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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
Is oA79 diode and oA71 diode are different?
The OA79 is a germanium based diode. This conducts in the forward biased direction at ~0.3Volts. Silicon diodes Conduct in the forward biased direction at ~0.6 or 0.7 volts. If you are wanting to detect weaker signals a germanium diode is a good choice. Nowadays we have good quality low price transistors that can amplify weak signals and the difference between the diodes is not that important in many circuits. Silicon is a very common material so is cheaper than germanium
Modern circuits = Good Pre-Amps = Less detection needed.
Older Circuits = Pre-Amps not so good = Better detection needed.
by chandan
EC 3rd year
What are the advantages of having all power stations connected to the National Grid?
More power on peak times
If one goes down, they can rely on the other power stations
This explanation was found on a OMRON newsletter:
Typically, a relay being tested for UL TV Rating sees an Inrush Load 10 times that of steady state current at 120VAC.
For example, a relay receiving TV-3 Rating sees approx. 30A Inrush for a very short duration at 120VAC and settles to a steady state current of 3A, 120VAC before cycling off. Relays must operate successfully for 25,000 cycles of TV Load Testing to receive a UL TV Rating.
What is the resistance of a torch bulb rated at 2.5 V and 500 mA?
well if the potential difference (voltage) that i apllied across the light bulb is exacty 2.5v (as it can vary due to the interal resistance of th batteris used) then you can use Resistance=Voltage/current (R=V/I) to calculatete resistance. Therefore since 500mA is equivlant to 0.5A R=2.5/0.5=5 ohms.
hopeully that is helpfull
What is a protective resistor?
The protecting resistor is put in series with the LED so that you have a voltage divider - the supply voltage is split across the LED ( max 0.6v) and the remainder across the protecting resistor. So if your supply is 6volts, 5.4v will be across the resistor,
Why capacitor is use in ac machines?
Capacitors are used in ac machines to assist the field during starting.
What is helical winding in transformer?
Helical winding is helically wound around the cylindrical generatrix leaving a duct gap of 4.5-6 mm wide between two adjacent turns around the height.
A turn of helical winding consists of several parallel rectangular conductors flat-wise and close to each other in the radial direction of the winding.
For uniform distribution of current between the parallel branches, transposition of conductors is used.
In the above diagram the transposition of helical winding turns in 3 places along the height: in the middle- the so called middle transposition (a) and the two group transposition (b),(c) are made so that the winding is divided along its height in approximately equal parts.
the no. of parallel conductors in one turn of a helical winding usually varies from 6-20. The helical winding is widely used in low voltage transformers of medium and especially of high voltage.
Why unity power factor is not economical?
If you have a poor power factor (say .8), and your local utility requires you to have .95pf or better, or be charged extra due to the poor power factor, there is no economic reason to buy more equipment to bump your power factor up to 1.0 as opposed to .95. Once you're above .95, you're just fining yourself.
- Unit Substitution
: Remove suspect part and fit ‘known working’ spare.
Does silver that has oxidized conduct electricity?
Not especially well. However, the oxidation is usually limited to the surface, so the pure silver "core" will still conduct.
Need of a voltage regulation in power system?
no maintain voltages from no load to full load depending on demand and to reduce losses
What is the winding up petition?
A winding up petition is a legal document used in England to initiate the process of closing a business down. These petitions are used by people or companies owed a significiant amount of money by a business as a tool to recover debts that are seriously past due.
Why does an oil furnace require a step-up transformer?
An oil furnace has a step up transformer to generate a spark to ignite the oil spray at the tip of the nozzle.
What is the 11kv phase to earth voltage?
6350.8 volts AC rms.
The phase to earth voltage is
( square root(3) ) x lower than the phase-phase
voltage on a 3 phase system.
A saw tooth wave form superimposed over a square wave form is TPZi wave form.
Most of the Inverters use this technology instead of pure sine wave form of out put.
What are feeders in power system?
"Feeders" are conductors which carry electric power from the service equipment (or generator switchboard) to the overcurrent devices for groups of branch circuits or load centers supplying various loads.
How current increases when the load increases in a generator?
Power is voltage times current. If you want to maintain constant voltage and yet increase power, then current must increase. Its simple math.
What is needed to perform a no-load bench test?
A bench and no load! Whatever you are testing has no load. It might be a generator or a motor for example. If a motor it wouldn't be connected to anything. If a generator it would have nothing plugged in.
How the three phase rectification is achieved?
You achieve three phase rectification with a three phase rectifier. There is one in the alternator of you car. You have three windings, connected delta, so there are three terminals. Three diodes are connected to these terminals, anodes towards the terminals, cathodes common and connected to the battery. Three more diodes (for a total of six) are connected to the terminals, cathodes towards the terminals, with the anodes common and connected to ground. At any one moment of time, one winding provides voltage to cause two diodes to conduct, charging the battery. As the alternator rotates, the windings and the diodes take turns, effectively providing a three phase AC to DC power source to the battery.
If you look closely, there is another set of three, smaller, diodes connected as well, anodes towards the terminals. These diodes provide power for the integrated regulator, but the six main diodes are large and heatsinked into the frame of the alternator.
What is compounding curve in synchronous motor?
The operation of a synchronous generator delivering power to a constant power-factor load is demonstrated by means of compounding curves. A compounding curve shows the field excitation needed to maintain rated terminal voltage as the load is varied.
