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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
There are 2 things that can be called a micrometer:
1/ A device for measuring short distances accurately. Typically to better than 1 thousands of an inch (thou) or 0.01mm. They look a bit like a small G clamp, something is placed between the jaws and it is lightly tightened, the thread has a gauge on it so you can see how big the thing between the jaws is.
2/ A very small distance, 1 millionth of a meter. Also written μm. (Or sometimes um.)
Additional Information
The above answer needs to be qualified. In fact, the above answer only applies to American English. In British English,
1. A micrometer is an instrument for measuring small thicknesses or diameters, as per answer 1, above.
2. The unit of measure is called a micrometre.
In other words, in British English, a meter is a measuring instrument, whereas a metre is a unit of measurement.
Explain limitations of the model circuit compared to the actual circuit?
A 'model' simplified circuit is a circuit that performs very closely to a real, usually far more complicated circuit. Model circuits are used to help analyse the behaviour of more complicated circuits. Often, there are various models which make different assumptions about the actual circuit, in many cases offering various degree of simplification. For example, there are several different model circuits that represent a transformer, with the simplest model assuming that the transformer has absolutely no losses whatsoever, and the more complicated models taking into account those losses. Another example of a model circuit is when we represent, for example, an inductor in terms of its inductance and resistance with these quantities being connected in either series or parallel.
How do you read motor circuit diagram?
You have to learn how to read it. First, you must find out and learn what the symbols stand for and something about the other things that are on that diagram. That diagram is just a road map with a lot of signs. You need to learn the sign language for that diagram.
What is reactive power in three phases system?
Reactive power occurs in an AC system when it has a load with a poor power factor such as an induction motor.
The power delivered is less than the voltage times the current by a factor called the power factor.
The real power and the reactive power combine according to Pythgoras, in other words if they are represented by two sides of a right-angle triangle, then the hypotenuse represents the volt-amps. In the equation kW is the power in kilowatts, kVAR is the kilovolt-amps of reactive power, and kVA is the kilovolt-amps:
(kW)2 + (kVAR)2 = (kVA)2
What is The process of changing a half-wave or full-wave rectified voltage to a constant dc voltage?
It is smoothing
Why does the rotation of the motor reversed when change the polarity across the main winding coil?
When changing the auxilary face winding connection the current flow in the winding is changed so that the rotating emf direction is changed . Thats why the motor rotates in opposite direction.
Which direction does a motor spin?
All motors have the ability to rotate in either direction. The motor has to be connected to additional equipment to make this happen. In a three phase motor a reversing magnetic contactor is used and in single phase motor usually a drum switch is used.
Which is more dangerous high-current or high-voltage?
current is the killer not volts, you can have thousands of volts but with out flow (current) the danger is minimal, but if you have voltage its very easy to induce current so be careful and let a professional take care of it if you do not know what you are doing.
What material is a bus bar made of?
with dc solid copper or aluminum
with 60 Hz ac inductance will force current to the outer surface if the conductor
so the busses in substations are generally aluminum or copper tubing
power transmission lines are steel cable with 1/8" aluminum sheath
high frequency or rf busbars and wire is generally tubing that is silver plated
the inductance lets current flow only in the very thinnest skin of the conductor
The primary reason that high-voltage outdoor busbars in substations are tubular is to provide them with mechanical strength.
If they were solid, and of equivalent cross-sectional area, then they would not be self-supporting to the same extent as tubes, and would require supports that are much closer together.
The 'skin effect', however, iscertainly taken into account when determining optimum diameter/thickness of these busbar tubes because the skin effect becomes more important with large-diameter conductors.
Indoor busbars, such as those found in metal-clad switchgear are indeed solid and, usually, of rectangular section, with supports that are much closer together than for outdoor, tubular, busbars.
At 60 Hz in copper, the skin depth is about 8.5 mm. Because the interior of a large conductor carries so little of the current, tubular conductors such as pipe can be used to save weight and cost.
