Electrical Machines
If the handle of a three point starter goes to back to OFF position, it may be due to

 zero or very low voltage supply.
 high filed circuit resistance.
 all of these.
 over load.

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Electrical Machines
A dc shunt generator, when driven without any excitation, showed an open circuit voltage of 12 V. When the field winding was excited, the voltage dropped to zero. It happened because

 field winding was wrongly connected
 field resistance was higher than critical resistance
 there was a break in the armature circuit
 there was no residual magnetism in the field circuit

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