Single Phasing

In this exercise, you will come to understand the effects of a single phasing happened to a running three-phase induction motor with a partial load. 

Single phasing is now caused in our case by blowing of a fuse.

The motor will continue running has single phase motor on the remaining single phase Supply. 

There will be current only in the two winding's.

These current will develop negative sequence currents in the rotor bars and stator winding. 

It will gradually show The Following signs of distress. 

There will be increase in noise level.

There will be decrease in speed. 

There will be overheating of rotor bars and stator winding's due to negative sequence currents.

There will not be any immediate damage to the motor because partial loads do not blow the other healthy fuses. 

If the load on Motor is increased very heavily, then it will stop under single phasing. 

The current in the two winding's  increase more then  full load current. 

The increase negative sequence currents now develop more heat in the rotor bars and stator windings. The rotor will become more hotter.
The insulation of stator winding's will fail causing short circuit or earth fault currents. 

All the fuses may start blowing now.

If useless are over sized by mistake, the stator windings get heated up heavily and finally, the motor goes on fire.