at "ambient" temperature, its size, and number of other things about its shape and mechanical construction. If an individual needs to operate a motor outside the manufacturer's ratings, it's a no-brainer that the manufacturer should be contacted to get information. The hook is economy. A lot of motors can be "pushed" a bit over their operating temperatures for a short time, but extended operation in the "red zone" will bring early failure. "Over-rating" a motor isn't a good idea if the objective is to save a few bucks. It will cost more in the long run to "cook" the unit and have to replace it than to get one that is rated for the operating conditions or to run cooling to the motor. This is really a question of engineering, and the smart engineer will cool a given motor or will get a different motor that is rated for the operating conditions.
Why less voltage drop with 240 wire vs 120 wire for the same length of run?
Voltage drop in wire is determined by the "gauge" of the wire, which is the thickness of it. A 12 gauge wire is thicker than a 14 gauge wire. The 14 gauge wire will have more voltage drop caused by the current passing through it because it is smaller and has more resistance.
Voltage drop will also be affected by the amount of voltage on a wire. It would be incorrect to assume that voltage drop is a percentage based on the length of the wire. The wire gauge affects the resistance of the wire, but assuming the same size (gauge) of wire, a higher voltage will have a greater force behind it than a lower voltage so essentially the resistance of the wire doesn't affect higher voltage as much as it does lower voltages.
If you were to compare electrical wiring with plumbing, voltage would be equivalent to water pressure, and amps would be equivalent to flow, or gallons per hour.
Additional Comments and Answer for European Electrical Installations
The questioner probably really means "Why is there less voltage drop for a cable operating at 240 V, compared to the same cable operating at 120 V".
If this is the case, then the answer is simple. For a load of any given power, the higher the voltage, the lower the resulting current. For example, let's suppose we have a 1000-W load operating at 230 V -this load will draw a current of 4.35 A. The same load operating a 120 V will draw a current of 8.33 A. So, for any given conductor size, the voltage drop (Iload x Rconductor) will clearly be greater.
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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.
Before you do any work yourself,
on electrical circuits, equipment or appliances,
always use a test meter to ensure the circuit is, in fact, de-energized.
IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.
What is a silicon-controlled rectifier?
A silicon-controlled rectifier is a semiconductor device that is used as a switch in an electrical circuit. It's a solid state direct current (DC) electronic switch. There is a ton of information including a detailed description of the SCR and a list of applications at the Wikipedia article. A link is posted below.
Yes, the total current delivered to multiple devices in parallel is the sum of the individual branch currents (the vector sum if there is inductive load).
Circuit breakers are resettable automatic switches that help protect against circuit overload (such as running too many hair driers and heaters on at one time) and faults (such as dropping the hair drier into a bathtub). Circuit breakers "operate" (or open) to stop current flow to the fault or overloaded circuit.
How commutator converts AC to DC?
There is no conversion of AC to DC a commutator is the key to creating straight DC voltage. "The commutator rotates with the loop of wire just as the slip rings do with the rotor of an AC generator. Each half of the commutator ring is called a commutator segment and is insulated from the other half. Each end of the rotating loop of wire is connected to a commutator segment. Two carbon brushes connected to the outside circuit rest against the rotating commutator. One brush conducts the current out of the generator, and the other brush feeds it in. The commutator is designed so that, no matter how the current in the loop alternates, the commutator segment containing the outward-going current is always against the "out" brush at the proper time. The armature in a large DC generator has many coils of wire and commutator segments. Because of the commutator, engineers have found it necessary to have the armature serve as the rotor(the rotating part of an apparatus) and the field structure as the stator (a stationary portion enclosing rotating parts). Which is the inverse of an AC Generator."
