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In DC generators lamination core are generally made of?

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In DC generators lamination core are generally made of silicon steel.

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Description : Identify the increasing order of voltage regulation of the following dc generators a same load :  (A) differential compound, shunt and under compound  (B) shunt, differential compound and ... C) under compound, shunt and differential compound  (D) shunt, under compound and differential compound

Answer : Identify the increasing order of voltage regulation of the following dc generators a same load : under compound, shunt and differential compound 

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

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

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

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

Answer : D.C. generators are connected to the busbars or disconnected from them only under the floating condition to avoid sudden loading of the primemover, to avoid mechanicaljerk to the shaft, to avoid burning of switch contacts.

Answer : D.C. generators are installed near the load centres to reduce line losses.

Answer : D.C. generators are normally designed for maximum efficiency around full-load.

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

Answer : In D.C. generators, the brushes on commutator remain in contact with conductors which lie under interpolar region.

Answer : In D.C. generators, current to the external circuit from armature is given through commutator commutator.

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.

Description : Two synchronous generators operating in parallel supply a common load of 2.5 MW. The frequency-power characteristics have a common slope of 1 MW/Hz and the no-load frequencies of the generators are 51.5 Hz and 51.0 Hz, ... system frequency is (A) 50 Hz (B) 51 Hz (C) 51.25 Hz (D) 51.5 Hz

Answer : Two synchronous generators operating in parallel supply a common load of 2.5 MW. The frequency-power characteristics have a common slope of 1 MW/Hz and the no-load frequencies of the generators are 51.5 Hz and 51.0 Hz, respectively. Then the system frequency is 50 Hz

Description : The desirable properties of transformer core material are  (1) low permeability and low hysteresis loss. (2) high permeability and high hysteresis loss. (3) high permeability and low hysteresis loss. (4) low permeability and hysteresis loss.

Answer : The desirable properties of transformer core material are high permeability and low hysteresis loss.

Description : Why are generators rated in kVA not in kW ?

Answer : Because It's rating of generator kva is apparent power. Kw is active power which we use. And one is kvar reactive power.

Description : Two synchronous generators G1, G2 are operating in parallel and are equally sharing KVAR (Lag) component of load. To shift part of KVAR from G2 to G1, while keeping terminal voltage fixed, the following action must be done

Answer : Two synchronous generators G1, G2 are operating in parallel and are equally sharing KVAR (Lag) component of load. To shift part of KVAR from G2 to G1, while keeping terminal voltage fixed, the following action must be done Raise If1 and lower If2

Answer : Large capacity generators are invariably hydrogen cooled.

Answer : Generators for peak load plants are usually designed for maximum efficiency at 50 to 75 percent full load.

Description : Brushes of DC machine are made up of ?

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

Description : From which material field coils of DC generator are made of?

Answer : Field coils of DC generator are usually made of copper.

Description : Reduction in core losses and increase in permeability are obtained with transformer employing?

Answer : Reduction in core losses and increase in permeability are obtained with transformer employing core built-up of laminations of cold rolled grain oriented steel.

Description : Core type transformers are popular in___________.  (A) High voltage applications (B) Low voltage applications (C) All of the above (D) None of the above

Answer : Core type transformers are popular in High voltage applications

Description : A single core lead sheathed cable with two dielectrics of permittivity 4 and 3, respectively, are subjected to same maximum stress. If the conductor diameter is 1.5 cm, the outer diameter of the first dielectric is (A) 1.125 cm (B) 1.5 cm (C ) 2 cm (D) 8 cm

Answer : A single core lead sheathed cable with two dielectrics of permittivity 4 and 3, respectively, are subjected to same maximum stress. If the conductor diameter is 1.5 cm, the outer diameter of the first dielectric is 2 cm 

Answer : The transformer laminations are insulated from each other by thin coat of varnish.

Description : The core construction is like spokes of a wheel in following transformer:  (A) Berry Type Transformer (B) Core Type Transformer (C) Shell Type Transformer (D) None of the above

Answer : The core construction is like spokes of a wheel in following transformer:  Berry Type Transformer

Description : The main purpose of using core in a transformer is to (A) decrease iron losses (B) eliminate magnetic hysteresis (C) reduce reluctance of the common magnetic circuit (D) prevent eddy current loss

Answer : Reduce Relucatnce of the common magnetic circuit.

