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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 back charging of power transformer?
Do you mean "back-feeding"?
Normally a power transformer takes a primary voltage and steps it up or down (usually down) to a secondary voltage. However, transformers are symmetrical; you can just as easily feed the secondary and generate the primary voltage.
This is particularly a problem with utility power distribution systems in a storm, such as a hurricane situation...
In a protracted power outage, some people are tempted to run backup generators to supply their inhouse loads while the utility company is effecting repairs. An intelligent user, one that reads the directions, will isolate the generator from the service distribution system so that it is impossible to back feed the service source.
Some people might ignore the directions and attempt to back feed their entire home. If they don't isolate the incoming mains breaker, this can back feed the distribution transformer and energize the primary line on the street, raising it to high voltage, such as 7620 volts.
This actually happened during Hurricane Gloria in 1985, and a utility worker was killed. Yes, the worker was at fault for assuming that the line was dead, but the homeowner was also at fault for ignoring the directions that came with the generator.
Unless you have the proper equipment to synchronize, backfeed, and isolate your generator, DO NOT EVER DO THIS.
What are power poles or lines?
um... isnt it kinda obvious? they are the cords that hang all over the place that carry electricity.
Is amp draw on a 220V motor per leg or combined?
Amp draw is always combined. 220V is uncertain if it is three phase or not, because there are both one phase and three phase applications of the 220V motor. In any case, the answer is always "combined".
Would you show me a diagram of a series circuit?
Diagrams are not supported with WikiAnswers, sorry, so you will have to use your imagination...
A simple series circuit can be built with a battery, a switch, and a light bulb. One end of the battery is connected to one end of the switch. The other end of the switch is connected to one end of the bulb. The other end of the bulb is connected to the other end of the battery.
If the switch is open, no current flows, and the bulb does not illuminate. If the switch is closed, current flows, and the bulb illuminates. By Ohm's law, the current through the bulb is proportional to the battery voltage and inversely proportional to the resistance of the bulb. Note, of course, that we are talking about hot resistance of the bulb, because cold resistance is an entirely different thing, due to the temperature coefficient of the bulb. Also, by Kirchoff's current law, the current at every point in this simple series circuit is the same and, by Kirchoff's voltage law, the voltage across the battery is the same as the voltage across the bulb.
Why is the capacitor used in tube light?
Starters in tube light uses capacitors to produce a momentary high voltage of 400V due to discharging of capacitor.
This momentary high voltage will start the gaseous discharge to priduce light by initial flickering .
now,if capacitor is not used , the power supply from the main cannot start the gaseous discharge .
What are the applications of choke coil?
choke coils are various depend upon the specifications it built....for example if u take 0-5 amp choke coil it is used in household applications like for florescent lamps....
What is self control of synchronous motor drive?
the self control of a synchronous motor is done using an inverter fed through a dc link.speed is controlled by varying the output frequency of the inverter by controlling the dc link voltage
What is the mean of in electrical uH?
The electrical abbreviation ( UH ) is a measure of inductance , as in a ferrite transformer core , inductors , choke etc. .
What are limitations for Kelvin's Law for size of conductor?
It might be best to start by stating Kelvin's law which is that the optimum economic size (cross-section area) of an electric conductor (cable) is achieved when the capital cost of the cable per year is equal to the cost of the electrical energy wasted in its resistance per year.
The theorem is derived by noting that the cable cost is proportional to A, the cross-section area, while the cost of wasted power is proportional to 1/A. The total cost is then given by C = k1A+k2/A. The minimum is found by differentiating and setting dC/dA=0 which gives the condition that k1A=k2/A therefore the minimum cost is achieved when the two separate costs are equal.
Under present conditions with low interest rates for capital costs, the optimum is achieved with a low current loading of around 1 to 2 amps per square millimetre. If more current is used, the wasted energy per year exceeds the annual capital cost of the cable, making a thicker cable more economic.
The main limitation of Kelvin's law is that it applies only in one set of economic conditions. If interest rates increase, or if the cost of copper rises, it becomes more economical to use a higher current loading in the cable.
What is the effective voltage for a peak voltage of 311 volts?
When the peak voltage is 311, the RMS voltage is 220. (311 * square root (2))
How shunt generators used in electroplating?
A shunt generator is used to provide electrons (electrical energy) to the electroplating machine.
# A two-terminal semiconductor device used chiefly as a rectifier.
2. An electronic device that restricts current flow chiefly to one direction. I didn't get third one, let me know. Thanks Pasha
The voltage and frequency ARE the output of the generator. If you change the fuel to the generator, it will change speed, and the voltage will change. Less fuel = less speed = lower frequency = lower voltage.
For normal power factors (pf=80%), you have 0.8 kW for every kva. In general however, kW = pf x kVA. Where pf is the power factor, it is the cosine of the angular difference between the voltage and the current of a circuit in alternating current circuits.
How do you calculate 3 phase kWh to amps when 8000 kWh monthly average is used?
It depends on the voltage. Please restate the question and provide the voltage.
In general, however, simply divide total power by KV to get KA. Remember the KWH is an integral, so you need to back calculate KW. If the month is a 30 day month, then KW is KWH / 30 / 1440. Then, if the load is star, simply divide by three; if the load is delta, divide by three and multiply by 1.732, the square root of 3.
Example: 480 three phase running star. 8000 / 30 / 1440 is 185 amperes. 185 divided by 3 is 62 amperes per phase. For delta, that becomes 107 amperes.
How many amps can a 250 va transformer carry?
A transformer is a power source.
It will provide voltage to a device.
Find the voltage rating on the device, say 24V.
250/24 = ~10A.
