0
Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
Why earth cable used along with the 11kV power cable?
If you are referring to an 11-kV underground cable, these are normally armoured and, in the case of older cables, have a lead sheath to prevent moisture ingress into the cable. The lead sheath and metal armour are earthed to ensure that, in the event of mechanical damage to the cable, there is a low-resistance path back to the source to sufficient earth-fault current flows in order to operate the circuit's protective system. Overhead lines do not normally have a separate earth conductor.
Why in DC it is called as Resistance and impedance in AC Circuits?
Resistance applies to both d.c. and a.c. circuits, and is determined by the resistivity, length, and cross-sectional area of a conductor.
In d.c. circuits, resistance is the only opposition to the passage of current. However, in a.c. circuits, the flow of current is opposed, not only by resistance, but also by reactance. Reactance is caused by a circuit's inductance or capacitance, or both, and varies with the frequency of the supply. Like resistance, reactance is also measured in ohms.
So, in a.c. circuits, the combination of resistance and reactance is called 'impedance'.
Impedance is not the algebraic sum of resistance and reactance, but the vectorial sum. So if, for example, an a.c. circuit had a resistance of 3 ohms and a reactance of 4 ohms, the impedance would be 5 ohms, not 7 ohms.
What measuring instrument is used to measure potential difference?
To Measure Voltage or potential difference you can use volt meter, there are diferent methode to measure DC voltage and AC Voltage.use a AVO meter and you can choose Voltage in each voltage range on the selector.a Volt meter instrument you can find it by manual methode and digital .Dont forget to read manual book before you will measure the voltage.
Comment
'Potential difference' is exactly the same thing as 'voltage'; they are synonymous.
What are the factors effect on the value of impedance when connect inductor and resistor in series?
Impedance (expressed in ohms) is the vector sum of a load's resistance and inductive reactance.
Resistance is determined by the length, cross-sectional area, and resistivity of the conductor, while the inductive reactance is affected by the inductance of the load and the frequency of the supply.
Resistance can also be affected by the 'skin effect' which causes the current to flow towards the surface of a conductor, reducing the effective cross-sectional area of the conductor. This is called 'a.c. resistance', and increases with frequency (at normal mains frequency, a.c. resistance is not markedly greater than d.c. resistance).
How do you calculate kwh in three phase?
In exactly the same way as you do so for a single-phase load. It's the product of the power of the load, expressed in kilowatts, and the during of operation, expressed in hours. (And the symbol of kilowatt hours is 'kW.h', not 'kwh')
How does a buck-boost transformer work?
A Buck Boost transformer is an auto transformer with a small primary to secondary voltage difference. It effectively adds or subtracts a few windings to the secondary to increase or decrease voltage.
Here is an example: Say I have a 110 v and want 120 v; I have an auto transformer with 120 windings, tapped at 110 and 120. If I connect the 110 connection to my incoming 110v line, the voltage at the 120 tap will be 120v.
How do you calculate capacitance to improve power factor in a industry?
A capacitor used to correct a lagging power factor has to take the right number of VAR (volt-amps reactive).
If you have a load of W watts with a power factor of P, the total VA (volt-amps) is W/P. For example a 400 watt load with a power factor of 0.8 draws 500 VA because 400/0.8=500.
The basic formula is that W2 + (VAR)2 = (VA)2
The VAR comes from this formula:
VAR = sqrt((VA)2 - W2)
So for the 400-watt load with a 0.8 power-factor, which draws 500 VA, the VAR is equal to 300.
On a 120 v supply the capacitor must draw 300/120 amps, or 2.5 amps, and its reactance is therefore 120/2.5 or 48 ohms.
The capacitance comes from this formula: 1 / (2pi times frequency times reactance).
On a 60 Hz system this is 1 / (377 times reactance)
So for a 48 ohm reactance the capacitance is 0.0005526 Farad or 55.3 microfarads.
This would completely correct the power factor in the example and the current drawn would come down from 4.16 amps to 3.33 amps, which would reduce the power lost in the supply wiring by 34%.
Can a 3 phase motor be converted into a single phase motor?
A three-phase motor will not start if one or two phases aren't connected. If while running one or two phases "drop out", it will continue to run for awhile, but will eventually burn out, unless connected to a motor saver.
