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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 is the base current in a transistor so much less than the collector current?
as the base current is very small compared to the emitter current,the collector current is nearly equal to the emitter current..
Is 108 volts normal on a outlet?
Like anything in life....It all depends. The factors that determine the voltage at an outlet are generally two fold: 1) how far the outlet is from the mains entrance of a house and 2) how much power is being drawn on the circuit the outlet is on. Higher current(power) will reduce the voltage at the end of a circuit. Basic Ohms law.
108 volts does seem to be significantly lower than normal. Typical house voltages are 120 vac and with some drops allows it might be a few volts lower. It also depends on how far the transformer is from your house. It is possible that the transformer has a significant load on it(e.g. drawing more power than it is designed for) and that will have an effect on the final voltage. You should measure other outlets to see if they are similar in voltage. If so, it is most likely the supplier. Just one other thing to check is another meter. Could it be that your meter is faulty(e.g. needs a battery replaced)?
Also, it depends on the country that you are in. US voltages are typically 120 vac or 240 vac for general home use. Industrial use will generally be 277 vac and higher ranging up to 480 vac for mid sized installations. These are generally 3 phase versus single phase for home use. In some cases homes will use what is called 2 phase. In general all voltages delivered to homes are measured from "Neutral" to line. This translates into 120 vac. If there is a transformer that has 2 phase capability on the distribution pole they generally bring in another phase which is 180 degrees out of phase with the original 120 volts and thereby making it 240 volts phase to phase.
Europe(in general) uses 230 vac but last I heard is being standardized to 240 vac. Some countries, such as Japan use 100/200 vac as standard home voltages.
What is the current carrying capacity of silver wire?
The current capacity varies depending on the length and diameter of the wire
Two resistors of 400 Ohm and 600 Ohm are in parallel What is the equivalent resistance?
Use the general equation for resistance in parallel:
1/R = 1/R1 + 1/R2
How do you change an ac motor to a DC motor?
Ac motor have slip ring, to remove the slip ring,connected to the commutator its a dc motor.
Why are most industrial loads placed in parallel with the source and in series with a switch?
The loads are in series with the switch so the switch can turn them on and off.
The loads are in parallel with each other so they each get the same voltage when the switch is turned on. (Kirchoff's voltage law)
You would not want the loads in series with each other because they would then have half the voltage and one quarter the power that you probably intended. (Assuming consistent impedance)
If you had the switch in parallel, and opened(turned off) the switch, there would still be a current along the whole circuit (except that which is in series with the switch)
What is the difference between neutral earthing resistance and solid earth?
The star point of a primary*-transformer's secondary winding is frequently connected to earth via an impedance, in order to limit the return current in the event of an earth fault close to the transformer. The impedance may be a resistor or an inductor, (choke) depending on the nature of the earth return. In general, if the earth resistance is low, then resistive earthing is used; if the earth resistance is high, then inductive earthing is used.
(*e.g. 33/11 kV)
For resistive earthing, the transformer secondary's star point is often connected to the centre electrode of a galvanized-steel tank which is solidly earthed. The tank is then filled with water, and it is the resistance of the water that provides the required resistance to earth. The actual resistance of the water is modified to the desired value by dissolving sodium carbonate into the water while measuring its resistance. The solution has a negative temperature coefficient of resistance, which means that, in the event of an earth fault, as the fault current increases, the increasing temperature causes the resistance of the water to decrease, thus accelerating the response time of the protective system.
A thin antenna has nothing to do with the physical size of the antenna. Any antenna whose length is less than (1/10) of the wavelength of the signal is thin antenna. A linear antenna is one in which the current distribution is linear or bears a linear relationship with some parameter, say voltage of the antenna......
Mukesh
On an analog ohmmeter, measurements are more precise and more accurate at the zero end of the scale.
What is the main work of transistors in an electronic circuit?
The main use of transistors in electronic circuits is as switches and memory storage
How the ka rating of mccb is calculated?
ka of mccb=transformer(KVA)x100/1.732xsecondary voltagex%impedence of transformer
Why is a sag provided in the transmission line?
Sag is provided in transmission lines in order to lessen the tension of the transmission lines. Sag literally means to be bend in shape. In overhead transmission lines , the difference in level between points of supports (towers or utility poles) and the lowest point on the conductor is called a sag.
