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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
How do you measure inductance?
You can use a LCR (Inductance, Capacitance, Resistance) meter if you can find one.
How do you wire a star delta motor?
This answer has been temporarily closed to changesbecause so many askers have been repeatedly splitting-off variants of the question such as "Can you give me simple diagram for star-delta starter".
Please note: diagrams cannot be included in answers.
The answer given includes plenty of details for anyone to be able produce a simple diagram showing how a 3-phase motor can be wired in star and delta configurations.
AnswerTo be able to wire a 3-phase motor either in star or delta, all 6 ends of the three sets of coils, called "windings", have to be exposed with suitable connection terminals.
The windings are often labelled A1, A2, A3 and B1, B2, B3, where "1", "2" and "3" denote the separate phase windings and "A" and "B" denote the beginning and end of each winding.
Another way of describing it is to say that the separate windings can be labelled:
Winding 1: A1 <---> B1. Winding 2: A2<---> B2, Winding 3: A3 <---> B3.
In star configuration either all the A's or all the B's are connected together and the 3-phase supply (consisting of three separate "phase lines" labelled L1, L2, L3) is connected to the remaining three connectors. For example, if you connect B1 to B2 and B2 to B3 to form the center of the "star" then you must connect supply L1 to A1; supply L2 to A2 and supply L3 to A3.
In delta configuration, connect B1 to A2, B2 to A3, B3 to A1. (If you draw that out as a schematic diagram, it will be a triangle.) Then connect supply L1 to A1; supply L2 to A2 and supply L3 to A3. (Exactly the same as the supply lines were connected before, for the star configuration.)
The initial making of those connections in "star" - and subsequent changing into "delta" after the motor has built-up sufficient speed - would all normally be handled by a "star-delta motor starter" unit. A good tip: before you ever start hooking one up, study its schematic wiring diagram carefully to be sure you really understand which of its terminals connect to which motor terminals, and where to connect each line of the 3-phase service cable.
Note:
Some 3-phase motors use an alternative way of labelling the windings: 1A, 1B, 1C and 2A, 2B, 2C.
Electronic motor-control systems, which offer soft-starts in DELTA configuration, are now replacing the use of manual or semi-automatic star-delta starters.
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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.
Before you do any work yourself,
on electrical circuits, equipment or appliances,
always use a test meter to ensure the circuit is, in fact, de-energized.
IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.
What is the function of an electrical load of a circuit?
its the alternatingg current
AnswerA load is any device, or group of devices, that draws energy from an electrical supply.
For example
- the filament of a flashlight is the load supplied by that flashlight's battery.
- a loudspeaker is the load supplied by an amplifier.
- your residence represents a load to your electricity supplier's distribution transformer. a whole geographical area represents the load supplied by the electricity grid.
In another use of the term, we say that a generator or transformer is 'loaded' when it connected to a load, but is 'off-load' when it is operating but not connected to a load.
What is the use of two capacitor with crystal in 8051?
The "requirement" of using two capacitors with the crystal in the 8051 is complicated, and based on many factors, such as series resistance, the design of the parallel resonant feedback circuit, stray or parasitic capacitance, startup stability, etc. Insight can be gained from Intel's Application Note AP-155 but, in the final analysis, from a purely pragmatic standpoint, the requirement is there simply because "Intel says so". Use the circuit from the data sheet.
Ac power formula and phase value?
Firstly all voltages and currents should be in RMS values. (divide peak values by root 2).
Apparent Power
|S| = VI = (P2+Q2)0.5
Complex Power
S = P + jQ
P = |S|cos(theta)
Q = |S|sin(theta)
theta = phase angle between voltage & current (can be calculated by finding total impedence of the circuit)
Power Factor = cos(theta)
How do you use a PC power supply for a car amp?
You will need old comp power supply.
+12 V is on YELLOW wires.
-(minus) or ground is BLACK
If you have ATX power supply (that one without wires going to power switch on front - all PC now have ATX) you have to short GREEN and BLACK on main (the biggest plug to start power supply.
So use any pair black/yellow to power car amplifier.
What is the use of electric actuated shut off valve?
Means you can shut it off from a distance. Useful either in an automatic system or if you don't want to have someone being around the valve when it's time to shut it off.
Why must power be turned off when measuring the resistance of a circuit?
If an external Voltage is applied to a multimeter while the multimeter`s function switch is in the Ohm meter position then the Ohmmeter is apt to be destroyed or disabled. Therefore the simplest answer is that the power must be turned off in order to avoid damage to the Ohm meter and possibly to yourself caused by Voltages present in the circuit while the power is own. Another reason of course is because a valid Ohm reading can not be obtained while Voltages are present across the resistance that is being measured because the Ohmmeter itself applies a Voltage across the resistance and then a sampling of the current through the unknown resistance is used by the Ohmmeter`s circuitry to cause a calibrated deflection of the Ohmmeter and thus display on the meter`s dial the Ohmic value of the unknown resistance.
