while running, a slip ring induction motor ,it got tripped and found 2 nos power fuses blown out.on inspection rotor winding IR value zero.ie after releasing the brushes. how it happens?. pl ans
when the motor is starting its an induction motor with a squirrel cage
while its getting up to speed the voltage across the slip rings will be very high
there is a field resister shorting the rings this is removed and replaced with dc
with a make before break field application relay
if the dc is applied before the motor is up to near synchronous speed the stator will need to have very high current to accelerate the mass of the machine
sometimes the controls are magnetic
sometimes a centrifugal switch
sometimes a timer
a compressor will have an unloader to minimise load on the motor before the dc is applied
however this is done
if dc is on the field before you get close to operating speed you will blow fuses
if the "failure" happened while running it could be a momentary power interruption or a momentary load interruption
if the controls didnt see it and restart the motor
you can dissect the fuses and see weather you had a short or an overload
or add a bit more detail about the equipment and incident
A motors locked rotor current is the same as the motors starting current. This is the point where the voltage is applied to a non rotating motor, time cycle zero. Because the motor is not rotation and generating a back EMF to oppose the inrush current, the current will go as high as 6 times the running current of the motor.
This is how an induction motor normally works, hence the name. The supply voltage is connected to the stator winding(s) and a current is induced in the rotor. A synchronous motor, on the other hand, will have current supplied to the rotor through slip rings and brushes. The rotor current is generally supplied as DC though, or else rectified in the rotor.
The direction an induction motor will turn depends upon the direction of the rotating field setup by the winding. Remember in AC the direction of the current reverses itself 120 times every second for a 60 hz system. So no it will not turn in the "direction" of the current.
The formula to calculate the rotor speed (N_r) of a cage rotor induction motor is given by: N_r = (120 * f) / P, where f is the supply frequency in Hz and P is the number of poles in the motor. This formula assumes the motor is running at near synchronous speed and neglects slip.
The current in an induction motor decreases as it accelerates due to reduced rotor impedance and increased back EMF. As the motor speeds up, the rotor reacts with the rotating magnetic field produced by the stator, causing a decrease in the current needed to maintain acceleration. This decrease in current helps to improve the motor's efficiency and reduce energy consumption.
Standard induction motor has a closed squirrel cage rotor, where as open ended induction motor has split phase rotor.
Induction motor is an AC electric motor which uses electromagnetic induction to induce the electric current in the rotor to produce torque.
explain wound rotor
short the rotor terminals.
rotor speed = 0
Yes, the induction motor has a rotor winding. It is usually one turn, shorted. This is how the magnetic fields generated in the stator induce a current in the rotor, which subsequently generates a torque from the opposing magnetic fields, stator to rotor.
The pullout torque is the maximum torque a motor can achieve. Also known as breakdown or peak torque. It occurs at the point where, the increase in the rotor current is exactly balanced by the decrease in the rotor power factor.
its impossible to give suppy to rotor of an induction motor,because of it a closed path for circulating currents.
rotor speed will decrease....the rotor current wil increase.....
rotor speed will decrease....the rotor current wil increase.....
Squirrel cage induction motors.
DOL(Direct Online starting) Star Delta starting Auto transformer starting Above methods are for squirrel cage induction motor Rotor resistance starting is used for wound rotor or slip ring induction motor