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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
When was the national grid set up?
The answer to this question will depend very much on which country the question is asking about?
Can full wave rectification be done by two diodes?
Yes, if the transformer secondary is centertapped.
How do you calculate full load for 500amp welding machine?
You need the input voltage and maximum input current specs found on the name plate.
Is The current in a circuit directly proportional to the impressed amperage?
I'm not sure what you are meaning by "impressed amperage", but current is measured in amperes (thus amperage), so I would say you're probably referring to the same thing (an apple = an apple kind of statement).
Out of step is also called power swings. OOS can be tripping or blocking. Power swings are just that - power changing direction, which results in oscillation between generators at different locations in the bulk electric system. At the "electrical center" of the system, the voltage will collapse to near zero during a power swing (similar to the standing waves formed by anchoring one end of a jump rope and moving the other end up and down). Out of step blocking is often used at such locations to keep relaying from tripping for this false close in three phase fault condition. Out of step tripping is used to island certain locations from others when power swings are too fast.
What is nonsinusoidal currents?
"nonsinusoidal current" is any current that is not sinusoidal - it could be a wave such as a square wave, triangle wave, etc. DC (direct current) is non sinusoidal. This term is often used in reference to currents that you "would expect" to be sinusoidal (such as the current to your house is sinusoidal at 50 or 60 hz) but aren't - such as transformer inrush current, magnetizing currents,...any current with large amounts of harmonics.
AC current is also (generally) not sinusoidal due to the way power supplies only conduct from the input when the rectifier filter capacitor needs to be recharged during each line cycle. That results in a pulsing current, even though the voltage is mostly sinusoidal.
What is the difference between rectified ac and dc?
Dc or direct current is and electrical current flowing in only one direction. Examples would be batteries or solar cells. ac or alternating current is current flowing or "alternating" in more than one direction. An example is the outlet you plug a cord into to power devices or appliances in your home or businesses. rectification of these is simply the conversion of one to the other, because sometimes the device your trying to power needs one type of current and the only available type current is the other. So in essence you have to convert or "rectify" one power source into one usable for your purposes. An example of this is a laptop. A laptop or any other type of mobile computer uses a battery for power, which is direct current. In order to keep your laptop battery charged you must plug in the ac adapter in a wall socket near by. The problem is your laptop uses direct current and what you are about plug your adapter into to power or charge your mobile computer is going to be alternating current. The two are not interchangeable. The solution lies with the actual ac adapter itself. If you'll notice there is a small to medium size box in the middle of the cord. The box is designed to convert, or "rectify" the type of current going from the wall to your mobile computer from ac to dc power.
What determines which one of the terminal of a rheostat in positive when connected in a series?
Electron flow is from negative(-) to positive(+), the rheostat would have to be on the negative side for the device being controled, before the device, e.g. light bulb.
AnswerIt doesn't matter. Rheostats don't have positive or negative terminals.
Is any power lost when converting from dc to ac?
Of course, when we convert dc to ac, we need to feed an electronic circuit using transformers that have a range efficiency between 80 to 90, depends on the iron composition of the frame.
What is skin effect and methods to reduce skin effect?
with the inductance of a conductor it tends to push current flow to the outside
to reduce the effect you make the conductor hollow
with 80 hz and Cu conductor the current is in the outer 8mm or so.
AnswerYou cannot really reduce the skin effect in ordinary conductors; for the sake of economy, you can use tubular conductors. Tubular conductors do not reduce the skin effect, but merely saves copper (if little current flows towards the centre, why have a centre!). However, special, insulated, conductors ('litz' wire) woven or braided in various patterns, can be used for special applications (e.g. high-frequency transformer windings) up to around 1 MHz or so. Because each strand has a very small cross-sectional area, and is insulated from its adjacent conductors, the skin effect is negligible compared with if it were a solid conductor.
What does a protection diode do?
It will conduct electricity when the voltage across its terminals reaches a certain value. Once the over voltage is extinguished, the protection diode becomes an open circuit again.
Therefore, you need to connect a protection diode between both wires to be protected (differential mode) and from each wire to ground (common mode).
Protection diodes are primary protection devices (fast reacting), but they cannot handle too much current. That is why they need to be used with secondary protection devices (fuses and gas arrestors) to provide better protection.
A relay is an electrically actuated switch. There are a number of contacts actuated by a soleniod. When the solenoid is energized the position of the contacts changes, "throwing" the switch. The terminology of switches and relay contacts is as such: (number)p-(st(no/nc)/dt) The number followed by p is the number of poles. This is the number of independent "switches" in the unit. The (number)p may be replaced with sp (single pole) meaning 1p or dp (double pole) meaning 2p. ST stands for single throw, there is only two contacts for each pole. ST is usually suffixed with NO or NC in relays standing for normally open and normally closed. Normally open contacts conduct when the solenoid is energized. Normally closed contacts conduct when the soleniod if off. DT stands for double throw, meaning that there are 3 contacts per pole: a common contact, a NO contact, and a NC contact. So: a 3p-st NO relay has 3 switches that close when energized. a sp-dt relay has one 3 contact switch. An electrically actuated 3-way switch, if you will. a dp-st NC relay has one switch that opens when the solenid is energized.
