Single phaseing
- Thread starter nathan1
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hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Single phaseing
Re: Single phaseing
This only happens with motors not coils. once you loose a phase you loose rotation. And if a motor tries to start up it wont be able to rotate. the motors other two phases will still have power to them but at a locked rotor amperage. these windings are not design to take that amount of current very long and if there is no over loads to protect them then they will burn up. A single phase motor use's a capacitor to give it rotation. But there is allot more to this than I can explain here.
Re: Single phaseing
This only happens with motors not coils. once you loose a phase you loose rotation. And if a motor tries to start up it wont be able to rotate. the motors other two phases will still have power to them but at a locked rotor amperage. these windings are not design to take that amount of current very long and if there is no over loads to protect them then they will burn up. A single phase motor use's a capacitor to give it rotation. But there is allot more to this than I can explain here.
stew
Senior Member
- Location
- federal way,washington
Re: Single phaseing
Re: Single phaseing
Its even worse when you loose a phase when the motor is already running. Loss of a phase on startup usually results in the overload device or ocp tripping. When the motor is running however the torque drops off dramatically but you keep running and the current goes up in the remaining 2 legs and quite often winding damage will occur before the overload or ocp trips.
Re: Single phaseing
Its even worse when you loose a phase when the motor is already running. Loss of a phase on startup usually results in the overload device or ocp tripping. When the motor is running however the torque drops off dramatically but you keep running and the current goes up in the remaining 2 legs and quite often winding damage will occur before the overload or ocp trips.
electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
Re: Single phaseing
Re: Single phaseing
The term "loosing a phase" or "single phasing" really means operating with only one phase, not loosing one. Since each of the three supply conductors carries two phases, an open supply conductor would mean the loss of two phases, not one.
Re: Single phaseing
The term "loosing a phase" or "single phasing" really means operating with only one phase, not loosing one. Since each of the three supply conductors carries two phases, an open supply conductor would mean the loss of two phases, not one.
stew
Senior Member
- Location
- federal way,washington
Re: Single phaseing
Re: Single phaseing
electricman you have me confused now. When one fuse blows the other 2 legs still supply voltage to the winding do they not? Thus the term dropping a leg or singlephasing.
Re: Single phaseing
electricman you have me confused now. When one fuse blows the other 2 legs still supply voltage to the winding do they not? Thus the term dropping a leg or singlephasing.
electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
Re: Single phaseing
Re: Single phaseing
Quote by Stew
Re: Single phaseing
Quote by Stew
Thats true but the remaining two conductors can only supply one phase, A,B or C
stew
Senior Member
- Location
- federal way,washington
Re: Single phaseing
Re: Single phaseing
so maybe thats why they call it single phasing then eh?
[ June 28, 2004, 11:04 PM: Message edited by: stew ]
Re: Single phaseing
so maybe thats why they call it single phasing then eh?
[ June 28, 2004, 11:04 PM: Message edited by: stew ]
Re: Single phaseing
Re: Single phaseing
Single phasing is typical phenomenon associated with 3 ph. motors.
In running condition of delta connected motor say, if one of the phase goes off, then current distribution in the wdgs is disturbed. And wdg. opposite to the phase lost will get overloaded.
In addition to this heating effect, there is additional heating because of negative sequence component predominancy which results in core heating. And hence tendency of m/c to burn faster during single phasing is more.
The current rise in other 2 phases during single phasing condition is subject to loading of m/c previous to single phasing. And hence lightly loaded m/c tends to burn faster during single phasing as protection is unable to detect them.
However the best protection for the same is electronic single phasing protection devices that works on negative sequence component sensing.
Re: Single phaseing
Single phasing is typical phenomenon associated with 3 ph. motors.
In running condition of delta connected motor say, if one of the phase goes off, then current distribution in the wdgs is disturbed. And wdg. opposite to the phase lost will get overloaded.
In addition to this heating effect, there is additional heating because of negative sequence component predominancy which results in core heating. And hence tendency of m/c to burn faster during single phasing is more.
The current rise in other 2 phases during single phasing condition is subject to loading of m/c previous to single phasing. And hence lightly loaded m/c tends to burn faster during single phasing as protection is unable to detect them.
However the best protection for the same is electronic single phasing protection devices that works on negative sequence component sensing.
stew
Senior Member
- Location
- federal way,washington
Re: Single phaseing
Re: Single phaseing
And in all star connected motors the 2 phases of the winding which still recieve power burn to a toasty black and the other phase is nice and clean.
Re: Single phaseing
And in all star connected motors the 2 phases of the winding which still recieve power burn to a toasty black and the other phase is nice and clean.
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