What are the similarities between voltage and current?
both involve electrons
both can be measured
both involve electricity
both can do parallel and series
What causes sudden voltage drop in houses incase of ac?
Often, this is due to a sudden increase in the load current due, for example, to the the starting current of a motor which has been switched on -this causes a temporary increase in the voltage drop along the line, which is often noticed when the lights in a property temporarily dim. Other causes could be due to external sources, such as a neighbour operating welding equipment.
Why must you use ac current for transformer?
Transformer is based on the principal of mutual inductance.Induction is produced due to sinusoidal wave form thats why we use Alternating current inspite of Direct current.
How do you get the proof for Delta Star transformation in capacitors?
Convert all your capacitances to their equivalent impedance, then use Y-Delta Conversion formulae. Impedances mix and match like resistances.
If the resistor version is: (Y to delta)
Ra = (R1*R2 + R2*R3 + R3*R1)/R2
Rb = (R1*R2 + R2*R3 + R3*R1)/R3
Rc = (R1*R2 + R2*R3 + R3*R1)/R1
Then the capacitor version looks like:
Ca = C1*C3/(C1 + C2 + C3)
Cb = C1*C2/(C1 + C2 + C3)
Cc = C2*C3/(C1 + C2 + C3)
How is transformer saturation avoided in class B push pull amplifier operation?
In class B amplifier no DC biasing required, thus lack of of DC current in inpunt and load, saturation of core avoided
Why is there a difference in current in a coil when you apply dc voltage and then AC voltage to it?
A coil has both resistance and inductance. When you apply a d.c. voltage, the opposition to current is the resistance of the coil. When you apply an a.c. voltage, the opposition to current is impedance -the vector-sum of the coil's resistance and its inductive reactance. Inductive reactance is proportional to the inductance of the coil and the frequency of the supply.
How do you tell the difference from 13.2 kv power line to 4.8 kv power line?
The higher-voltage line will have longer insulators and the line conductors will be further apart. And the symbol for kilovolt is 'kV', not 'kv'.
Can the neutral conductor be downsized in a 3 phase electrical system?
Yes, you can reduce the neutral in a three phase system. you must figure the unbalanced current the neutral will carry and also make allowances for any harmonics that may be present.
What is the difference between contactor transformer?
Relays and Contactors are electromagnetic switches. The only
difference is that relays are usually used for low voltage
applications while contactors are used for higher voltage
application. Contactors usually have Overload protection.
Some examples that I can give (at least in Manufacturing of
Industrial Control panels):
-Relays are use as electromagnetic switches to control
certain parts of a circuit (low voltage application). A
better example would be such as if you want your circuit to
sound a horn when a certain abnormality is happening at a
certain period of time, then depending how you set up your
circuit, a specific relay will either open or close and you
horn will start making the sound.
-Contactors can be used for example, to start motors or a
number of motors that require a higher voltage in order for
the motor or motors start working. In the example that I
just gave, contactors work as starters.
How do you improve the flux linkage between the primary and secondary windings in a transformer?
by using an iron core
Can reactive power be used to power a bulb?
The 'type' of power is determined by the load. If the load is resistive (e.g. a lamp) then the rate at which it consumes energy is termed 'true power', expressed in watts.
You seem to be under the impression that reactive power is 'pushed out' into a load. This is quite false; the loaddetermines the power.
How can connect tow power supplies together?
By rigging the cables but i wouldn't recommend that at all.
Do gu10 led bulbs save energy?
It is stated that gu10 light bulbs use less than 10 percent of what a normal halogen light bulb does. This is a great difference.
They save a huge chunk of your energy bill and return save you a lot of money. Although they do cost quite alot more than the normal gu10 bulb you have to remember that they last around 20,000 hours.
You can calculate how much they are going to save you with an energy saving calculator. See Sources and Related Links.
Why potential transformers have large number of primary turns and a few number of secondary turns?
Transformers consist of number of turns so as to produce flux that is link with the core to produce an emf due to which current in the secondary winding produces.
as by the equation-
E1/E2=N1/N2=I2/I1
Why chopped impulse voltage is needed?
When lightning disturbance directly strikes on transformer terminal and flashover occur forming chopped wave. To confirm this situation, Chopped wave needed.
Mahendra Soni
