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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 kirchhoff's voltage law is applicable for open circuit?
Kirchoff's Voltage Law does not work, per se, for open circuits. You need a closed circuit for it to make any kind of sense.
The signed sum of the voltage drops going around a series circuit is equal to zero.
That means you have a closed circuit.
However, it can be argued, correctly, that an open circuit is simply one that has two nodes with infinite resistance between them. Assuming that all of the other nodes have something less than infinite resistance between them, then Kirchoff's law does work, of sorts, in that the voltage drop across all nodes that are not voltage sources will be zero, because there is no current, and the voltage drop across the two nodes with infinite resistance will be equal to the sum of the voltage rises across the voltage sources. Current sources in such a circuit will not work, because, with zero current, they would attempt to generate infinite voltage.
AnswerKirchhoff's Voltage Law does indeed apply to an open circuit, because the voltage drop across the open part of the circuit is numerically equal to the supply voltage and, hence, the algebraic sum of the voltage drops around that particular loop is zero.
Kirchoff's Voltage Law does not work, per se, for open circuits. You need a closed circuit for it to make any kind of sense.
The signed sum of the voltage drops going around a series circuit is equal to zero.
That means you have a closed circuit.
However, it can be argued, correctly, that an open circuit is simply one that has two nodes with infinite resistance between them. Assuming that all of the other nodes have something less than infinite resistance between them, then Kirchoff's law does work, of sorts, in that the voltage drop across all nodes that are not voltage sources will be zero, because there is no current, and the voltage drop across the two nodes with infinite resistance will be equal to the sum of the voltage rises across the voltage sources. Current sources in such a circuit will not work, because, with zero current, they would attempt to generate infinite voltage.
Read more: http://wiki.answers.com/Why_kirchhoff's_voltage_law_is_applicable_for_open_circuit#ixzz1i2fWNqfN
What happen if the iron core is replaced by gold in the case of transformer?
You will have a very expensive but worthless transformer. Gold is not a ferromagnetic material, so it will not contain the magnetic flux needed to link the separate windings.
What are the uses of derivatives in electrical engineering?
When you are talking about field and line calculations, complex differential equations are sometimes the best way to represent electrical characteristics. current and voltage in AC applications is defined using differential equations. You may use derivatives in control system modelling. There are many others.
Why are electrical engineers needed?
To construct electrical systems upon which we base modern society.
What is the principle and working of clevenger apparatus?
three fosters control the work of clevenger: boiling temperature of the distillator density and hydrophobic ability.
How do you calculate safe working load of a bollard?
To calculate the safe working load of a ship's bollard, you need the working stress and the force applied. These two will help you compute the safe working load.
What would happen if the starting and running windings were identical?
There will be no angular displacement between the two windings and machine will not run.
Why is a 3 phase induction motor is used in electric trains?
AC induction motors are not always used in trains as traction engines, however they are a popular choice. AC induction motors are very simple and reliable and aside from bearing wear they have no parts that wear out. This is because the power used by the rotating parts is supplied by the magnetism like in a transformer and so there are no slipping brushes.
Most train systems actually use a DC supply, then a device called an inverter is used to convert the DC to variable frequency to drive the AC motor and control its speed. When this is done the AC induction motor is a very reliable and flexible engine and even allows energy recovery when the train is breaking.
What three devices are usually found in series with the Y terminal of a low voltage control circuit?
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What is the formula for calculating the full load current of 300 HP motor?
One horsepower electric is defined as 746 watts, so 300 horsepower is 224 KW. You don't say what the power factor is, so lets assume 0.85. Divide 224 KW by 0.85, and you get 263 KVA. You are running three phase, no doubt, so divide by 3 to get 88 KVA per winding. Lets assume 480 three phase delta, so divide by 480 to get 183 amperes per winding. Finally, look at motor efficiency. Lets assume 0.95, giving 192 amperes per winding.
To translate between winding current and phase current in balanced three phase delta, multiply by the square root of 3, giving a phase current of 333 amperes per phase.
