Related Questions

If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
A Demagnetization only
B Cross magnetization as well as magnetization
C Cross-magnetization as well as demagnetizing
D Cross magnetization only
_______ brushes are fragile and cause excessive wear of commutator,
A Natural graphite
B Hard carbon
C Electro graphitic
D Metal graphite
In D.C. generators, the brushes on commutator remain in contact with conductors which
A Lie under South Pole
B Lie under North Pole
C Lie under interpolar region
D Are farthest from the poles
The number of brushes in a commutator depends on
A Speed of armature
B Type of winding
C Voltage
D Amount of current to be collected
The insulating material used between the commutator segments is normally
A Graphite
B Paper
C Mica
D Insulating varnish
Electrical contact materials used in switches, brushes, relay must possess
A High thermal conductivity and high melting point
B Low thermal conductivity and low melting pointL
C High thermal conductivity and low melting point
D Low thermal conductivity and high melting point
The rapid wear of brushes takes place due to
A Abrasion from dust
B Excessive spring pressure
C Rough commutator bars
D All of the above factors
To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
A Just ahead of magnetic neutral axis
B In magnetic neutral axis
C Just behind the magnetic neutral axis
D None of the above
Copper brushes in D.C. machine are used
A Where low voltage and high currents are involved
B Where high voltage and small currents are involved
C In both of the above cases
D In none of the above cases
Armature coil is short circuited by brushes when it lies
A Along neutral axis
B Along field axis
C In any of the above positions
D In none of the above positions

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