Answer / tathagata

If single phase motor is supplied by ac supply, it will rotet
because single phase motor are universal motor. So it work
for both AC & DC.

But the DC supply must be less than its AC rating, because
in DC there is no reactant .

I=V/(R+jX) (AC)

I=V/R (DC)


So current is vary high which may burnt out the winding.

Answer / santosh

torque in single phase induction motor is produced due to rotating magnetic field. if this motor is fed from dc, the rotating magnetic field is absent and the machine will not run.
also in the absence of reactance in DC, the machine will try to draw high current which will damage the winding.

Answer / alan jenkins

In a nutshell it depends what type of motor it is, some motors with a wound rotor and brushgear will run on AC and DC, however AC induction motors will not rotate, the DC current will have a locking effect on the rotor, hence DC injection braking (anyone heard of that ?)leaving a DC current on these motors for any length of time will heat up the windings.

Sir we have 12.5 MVA(110/11KV) transformer (Y-Y) connected,which tripped showing earth fault,when we charged transformer it stood OK ,but on connecting 11 KV feeders it tripped showing earth fault.our service engineers found that the B phase and R phase phase connecting to neutral broken from HV OLTC(on load tap changer),and R phase and Neutral is ok.Dissolved gas analysis shows that accetline content is high,tan delta value is 12.My dout is it is an internal fault of transformer,why REF or diffrential relay is not acted?

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