Why buchholz relay installation is slidely incliend?
If you look carefully at a Buchholz Relay, it is not
'slightly inclined'. In fact, it is perpendicular. However, it is located in an inclined pipe between the transformer and the oil expansion tank above the transformer. The reason why the pipe is inclined is to allow any gas generated by a fault in the transformer to move upwards towards the expansion tank. This gas will then collect inside the relay, causing the warning float to move downward and trigger an alarm inside the substation.
Read more: Why_buchholz_relay_is_slightly_inclined
What is the load side of a transformer?
The load side of a transformer feeds the device, such as a light or motor. It is the output of the transformer. The input, or line side, provides the voltage that is to be transformed, either up or down, to supply the load side.
AnswerA transformer's primary winding is connected to the supply voltage, and the secondary winding is connected to the load.
Current ratio would normally increased by?
The current ratio is an accounting measure of liquidity and is defined by:
Current Assets / Current Liabilities
In order to increase the current ratio, either increase current assets (e.g. cash, inventory, accounts receivable) or to decrease current liabilities (e.g. accounts payable, notes payable).
Why shunt field resistance is high incase of dc shunt motor?
Back emf is proportional to the flux in the field winding.
Flux in the field winding is proportional to the mmf in the winding.
mmf = current passing through the winding * no of turns in the winding
To attain the required mmf we can use more current and less turns ( or ) less current and more turns .
As the power loss in the field winding is considered it is
Power loss = Square of voltage / resistance
As the voltage is constant for a high resistance it is possible to have less losses. So we prefer for high shunt field resistance.
As the field resistance is high current is less , so no of turns in the shunt field will be more to attain the required mmf.
Answer'Shunt' is an archaic term for 'parallel', so the shunt winding is in parallel with the supply voltage which means its resistance must be relatively high to limit the current passing through it.
Incidentally, the back-emf. is not proportional to the flux, but to the rate of change of flux.
What are Examples of ipod closed loop system?
Consider it a kiosk as such. You will not be able to be "kicked out to the web", it is like a website without outside links. You can interact with the iPad through touch, but all links remain with the site.
Magnetomotive force establishes magnetic flux in a magnetic circuit, which is opposed by the reluctance of that circuit. It's easy to relate these magnetic quantities to the equivalent quantities in an electric circuit:
- magnetomotive force is equivalent to electromotive force
- flux is equivalent to current
- reluctance is equivalent to resistance
A magnetomotive force (mmf) is created whenever an electric current passes through a coil. It's magnitude is determined by the product of the current (I) flowing through the coil and the number of turns (N): mmf = I N
The unit of measurement of magnetomotive force is the ampere. Although, to prevent it from being confused with the unit of measurement for current, it is usually spoken as "ampere turn".
What would be the effective capacitance if two capacitors are connected in parallel?
A: the capacitance will increase. in series it will decrease accordingly
CPARALLEL = Summation1-N (CN)
CSERIES = 1 / Summation1-N (1 / CN)
Who is the industry leader in electric lamp bulbs and tubes?
General Electric Lighting is widely acknowledged as the industry leader, a position it has maintained for years. The firm sells about 500 million standard incandescent bulbs and 10 million compact fluorescent bulbs
Can a charged capacitor be used as an energy source?
Yes, but typically for a short period of time depending on the capacitance and the load. For example in a motor application a starting capacitor will charge and then discharge to provide the extra boost to get a motor started.
Yes, but only for limited periods of time or for very low power loads. For example modern CMOS static RAM chips need only a few microamperes and often much less to hold data. This can frequently be supplied for quite some time by a simple supercapacitor. I once worked on an avionics unit that had to handle main powerbus dropouts of up to 15 minutes duration inflight, then resume operation when the powerbus came back up with no dataloss. This was handled in the unit's powersupply assembly by a secondary independent switching powersupply for backup RAM power during a main powerbus dropout. While the powerbus was up, it ran the main switching powersupply which supplied various voltages the unit needed including +5V to the RAM, also a large capacitor was kept fully charged to about 170V. When the powersupply assembly detected a main powerbus dropout and before the capacitors for the +5V to the RAM discharged, the secondary independent switching powersupply was turned on and it used the large capacitor as its energy source to supply +3.3V to the RAM to hold data. It could continue supplying this +3.3V backup RAM power until the large capacitor had discharged to roughly 10V, which took a little longer than 17 minutes.
