Description : Electrical machines having power outputs ranging from a few kW upto approximately 250 kW may be classified as (a) small size machines (b) medium size machines (c) large size machines (d) any ofthe above
Last Answer : (b) medium size machines
Description : Electrical machines having a power output upto about 750 W may be called_______machines. (a) small size (b) medium size (c) large size (d) any of the above
Last Answer : (a) small size
Description : In ______ machines, the size of the shaft is decided by the critical speed which depends on the deflection of the shaft. (a) small (b) medium (c) large (d) any of the above.
Last Answer : (c) large
Description : In D.C. machines, the ____ in field mmf results in increase in size and cost of machines. (a) increase (b) decrease (c) either of the above (d) none of the above
Last Answer : (a) increase
Description : When the two coil sides forming a coil are spaced exactly one pole pitch apart they are said to be of (a) short pitch (b) full pitch (c) either of the above (d) none of the above
Last Answer : (b) full pitch
Description : The winding where dummy coils are used is sometimes called (a) duplex winding (b) triplex winding (c) forced winding (d) none of the above
Last Answer : (c) forced winding
Description : In D.C. machines, ir order to prevent excessive distortion of field form by the armature reaction, the field mmf must be made (a) equal to that of armature mmf (b) less in comparison with the arma¬ture mmf (c) large in comparison with the arma-ture mmf (d) none of the above
Last Answer : (c) large in comparison with the arma-ture mmf
Description : D.C. machines designed with a large value of air gap length have (a) worst, ventilation (b) poor ventilation (c) better ventilation (d) none of the above
Last Answer : (c) better ventilation
Description : The operation of a D.C. machine with large air gap lengths is comparatively (a) quiet (b) noisy (c) either of the above (d) none of the above
Last Answer : (a) quiet
Description : The high voltage winding is usually which of the following type ? (a) Cylindrical winding with circular conductors (b) Cross-over winding with either circular or small rectangular conductors (c) Continuous disc type winding with rectangular conductors (d) All of the above types
Last Answer : (d) All of the above types
Description : In D.C. machines the number of slots per pole usually lies (a) between 2 to 4 (b) between 6 to 8 (c) between 9 to 16 (d) between 20 to 30
Last Answer : (c) between 9 to 16
Description : In D.C. machines the usual limit of slot pitch is (a) between 5 to 10 mm (b) between 10 to 15 mm (c) between 15 to 20 mm (d) between 25 to 35 mm
Last Answer : (d) between 25 to 35 mm
Description : In D.C. machines the width of the duct is usually (a) 4 mm (b) 6 mm (c) 8 mm (d) 10 mm
Last Answer : (d) 10 mm
Description : Machines cooled by direct cooling method may be called (a) "supercharged" (b) "inner cooled" (c) "conductor cooled" (d) any of the above
Last Answer : (d) any of the above
Description : Multiple inlet system of air cooling of turbo-alternators can be used for machines of rating upto (a) 10 MW (b) 30 MW (c) 60 MW (d) 150 MW
Last Answer : (c) 60 MW
Description : is universally used for windings of electrical machines because it is easily workable without any possibility of fracture. (a) Silver (b) Steel (c) Aluminium (d) Copper
Last Answer : (d) Copper
Description : The action of electromagnetic machines can be related to which ofthe following basic principles ? (a) Induction (b) Interaction (c) Alignment (d) All of the above
Last Answer : (d) All of the above
Description : Commercial available medium size machines have a speed range of ______ . (a) 200 to 400 r.p.m. (b) 600 to 1000 r.p.m. (c) 1000 to 1500 r.p.m. (d) 2000 to 2500 r.p.m.
Last Answer : (d) 2000 to 2500 r.p.m.
