Answer / deepak rathor

in this case alternator wil work as induction generator, as
reactive power supplied by AVR wil be zero due to loss of
excitation, generator wil be in asynchronous mode.

Answer / abubakr

when excitation is lost due to fault or field breaker
tripping . Reactive power will be supplied by the system and
generator will work as induction generator and its speed
will rise a little . generator which was in over excitation
mode will work in underexcitation .
but there is under excitation limit which should not be
reached so we should detect loss of excitation and trip
generator

Answer / sunil kumar

when the excitation is lost,alternator tends to behave as
induction generator because there is no opposition to the
rotor as flux is zero, rotor speed tends to increase beyond
synchronous speed and by reactive power from the grid the
machine behaves as induction generator as slip is negative
and reverse power flows which will be taken care by
directional relay.

Answer / nishad

Generator will not produce any output voltage and it will trip the generator output breaker by the loss of excitation monitor protection relay or under voltage relay. If the breaker not trips by these relay, it will trip by reverse power relay. Due to the presents of Reverse Power relay, it will not allow the Generator to run as an induction generator and will trip the Generator breaker, thus it protect the generator from further severe fault. Again, if it not trips by these all protections, alternator will work as induction generator due to the residual magnetism in the field core when it is running in parallel and it will give the over load to another generator as a result, it will trip entire system. Also, as an alternator typically isn't designed to operate as an induction machine, the windings on these machines will heat up and damage. Therefore, need to make sure the reliability of protection relays to avoid such faults.

Answer / atul

if excitation fails let d case of hydro generator the prime
mover is turbine. since turbine ic moving and is coupled
with generator shaft and no flux to control its speed it
will go out of path or speed will increase beyond
synchronism

Answer / ramlakhan y adav (ballia)

when the excitation is removed then the alternator work as a
asynchronous motor will draw the power from reverse supply.

Answer / manjeet

duction generator as underexcitation .
but there is under excitation limit which should slip is
negative
and reverse power flows which will be taken care by

Answer / sudheer

if excitation failed , the alternator will stop making
voltage.because when exciter fails, the main winding will
not produce rotating magnetic field, so voltage will not
produce.

Answer / raj

Every one is right but one more thing will happen that is
Alternator will work like motor and will draw power from
other source ( with that it synchronised )known as reverse
power and further RPR will trip the Alternator breaker.
(Approx continuous rating for reverse/negative power is 10%)

Answer / vijin

if the excitation fails the motor will simply stops,because
it loses the magnetic locking capability by the removal of
dc supply. the motor has no field suplly to generate
necessary emf while running by virtue of the inertia.

in transformer star connection with neutral are shorted. is there is any effect.

1 Answers  

What is difference between Step Up Transformer & Booster Transformer? can we used instead of any one?

2 Answers   CS,

give me atleast four differences between circuit and network

0 Answers  

Based on CPI/CGPA they shortlist the candidates & than directly start Interview so there is no Written Exam or GD Only PI.Interview held @ MNNIT , ALLAHABAD On-Campus on 6th,Aug, 2007 & the Questions asked to me by Interview Board ( 4 People) are from HR/SummerTraining/BTP/Subject-core, POWER SYSTEM & MACHINE. time duration of I/V is about 15-20 Minutes. HR- Q.1 Name,hobbies & About family background ? Q2.What u know abt NTPC ?? Q3.Why u want to choose NTPC as ur Carrier's starting i.e power sector not any other Oragnisation or sector ?? Techincal Questions- Q1.What is the reason for transformer Noise ?? Q2.Which material is used for making Transformer oil & How u measure its dielectric strength & Name the test ? Q.3 Which Machine u will prefer 2 use if flammble gases are coming out at a place & why ?? Q4.What is relation b/w Transmission Lines & Communication Lines ? Q5.What is the maximum capacity Synchronus Machine & total powerGeneration in our country ? Q.6 In india Power generation is at 50Hz while in America its 60 hz ,why so ?? Advantage or disadvantage ?? Q.7 Maximum Generation Voltage in india ? Q8. What is the Voltage regulation & why its required n how much is permissible ? & causes of voltage variation ?? Q.9 Why electric shock is feel ?? n in a Electric Train why we didnt feel that ? Q.10 Have u seen/ experience of any power plant/ industry related to the power sector ? so these are the questions which not too diffcult i think was asked to me.

6 Answers   NTPC,

voltmeter kya hota hy ?

2 Answers  

How can i calculate heat load ?

3 Answers   DSSR, NSN,

why in an industry; machine having rated 200 h.p stopped after power factor is maintained above 0.97 lag by control panel in view-of energy saving

0 Answers   HCL,

Can any one provide the inspection procedure of MIMIC for VFD panel? Details: If someone wants to have a mimic in the VFD panel what are inputs considered for the mimic(like on,off,trip) whether we are able to add speed variation in the mimic(if so how can we get) and what are the parameters to be checked in the MIMIC during inspection?

0 Answers  

How the over load setting for HT Motors calculated-provided in Numerical Relay

0 Answers   Damodar Valley Corporation,

1.what is difference between ATS & STS main use. 2.what is difference between ACB& VCB With symobles,and main partes, manimum range. 3.How many types of relays and main function.

0 Answers   Visa,

We have laid the single core Armoured cable 7 nos ( 2 each phase & 1 neutral ) to cater our electrical load . the issue is though we have Glanded the cable both the end also givan the earthing to the panel both the end we are facing a heavy sparking at the gland side. what could be the reason.

12 Answers  

how net resistance islow in star connection and viseversa in delta connection...? if anybody could explain in detail it wud be helpful.

0 Answers