Answer / sushil verma

During stsrting of motor the intake current normally 5-6
times of rating current,because to genarate intial torque
we need to grnerate back EMF which required high magnetic
field.To generate this EMF motor draws high current during
starting

Answer / rajesh tokalapudi

In case of motor current is given by i=(v-e)/r.here
v=suplly voltage,e=back emf and r=resistace.during starting
back emf is zero.then i=v/r.generally motor resistance is
low.so during starting motor draws high current,which is
normally 5 to 6 times its normal operating current.

Answer / ravi

In ac induction motor it take starting current around 7 times the full load current. The reason is during starting when we applied a voltage to stator it produce a rotating magnetic field which is rotating with its synchronous speed. The rotor speed is zero and slip is 100% so a large amount of magnectic field cuts the rotor surface and produce heavy current to flow from its and when the rotor catch its speed the amount of field cutting the rotor reduce and slip is also low and current become normal.

Answer / yusuf

f'=sf
f'=rotor frequency
s=slip(ns-n)
f=stator frequency
During starting slip will equal to 1 due to rorot at rest that's why rotor runs same as stator frequency during starting.when rotor runs slip will reduced & motor current reduced to normal

Answer / saeid

The answer is different for different kinds of motors.
However, for all of them there is a similatr reason that
is, there is transient condition during statr up that cause
thier winding impedance become different than runing time.
So because transient impedance is much less than staedy
stat impedance, the starting current is much higher than
runing current.

Even it happen for DC motor.

As I said in the begining, there are some other reasons
that make starting current different for DC(12 to 20times),
induction(6 to 10times) and synchronuose (12 to 20times),
motors.

Answer / ganesh

why we can use power electronic devices in power systems

Answer / aecas

ask from shah sahib. aik tou tum parhatay nai ho na ....

Answer / gunasekaran

because due to the large air gap between stator and rotor
wdg for 3phase motor comparably less than single phase motor
because less air gap. for 3phase motor it is taking around
30-50% full load current for single phase 60-70%full load
current.

Answer / guest

During starting
1.In a DC motor the back emf is zero
2.In a AC motor the frequency is zero(slip is 0),hence
reactance(z) is zero,I=(v/z) hence current is infintiy

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