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

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
by

1 Answer

Answer :

(d) 5.4 to 6.2 A/mm2
by

Related questions

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

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

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

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

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

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

The winding where dummy coils are used is sometimes called (a) duplex winding (b) triplex winding (c) forced winding (d) none of the above

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

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

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

In transformers using hot rolled steel, the cross-section of the yoke is made about _____ greater than that of the core (a) 5 percent (b) 10 percent (c) 15 percent (d) 30 percent (e) none of the above

Description : In transformers using hot rolled steel, the cross-section of the yoke is made about _____ greater than that of the core (a) 5 percent (b) 10 percent (c) 15 percent (d) 30 percent (e) none of the above

Last Answer : (c) 15 percent

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

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

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 : 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

Last Answer : (a) small size

Power transformers have rating (a) equal to 50 kVA (6) equal to 100 kVA (c) above 200 kVA (d) none of the above

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

The density of hydrogen is _____ times the density of air. (a) 0.07 (b) 1.5 (c) 2.5 (d) 3.5

Description : The density of hydrogen is _____ times the density of air. (a) 0.07 (b) 1.5 (c) 2.5 (d) 3.5

Last Answer : (a) 0.07

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

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

Helical windings are used in (a) distribution transformers (b) power transformers (c) shell type transformers (d) none of the above

Description : Helical windings are used in (a) distribution transformers (b) power transformers (c) shell type transformers (d) none of the above

Last Answer : (b) power transformers

Power transformers should be designed to have maximum efficiency (a) at one-fourth load (b) at one-half load (c) at or near full load (d) any of the above

Description : Power transformers should be designed to have maximum efficiency (a) at one-fourth load (b) at one-half load (c) at or near full load (d) any of the above

Last Answer : (c) at or near full load

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

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

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

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

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 : 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

Last Answer : (e) All of the above

Disc windings are primarily used in (a) short capacity transformers (b) medium capacity transformers (c) high capacity transformers (d) any 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

Multi-layer helical windings are commonly used in the transformers as high voltage windings (a) upto 20 kV (b) upto 50 kV (c) upto 80 kV (d) for 110 kV and above

Description : Multi-layer helical windings are commonly used in the transformers as high voltage windings (a) upto 20 kV (b) upto 50 kV (c) upto 80 kV (d) for 110 kV and above

Last Answer : (d) for 110 kV and above

Cylindrical windings using circular conductors, employed in transformers, are (a) single layered (b) double layered (c) multi-layered (d) none of the above

Description : Cylindrical windings using circular conductors, employed in transformers, are (a) single layered (b) double layered (c) multi-layered (d) none of the above

Last Answer : (c) multi-layered

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

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

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

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

Direct water cooling of rotor winding presents (a) no mechanical difficulties (b) lesser mechanical difficulties (c) greater mechanical difficulties (d) none of the above

Description : Direct water cooling of rotor winding presents (a) no mechanical difficulties (b) lesser mechanical difficulties (c) greater mechanical difficulties (d) none of the above

Last Answer : (c) greater mechanical difficulties

With direct water cooling it is possible to have ratings of about (a) 200 MW (b) 300 MW (c) 400 MW (d) 600 MW

Description : With direct water cooling it is possible to have ratings of about (a) 200 MW (b) 300 MW (c) 400 MW (d) 600 MW

Last Answer : (d) 600 MW

In self cooled motors the cooling time constant is about ______ than the heating time constant because cooling conditions are worse at standstill. (a) 2 to 3 times greater (b) 3 to 4 times greater (c) 4 to 5 times greater (d) none of the above

Description : In self cooled motors the cooling time constant is about ______ than the heating time constant because cooling conditions are worse at standstill. (a) 2 to 3 times greater (b) 3 to 4 times greater (c) 4 to 5 times greater (d) none of the above

Last Answer : (a) 2 to 3 times greater

Machines cooled by direct cooling method may be called (a) "supercharged" (b) "inner cooled" (c) "conductor cooled" (d) any of the above

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

cooling is the process of dissipating the armature and field winding losses to a cooling medium circulating within the winding insulation wall (a) Direct (b) Indirect (c) Conventional (d) Any ofthe above