Description : State the material used for making (1) Magnetic Core (2) Fuse element  

Answer : The material used for making of:  (1) Magnetic Core : Iron, cobalt, Nickel, CRGO, HRGO , silicon steel  (2) Fuse Element: Tin- lead wire, Tinned copper wire 

Description : State any four characteristics of core type transformer.

Answer : Characteristics of core type transformer: i) It has one window. ii) It has one magnetic circuit. iii) Core surrounds the winding. iv) Average length of core is more. v) Area of cross ... Better cooling for winding. vii) Mechnical strength is comparatively less. viii) Repair and maintenance is easy.

Description : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is

Answer : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is 0.707

Description : A single core cable is designed to work for a single phase system with a peak voltage of 220 kV. The maximum permissible stress in the dielectric is not to exceed 20 kV/mm. For economical size, the overall core diameter of the cable is (A) 28.2 mm (B) 26.4 mm (C) 24.4 mm (D) 22.0 mm

Answer : A single core cable is designed to work for a single phase system with a peak voltage of 220 kV. The maximum permissible stress in the dielectric is not to exceed 20 kV/mm. For economical size, the overall core diameter of the cable is 22.0 mm

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

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

Answer : When a conductor carries more current on the surface as compared to core, it is due to skin effect.

Answer : Material used for construction of transformer core is usually silicon steel.

Description : When secondary of a current transformer is open-circuited its iron core will be?

Answer : When secondary of a current transformer is open-circuited its iron core will be hot because of heavy iron losses taking place in it due to high flux density.

Description : The size of a transformer core will depend on?

Answer : The size of a transformer core will depend on frequency and area of the core.

Description : Why does the core of a transformer need to be laminated?

Answer : Transformer cores are laminated to reduce eddy current loss.

Answer : Transformer core is laminated to reduce Eddy current losses.

Description : In dc machines, the armature windings are placed on the rotor because of the necessity for  (1) electromechanical energy conversion (2) generation of voltage (3) commutation (4) development of torque

Answer : 3  Commutation

Description : In a DC generator the windings of interpoles are connected :  (A) in series with main field winding, to create a pole,of same polarity as the main pole ahead in the direction of rotation.  ... winding, to create a pole of opposite polarity as the main pole ahead in the direction of rotation.

Answer : In a DC generator the windings of interpoles are connected :  in series with the armature winding, to create a pole of same polarity as the main pole ahead in the direction of rotation. 

Description : 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

Answer : In a dc machine, interpoles are used to neutralize the effect of armature reaction in the interpolar region

Description : What are the speed control methods of dc motor?

Answer : Field control of DC motor Armature control of DC motor

Answer : D.C. Series motor is generally preferred for cranes and hoists.

Answer : The starting resistance of a D.C. motor is generally low.

Description : The fall in speed of a dc generator due to increase in load can be corrected by  (1) cooling the armature.. (2) increasing the excitation. (3) reducing the load voltage. (4) increasing the input to the prime mover

Answer : It   can  be  corrected  by  increasing  the  input  to  the  prime  mover.

Description : In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is :

Answer : In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is : 0.075

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

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 : The function of a brush and commutator arrangement in a dc motor is to  (1) produce unidirectional torque (2) produce unidirectional current in the armature (3) help in changing the direction of rotation of the armature (4) reduce sparking

Answer : The function of a brush and commutator arrangement in a dc motor is to produce unidirectional torque

Description : Describe the reason of using dc series motor for electric trains.

Answer : Electric trains require an inverse torque speed characteristics for proper operation. That is a higher torque is required at start (when speed is nil or low) and as the train picks up ... torque - speed characteristics of DC series motors match, these motors are suitable for electric trains

Description : A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The net Voltage across armature resistance at the time of plugging will be

Answer : A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The net Voltage across armature resistance at the time of plugging will be 474 V

Description : 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

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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