That's a lot of current, requiring very large windings and conductors, and it would be a very large motor. I would use a motor with a higher voltage, perhaps 4160. This would bring the current down to around 22 amperes per winding, or 38 amperes per phase, a more reasonable value for such a large motor.
Why are the brushes of a dc machine always placed at the neutral points?
The function of brush is to collect current from rotating commutator and supplies the current to external stationary load.
The brushes of a DC machine are placed at neutral points because the current in the rotating part drops to zero at the neutral point.
If brushes are placed in location other than the neutral points, then the current may be switched off and it causes magnetic field and it may also create voltage spikes and arc at brushes.
What is the job of a wire in a torch?
To conduct the flow of electrons/electricity from the battery to the bulb and back.
The secondary voltage of a transformer with a turns ratio of 5 to 1, and primary voltage of 200 is 40. (5 to 1)
Which component slow down the current in circuit?
An inductive load can cause current to lag voltage in an AC circuit. An increase in resistance will decrease amount of current flow.
What is the similarity between Programmable Logic Controller and relay?
There aren't any similarities. They are different types of components.
What are devices that obey ohm's law called?
All devices obey Ohm's law. That is why its called a law.
The misunderstanding is that Ohm's law does not say that resistance is constant - it says that resistance is voltage divided by current.
Very few devices actually have constant resistance. Even the resistor is not constant, due to thermal properties.
AnswerI beg to differ with the previous answer.The term you are looking for is a 'linear' device. 'Non-linear' devices, on the other hand, include some semiconducting devices, such as diodes, but also includes certain metals such as tungsten. What it basically comes down to is that if there isn't a linear relationship between current and voltage, then the device is not obeying Ohm's Law!
Ohm's Law simply states that, 'providing external factors such as temperature remain constant, then the current flowing in a circuit is proportional to the applied voltage'. It most definitely doesn't say that 'resistance is voltage divided by current'!! In fact, it doesn't even mention resistance!
Ohm's Law is not an equation, despite it often being taught as such in high schools by teachers who should know better, but who misinterpret the Law by over-simplifying it (some high school teachers shouldn't even be teaching science, as they are responsible for many other misconceptions too!).
For current to be proportional to voltage, there must be a constant of proportionality. This is called conductance, expressed in siemens. However, it is more usual to use the reciprocal of conductance, which is resistance, expressed in ohms, that is: U = R I, where Ris a constant.
In other words, Ohm's Law is only true providing resistance is constant. So an incandescent lamp, for example, which uses the non-linear metal tungsten, as a filament, does not obey Ohm's Law. This is because its temperature increases significantly as the voltage across it is increased and, so, the resulting current does not increase proportionally with that voltage. Even 'linear' devices become 'non-linear' at some point, usually at extreme temperatures, once again reinforcing the fact that Ohm's Law only applies providing the temperature doesn't affect resistance.
To put it another way, if there isn't a straight line relationship between current and voltage, then the device ain't obeying Ohm's Law!
However, for any given voltage, you can certainly use the equation R = U/I to determine what the resistance happens to be at that particular voltage-but that isn't what Ohm's Law says. Ohm's Law isn't about a what happens at a particular voltage! It's about the current remaining proportional to the current over a wide range of voltage variation.
when earth fault occurs very near to the neutral point of wye winding, the voltage available for driving earth fault current is small. Hence fault current is low. Relay has to be too sensitive and then it can operate for spurious signals like external faults, switching surges etc.
What does the term floor load mean when loading an overseas container?
The floor load in an overseas container is the amount of load the floor is capable of holding.
What is the name principle of 3 phase induction motor?
Transformer action. There is no electrical connection between the stator and the rotor, and voltages get induced into the rotor bars when they are swept by lines of magnetic flux created by the stator windings.
What is the difference between the transmission line and feeder?
Think of a river getting fed by streams and creeks. These feeders increase the water flowing in the river like electrical feeders increase the current in the transmission line.
