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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 an example of mutual inductance?
A transformer because, to work, it must use mutual inductance between its separate windings.
Why does a ac voltage applied across a load resistance produce alternating current in the circuit?
Because V = I x R or Voltage = Current x Resistance. Since resistance is linear there is a linear relationship between Current and voltage. If you have DC voltage you have DC current and if you have AC Voltage you have AC current. Note that there is a linguistic recognition of this relationship in that the voltage is described in terms of the current.
Wiring diagram to convert a 3 phase 480 volt generator to 277 volt?
You should not need a wiring diagram. If the generator has a star point (wye) connection then the phase voltage to ground (star point) is 277 volts. 480/1.73 = 277.
Current equals Voltage divided by Resistance. 9/2=4.5 amps.
How three phase induction motor works without stator?
with 3 phase the rotating field is already set up when power is supplied
with single phase you use a capacitor and a second winding to set up the rotating field
Which instrument is used to test insulation breakdown of a conductor?
Because contemporary testing is more complex and includes provisions for assessing a broader spectrum of characteristics (and doing it more accurately), we have specialized test equipment to handle it. In the case of insulation breakdown, it can be tested with an insulation breakdown test set. In the "old days" of testing, a megohm-meter or megger was used to "slam dunk" an evaluation.
How are circuit breakers connected with the other elements in a circuit?
Both of these devices are safety devices used to open a faulted circuit and stop the current flow.
What are the Advantages and disadvantages of electro-pneumatics?
ADVANTAGES OF PNEUMATICS.
1. Simplicity of Design And Control
The control machines are easy to design. i.e they can be manufactured using standard cylinders & other components. Controlling mechanism simply contains two ON-OFF states, so its easy to implement and understand.
Also these components have versatile usage, they can be used in many situations. Pneumatics are easy to install and have useful mechanical movements. For an instance Straight-line movements can be obtained without further adjustments, such as levers, cams...etc
2.Reliability
pneumatic control mechanism is well known for its long lasting operation life time. In fact they need very little maintenance but operates continuously with high reliability.
Air /gas used as the working fluid is less likely to damage the equipments since gas are good in absorption of shock, and excessive forces, but hydraulics react directly transferring the stress to mechanical parts.
3.Safe to use
Pneumatic controls have high safety profile due to many reasons. Air used in these are fire proof, and less vulnerable to explosions and electric hazards. These are adoptable in extreme weather conditions, and we can rely on their continuous operation. This is because compressed air can stay in good condition in high temperature fluctuations, unlike hydraulic s ystems that tend freeze or boil in these situations.
Even a leak occur there is less chance of getting fire. Also there is no toxicity in air used, so we can expect no harm to living beans. Since pneumatics are sound in safety, very less precautions need to be taken.
4.Storage
Compressed Gas can be stored easily, and once compressed, above a certain threshold level they can be operate with out further need of compressing. This feature allows the use of machines when electrical power is lost.
5. Clean
Since working fluid is purified air, there is no messy waste produce at the end of the day. A little leak will not make the surrounding shady. Also, since ir is used no risk of toxic hazards t o machines or humans. Industries like pharmaceutical, food..etc tend prefer pneumatics for their cleanness.
6. Easily transported
Air is easily obtainable from atmosphere and can be used with little purification. Air can be pumped to long distances in pipelines, so can control pneumatic equipments for long distances. This makes central controlling possible. These also requires no return line, so easy to manage and cost effective.
7. Light in weight
Air is very light compared with other fluids, which are very heavy. They don't need high power to transfer.
8.Cost Effective
This is a very economical controlling mechanism. The Pneumatics require low maintenance cost, since wear of equipments are very less. These operates at low pressure , so equipments can be produced for low cost using cheap materials. In contrast hydraulic controlling systems require high pressure, so need tough materials, which comes in high prices.
9 high speed working medium
Compressed air controllers are able to achieve high work speeds, the flow rate may go up to 20 m/s, while hydraulics is restricted around 5m/s.
10.safe operation in Overloads
The shock absorbent properties of air make overloading safe. Under excessive forces air can compress easily avoiding damage to equipments.
11 Variable pressure
Pneumatic systems can work in various pressures, this also alow the speed control.
DISADVANTAGES OF PNEUMATICS.
1. Air is largely compressible, which may be good for some reasons, but the major draw back is the inefficiency in accurate positioning and speed controlling. These often need to be tuned to work correct and sound. Since Compressible,not possible to achieve uniform and constant piston speeds.
2.Unable to work with heavy loads (commonly used working pressure of 7 bar, the require output force is economical only up to about 20 KN to 30 KN ) Unlike hydraulics or electrical system these cant be used for heavily loaded operation.