For the same reasons as above it is also a good practice to discharge all the capacitors in the circuit after the power is turned off and before any in circuit resistance measurements are made.
Why aren't LED lighting systems replacing fluorescent and incandescent lighting?
LED lighting is replacing fluorescent and incandescent in many cases. LED lighting is much more efficient than incandescent, and about the same as fluorescent. However, LEDs are expensive, requiring a huge initial investment. There are claims they will pay back the investment over time because they last a long time and require low maintenance, but not everyone believes those claims and LEDs have not been around long enough to know.
LEDs, fluorescent and incandescent provide different qualities of light so some sources are better for some applications. For example, only incandescent is full spectrum.
Also, LED lamps can only be made in limited light output for size, due to the problems with removing the heat they generate. Some new LED lamps have fans or other active cooling mechanisms.
Why is it marked 6500k on fluorescent lamps?
If a fluorescent lamp is labeled 6500 oK that is the color temperature of the light it emits.
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The number 6500 refers to the temperature (measured in degrees Kelvin) at which a specific theoretical material (referred to as "black body") will glow the color of sunlight at noon.
What equipment uses a crystal oscillator in its operation?
Your quartz watch, your cell phone, all electronics that uses a computer inside. The quartz crystal forms the time base for the digital pulses.
Crystal oscillators are also used in radio receivers and transmitters to provide accuracy in frequency selection.
In a transmitter it provides the exitation frequency. In the receiver it provides the local oscillator in a superhetrodyne setup.
Multifrequency devices (tunable and channelised radio) take the local oscillator and multiply and divide it, to provide a comparison frequency for a voltage controlled oscillator (VCO). The VCO is then controlled by a Phase Locked Loop (PLL) which holds the required frequency very accurately.
Not usually. The rule of thumb is 300% of the full load amps. The only way that you can check this inrush current is to have a clamp on amp-meter with the setting on Hold. What this does, is sense the highest current at start up and holds the reading on the screen until you release it. If you try and start a motor under a high inertia load the current will rise above a normal inrush level. Disconnect the load from the motor to establish that it is the load that is causing the high amperage and not the motor's internal wiring.
What is circuit diagram for AB plus AB?
Is your question from digital electronics if yes than, AB + AB = AB ;and we can get this by using an 2 input AND gate(7408) where the two inputs are A & B and output will be AB.
Only valid in digital domain.
Can 11kv breaker be installed on 6.6kv line?
Yes. But,circuit breaker are usually rated in terms of current they can interrupt,not the voltage.
What is the power when there are 500mA of current through a 4.7k Ω resistor?
p=i square x r = 500ma * 500ma = .25 * 4.7k = 1175 watts
How many lumens are in a 60 watt bulb?
That depends a LOT on the technology used - some technologies are much more efficient than other (converting a higher percentage of the power used into visible light).
How to prevent overloading of an electric circuit?
Generally circuit overload is prevented by a voltage regulator with a diode wired in parallel with the cathode end at the power source end of the voltage regulator. Some circuits use a fuse to prevent too many amperes from entering the circuit. If the circuit one is trying to protect is from a computer that turns off and on switches to another circuit that uses more power, a relay is used such that the lower power circuit of the computer runs through the coil terminals and the higher powered circuit runs through the switch terminals.
7407 is "Hex Buffers/Drivers With Open-Collector High-Voltage Outputs". Buffers are used to clean up a noisy signal, to change from one voltage to another, or to convert a high output impedance to a low output impedance.
Why ground the neutral of a 3 phase ac motor?
In a three phase motor each leg (3 phases) in the down cycle alternating at 1/60 per second servers as a neutral, you are only required to ground (green) the frame of the motor for safety. This is similar In a single phase motor wired for 240v (2 phases) the same thing happens and you are only required to ground (green) the frame of the motor for safety. From: Ken F
Why fuses melt to prevent circuit overloads?
Fuses "melt" to prevent overloads because that is what they are supposed to do.
Fuses are designed, manufactured, and used to prevent overloads [including short circuits which are the ultimate overload] from overheating conductors [wires] the heat from which will melt and damage the wire's insulation, and if severe enough melt the wire itself, and probably cause a fire.
Conductors/wires can only safely carry a limited amount of current [measured in Amperes (Amps)] before resistance heating comes into play, which must be prevented.
A fuse is nothing more than a wire smaller than the circuit wire it's intended to protect.
Therefore, when the current flow exceeds the ability of the smaller fuse wire to carry it, the fuse heats to the point it melts, thus "opening" the circuit [like an automatic switch], cutting off the flow of current, thus protecting the conductor/wire itself.
As the current carrying capability of the fuse is intentionally designed to be LESS than that of the wire it is supposed to protect is capable of carrying, then the wire is not exposed to unsafe amount of current flow.
Again, fuses melt ["blow"] because they are supposed to!!!!!
Can a 3 pole 100 amp 600 volt disconnect be used for 3 phase 250 volt?
Yes. But if you don't know the answer to the question please hire a professional. The life you save may be your own.
