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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
Can a dc motor generates ac current?
if you have something that rotates 360 degrees, it ends up back where it started. the geometry produces a sine wave. DC generators have a design that switches during rotation, or otherwise they generate AC then convert it.
Why should you use a proper fuse with proper specifications?
If you use a fuse that's too slow, or too highly rated, the excess current passing through the circuit may damage both equipment and wiring.
If you use a fuse that's too fast, or with too low rating, it may blow prematurely preventing the equipment from working properly.
How do you check dc voltage... series or parallel?
If you are asking how a voltmeter should be connected in a circuit, then the answer is that it should be connected in parallel with the device across which you want to determine the voltage. This applies whether the circuit is d.c. or a.c.
What is an inductor and its current rating?
An inductor is an electrical component, usually a coil, designed to offer a specific value of inductance (measured in henrys). As the operating current of an inductor affects its inductance its inductance value (inductors are not linear devices, due to their hysteresis characteristics) is normally expressed for a specific range of operating currents.
How much will it Cost to upgrade an electricity supply from phase 1 to phase 2 for a Melbourne home?
If you are asking whether it is possible to upgrade from single phase to two phase, then you should understand that a two phase system is archaic and will not be available from your electricity supply company. If you are asking whether your company can supply two lines (out of three) it's quite unlikely -they will normally supply single phase or three phase! You can likely upgrade to three-phase if you have a reason to do so -e.g. to operate three-phase motors. As for the cost -you'll have to check that our yourself!
What device may be wired into the starting circuit of a motor to improve the starting torque?
I assume a 3 phase, AC induction motor.
A star delta starter or a soft starter can be used. A soft starter is better compared to a star delta starter, but it is more expensive.
Why should network cables and other low-voltage writing not pass close to fluorescent lights?
Fluorescent light emit a small amount of electrical noise, which can be picked up by external wires if they are too close.
Which AC input transformer required for 5volt dc output power supply?
It depends on the required output current, load rejection factor, and ripple. Also, efficiency enters into the picture.
How can you connect current transformer to ammeter in three phase?
You use three CTs, one per line conductor, each feeding a separate ammeter,
What is the armour cable size for 45kw 3phase ac motor 2965rpm?
At 2965 rpm it sounds like an induction motor for a 50 Hz supply.
A 45 kW motor would draw about 55 kW from the supply with a power factor of 0.85, so that is 65 kVA, and on a 415 v 3-phase supply that is a current of 90 amps. For armoured XLPE cale the size needed is at least 16 mm2
Probably 25 mm2 would be preferred for a permanent installation but it would depend on how the cable is installed, how much free air movement there is around it etc.
Why can you ignore the resistances of wires in circuits with lower current?
Actually, it depends on the resistance of the other components in the circuit, and not so much on whether or not the total circuit current is low or not. Often, conductor resistance is ignored because it is so much lower than the active components that it does not matter. In a circuit with low resistance components, however, conductor resistance can be important, even if the total current is relatively low, because the voltage drop over the wire becomes a significant part of the overall circuit.
To answer the specific question, even though its slightly misleading, conductor resistance does tend to become important in high current circuits because the voltage drop over the conductor (Ohm's Law: Voltage is current times resistance) can become high. Even in high current circuits, however, if the conductor is substantially less resistive than the components, the tendency is still to ignore it, except that you have to account for heating of the conductors along with heating of the components.
Is 3 phase induction motor is self starting?
Yes, that is one of the major advantages of a three-phase induction motor.
How do you turn a unipolar stepper motor into a bipolar stepper motor?
5 wire: For 5 wire motors you need to determine which wire is the common wire.
To do that use an ohm meter to find the wire that has the lowest reading to all 4 of the other wires that is the common. You will not connect anything to this wire in bipolar mode however to figure out which wires must be paired we need to hook it up to the positive terminal of a power supply or battery. Hook up one of the other 4 wires to ground. Note how hard it is to turn the motor shaft. Leave this wire connected and hook another wire to ground. Check how hard it is to turn the motor shaft. Disconnect that wire and connect to the next wire. When one of the three other wires is connected the shaft will turn with almost no effort. That wire and the first wire connected to ground are Motor phase A The other two wires should be paired and would be phase B. A pair of vise locks on the shaft will make it easier to turn the motor shaft. A vise helps to hold the motor. It does not matter that the center of the coils are connected. That point will always be the same voltage for all power connections to the motor at about 1/2 voltage supply. The common wire should be left unconnected.