3. Air used needs to be purified, air containing moisture may lead to corrosion of the equipments.
What is electromagnetic induction?
Electromagnetic Induction mainly deals with the ways that energy is shifted about between Electric and Magnetic fields in various circumstances. Here are some major examples:
1. A moving Electric Current Induces a Magnetic field: Electromagnets.
2. A moving conductor in a magnetic field Induces an Electric Current: The Dynamo or Electric generator.
3. An Electrified Conductor in a Magnetic field Induces motion in the Conductor: The Electric Motor.
Related Information:
Albert Einstein's considerations of inductance, an Electrified length of conductor moving through a Magnetic Field in an empty volume of space, led him to his theory of Special Relativity.
What is the formula to calculate AC resistance if the DC resistance is known?
AC resistance is the term used to describe the elevated value of resistance due to the reduction in a conductor's effective cross-sectional area due to the the skin effect caused by an alternating current. The skin effect describes how AC current tends to flow towards the surface of a conductor, rather than being distributed across the entire cross-sectional area as is the case for a DC current.
For 50/60 Hz supplies the skin effect is not great and, so, there will not be a great difference between the DC resistance and AC resistance of a winding. Accordingly, it will be very difficult to calculate the winding's AC resistance, as its value is likely to be masked by experimental error and the accuracy of the instruments.
In theory, by using a wattmeter and an ammeter, the resistance of a load -in this case a winding- the readings can be inserted into the equation: R = P/I2. Using a DC supply will reveal the (DC) resistance value, and using an AC supply will reveal the AC resistance value. As explained, a combination of experimental error and instrument accuracy is very likely to mask any actual difference between the two resulting values.
So, at mains' frequencies, the difference between AC resistance and actual (DC) resistance would be very difficult to determine with any degree of accuracy.
Ohm's Law states Voltage = Current x Resistance. You rewrite the equation as Current = Volts / Resistance to solve for current.
How much current at 240 volts passes through a wire with a resistance of 100 ohms?
current = voltage/resistance
Assuming the 240 volts is across the 100 ohm wire, 2.4 amperes
power = current * voltage
Resulting in the wire dissipating 576 watts... One hot wire!
How do you calculate contact resistance?
Resistance is resistance , no matter if it is contact resistance or any other resistance. And formula is R = V / I.
Why you use auto transformer in a substation?
An autotransformer is different from a "normal" transformer in that it uses the same winding for both input and output, with a tap somewhere along the winding for an additional connection for the input or output (whichever is the smaller value).
When an autotransformer is configured to output a lower voltage than the input, the input AC line is connected to the ends of the winding and the output line is connected between one end of the winding and the tap at some midpoint that is proportional to the difference between the input voltage and the desired output voltage. The input voltage induces a magnetic field in the core, and the magnetic field then induces a voltage between the tap and the common end of the transformer. To use an autotransformer to output a higher voltage than the input, the input is connected between the tap and the common end, and the output is connected between both ends.
Autotransformers are most often used as variable transformers with a sliding tap that runs along the outside of the winding which is wound around a toroidal core. Moving this tap changes the output voltage of the transformer. A major disadvantage of the autotransformer is that it doesn't completely isolate the output side from the input side, and dangerous voltages and currents can appear on the output side, especially DC voltages and currents which can travel through the coil unimpeded.
The undisputed industry standard for the above is as follows:
Three phase Low Voltage panels (110/208-240volt) are marked as follows from left to right as you look at the panel or other electrical control/distribution:
Phase A conductors are Black, Phase B conductors and Red, and Phase C are Blue.
Three phase High Voltage panels (277/480volt) are marked from left to right as:
Phase A conductors are Brown, Phase B are Orangeand Phase C are Yellow.
Single phase line and branch conductors are not color coded.
Note that the National Electric Code does not specify conductor colors with the exception of the grounded conductor, (the neutral) which is to be have insulation or marking tape which is to be white or grey. The industry standard here is that white is used for low voltage neutrals and grey for high voltage. The code also requires that the earth ground, or grounding conductor is to be green or bare copper. The only other specified conductor colors in the code are for conductors on the secondary side of an isolation transformer panel in an hospital operating room. Chances are you don't need that information.
Answer for countries in Europe and other world areas running a 50 Hz power supply service.In the UK red, yellow and blue were the standard colours used for labelling the line wires in a 3-phase circuit until 2006 when the Wiring Regulations were changed so that the standard colours are now brown black and grey to conform with the standard colours common in mainland Europe. These colours, however, are stillstandard in the electrical supply industry. The sequence of these colours also defines the standard phase sequence of the supply.For more information see the answer to the Related Question shown below.
How does a transistor work as a switch explain with diagram?