Description : cooling is the process of dissipating the armature and field winding losses to a cooling medium circulating within the winding insulation wall (a) Direct (b) Indirect (c) Conventional (d) Any ofthe above

Last Answer : (a) Direct

With conventional hydrogen cooling it is possible to increase the rating of a single unit to (a) 50 MW (b) 100 MW (c) 200 MW (d) none ofthe above

Description : With conventional hydrogen cooling it is possible to increase the rating of a single unit to (a) 50 MW (b) 100 MW (c) 200 MW (d) none ofthe above

Last Answer : (c) 200 MW

Which ofthe following is an advantage of hydrogen cooling ? (a) Increase in efficiency (b) Increase in ratings (c) Increase in life (d) Smaller size of coolers (e) All ofthe above

Description : Which ofthe following is an advantage of hydrogen cooling ? (a) Increase in efficiency (b) Increase in ratings (c) Increase in life (d) Smaller size of coolers (e) All ofthe above

Last Answer : (e) All ofthe above

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

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

Which ofthe following methods is used for air cooling of turbo-alternators ? (a) One sided axial ventilation (b) Two sided axial ventilation (c) Multiple inlet system (d) All ofthe above

Description : Which ofthe following methods is used for air cooling of turbo-alternators ? (a) One sided axial ventilation (b) Two sided axial ventilation (c) Multiple inlet system (d) All ofthe above

Last Answer : (d) All ofthe above

On which of the following variables heat convected depends ? (a) Power density (b) Temperature difference between heated surface and coolant (c) Thermal resistivity, density, specific heat (d) Gravitational constant (e) All ofthe above

Description : On which of the following variables heat convected depends ? (a) Power density (b) Temperature difference between heated surface and coolant (c) Thermal resistivity, density, specific heat (d) Gravitational constant (e) All ofthe above

Last Answer : (e) All ofthe above

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

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

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

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

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

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

Hydrogen has a heat transfer co-efficient _____ times that of air (a) 1.5 (b) 2.5 (c) 3.5 (d) 4.5

Description : Hydrogen has a heat transfer co-efficient _____ times that of air (a) 1.5 (b) 2.5 (c) 3.5 (d) 4.5

Last Answer : (a) 1.5

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

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

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

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

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 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

_____ brushes are fragile and cause excessive wear of commutator, (a) Natural graphite (b) Hard carbon (c) Electro graphitic (d) Metal graphite

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

The design of mechanical parts is particularly important in case of _____ speed machines. (a) low (b) medium (c) high (d) any of the above

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

Which of the following methods is most accurate ? (a) Equivalent current method (b) Equivalent power method (c) Equivalent torque method (d) Method of average losses

Description : Which of the following methods is most accurate ? (a) Equivalent current method (b) Equivalent power method (c) Equivalent torque method (d) Method of average losses

Last Answer : (a) Equivalent current method

Which of the following methods does not take into account the maximum temperature rise under variable load conditions ? (a) Equivalent power method (b) Equivalent current method (c) Method of average losses (d) Equivalent torque method

Description : Which of the following methods does not take into account the maximum temperature rise under variable load conditions ? (a) Equivalent power method (b) Equivalent current method (c) Method of average losses (d) Equivalent torque method

Last Answer : (c) Method of average losses

By which of the following methods motor rating for variable load drives can be determined ? (a) Method of average losses (b) Equivalent current method (c) Equivalent torque method (d) Equivalent power method (e) All of the above.

Description : By which of the following methods motor rating for variable load drives can be determined ? (a) Method of average losses (b) Equivalent current method (c) Equivalent torque method (d) Equivalent power method (e) All of the above.

Last Answer : (e) All of the above.

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

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

The flash point of transformer oil should be higher than (a) 40°C (b) 60°C (c) 80°C (d) 104°C

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

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

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

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

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

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

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

Dummy coil should not be used in (a) small machines (b) large machines (c) either (a) or (b) (d) none of the above

Description : Dummy coil should not be used in (a) small machines (b) large machines (c) either (a) or (b) (d) none of the above

Last Answer : (b) large machines

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

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