01․ Two DC generators having equal open-circuit emfs but slight different load characteristics are operating in parallel, then
02․ The magnetic field which initially induces emf in the armature in a self excited DC generator is because of
03․ In a 12 pole triplex lap wound DC armature, each conductor can carry current of 100 A. The rated current of this armature is
Armature current = 12 X 3 X 100 A = 3600 A.
04․ Compensating winding are used to rectify the flux density waveform at
Compensating windings is embedded is slots located in the faces of the main poles and is connected in series with armature in as manner so that the direction of current through the compensating conductors in any pole face will be opposite to the direction of current through the adjacent armature conductors.
05․ Resistance commutation is used generally in case of
In fractional kW DC machines, commutation can be improved by replacing low resistance copper brushes by comparatively high resistance carbon brushes.
06․ DC generator will not build up voltage
DC generator cannot build up voltage if it has no residual magnetism and its field resistance is more than the critical resistance.
07․ Wave winding is employed in DC machine of
Wave winding are high voltage rated, since the number of coils in series between commutation segments permits a high voltage to be built up easily than with lap winding current rating of wave winding is taken low.
08․ A 4 pole DC generator runs at 750 rpm and generate an emf of 240 V. The armature is wave wound and has 792 conductors. If the total flux from each pole is 0.0145 Wb. What is the leakage co-efficient?
Where E = generated emf, N = speed, P = number of pole, φ = Working flux per pole, A = 2( wave wound ) and Z = number of conductor.
09․ In a 6 pole DC machine, 90 mechanical degrees correspond to which of the following electrical degree?
Where P = number of pole, θm = mechanical degree and θe = electrical degree.
10․ The armature reaction mmf in a DC machines has a form of
The effect of the armature mmf upon the field distribution is called the armature reaction. If the conductors are uniformly distributed over the surface of the armature mmf under load has a triangular waveform.