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 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 : In direct cooled system using hydrogen both stator and rotor conductors are made (a) solid (b) hollow (c) perforated (d) any ofthe above
Last Answer : (b) hollow
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
Last Answer : (a) increase
Description : In D.C. motor construction, commutating windings are wound on _________________. A. opposite main poles B. interpoles C. adjacent main poles D. the rotor core
Last Answer : Answer: B
Description : The introduction of interpoles in between the main poles improves the performance of DC machines because: (A) the interpole produces additional flux to augment the torque developed (B) the flux waveform ... of the armature is removed (D) a counter emf is induced in the coil undergoing commutation
Last Answer : The introduction of interpoles in between the main poles improves the performance of DC machines because: a counter emf is induced in the coil undergoing commutation
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 compound-wound motor, a portion of the line current flows through the _____________. A. inertial poles B. stator C. shunt field coils D. frame
Last Answer : Answer: C
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 : 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 : 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 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 heated parts of an electrical machine dissipate heat into their surroundings by which of the following modes of heat dissipation ? (a) Conduction (b) Convection (c) Radiation (d) All ofthe above
Last Answer : (d) All ofthe above
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 : Basic electrical motor action depends on _______________. A. a conductor rotated within a magnetic field B. a current carrying conductor placed in a magnetic field C. the relative force of the commutator and commutating poles D. the relative force of the armature and interpoles
Description : An AC circuit has capacitance arranged in series. If the line voltage remains constant, the capacitive reactance value can be varied by changing the _____________. A. line frequency B. resistance C. number of commutating poles D. number of interpoles
Last Answer : Answer: A
Description : The speed of a squirrel-cage motor is usually changed by _____________. A. varying the frequency to the machine B. adding resistance in series with the stator windings C. adding resistance in parallel with the stator windings D. changing the number of connected poles in the stator
Last Answer : Answer: D
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 width of the duct is usually (a) 4 mm (b) 6 mm (c) 8 mm (d) 10 mm
Last Answer : (d) 10 mm
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 : A practical formula for determining the thickness of insulation between low voltage and high voltage windings is (a) 1 + 0.2 kVmm (6) 2 + 0.5 kVmm (c) 4 + 0.7 kV mm (d) 5 + 0.9 kV mm
Last Answer : (d) 5 + 0.9 kV mm
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 275 kV transformers, using cold rolled grain oriented steel, which of the following values of flux density may be used? (a) 1.0 Wb/m2 (b) 1.1 Wb/m2 (c) 1.3 Wb/m2 (d) 1.6 Wb/m2 (e) None of the above
Last Answer : (d) 1.6 Wb/m2
Description : Power transformers have rating (a) equal to 50 kVA (6) equal to 100 kVA (c) above 200 kVA (d) none of the above
Last Answer : (c) above 200 kVA
Description : By which of the following methods the temperature rise of windings and other parts may be determined ? (a) Thermometer method (6) Resistance method (c) Embedded temperature detector method (d) Any of the above
Last Answer : (d) Any of the above
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 ____ 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
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 : 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
Last Answer : (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
Last Answer : (d) Cast-iron
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
Description : The cylindrical windings using circular conductors are used for current rating of (a) upto 20 A (b) upto 40 A (c) upto 60 A (d) upto 80 A
Last Answer : (d) upto 80 A
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 : Which of the following is the basic consideration in the design of insulation ? (a) Electrical considerations (b) Mechanical considerations (c) Thermal considerations (d) All of the above
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 : 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 : The usual values of maximum flux densities for distribution transformers using hot rolled silicon steel are (a) 0.5 to 0.8 Wb/m2 (b) 0.8 to 1.0 Wb/m2 (c) 1.1 to 1.35 Wb/m2 (d) 1.4 to 1.8 Wb/m2
Last Answer : (c) 1.1 to 1.35 Wb/m2
Description : D.C. windings are (a) sometimes 2-layer type (b) never 2-layer type (c) always 2-layer type (d) none of the above
Last Answer : (c) always 2-layer type
Description : The voltage control in electric supply networks in required on account of which of the following reasons ? (a) Adjustment of voltage at consumers premises within statutory limits (b) Control of ... daily and seasonal voltage variations in accordance with variations of load (d) All of the above
Description : The flash point of transformer oil should be higher than (a) 40°C (b) 60°C (c) 80°C (d) 104°C
Last Answer : (d) 104°C
Description : The forced oil and air circulation method is usual one for transformers of capacities (a) upto 5 MVA (b) upto 10 MVA (c) upto 20 MVA (d) 30 MVA upwards
Last Answer : (d) 30 MVA upwards
Description : Transformers with a capacity of upto _____ have a cooling radiator system with natural cooling (a) 2 MVA (b) 5 MVA (c) 7.5 MVA (d) 10 MVA
Last Answer : (d) 10 MVA
Description : The heat dissipating capability of transformers of ratings higher than 30 kVA in increased by providing which of the following ? (a) Corrugations (b) Fins (c) Tubes (d) Radiator tanks (e) All of the above
Description : Disc windings are primarily used in (a) short capacity transformers (b) medium capacity transformers (c) high capacity transformers (d) any of the above
Last Answer : (c) high capacity transformers