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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 are the effects of reverse polarization in electronics?
When a magnet's polarity is reversed, the changing magnetic lines of force cutting across wiring induces a voltage in them. This principle is used primarily in motors.
Or perhaps this refers to applying DC power to a device in reverse polarity by mistake. If the device is well designed, it will have a safety diode in the power input area to prevent damage, but if the diode is not present, reversing the power polarity will probably destroy every semiconductor junction in it.
Which relay in the maxifuse relay center of a 1994 Oldsmobile Regency 98 is the ignition relay?
There should be a sticker on the inside of the cover according to my owners manual but there is not a sticker on mine.
How do servo motors alter the RPM?
servo motors change their rpm as instructed
servo motors recieve instructions from a controller to do some action
servo motors generally have feedback so the controller can see where they need to go
servo motors can be electric air or hydrolic powered
an example:
cars have a cruse control
you set a desired speed of travel
the vacuum powered servo motor controls the throttle of the gas engine
the transmission controls the ratio of gearing so the engine is not overloaded
at some point when conditions are satisified you will get the correct speed ...
if you go over the desired speed the vacuum powered servo motor backs off
which eventually controls the differential driving rpm of the rear wheels
here again the servo motor can be considered to be the valve on the vacuum bladder or the entire drive train
Where can you find a current photo of Junk on a Bunk?
Try doing a search of US Military equipment. I was in the Army 30 years ago, and I know it has changed. "Junk on a Bunk" is an old expression dating back over 100 years. It is a display of field equipment laid out for inspection on the bed (cot or bunk).
Why current decreases when increase in viscous friction of dc motor?
I think your question could be rephrased as:
"When viscous friction increases, why does currentdecrease?". Though the latter is not directly dependent on the former, or vice versa, in most motors this is the case. To understand exactly why this happens we need to look into the constructional features of a motor.
All motors have a rotor (the spinning part) and a stator (the stationary part). In linear motors the part the slides along can be thought of as the 'rotor', and the non-moving base, as the 'stator'. The motor spins by causing like poles on the stator and rotor to oppose each other (different motors - AC, DC, brushless - do this in different ways). Read up about this on Wikipedia, HowStuffWorks, or just Google around. For maximum efficiency it is desirable to build the rotor and stator in such a way that there is very little space between the two. This allows a high degree of magnetic flux linkage/concentration between the rotor and stator. Between the rotor and stator is a small air gap. Air, like all fluids, has viscosity (a sort of 'stickyness', if you will). Viscous force appears between two sliding objects which have a liquid in between them. The closer the sliding surfaces, the greater is the viscous force. Viscous force also depends on the area of the surfaces, their relative velocity, and the liquid's properties. For a detailed derivation please refer to any text on fluid dynamics.
Another important motor characteristic is back EMF (BEMF), which is induced in motor coils due to magnetic interaction. The faster a rotor spins, the greater the magnitude od back EMF. Back EMF, as its name suggests, has a polarity opposite to the applied (battery/power source) EMF. It is the back EMF which causes a reduction in motor current, since it partially cancels out the applied EMF : (Applied EMF-Back EMF)=(Effective EMF). Since the coils in the motor have unchanging resistance, a lower apparent EMF imples lower current.
Now let us link these two phenomena:
low speed-->low BEMF-->high current
also;
low speed-->low viscous friction
but:
higher speed-->higher BEMF-->lower current
and:
higher speed-->higher viscous friction
I hope this clears things up.
Rohit de Sa,
Engineer,
Mercedes-Benz,
INDIA
I am not sure whether I am answering your question or if I have missunderstood how you have written it, but I am assuming you mean why do pigeons not get electrocuted when sitting on power lines.
The answer to this is simply that if they are sitting on one wire (one phase) and not touching any other wire (whether is be another phase, earth or neutral). They will not be electrocuted due to the fact that current needs a path to travel. Voltage (otherwise known as potential difference) is the difference in potetnial between two conductive materials. Now a Pigeon would carry current (just like humans) and be electrocuted IF it was to touch two wires at the same time, as it is making itself a part of a circuit (in this case it would be a short circuit.) But if it is only touching a wire that is, for example, 11,000 volts, and is not touching any other conductor of another phase, or earth potential. then the Pigeon itself would be at the same potential as the 11,000 volt line and be perfectly fine.
I hope this answers your question.
It is very rare to have three-phase electricity coming into a residence. One of the wires is probably the neutral (It will be white or black with white stripes.) The ground comes in from a ground rod near the main, and connects to the ground coming from the meter, AND (If the main fuse box is the first disconnecting means,) the neutral and ground bars have to be bonded together in the box.
Why dc voltage increased less rapidly as the dc current increases at three phase alternator?
if you mean in your question Why the generated voltage (AC voltage) increased less rapidly as the dc current increases at three phase alternator?
the answer is:
because the magntic material that used in the 3 phase alternator will reach to satruration case of producing the magnatic flux so will happen a knee saturation curve in (I dc) versus (E ac) curve.
Engr. Emad
What do circuit breakers and fuses have in common?
Both fuses and circuit breakers cut off a circuit from its power supply when the total current through the circuit exceeds the current rating of the fuse or circuit breaker, usually due to a short to ground or overloading of the circuit. Both use materials that respond to heat.
What is the minimum value of high voltage?
Well, the word "high" can have different meanings in various work-areas.
To an electronics specialist, "high" voltage can be anything above 5-10 V.
To a home-electricity-technician, "high" voltage is anything above 50 V.
To an electricity-company-technician, "high" voltage is anything above 230 V.
It is better to ask for a clarification each time you here the term "high voltage".
