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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 speed control of DC shunt motor is necessary?
The total voltage of the batteries or DC power source connected to a shunt motor affects how first it moves. Increasing the DC voltage will make the shunt motor run faster.
Why do you calibrate and recalibrate measurement equipment?
Usually, when you measure something that requires calibration, that work is generally considered important either monetarily or socially. So, you want to make sure you are sure because things are riding on your measurements. The short answer is so you don't screw up :)
Why are glass insulators used on power lines?
The large glass insulators are easy to mould, and are strong, well able to insulate the pylons from the high voltage the cables are designed to carry.
What is race problem in flip-flops?
When you have asynchronous logic (not clocked) each path has different delay times through the gates. Usually depending on the number of gates it passes. When you have logic that can go in a different state when signals enter in different order, you have a race problem. It means that the signal are "racing" and the fastest one wins.
Function of earth fault relay?
An "earth fault relay" is a bit ambiguous. A relay used in the power system to detect neutral or ground faults measure the vector difference of the three phase power, or measure the neutral current directly. If current is above a set trip point, the relay will operate.
If you are referring to GFCI's, they effectively measure the current flowing in and the current flowing out on the two "hot" wires, and if these do not cancel each other out, then the GFCI will trip. This is because if current in does not equal current out, then some current must be flowing out a different way (to ground!).
What are the advantages of DC machines?
DC engines were the first sort generally utilized, since they could be fueled from existing direct-current lighting force conveyance frameworks. A DC engine's velocity can be controlled over a wide range, changing so as to utilize either a variable supply voltage or the quality of current in its field windings. Little DC engines are utilized as a part of instruments, toys, and apparatuses. The widespread engine can work on direct current however is a lightweight engine utilized for compact force apparatuses and machines. Bigger DC engines are utilized as a part of impetus of electric vehicles, lift and raises, or in drives for steel moving plants. The appearance of force hardware has made supplanting of DC engines with AC engines conceivable in numerous applications.
What is the difference between commutator and rectifier?
commutator also acts as an mechanical rectifier in the case of dc machines.by deviding the commutator into two parts that will accept the +ve cycle & ignore the -ve cycle.so it act as a rectifier.
How do you calculate the transformer turns ratio?
For an ideal transformer, the voltage ratio is the same as its turns ratio.
What is a non polarized capacitor?
A polarized capacitor is one which has a polarity, positive on one terminal, negative on the other. This makes it superficially look like a battery. In use, the capacitor has its positive voltage always higher than that on the negative terminal, it matters that this is the case and this gives rise to the term polarized. This sort of capacitor is commonly found in power supply filters.
Why lights in classroom is connected in series or in parallel?
only two connections are possible.. parallel connection is always desired than series. .
What are two types of EMF induced in a double wound transformer?
1. self- induction2. mutual- induction
How is direction of rotation for single phase induction motor determined?
A single phase induction motor is not self starting; thus, it is necessary to provide a starting circuit and associated start windings to give the initial rotation in a single phase induction motor. The normal running windings within such a motor can cause the rotor to turn in either direction, so the starting circuit determines the operating direction.
Why neutral wire carry no current?
Usually yes, sometimes no. For instance:
The neutral in a single-phase, 120V (in the US) branch circuit, such as one feeding receptacles, does.
The neutral in a 120/240V circuit feeding a 240V appliance does not.
The neutral in a 480Y feeder feeding a balanced load does not.
A neutral is there because of the possibility that current flow could occur. For instance, in a US household, with 120/240V service, if you plugged in 5 100 watt lamps on one side of the line, and another 5 100 watt lamps on the other hot leg, there would be no neutral current in the service cable feeding the house. The loads are said to be 'balanced'. The 500 watts of power flowing into the first hot leg goes through the first set of lamps, then the second set, then out the other hot wire. Neutral current still flows in the individual branch circuits, of course.
Now, if you moved one of the lamps to the other side, 600 watts would be coming into that side, but only 400 would be going back out the other hot wire, so 200 watts would flow through the neutral.
What causes insulation breakdown in transformers?
The main cause of insulation breakdown is excessive temperature. However, it can also be caused by excessively-high electrical stress due to sharp corners or other protrusions in the conductor which act to intensify the electric field beyond the capability of the insulation.
