What to expect during phase failure? 1

[Power0020]

I am a bit confused with the notation that a star wound induction motor will suffer no overcurrent during phase failure while the delta connected one will get higher current.

Equations for start or delta loading shows that no change for a star but with delta connected load, faulty condition will have about 86% of the healthy line current with the same phase current and half of it for the faulted branch (two phases connected in series).

Any clue?

 

[waross]

The good phase induces current in the rotor. The rotor current sets up a magnetic field. The rotating rotor field induces back EMFs in all three stator phase windings. The healthy phase must supply all the energy to drive the load. In addition, the back EMF in the de-energized phase will try to supply current to any loads connected to that phase between the motor and the point that the phase is open.
In the event that a plant loses one incoming phase, any motors that are running will try to replace that phase, until their unbalance protection clears them off line.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

single phasing in wye (star) connected motor

single phasing in delta connected motor

Muthu

http://www.edison.co.in

 

[power1966]

If the motor is working you should receive only current unbalance which will stop the motor if there is such protection. Also will make heating the MOTOR
If the over-current protection correctly oriented the MOTOR will stop after a TIME