6 wire: With the six wire version hook up the ohm meter to one wire probe the other five wires. three wires will be open they will be phase B. The other two will show a resistance one about twice that of the other or nearly the same value. If the values are the same the first wire you connected to was the center tap and is not used. The other two wires are phase A. If the values are different The low resistance is the center tap and is not used. The first wire you connected to and the high resistance wire is Phase A. Now connect the ohm meter to one of the wires that had an open circuit. Test the resistance to the other two wires and use the same logic to determine which wires are phase B.
8 wire: First you need to sort the wires out to coil pairs. Use your ohm meter. Hook up to one wire and check the other 7. Only one wire should show as connected. That is the other wire for coil 1 pair. Do the same for the remaining wires until you have identified all 4 coil pairs. Now use a power supply and hook one wire from coil 1 to positive. Hook the other wire from coil 1 to negative. Note how hard it is to turn the shaft. Leave coil 1 connected. Hook one wire from coil 2 to positive the other to negative. Turn the shaft. Reverse the wires to coil 2. Turn the shaft. Try the other two wire pairs. One connection for one of the wire pairs will allow the shaft to turn with almost no effort. When that pair is reversed the effort to turn the motor will be very hard. That pair of coils will be phase A. Hook them up so it is very hart to turn the motor shaft. Mark the polarity for phase A coil wires. Disconnect phase A wires and connect the other coil wires up to the power supply. Turn the shaft. Is it easy or hard. If it is easy reverse one of the coils. It should now be hard to turn the motor shaft. Mark the polarity for phase B coil wires. The phase coils can be connected in parallel or series. Just make sure you maintain the connection polarity that gives the highest torque to turn the shaft.
With an AC and a DC voltage source in series, the DC voltage can be added to the RMS value of the AC voltage to give the effective voltage.
What is the difference between audio generator and signal generator?
Audio generator will produce some range of frequency and level of a test signal meant for audio.
A signal generator will produce a test signal but is a more general classification. For example a audio generator is a signal generator. When you know what type of signal you are looking for, then a signal generator will be called that type of signal. all depends on what you are testing.
examples:
video -> video signal generator
audio -> audio signal generator
What are the applications of equivalent circuit of a single phase transformer?
Equivalent circuits allow you to treat the transformer itself as being 'ideal', while treating its losses, etc., as external elements to which the normal laws of networks apply.
Why voltage of transformer go up beyond the set voltage when carrying out transformer test?
Transformers without regulators in them will output voltage depending on the voltage coming in.
For instance if you have a 230v to 110v transformer then you will have a ratio of 23:11
this means for every 23 turns in the transformers primary side you will get 11 turns on the secondary, so if you have an input voltage of 247v then the output voltage will be around 118v, conversly if you have an inout voltage of 221v then the ouplut voltage will be around 106v.
What is the role of power transformers in power systems?
Power transformers are used in electricity transmission and primary-distribution systems. They are used to increase (step up) the voltage supplied by generators at power stations to the extremely-high voltages necessary for electricity transmission and, at bulk power centres, to incrementally reduce (step down) those voltages to lower levels.
Transmission is only possible at high voltages because, for a given load, the higher the voltage the lower the resulting load current. Reduction in load current results in manageable voltage drops along the line, conductors of practical size/weight, and minimises the line losses.
Which current does a street lamp use ac or dc?
Unless the street lamp is a self-contained, battery-operated, solar-charged model, it almost certainly would be an ordinary AC-powered light.
First of all, let's get the terminology correct -there is no such thing as a 'voltage difference'. 'Voltage' is another word for 'potential difference', so 'voltage difference' would mean 'potential difference difference', which doesn't make any sense! So you should be referring to the voltage across the holes of an outlet, not the 'voltage difference' across those holes.
The voltage produced by a generator in the power station produces a much greater voltage (up to 30 000 volts) than the voltage that appears across your outlet (120 V in North America or 230 V in Europe). Furthermore the generator's voltage gets increased even higher (hundreds of thousands of volts) before the electricity transmission can take place. Eventually, those high voltages are reduced, using transformers, until it reaches your outlet.
What is the function of the triggering circuit in an oscilloscope?
It's for analyzing aperiodic waveforms.
An aperiodic waveform is one that occurs at...well, random intervals. The sine wave of a powerline is a periodic waveform: it runs all the time, so the period of the wave is either 0.0166 seconds (60 Hz power), 0.02 seconds (50 Hz power) or 0.0025 seconds (400 Hz aircraft power).
If the wave just comes up whenever it feels like it, that's an aperiodic waveform, and it's much easier to analyze them if the sweep only starts at the beginning of a wave.
Can a a electric substation in a city use transformers to increase the power output?
No! A transformer changes voltage levels, not power levels. In fact, the output power of a transformer is actually a little lower than its input power, due to the efficiency of a transformer.