2000MCM wire has resistance about 23% higher at 60Hz AC than DC
source NFPA bulletin 7 sometimes called NEC
for uk and sqMM and 50hz i have added a link
insignificant for someone who works for power companies is understandable
since fuel cost is insignificant it is passed right on to the customer
IR losses are insignificant also
this is why a 50KVA transformer on the pole supplies 7-10 houses with 200A services 4/0 copper into the house #2AL drops with #8 solid copper going to the poles that feed 7 of the 10 drops
power company is a misnomer in the USA it is a power DISTRIBUTION company
hence fuel cost is insignificant ir losses are insignificant.
Just swap two of the phases over.
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Care must be taken when swapping wires on a star delta system.
Reversing the wrong set in the motor box and getting the wrong wires could accidently reverse the wrong set of windings.
This would cause the star magnetic to be rotating in the correct rotation and then when it switches to delta the motor tries to reverse causing a locked rotor condition and spiking the voltage very high and hopefully tripping the overload protection.
The correct place to swap the two legs is at the supply side of the star contactor.
Why is a power supply dangerous even after the power is disconnected?
Power supplies have large capacitors in them. These capacitors store electricity in them even when mains power is shut off. If you were to touch the connections on the bottom of the capacitors, you could receive a potentially lethal shock. For this reason, you should never disassemble a power supply unless you have received training in how to properly discharge the capacitors.
More answers
Because of the big electric charge held within the capacitors inside it.
Computer power supplies have very large capacitors (elements that store charge) that could give you a very powerful shock if you managed to discharge them. They're like batteries that let go of all their charge at once.
Capacitors store energy (power) for an indefinite time. Touching both leads of any charged capacitor can give you a real good jolt.
For example, the tube of an old-fashioned television set is a giant capacitor in electronic terms: even though a TV may have just been switched off and unplugged, there may still be about 40,000 volts stored up in its cathode ray tube (CRT) that will cause great harm unless proper precautions are taken to discharge it safely.
What electric device smooths the pulsed DC to a smoother DC?
In power supplies both coils and capacitors are used to smooth the pulsing DC output.
Temperature affects the resistivity of materials which, in turn, affects their resistance. For pure metal conductors, their resistance increases with temperature. As an inductor is often made from a coil of copper wire, its resistance will increase whenever its temperature increases. If it is important for the resistance to remain constant over a wide variation of temperature, then alloys, such as constantin, are used instead of copper. These alloys maintain an approximately-constant resistance over a wide range of temperatures.
Comparison between Yokogawa Emerson DCS?
I've spent a few years involved in the specification and requisitioning of a large (10 000+ I/O) Honeywell DCS, and before that I spent 2 years doing the same for a large yokogawa DCS.
When it came to both the hardware performance/capability and the quality of engineering, there is no comparison, Yokogawa won by a long way. I can't comment on price.
A few gripes I've had with Honeywell:
1) Inter-plant signals - signals had to be hardwired between controllers if they are to be passed from one community/domain to another to maintain a scan rate of 1 second. Sort of takes word 'distributed' out of DCS.
2) Graphics are very limited in the number of tags/variables and many of them had to be split up - much to the operators dismay.
3) Sheer volume of unnecessary documentation - for example, they submitted a 50 page document for review describing the typical software for a differential pressure indication.
The industry has changed a lot of the past few years especially with increased pressure for good resources so I'm sure all DCS vendors are subjected to the same engineering quality problems. Therefore will not go into the engineering issues we had.
Hope that helps.
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I am not fully agree with the above explaination. You may be a Yokogawa supporter, but don't just give false information to other.
1) Inter plant connectivity can be achieved through DSA (Distributed Server Architecture) configuration.
2) Graphics are built for man-machine interface only. Off course, if you want the whole plant to be in one graphic page then that's create performance issue. If you built and arrange your graphic pages properly, there should not be any issue raised.
3) Nobody will agree that 50pages are submitted for a pressure loop description. I have seen SDM (Software Design Manual) from Honeywell used for a particular project. It was nice and explanatory.
regrds
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The one u said on the new Honeywell DCS ... EPKS ....
I am using Honeywell for a long time.... but as a customer we are looking at the work quality
and products ..... I am not sure about Yokogawa but I believe it does have similar problem like Honeywell...
Products problem:
1. Too many bugs
2. No experties in Malaysia for new products
3. SUpport team lack of compentency
4. Product reliability and availability weak...
and all of this contribute more cost to customer where they had to pay them just to fixing things that they also not really expert...
this the reason why user keep asking and concern on the cost for them to repair.
anyway .. both system has their own weakness... so the only ways is how we ensure they
deliver the good quality one..
