Single Phasing Causes, Effect And Protection

                       Single phasing refers to operating 3 phase motor with any one of the 3 phase connection is missing. During single phasing no current will pass through one line while the other two lines carry approximately 2.4 times the normal current value for the load.

Causes of single phasing
     >One of the fuse may blown off
     >Line wires are broken
     >Relay contacts may be damaged
     >Contact joints are not conducting properly

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 Effects of single phasing
     >When one phase breaks the current in the remaining two phases increases about 2.4 times the     normal current value.
     >Due to single phasing uneven torque will be produced and it may cause vibration of the motor and the motor became noisy.
     >Generator may get overloaded
     >Single phasing may reduce the speed of the motor.
     >Motor winding may melt due to overheating
     >If single phasing happened on running motor, motor will continuously run until the wingdings burns off
     >It is impossible to start a motor with single phasing.

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     Protecting Devices To Avoid Single Phasing
> Overload Relay: Which will trip the motor if the current exceed normal value
> Thermistors: It is a type of resistor whose resistance is dependent on temperature placed on windings. Any increase in current heat the winding which is detected by the thermistor and send the signal to trip the motor.