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Why is the transformer rated in KVA?
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Answered by: NagaseshaReddy.M
- Sep 10th, 2007
kVA is the unit for apparent power. Apparent power consists of active and reactive power. Active power is the share of the apparent power which transmits energy from the source (generator) to the user. Reactive power is the share of the apparent power which represents a useless oscillation of energy from the source to the user and back again.
It occurs when on account of some ?inertia? in the system there is a phase shift between voltage and current. This means that the current does not change polarity synchronous with the voltage. But the heat generated in a winding as well as the eddy current losses generated in a transformer core depend on the current only, regardless of whether it aligns with the voltage or not.
Therefore the heat is always proportional to the square of the current amplitude, irrespective of the phase angle (the shift between voltage and current). So a transformer has to be rated (and selected) by apparent power.Raghu
- Feb 9th, 2018
In transformer there is two losses
1. Iron loss
2. Copper loss
The iron loss is depands on Voltage
And the Copper loss is depands on current.Umar Naik
- Nov 26th, 2017
There are cu losses and iron losses which are not dependent on power factor thats why we rated it in KVA.
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What is the power ratio between power in Star and Delta circuit?
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KaranSorout- Member Since Jul-2006 | Jul 13th, 2006
The power ratio between Star to Delta is 1:3
Explanation:
Let?s suppose Vs be the supply voltage per phase.
So the line voltage of the supply will be ?3Vs.
Now assume any type of load; for simplicity I?m assuming it a only resistive load.
And let it be ?R? per phase.
For Delta connected load:
Calculation for per phase power; PD= I2R
Where I ? load current (per phase)
And,
I = ?3Vs/R {as line voltage of the supply is directly applied to the phase of the delta load}
So,
Pd = (?3Vs/R )2R = 3Vs2/R watts per phase.
For 3 phases:
P3D = 3Pd = 3*3Vs2/R = 9Vs2/R watts.
Now for Star connected load:
PS = I2R = (Vs/R)2R = Vs2/R watts
For 3 phases: P3S = 3PS = 3 Vs2/R watts
Conclusion:
P3S / P3D = 3Vs2/R / 9Vs2/R = 1/3
It may be better concluded by drowing figures. If any variations, can connect to me through karan.sorout@gmail.com
RUP KAMAL KUTUM
- Feb 3rd, 2018
Well first you assumed voltage per phase as Vs and Line voltage as sqrt(3) x Vs: Which is for star connection. Then, you assumed the same thing for Delta Connection(where line and phase voltages are t...
Anbumozhi R
- Dec 3rd, 2017
Power is Same. Whether it is star to Delta conversion or Delta to star conversion. Power is 1:1
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For a 100kw generator, only 50kw of load is connected. Will the generator generate only 50kw or 100kw? If it generate 100kw what happens to rest of the 50kw. What happens if we connect more than 100kw of load?
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Answered by: joe
- Dec 23rd, 2006
100 kw is the full load rating of the generator..... ..that means it can supply 100 kw without exceeding in specified temperature limits .that doesnt mean that it wont be able to supply a load more than 100 kw,it can but not for a longer period of time.after sometime the generator will burn out.if a load of 50 kw is connected to generator the generator will generate only 50 kw& not more than that.the generator will generate power only according to the requirement.
Dharmender
- Feb 7th, 2018
Connected Load is 96kw &125kvaDG set will have run stand by unit for Hotel is suitable plz give your technical supporting answer
Mayilsamy Kasipandi
- Jul 11th, 2017
The Generator produce the power is exactly what we withdraw as load. 100 kw genset can produce 1 kw to 115kw power depending upon the connected/withdrawing load. Normally the generator can produce 115% of designed rating.
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Phase and Neutral
What is the difference between phase and neutral?
sarita
- Nov 16th, 2014
Phase contain supply voltage i.e heavy electrons or protons and neutral contain no supply voltage and neutral charges.
saadsms
- Oct 26th, 2014
1- in one phase case : Phase is supply voltage weather neutral is returning path the same current for that supply voltage. 2- in three phase case : - in balanced load current returned to earth = 0 - ...
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Transformer Neutral Earthing
Why the transformer neutral point connected to earth?
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Power Factor
What do you mean power factor?What is the use of Power Factor?
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rahulr30- Member Since May-2008 | May 30th, 2008
Power factor is the ratio of Active ppwer to apparent power in sysytem,It is an index to see how much of the energy is actually being utilized to do useful work
veerateja
- Jun 11th, 2011
pf is the co-sine of phase angle b/w voltage and current.Generalley it is leading or lagging depanding on the load whether it is inductive(lag) or capactive(lead).Take voltage as reference the current...
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Change in Frequency
Why do we maintain 50hz frequency? What happens when we change this frequency to any other value?
maxandrean
- Jul 5th, 2010
AC Electrical Network need to have a syncron phase for them to work. Any differences in term of frequency will shift out this syncronisation and lead the whole system to fail.
sankar_jkpm
- Feb 3rd, 2010
In our India, all the electrical power generation is based on 50 Hz. (50 cycles per second) with respect to the production of flux in alternator. So the electrical utility products are designed f...
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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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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...
Electrical Engineering Interview Questions
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