# In a four-pole D.C. machine?

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### Answer :

In a four-pole D.C. machine alternate poles are north and south.

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Last Answer : In a D.C. machine stray loss is the sum of iron loss and mechanical loss.

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Last Answer : To avoid formation of grooves in the commutator of a D.C. machine the brushes of opposite polarity should track each other.

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Last Answer : Open circuited armature coil of a D.C. machine is identified by the scarring of the commutator segment to which open circuited coil is connected and indicated by a spark completely around the commutator.

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Last Answer : In case of D.C. machine winding, number of commutator segments is equal to number of armature coils.

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Last Answer : Iron losses in a D.C. machine are independent of variations in load.

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The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is  (1) 1000V (2) 100V (3) 600V (4) 10,000V
Last Answer : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is 1000V

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A 36 slot, 4 -pole, dc machine has a simplex lap winding with two conductors per slot. The back pitch and front pitch adopted could be respectively
Last Answer : A 36 slot, 4 -pole, dc machine has a simplex lap winding with two conductors per slot. The back pitch and front pitch adopted could be respectively 19,17

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Why poles of dc machine are laminated?
Last Answer : Poles of DC machines are laminated to reduce the eddy current losses in the poles.

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Last Answer : Copper losses,iron losses,variable losses , constant losees

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Explain concept of back emf in DC machine. State how it governs armature current.
Last Answer : Back emf: When the armature of DC machine rotates under the influence of driving torque, the armature conductors move in the magnetic field and cut it and hence emf is induced in them. The ... flow of armature current i.e. it automatically changes the armature current to meet load requirements.

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A 200 V DC machine supplies 20 A at 200 V as a generator. The armature resistance is 0.2 Ohm. If the machine is now operated as a motor at same terminal voltage and current but with the flux increased by 10%, the ratio of motor speed to generator speed is
Last Answer : A 200 V DC machine supplies 20 A at 200 V as a generator. The armature resistance is 0.2 Ohm. If the machine is now operated as a motor at same terminal voltage and current but with the flux increased by 10%, the ratio of motor speed to generator speed is 0.87

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Aluminium is not used as winding wire for the armature of a dc machine because  (1) aluminium has low resistivity (2) a large winding space is taken by aluminium conductors and creates ... ) the thermal conductivity of aluminium is low (4) aluminium has low conductivity as compared to copper
Last Answer : Aluminium is not used as winding wire for the armature of a dc machine because  (2) a large winding space is taken by aluminium conductors and creates jointing problems (3) the thermal conductivity of aluminium is low (4) aluminium has low conductivity as compared to copper

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In a dc machine, interpoles are used to  (1) neutralize the effect of armature reaction in the interpolar region (2) generate more induced emf in the armature (3) avoid interference of the armature flux with the main -field flux (4) reduce the demagnetizing effect of armature reaction
Last Answer : In a dc machine, interpoles are used to neutralize the effect of armature reaction in the interpolar region

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The magnetic neutral plane shifts in a dc machine (A) in the direction of motion of motor (B) in the direction of motion of generator (C) due to increase in the field flux (D) cause reduction of flash over between commutator segments
Last Answer : The magnetic neutral plane shifts in a dc machine in the direction of motion of generator

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What is the percentage of stray losses in DC machine?
Last Answer : Percentage of stray losses in DC machine is about 1 % .

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Brushes of DC machine are made up of ?
Last Answer : Brushes of DC machine are made up of carbon.

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Last Answer : Iron loss, copper loss and mechanical losses these are the losses in DC machine.

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Eddy currents are induced in the pole shoes of a D.C. machine due to?
Last Answer : Eddy currents are induced in the pole shoes of a D.C. machine due to relative rotation between field and armature.

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Last Answer : In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called armature.

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The armature current on symmetrical 3 phase short circuit of a synchronous machine (salient pole)  (A) has q -axis current only (B) has d -axis current only (C) has both d and q axis currents (D) cannot be divided between q and d axis currents
Last Answer : The armature current on symmetrical 3 phase short circuit of a synchronous machine (salient pole) has d -axis current only

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Last Answer : In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be 8.

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Last Answer : In D.C. generators the pole shoes are fastened to the pole core by counter sunk screws.

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What is the function of the roll forming machine ?
Last Answer : It is much easier to make croissants and other dinner rolls with a roll forming machine, than it is to roll the croissants by hand. The primary function, therefore, is to take the mixed dough and to thin it, then fold it, to prepare the dough for baking.

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UNIT 1 fundamentals of AC rotating machine Contents 1.1 Introduction 1.2 Advantages 1.3 Parts of AC machines 1.4 Synchronous speed 1.5 AC winding 1.6 Winding factor ( ... alternator or generator 1.9 Numericals 1.10 Harmonic 1.11 Slot harmonics 1.12 Harmonics minimization
Last Answer : 1.2 Advantages: In practices most of alternator have rotating magnetic field type construction with stationary armature due to following reason. The generation level of AC voltage may be in the range ... at high speed. Only two Slip rings are required to excited the field by AC supply.

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Analyze the differences of FOC and DTC. The switching frequency of FOC is 1.3 kHz and the average switching frequency of DTC is the same.

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Last Answer : In 8085 microprocessor, how many T-states does OPCODE FETCH machine cycle normally require (i.e., when HOLD and WAIT signals are NOT forced)? A) 4 to 6 B) 3 to 8 C) 2 to 3 D) 8 to 12

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In a synchronous machine, if the field flux axis ahead of the armature field axis in the direction of rotation, the machine is operating as  (1) synchronous motor (2) synchronous generator (3) asynchronous motor (4) asynchronous generator
Last Answer : In a synchronous machine, if the field flux axis ahead of the armature field axis in the direction of rotation, the machine is operating as synchronous generator

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The 'Equal area criterion' for the determination of transient stability of a synchronous machine connected to an infinite bus  (1) ignores line as well as synchronous machine resistance ... consideration the possibility of machine losing synchronism after it has survived during the first swing.
Last Answer : 1

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During a disturbance on a synchronous machine, the rotor swings form A to B before finally setting down to steady state at point C on the power angle curve. The speed of the machine during oscillation is synchronous at point(s)
Last Answer : During a disturbance on a synchronous machine, the rotor swings form A to B before finally setting down to steady state at point C on the power angle curve. The speed of the machine during oscillation is synchronous at point(s) only at C

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Torque angle for the synchronous machine is the angle between (A) stator magnetic field and rotor magnetic field (B) stator magnetic field and net magnetic field in the air gap (C) rotor magnetic field and net magnetic field in the air gap (D) excitation voltage and impedance voltage drop
Last Answer : Torque angle for the synchronous machine is the angle between rotor magnetic field and net magnetic field in the air gap

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Last Answer : The wattage of motor for driving domestic sewing machine will be around 100 to 150 W.

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Last Answer : To limit the operating temperature an electrical machine should have proper current rating.

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Last Answer : Synchronsizing power of a synchronous machine is inversely proportional to the synchronous reactance.

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