# Eddy currents are induced in the pole shoes of a D.C. machine due to?

Eddy currents are induced in the pole shoes of a D.C. machine due to?

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

## Related questions

Description : The eddy current loss in a dc generator is 400 W at 40 Hz frequency of reversal and constant flux density. When frequency is increased to 50 Hz., eddy current loss is :  (A) 256 W (B) 320 W (C) 500 W (D) 625 W

Last Answer : The eddy current loss in a dc generator is 400 W at 40 Hz frequency of reversal and constant flux density. When frequency is increased to 50 Hz., eddy current loss is : 625 W

Description : Explain following techniques related to energy conservation in transmission and distribution system. (i) By balancing phase currents (ii) Variable technical losses (I2R losses).

Last Answer : (i) Balancing Phase currents: Proper (healthy balanced) three phase loads always draw equal currents in all lines but single phase loads in the 3 phase 4 wire system or loads connected between two ... . 11) Minimize I2R losses. 12) Balance the load currents. 13) Regulate the system voltages.

Description : The transient currents are associated with the?

Last Answer : The transient currents are associated with the changes in the stored energy in the inductors and capacitors.

Last Answer : In a single phase power factor meter the phase difference between the currents in the two pressure coils is exactly 90°.

Last Answer : For handling greater currents induction wattmeters are used in conjunction with current transformers.

Last Answer : Interruption of large currents by relay requires arc suppressing blow out coils, wide separation of the opened contacts, high speed opening of contacts.

Description : Give two applications of each : 1) Eddy current sensor 2) Optical sensor.

Last Answer : Eddy current sensor : 1. Detection of non-magnetic but conductive materials. 2. Displacement sensing 3. Position sensing Optical sensor : 1. Position Detection 2. Velocity Detection 3. Acceleration Detection 4. Direction Detection

Description : Which of the following can reduce the Eddy current losses? A) By making the core of a stack of plates electrically insulated from each other B) By making the core of solid block C) By increasing the applied voltage  D) None of these

Last Answer : Which of the following can reduce the Eddy current losses? A) By making the core of a stack of plates electrically insulated from each other B) By making the core of solid block C) By increasing the applied voltage  D) None of these

Description : Eddy current damping cannot be used for moving iron instrument because

Last Answer : Eddy current damping cannot be used for moving iron instrument because the presence of a permanent magnet required for such purpose would affect the deflection and hence the reading of the instrument

Description : A ferrite core has less eddy current loss than an iron core because?

Last Answer : A ferrite core has less eddy current loss than an iron core because ferrites have high hysteresis.

Last Answer : The disc of an instrument using eddy current damping should be of conducting and non-magnetic material.

Description : What is the difference between eddy current and hysteresis loss?

Last Answer : Loss occurred by magnetising and demagnetising process is called histerisis loss and the current flowed due to the magnetic field produced by the electric field applied is called eddy current losses

Description : Explain hysteresis loss, eddy current loss and skin effect limitations with reference to magnetic material.

Last Answer : Hysteresis loss: Hysteresis loss is a loss which occurs due to the friction of magnetic domain due to the change in magnetic field in ferromagnetic material like iron. Hysteresis loss causes power loss ... loss in transformer is given by, We=Kef2Kf2Bm2watts Skin effect limitations:

Description : what is eddy current ?

Last Answer : In magnetic circuits when we supply current to coil which wound on some core( of iron cast iron, ferrite ) material it produce magnetic field but there is small amount of flux which also ... heat and losses in magnetic circuits..for good working conditions we always try to minimize eddy current

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

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

Description : 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

Description : If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be?

Last Answer : If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be zero.

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.

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

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

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.

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

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

Description : 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

Last Answer : If  equalising bar is connected to the 2 DC generators  the current will be equal in 2 generators irrespective of parallel connection so that we connect equaliser bar

Last Answer : The critical resistance of the D.C. generator is the resistance of field.

Last Answer : A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be about 2 V.

Last Answer : In a level compounded D.C. generator, full load terminal voltage is equal to no-load terminal voltage.

Last Answer : In a D.C. generator in case the resistance of the field winding is increased, then output voltage will decrease.

Last Answer : A D.C. generator can be considered as rotating amplifier.

Last Answer : In a D.C. generator, the critical resistance refers to the resistance of field.

Last Answer : Flashing the field of D.C. generator means creating residual magnetism by a D.C. source.

Last Answer : If a D.C. generator fails to build up the probable cause could not be field resistance less than the critical resistance.

Last Answer : In D.C. generators on no-load, the air gap flux distribution in space is flat topped.

Last Answer : In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when there is no load on|he generator.

Last Answer : The e.m.f. generated in a D.C. generator is directly proportional to speed of armature.

Last Answer : In D.C. generators the polarity of the interpoles is the same as that of the main pole ahead.

Last Answer : In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when number of poles is 2.

Last Answer : D.C. generator generally preferred for charging automobile batteries is long shunt compound generator.

Last Answer : For the parallel operation of two or more D.C. compound generators, we should ensure that series fields of all generators should be either on positive side or negative side of the armature.

Last Answer : Satisfactory commutation of D.C. machines requires brushes should be of proper grade and size, brushes should smoothly run in the holders, smooth, concentric commutator properly undercut.

Last Answer : The armature core of a D.C. generator is usually made of silicon steel.

Last Answer : In a D.C. generator the ripples in the direct e.m.f. generated are reduced by using carbon brushes of superior quality.

Last Answer : Compensating windings are used in D.C. generators to neutralise the cross-magnetising effect of the armature reaction.