Explanation: While erecting an overhead line, it is very important that the conductors are under safe tension. If the conductors are too much stressed between the supports ( towers, utility poles), then the stress on the conductors may reach to an unsafe level and the conductor may break due to excessive pressure ( i,e tension). in order to permit safe tension in the conductors, the conductors ( i.e the transmission lines) are not fully stretched but are allowed to have a dip or a sag.
What are the advantage of state space equation representation?
There are several advantages to using the state space representation compared with other methods. Some of these are:
the ability to easily handle systems with multiple inputs and outputs;
the system model includes the internal state variables as well as the output variable;
the model directly provides a time-domain solution, which ultimately is the thing of interest;
the form of the solution is the same as for a single 1st-order differential equation;
the effect of initial conditions can be easily incorporated in the solution;
the matrix/vector modeling is very efficient from a computational standpoint for computer implementation
What is the difference between capacitance and stray capacitance?
Capacitance is an ability to store an electric charge.
"If we consider two same conductors as capacitor,the capacitance will be small even the conductors are close together for long time." this effect is called Stray Capacitance.
Does a 800 amp service required to be in a one hour rated room?
You obvioulsy do not know what you are talking about. The question as stated makes no sence.
How do you calculate the cable length for the building?
Decide on the path for the cable, site visit to verify length of conductor avoiding any obstacles. (Other services, ducts, structural beams.) Add a small percentage to allow for bends and connection at each end.
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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.
A Buchholz relay is used to monitor large transformers for oil loss or insulation breakdown, and is located in an inclined pipe between the transformer itself and its oil conservation tank (located above the transformer).
It consists of a normally oil-filled chamber containing two floats: an upper float and a lower float. Each float is fitted with a mercury switch, and the lower float is fitted with a deflection baffle.
If the oil level should drop, as a result of a leak in the transformer tank, the oil level in the relay will fall, and the upper float will deflect downwards, closing its mercury switch and triggering an alarm in the substation. Should the oil level continue to fall, the lower float will deflect downwards, closing its mercury switch and trigger the transformer's protection circuit -disconnecting the transformer.
Minor arcing due to a breakdown in winding insulation will generate gas; this will accumulate in the Buchholz relay, causing the oil level to fall, causing the upper float to deflect and trigger an alarm. A major breakdown in winding insulation will create a pressure wave which will travel through the Buchholz relay, causing the lower float's deflection baffle to deflect that float, activating the protection circuit and disconnect the transformer.
A test valve at the top of the Buchholz relay will allow any gas collected within the relay to be tested. The nature of the gas will indicate whether it is due to a breakdown of the oil, or of winding insulation.
Modern electronic multimeter measures resistances by?
forcing a constant current and measuring the voltage across the unknown resistor.
What are the characteristics of a simple circuit?
A simple circuit consists of a source of electro motive force ( EMF or voltage V )
This could be a battery,dynamo or solar cell. The circuit should do something, like light a lamp. For the lamp to glow there must be a flow of electrons called an electric current measure in Amperes (I). For the current to flow the circuit must form a closed loop, like a daisy chain. A switch is a device that breaks this loop and controls the state of the circuit.
Closed circuit, switch closed, = lamp on
Open circuit, switch not closed = lamp off
Single phase and three phase circuit?
Yes, there is a difference between single phase and three phase circuits.
What is the effect of armature over voltage in a dc motor?
Overvoltage on DC motor armature can be detrimental to the life of the windings. Most modern drives have voltage feedback and detect this condition.
A likely cause is loss of speed feedback, voltage feedback or the load driving the motor beyond what the drive can handle.
Fixes for the above: -check and mend the feedback circuits and associated hardware (cable, tachos, input cards, processor cards)
-change from a single quadrant to a four quadrant drive
-install a braking resistor
-inspect the mechanical system to ensure there are no wild split points in the gearing
What is the difference between LC and RC filters?
LC means coil capacitance circuit RC means resistance capacitance circuit
WORKING principle of permanent magnet moving coil instrument?
The working principle of these instruments is same as that of the d'Arsonval type of galvanometers, the difference being that a direct reading instrument is provided with a pointer and a scale.
The basic principle of this device is the interaction of magnetic field of the compass (a permanent magnet) and the field around the conductor (a simple electromagnet)
Inductive ammeters work because of what principle?
Inductive Ammeters do not make physical contact with the circuit, but measure the strength of the magnetic field surrounding the wire carrying the current and measures the strength of the magnetic field that surrounds any conductor carrying a current.
This means that the meter probe surrounds the wire(s) carrying the current and measures the strength of the magnetic field that surrounds any conductor carrying a current.
