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WorksheetsDC Machines and Transformers
Total questions: 20
Worksheet time: 5hrs 0mins
A dc motor takes an armature current of 110A at 480V.The armature circuit resistance is 0.2ohm.The machine has 6 poles and the armature is lap connected with 864 conductors.The flux per pole is 0.05Wb.Calculate the (i)the speed ii)the gross torque developed by the armature?
636rpm,756Nm
686rpm,790Nm
783rpm,813Nm
788rpm,823Nm
A 250V shunt motor has an armature resistance of 0.5 ohm and runs at 1200 rpm.when the armature current is 80A.If the torque remains unchanged,find the speed and armature current when the field is strengthened by 25%
(a)
Why compensating and interpoles are provided in dc machine?
4)A 4 pole 250V dc series motor has a wave wound armature with 496 conductors .Calculate i)gross torque
The value of flux per pole under these conditions is 22mWb and the corresponding iron,friction and windage losses total 810W.Armature resistance is 0.19ohm ,field resistance =0.14ohm
190Nm
173.5Nm
188Nm
159Nm
Plz refer Q.No.4,calculate the speed of DC series motor
800rpm
761rpm
642rpm
909rpm
Refer Q.No.4,find the efficiency of the motor?
86.9%
81.9%
75%
89%
What is the function of swinburnes test?
The maximum efficiency of a 100KVa transformer having iron loss of 900kW and FL Cu loss of 1600W occurs at (a) kVA
Transformer cores are laminated to
(a)
Why thyristor control of dc series motor is employed?
The equivalent resistance of primary of a transformer having K=5 and R1=0.1ohm when referred to secondary it becomes
0.5ohm
0.02ohm
0.004ohm
2.5ohm
The ordinary efficiency of a transformer is maximum when
(a)
The main purpose of performing open circuit test on a transformer is to measure its
(a)
A 4 Pole DC Generator has awave wound armature with 792 conductors .The flux per pole is 0.0121Wb.Determine the speed at which it should run to generate 240V on no load?
792 rpm
751 rpm
698rpm
780rpm
In dc generators armature reaction is produced actually by
(a)
IN dc generator,the effect of armature reaction on the main pole flux is to
(a)
What causes sparking at the brushes
What is meant by armature reaction?
The commutation process in a dc generator basically involves
Why parallelling of DC Generator is needed?