Who are using in India metering current transformer of which IFS 2.5?
ya mom u stupid noob.
what do u expect from a sentace that doesnt make sense. ure metal.
Field control of dc servo motor?
Relation is
F=pi*i*L*sin theta
But T= r*f
so T= pi*i*r*L*sin theta
pi(flux) and i (current) are changeable while all others are constant.
so
T= k pi * i
Dc servomotor Under Feild Control:
** Armature Current is Kept Constant
** Flux can be varied
The armature current can be kept constant by applying a constant current source at armature winding of DC servoMotor
Torque generated by the dc servo motor is controlled by feild current..
This mode of operation is called Feild Control
What reading would you get if a voltmeter is placed in series across a load in closed circuit?
In series and across the load are contradictory statements. Some voltmeters are really capable of voltage, current and resistance measurements. To measure current the meter either has to be a clamp on type or one that goes in series with the load. You measure voltage drop across the load as described above.
A cold conductor is the insilation for a cold object to keep the coolness inside and the warmess out.
Where maximum power transfer is used?
Tuning antennas is one example.
Speakers in a stereo system is another.
What is the purpose of a motor controller?
A motor controller is a device that controls an electric motor. Most motor controllers require a manual and automatic function, forward and reverse rotation, and speed control.
You've got to be kidding! The answer would require a chapter in a textbook, and not a response in this forum.
What is synchronous reactance?
Synchronous Reactance (in a generator analysis domain) is and equivalent series per-phase inductance term (think per-phase winding resistance) and is mainly composed of the machine's per-phase leakage inductance (equivalent series inductance of primary and secondary flux leakage) and armature reaction (distortion in flux introduced by an armature current in a machine, once again on a per-phase basis; described as a series inductance). L_SyncReac=L_leakage+L_ArmatureReaction. That sort of touches the surface of synchronous reactance.
What is the effect of insulation failure in three phase system?
ground faults are the most common problem.
How do you identify step up or step down transformer from phasor diagram?
Number of turns
AnswerI assume that you have a phasor diagram of a transformer, and wish to identify the primary phasors and the secondary phasors?
For a three-phase transformer, this is fairly straightforward, provided the usual procedure for drawing a phasor diagram has been followed. Whenever you start to draw anysort of phasor diagram, you usually start by selecting a phasor of reference and draw that in the horizontal positive direction. For a three-phase transformer, the phasor of reference is usually the primary phase voltage A (or however else it is identified: R, red, or whatever). The remainder of the primary phase voltages are then drawn, enabling the primary line voltages to be constructed (which, in the case of a primary delta are the same as the primary phase voltages!). So if you can identify the phasor of reference, then you have identified the primary-winding phasor diagram. As the primary and secondary voltages are not usually drawn to scale, relative to each other, you can't assume a turns ratio from the phasor diagram. The labelling might also help, as high-voltage phase and line voltages are identified by upper-case letters, while low-voltage phase and line voltages are identified using lower-case letters -but, remember, these identify high- and low-voltages, not which is primary and which is secondary (primary winding is connected to supply/secondary winding is connected to load).
For single-phase transformer, the phasor of reference is the flux set up in the magnetic circuit, and voltages/current phasors are drawn relative to this. In this case, the primary line and induced voltages are usually identified as V1 and E1, and the secondary induced voltage as E2 (sometimes, the Es and Vs are interchanged). Again, the lengths of the primary and secondary voltages are not necessarily to scale relative to each other.
What does 630mm sq signify in a cable?
It would normally be expressed as mm2, rather than 'mm sq', but it refers to a cable's cross-sectional area in square millimetres -the standard way of measuring cables outside North America.
Why does every electrical circuit need a fuse?
Electrical circuits use fuses to prevent electrical overload to the circuit, and possible electrical fires stemming from the overloaded circuit. A household electrical system can be compared to your home's plumbing. Just as water is pressurized coming from a city's water supply, so is the electricity coming from your local utility provider. The pressure of current is "voltage." The current carrying capacity of electrical wires is "amperage." Just as larger wires can handle a greater capacity of water, so may larger guage/diameter wires handle greater voltage. When you go to your local hardware store, you buy wire based on its amperage. Your home is specifically wired according to the placement of appliances or items that use electricity. For example, the outlet behind your refrigerator is most likely a 20 to 30 amp circuit, as the refrigerator demands a greater volume of electricity to keep the items inside it cool. Whereas, the outlet in your bedroom may only be a 15 amp circuit, as the items you plug into it may be a lamp or clock radio, which do not demand as much electricity as a refrigerator. All the electrical circuits in a home begin at a fuse box. The city's power supply is routed into your home's fuse box. In the fuse box, the electricity is distributed to all the electrical circuits in your home. At the beginning of each circuit is a fuse or circuit breaker. The amperage of a fuse or circuit breaker is based upon the demand of power each circuit must serve. The fuse for the circuit that powers your refrigerator is of a greater amperage than the circuit that powers the lamp next to your bed. Inside each fuse is metal element that melts when the circuit is overloaded and gets too hot. The element in a 15 amp fuse melts at lower amperage than would the element in a 30 amp fuse. If you attempted to plug your kitchen's refrigerator into the outlet in your bedroom, the circuit would get too hot, and back at the fuse box, the element in the fuse at the beginning of that circuit would melt or "blow". This essentially breaks the circuit, stops the flow of electricity, keeps the wires in that circuit from overheating, and helps to prevent electrical fires by doing so. Many homes today use circuit breakers in lieu of fuses. The circuit breaker is a spring loaded switch that turns itself off when a circuit becomes overloaded, or gets too hot. I hope that answered your question.