If you use a UK 240v to 110v yellow transformer and plug in to us 230v 60hz what happens?
It depends on the device itself. If it is an ordinary light bulb or the filament type, it may glow very lightly and it will convert electricity to heat rather than light.
If your device is an electrical motor, it will draw more current than normal and will probably burn out.
In science to prevent overloading in a parallel circuit you could install a what?
you can use a fuse or circuit breaker
What is the place in the home that contains the circuit breakers?
The ciruit breaker box. This is usually mounted near the main power source in the home. Try the basement, the back porch, or near the kitchen. If all else fails, go outside and look where the power meter is. The breaker box should be nearby inside the home. In many homes the electrical panel is in the basement. In homes that do not have basements the electrical panel is placed in the garage.
When was the voltage discovered?
No-one 'discovered' the volt. The volt was named in honour of an Italian physicist, long after his death.
It means Current Transformer is used for measurement of electric currents, together with voltage transformers
What do ground do in a circuit?
Circuits are on the ground for a few reasons one is to prevent contact with dangerous voltage if the electrical insulation fails. Also been on the ground limits the build- up of electricity static.
Frequency to voltage converter IC's?
First of all that's an incomplete question, in fact it could hardly even be called a question. Nevertheless I will attempt to answer what I think the question might be.
A Frequency to Voltage converter simply converts a frequency to a voltage as the name would imply. The voltage output will vary linearly with the frequency input (assuming it was designed properly). They can be useful in devices such as tachometers or speedometers.
Here's one example of a such an IC:
http://www.national.com/mpf/LM/LM2907.html
What size breaker for a 3 phase 230 volt 50 amp motor?
The CEC states for a full load current rating of a motor drawing 50 amps a wire capacity of 62.5 amps is needed. For protection, non time delay fuse is 150 amps, time delayed fuse is 80amps and for a circuit breaker the rating is 125 amp.
What happens to resistance when the conductor diameter is increased?
Simply Stated: As electrons move across a wire, they constantly collide with atoms making up a wire. These collisions impede the flow of electrons and are what cause the wire to have resistance. Thus, if the diameter of the wire were larger, it would only make sense that the electrons don't collide as much, therefore creating less resistance due to a larger wire. This is all in accordance to Ohm's law. The resistance is the ratio of the voltage difference across an object to the current that passes through the object due to the existence of the voltage difference. If the object is made of a material that obeys Ohm's Law, then this ratio is constant no matter what the voltage difference is.
Consider a copper wire that passes some amount of current, say 1 A, when a voltage difference of 1 V is applied between the ends of the wire. Now consider an identical but separate wire connected across that same 1V potential difference. You would expect that it would also conduct 1 A.
Now think of joining those two wires together side by side into one, thicker wire. It is reasonable to expect that this wire should carry 2 A of current if the potential difference across the wires is still 1 V. Thus, the new, thicker wire will have a reduced resistance of 1/2 Ohm compared to the original wire with its resistance of 1 Ohm.
Basically, a thicker wire creates additional paths for current to flow through the wire.
What is the difference between a single phase and a 3 phase circuit?
Single phase power has a sine wave voltage that crosses zero before reversing its polarity. In the region near the zero-crossing there is not much power. At zero there is none at all. So single phase loads often need some trickery to deliver output in this area. Often it is just the inertia of the motor or appliance. Three phase power is always delivering power on one of its phases, and is thus preferred for generators, motors, machines and appliances that use lots of power. If the application is large power, or small power with weight restrictions (like automobiles!) Three Phase is preferred. DC (Direct Current) is the next step up for smooth high-power devices but requires rectification, regulation and smoothing to be useful.
Another problem with DC is that, for efficient long distance transmission, it cannot be simply converted to much higher voltages than the voltage at which it was generated at the power station. Similarly DC cannot be transformed down to safer, much lower mains voltages for use by consumers.
AC (Alternating Current) is used for high power generation and distribution because it can easily be transformed, using Transformers, to achieve very efficient power transmission over very long distances and can then be transformed down to low voltages for distribution to consumers. Two phase, and higher multi-phases are also used but very rarely.