Description : The design of mechanical parts is particularly important in case of _____ speed machines. (a) low (b) medium (c) high (d) any of the above
Last Answer : (c) high
Description : The distance between the starts of two consecutive coils measured in terms of coil sides is called (a) front pitch (b) winding pitch (c) commutator pitch (d) back pitch
Last Answer : (b) winding pitch
Description : The change in flux linkages can be caused in which ofthe following ways ? (a) The flux is constant with respect to time and is stationary and the coil moves through it (b) The coil is stationary with ... above occure together, i.e., the coil moves through a time varying field (d) All ofthe above
Last Answer : (d) All ofthe above
Description : Yokes with rectangular cross-section are used for (a) small capacity transformers (b) medium capacity transformers (c) large capacity transformers (d) any of the above
Last Answer : (a) small capacity transformers
Description : Aluminium when adopted as a conductor material in ______ transformers, decreases the overall cost of the transformer (a) small size (b) medium size (c) large size (d) any of the above size
Description : The weight of copper of both armature and field windings decreases with _____ in number of poles. (a) increase (b) decrease (c) either of the above (d) none of the above
Description : The insulation between windings and grounded core and the insulation between the windings of the same phase is called (a) minor insulation (b) major insulation (c) either of the above (d) none of the above
Last Answer : (b) major insulation
Description : are always double layer type. (a) Closed windings (b) Open windings (c) Either of the above (d) None of the above
Last Answer : (a) Closed windings
Description : are used for construction of core of electromagnets. (a) Soft magnetic materials (b) Hard magnetic materials (c) Either (a) or (b) (d) None of the above
Last Answer : (a) Soft magnetic materials
Description : electromagnets generally function as holding magnets. (a) Tractive (b) Portative (c) Either of the above (d) None of the above
Last Answer : (b) Portative
Description : Tractive magnets are operated from (a) a.c. supply (b) d.c. supply (c) either a.c. or d.c. supply (d) none of the above
Last Answer : (c) either a.c. or d.c. supply
Description : The time taken by the machine to attain 0.632 of its final steady temperature rise is called (a) heating time constant (b) cooling time constant (c) either (a) or (b) (d) none of the above
Last Answer : (a) heating time constant
Description : The noise produced by a ______ cooled machine is less as the rotor moves in a medium of smaller density. (a) air (b) hydrogen (c) either (a) or (b) (d) none of the above
Last Answer : (b) hydrogen
Description : The efficiency of a machine should be as ______ as possible to reduce the operating cost. (a) high (b) low (c) either of the above (d) none of the above
Last Answer : (a) high
Description : A current density of _____ is ilsed for large power transformers with forced circulation of oil or with water cooling coils (a) 1.5 to 2.5 A/mm2 (b) 3.5 to 4.5 A/mm2 (c) 4.0 to 5.0 A/mm2 (d) 5.4 to 6.2 A/mm2
Last Answer : (d) 5.4 to 6.2 A/mm2
Description : For large power transformers, self oil cooled type or air blast type which of the following values of current density may be used ? (a) 1.0 to 1.2 A/mm2 (b) 1.5 to 2.0 A/mm2 (c) 2.2 to 3.2 A/mm2 (d) 3.2 to 4.2 A/mm2
Last Answer : (c) 2.2 to 3.2 A/mm2
Description : Which ofthe following materials is used in the manufacture of resistance grids to be used in the starters of large motors ? (a) Copper (b) Aluminium (c) Steel (d) Cast-iron
Last Answer : (d) Cast-iron
Description : In induction motors, the length of air gap in kept as small as mechanically possible is order to have (a) low power factor (b) high power factor (c) high over load capacity (d) any of the above
Last Answer : (b) high power factor
Description : Which of the following methods may be adopted to reduce the effects of armature reaction ? (a) Increase in length of air gap at pole tips (b) Increasing reluctance of pole tips (c) Compensating windings (d) Interpoles (e) All of the above
Last Answer : (e) All of the above
Description : In a D.C. machine, the value of peripheral speed should not, normally, exceed (a) 10 m/s (b) 20 m/s (c) 30 m/s (d) 40 m/s
Last Answer : (c) 30 m/s
Description : In a D.C. machine the current per brush arm should not be more than (a) 100 A (6) 200 A (e) 300 A (d) 400 A
Last Answer : (d) 400 A
Description : In a D.C. machine the number of brush arms is _____ the number of poles. (a) less than (b) equal to (c) greater than (d) none of the above
Last Answer : (b) equal to
Description : Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ? (a) Increased I R losses (b) Increased core losses (c) Poor commutation (d) Change in motor parameters (e) All of the above
Description : ________ is the common method of applying brushes to the commntator. (a) Radial (b) Trailing (c) Reaction (d) All of the above
Description : Which of the following brushes can be used for high values of current density ? (a) Metal graphite brushes (b) Hard carbon brushes (c) Electro-graphitic brushes (d) Natural graphite brushes
Last Answer : (a) Metal graphite brushes
Description : _____ brushes are fragile and cause excessive wear of commutator, (a) Natural graphite (b) Hard carbon (c) Electro graphitic (d) Metal graphite
Last Answer : (a) Natural graphite
Description : is usually used for brush rockers (a) Mild steel (b) Copper (c) Aluminium (d) Cast-iron
Description : The laminations of the armature of a D.C. machine are usually _____ thick. (a) 0.1 to 0.2 mm (b) 0.2 to 0.3 mm (c) 0.3 to 0.4 mm (d) 0.4 to 0.5 mm
Last Answer : (d) 0.4 to 0.5 mm
Description : The stator of a D.C. machine comprises of (a) main poles (6) interpoles (c) frame (d) all of the above
Last Answer : (d) all of the above
Description : D.C. servomotors are used in (a) purely D.C. control systems (6) purely AC. control systems (c) both D.C. and AC. control systems (d) none of the above
Last Answer : (a) purely D.C. control systems
Description : Which of the following in an application of D.C. motors? (a) Traction (b) Drives for process industry (c) Battery driven vehicles (d) Automatic control (e) All of the above
Description : The surge phenomenon is particularly important in case of (a) low voltage transformers (b) medium voltage transformers (c) high voltage transformers (d) any of the above
Last Answer : (c) high voltage transformers