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Transformer Signal
What is the benefit of using ac signal in a transformer?
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sinhasunilk- Member Since Jul-2010 | Jul 3rd, 2010
Transformer can only operate with A.C supply. Voltage will induce in the secondary winding of transformer only when there is a change in flux. The induced voltage in the secondary winding is no. of turns in secondary x rate of change of flux. In D.C circuit the rate opf change of flux is Zero, hence induced voltage in secondary winding is Zero and no Back MMF produce in the magnetic circuit of core of transformer.?This will result in very high current drawal in the primary winding and will result in burning of primary winding of transformer. We can not think of applying D.C source in transformer.??
SURAJTHEGREAT
- May 5th, 2012
The reason why dc signal cannot applied to a transformer is that f=0,reluctance is 0,very high current flows through windings and it is burnt out!
sinhasunilk
- Jul 3rd, 2010
Transformer can only operate with A.C supply. Voltage will induce in the secondary winding of transformer only when there is a change in flux. The induced voltage in the secondary winding is no. of tu...
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Measure Earth Resistance
How earth resistance is measured? What should be its value?
soulzangel
- Oct 4th, 2010
Earth resisitance can be measured using megger or earth tester and thr resisitance of proper earthing must always be less than 10 ohms and for sensitive installations such as very sensitive communication and computer systems about 2 ohms is recommended.
veerateja
- Jul 9th, 2010
Earth resistance is measured by means of earth tester or megger. The earth resistance must and should be less than 0 to 5 ohms. If it is above the 5 ohms we say earth resistance is not good.
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Transformer Humming
What causes transformer humming?
Krishna Kant Gupta
- Mar 13th, 2012
Humming sound in the transformer is due to the stray losses in the transformer due to the leakage flux.this flux produce eddy currents in the nearby conductive areas.The humming sound is the result of...
bittu123
- Nov 9th, 2011
Humming sound caused by magnetostriction phenomenon. Magnetostriction is change in physical dimension of material because of change in magnetic field.
Since, there is varying magnetic field in transformer causes vibration of core in gap available due to bad insulation. and starts soud hum -
Star Type Transformer
Why are we employing star type transformer at transmission end and delta type transformer at receiving end?
UMESH KUSHWAHA
- May 23rd, 2012
Its not necessary to use only Delta type T/F at receiving end, we can also used star type but in this case at same voltage level two star neutral point create due to which Harmonic create for avoiding this we prefer opposite combination at sending end and receiving end.
vishal badlas
- May 19th, 2012
Bcoz at the transmission side especially for secondary distribution we need neutral wire for getting single phase supply and star type is only one which provide neutral. at receiving side to step up voltage we need delta type connection.
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Alternator
An overexcited alternator gives current at which power factor?Why?
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What are the technical reasons for soaking transformers for various times before allowing them to pick load after a fault or maintenance outage or as a new installation.
niceashwin79
- Dec 21st, 2010
I believe it is not soaked in water but is soaked in oil.It kept for some time because to remove all moisture and air if any trapped in insulating material and windings.
SAMIR K CHATTERJE
- Nov 17th, 2007
To improve IR value of the transformer so that it would have higher dielectric strength indeed.
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Is possible to increase the voltage without using transformer? why?
bittu123
- Nov 7th, 2011
I went through all answer, seems all are correct.... But lemme be more precise.. Except transformer..... 1. CHOPER: It is said to be DC equivalent of AC transformer, so can be used to increase and d...
santosh
- Nov 7th, 2011
We can step up and down dc voltage using chopper circuit
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What is meaning by the SKIN effect in electrical circuits
veerateja
- Jun 2nd, 2011
In ac electrical circuits due to varying magnetic fields they induce eddy inside the center of conductor .Due to the induced eddy currents they restrict the current flow on the center and pushes the c...
ravs42
- Aug 8th, 2010
When alternating current flows thru the conductor, magnetic field intensity in the inner side is more, as a result flux concentrated on the inner conductor is very high. Since inductance of the coil i...
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What is the voltage drop for 100kw motor if the length of the cable is 200m and what is the cable size.
soumendasbiswas
- Oct 21st, 2009
1.The (0.48) is it resistivity of conductor ? or any other value Well here 0.48 is the estimated voltage drop in XLPE cable.(You can get this value from any cable manufacture catalogue)2.You hav...
mustafa_musvi
- Oct 20th, 2009
Mr Biswas please specify Below is the case you mentioned regarding cable losses I have 2 questions request for your answer1 The (0.48) is it resistivity of conductor ? or any other value 2 You hav...
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When we connect the capacitor Banks in Series with the circuit
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Answered by: cvk
- Oct 6th, 2007
The series capacitor is conected to compensate for the line inductance and thus decrease the line reactance so that more power can be tranferred through the line (EV/X sin(delta)) and thus the system stability can be increased.
cvk
- Oct 6th, 2007
The series capacitor is conected to compensate for the line inductance and thus decrease the line reactance so that more power can be tranferred through the line (EV/X sin(delta)) and thus the system stability can be increased.
its_Kishu
- Mar 10th, 2007
Hello...... The question is about connecting Capacitors in SERIES. Series connection is done for improvin...
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When there is a sudden loss in the demand what happens to the transformer and generation?
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csbalu- Member Since Aug-2009 | Aug 29th, 2009
When there is a sudden loss of load, The Generator terminal voltage increases due to the fact that the IX drop in the generator winding decreases. The EMF generated being the same the reduced reactance loss leads to a sudden rise in generator voltage..but the AVR (Automatic Voltage Regulator) will act instantly to bring this voltage to the set value by reducing the excitation.
There is practically no effect of this on the transformer barring the reduction in I2R (copper Losses) and reduced IX drop.csbalu
- Aug 29th, 2009
When there is a sudden loss of load, The Generator terminal voltage increases due to the fact that the IX drop in the generator winding decreases. The EMF generated being the same the reduced reactanc...
spcspc1654
- Jul 19th, 2009
When there is a sudden loss in the demand then there is over-excitation of the generation and the power factor is increased. Also the rotor angle of generator is changed (unstable) for a while.
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CT connection for T/F differential protection
Why CTs are connected in star on T/F delta connected winding side & in delta on T/F star connected winding side for T/F differential protection?
bejoyengineer
- Mar 1st, 2009
The differential relay will not activate when we energize the transformer as the relay will activate only if there is a difference in the flow of current and that to if it exceeds the setting values.
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Wattmeter reading
Why does wattmeter's reading go negative?
bittu123
- Nov 9th, 2011
Suppose, phase difference between V and I is "A"(angle). and wattmeter reads +ve. Now if phase difference became (A+180), wattmeter will read -ve of same magnitude.
It simply means, direction of power flow gets changed just because of changing in direction of either current or voltageSURAJTHEGREAT
- Mar 3rd, 2009
If you have seen the wattmeter ratings, it will be (300V,10A,UPF) (Voltage, Current, Power Factor) That is wattmeter needs voltage and current to measure power. So a wattmeter consists of t...
Electrical Engineering Interview Questions
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