A synchronous condenser (also known as a synchronous capacitor or synchronous compensator) is a DC-excited synchronous computer (large rotating generators) whose shaft is now not connected to any using equipment.
What is the difference between shunt generators and series generators?
1. In Shunt generators armature current is equal to sum of field current and load current whereas in series generators field current and load current is same.
2. Shunt generators field winding has high resistance and large no of turns as compared to series generators.
3. Shunt generator field winding has thin conductor and series generator has thick.
How many amps are in 400 horsepower with 480 volt three phase?
This might help you. First and foremost is the information the manufacturer puts on the nameplate of the motor. Second, the generic amperage can be found on motor charts that are on the Internet. Third you can use a formula to find the approximate amperage. HP = Amps x Volts x 1.73 x %Eff x pf/746. Transposed for Amperage, Amps = HP x 746/Volts x 1.73 x %Eff x pf. Use power factor = .9. Eff = 746 x Output HP/Input watts use 1.5. For estimating a 400 HP motor running on 480 volts. Amps = 400 x 746/ 480 x 1.73 x 1.5 x .9 = 298400/747.36 = 399.27 amps. See how much easier it is to read the nameplate.
Can you use 24 volt transformer to powers 12v lights?
You can if you want to connect two 12 volt lights in series with each other. Make sure that the 12 volt lights are rated for AC and not DC.
CommentFurther to the above answer, you must also ensure that the two lamps have identical power ratings, or the lamp with the lower power rating will be brighter than the one with the higher power rating!
What is the instantaneous voltage at 180 degrees for peak voltage of 150 volts?
Zero. If voltage starts at zero at zero degrees, it rises to peak voltage at 90 degrees. Voltage then reaches zero at 180 degrees and heads for negative peak voltage at 270 degrees and then back to zero at 360 degrees.
What is the voltage of a pylon?
there are 3 main types of power pylons,400,000volts(400kv) usually there are 4 wires on each arm,275,000volts(275kv)usually 2wires,and 132,000volts(132kv)usually 1 wire.
CommentPylons, or to give them their correct name, 'towers', are used in electricity transmission systems and, to some extent, in distribution systems. Their operating voltages depend on the electricity standards in the country in which they are used. As pointed out in the original answer, in the UK, transmission voltages are 400 kV, 275 kV, and 132 kV; towers are also used, in some cases, to support distribution lines that operate at 66 kV and 33 kV (although these are more-commonly supported on poles).
In most cases, each tower supports two separate circuits -one on either side of the tower- with each circuit comprising three 'lines' (L1, L2, and L3)- often with one circuit having its line sequence reversed.
As the original answer indicates, at higher voltages, each 'line' consists of 'bundled' conductors (four per line at 400 kV, two per line at 275 kV). The purpose of bundling these conductors is to reduce the electric field stress that would otherwise exist at the surface of single conductors.
Why does under voltage cause overheating?
Overheating is a result of too much current flowing. AC motors are constant power devices, meaning they require the same amount of power to spin under a specific load. Power is equivalent to voltage times current. If voltage to a motor sags, the motor will attempt to make up the lack of voltage with an increase in current so the power stays the same. If voltage sags too much, the motor will overheat.
How do you calculate kvar of capacitor bank if you know only the kw?
Your question is rather vague. Are you asking how do you determine the reactive power of a capacitor bank necessary to improve the power factor of a load (in which case, is it a single-phase or a three-phase load), or are you asking how to convert a capacitor bank's capacitance into reactive power?
If the former, then you need to know the reactive power of the load before power factor-improvement, and the resulting reactive power after power-factor improvement, and the difference between these two will tell you how much reactive power you need to add in the form of capacitors.
Is BJT is a current control device or voltage control device?
transistor is a current controlled device. as the current flows through the base of the transistor , it works like a close switch.
What size resistor is needed to drop 24 volts dc to 12volts dc?
Its dependent what will by rated power of the device (current).
What is the density of transformer oil?
Density of Transformer Oil at 29.5oC is 0.89g/cm3.
The exact density of transformer oil depends upon the manufacturer but, expressed in SI units, is typically a little less than 900 kg/m3 at 20oC. The J&P Transformer Book states that 'a limit of 895 kg/m3 at 20oC ensures that the temperature (of the oil) must fall to -20oC before the density of the oil would exceed that of ice' -thus ensuring that if ice forms, then it would remain at the bottom of the tank.