In brief and in the most general terms, a transistor is a 3-terminal semiconductor device capable of changing its resistance in a "controlled" way. It is like the valve (the hose bib) that you open to turn on the water to your hose. The valve allows you to apply a little energy (from your hand) to control lots of energy (the water pressure). That's amplification. Let's peek in on this and make some simple comparisons. A transistor has an emitter, a collector and a base. The emitter and collector could be considered "input and output" terminals in the most basic sense. As for the base, it is the "control terminal" just like the handle on the faucet. By applying a small voltage to the base to "turn on" the device, we can get current to begin flowing. First a little, and then, by turning it on more, a lot. Eventually the device will be "all the way on" and will be allowing maximum current to flow through it. The opposite will be true when we turn the device off. That's it. Oh, but let's take a moment to look at the implications, shall we? Imagine turning on the water really, really fast. Like almost instantly on. Then off the same way. By turning the transistor on and off "instantly" and looking at the result, we'd get "ons" and "offs" from it. That's 1's and 0's there, and it's binary. That's how we can make a digital signal. And this process is exactly at the heart of how the microprocessor in all digital computers works. You probably saw that coming. Let's look at one other thing. You're familiar with sound, which is mechanical energy. It's like a vibrating string on a guitar or the membrane ("skin") on a drum, just to cite a pair of examples. That movement creates harmonic or oscillating motion and the sound. If we want to create the electrical equivalent, we have to open and close that water valve as quickly as the frequency of the vibrations. That's not really possible with the valve, but with the transistor, we can apply a changing voltage to the base as fast as any "regular" mechanical vibration. If a string vibrates at 1000 cycles per second (1000 Hertz), we can change the voltage to the base at that rate. Let's slow the action down. Note that we start turning on the transistor, then we turn it on a bit more, then a bit more. At some point we've reached a "peak" and then we start turning it off, and off a bit more and off a bit more until it's off. The rateat which we do this corresponds to the frequency of the signal being amplified by the transistor. And how far we actually turn the transistor on before turning it back off corresponds to the amplitude of the signal we are working with. The transistor has largely replaced the vacuum tube, which was originally called an electronic valve. Having wandered around in this discussion, you may be able to see why the terminology (which is a bit "old school" now) can still be fairly applied - even to the transistor.
How wheatstone bridge measure unknown resistance?
A Wheatstone bridge measures an unknown resistance by balancing two legs of a circuit. It consists of four resistors arranged in a diamond shape, with a power source and a galvanometer connected between the junctions. By adjusting the known resistances until the galvanometer reads zero (indicating no current flow), the ratio of the known resistances can be used to calculate the unknown resistance using the formula ( R_x = \frac{R_2}{R_1} \times R_3 ). This method allows for precise measurement of the unknown resistance without direct current flow through it.
What devices use electric motors?
Answered any number of times - let me see if I can get some less common ones
Almost any toy that moves and uses batteries
iPhone (or any cell phone with a vibrator setting)
power windows
printer
microwave oven
DVD drive
sink garbage disposal
a laser barcode scanner ( like at a grocery store - a motor spins the mirror to allow the laser to scan )
gas pump ( like at a gas station )
paper shredder
garage door opener
a water tower
an elevator
What is the procedure for measuring current?
A: The procedure is very simple must have a voltmeter and must have a very low value of shunt in series with the circuit whereby the IR drop will be converted into amps. That works for DC only. For AC the signal is rectified and then measured or a flux clamp can measure the current
How do volts change in a series and parallel curcit?
Series: The same amount of current flows through each component. The voltage drop on each component is determined by the resistance (or reactance for AC) of the component.
Parallel: The same amount of voltage is applied to each component, and the current flowing through a component is determined by its resistance (or reactance).
Is industrial current is ac or DC?
The current that is transferred through cables over long distances is AC. The main reason for this is because it is easier to handle. For example, it is easy to convert an AC current to a higher or a lower voltage with transformers. Transformers don't work for DC.
Which circuit the ammeter connected in parallel?
An ammeter is always connected in series and a vlotmeter in parallel
What happens to the total resistance in a parallel circuit with a short?
In case of parallel circuit the effective resistance is given by
Reff = R1*R2*R3 /(R1R2 +R2R3 +R3R1)
As short circuit takes place then anyone R1,R2,R3 becomes zero. Hence Reff becomes zero.
Does the maximum power transfer condition states maximum efficiency condition?
Answer Pmax=E^2/(4xRs)
The maximum power is transferred when the load impedance is the complex conjugate of the source impedance. For a dc circuit or a purely resistive circuit, the load resistance equals the source resistance.
What is the definetion scaler quantities?
Scaler Quantities are those which are completely specified by their magnitude
expressed in suitable units without any mention of direction .
Posted by yousufkhan {yousufkhan_1@yahoo.com}
