what will happen when excitation of a synchronous machine
is suddenly reduce to zero when it is running at full
Answers were Sorted based on User's Feedback
Answer / vidhya
if its a salient pole synchronous generator whose synchronising power is P=E*v/x+v2/2[1/Xq-1/Xd], where Xq and Xd are quadrature axis reactance and direct axis reactance respectively as can be seen the first term is dependent on excitation (E=field emf) this term will be =0 but the 2nd term does not depend on E hence the synchronous generator (salint pole) will keep supply power but this power is reluctance power and thus the synchronous gen will act as reluctance generator.many might think if E=0 how v(terminal voltage ) is not=0.well thats bcoz the output of generator is connected to infinite bus whose terminal voltage is always maintained at V.
|Is This Answer Correct ?||15 Yes||1 No|
in case of a synchronous motor once the excitation is cut
off , then the motor starts to run as an induction motor,
this is because a synchronous motor by itself is not self
starting , and is first started as a squirrel cage
induction motor , once the motor attains about 95% of
synchronous speed then the excitation is applied due to
which the the copper bars are effectively removed from the
circuit as they revolve with the sane speed as the rotating
flux , once the excitation is cut off , the relative motion
between flux and the copper bars come into action and the
motor starts operating as a induction motor.
|Is This Answer Correct ?||26 Yes||16 No|
Answer / dileep
there ars two types of rotors 1).salient 2).cylendrical.when the excitation is off,the salient motor will continue to run synchronous speed because of reluctance power .if it is a cylendrical rotor it will work as induction motor
|Is This Answer Correct ?||12 Yes||4 No|
Answer / b. b. shukla
Practically, in this case, The motor will draw a high current and finally the relay/safety equipment will trip the motor, because -- it will try to run like an induction motor with dampening winding bars acting as rotor conductors. but it will not be sufficient to fulfill the load requirement. therefore the motor will draw high current and its speed will slow down and finally zero. Accordingly the back emf of rotor will reduce, motor current will increase and finally the motor will trip/burn out.
|Is This Answer Correct ?||11 Yes||3 No|
Answer / jamshed hussain (from quest)
In synchronous generator the excitation is given to the rotor circuit and magnetic field is produced. If the excitation is reduced to zero then there will be no magnetic field. It means that no excitation, no magnetic field, so there will be no generation.
|Is This Answer Correct ?||4 Yes||4 No|
Answer / k.prakashchandra
If the prime mover is not working ,the synch generator will
run as induction motor and if the prime mover is still
driving , it will run as induction generator.It may be
noted that in large generator, field is the rotor
|Is This Answer Correct ?||3 Yes||5 No|
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