when three 3 phase motor is suddenly single phased .
it will giving sound and its speed lower down. it
may also burn . and mcb or proction will come in
action. because current will rise very high in this
Motor is running as a single phase motor with lower speed
and creating noise. In this situation it will drawing higher
current. If it runs for long time then insulation may get
damage and ultimately burnout the winding.
If a three phase motor is suddenly single phased, nothing
will happen to the motor. Perhaps the motor will coast down
to stop. Single phased means only one phase out of three is
connected to the motor, and since the neutral is never
connected to a three phase motor, there fore no current
will flow into the motor and hence motor will stop as usual.
Usually when talking about "single-phased" motor, it means
that two of three phases are connected. In these cases, the
motor will slow down, and the phase currents for the
remaining phases will be increased. I don't know how much. I
am also not sure if the overload device would cut-off the
motor from power supply. Unless problem is not noticed, the
motor will most likely burn. When the motor is opened, you
should be able to see that 2 of the 3 phase windings are
black, and one is good looking (if motor is Y-connected)
If protection is proper then it will operate and stops the
motor. If there is no protection which is the normal case
in LT motors, then winding will burn there are two diffrent
pattern which will apear depending on the type of winding
connection i.e. delta or star.
You will find most of the winding failure in LT motors
happens due to single phasing.
If a three phase induction motor is suddenly single-phased
while running, no distinct change will happen if it is
running under noload condition. You will just hear a
hunting sound and the the motor will continue to run with a
slightly lowered speed and increased current, but if the
motor is running under loaded condition it will stop down
and take excessive current due to single phasing and the
protection circuit will trip, if protection ckt is not
installed the motor will be ultimately burnt due to
excessive locked rotor current.
And note: This experiment is tested.
first. if motor conected in star than the winding which one
not gating phase it remain but other two winding which got
their phase they come in series and they burn becaz they
got 415v on the behalf of 230v. time is depend on load if
motor run on full load than motor burn in 15 to 20min if
motor run on half load means50% than its take more time as
well as incase of delta if R phase blown than Bphase of
winding burn becaz RandYphase winding come in series and B
winding got double phase so it burn. thanks for read
A synchronous motor is operating at a leading power factor .if
the applied voltage is decreases ,(the excitation remains
constant ) ,the motor current
a)increases b) decreases c)remains same d) none of these