Which bearings preferred for all large power motor?

Which bearings preferred for all large power motor?  
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1 Answer

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Plain bearings  
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Related questions

The reactive power drawn by a motor from an AC generator is the power which is _____________. A. used to establish the magnetic field of the motor B. lost in overcoming friction in the bearings C. strictly converted to heat generated by current flow through the windings D. transmitted directly through the rotor shaft to perform useful work

Description : The reactive power drawn by a motor from an AC generator is the power which is _____________. A. used to establish the magnetic field of the motor B. lost in overcoming friction in the ... by current flow through the windings D. transmitted directly through the rotor shaft to perform useful work

Last Answer : Answer: A

To protect the rotor of a motor disassembled for maintenance or overhaul, it should be ___________________. A. suspended by wire slings in one corner of the shop B. stowed upright on its shaft C. supported by two 'V' notched wood blocks D. returned to the frame as soon as the bearings are removed

Description : To protect the rotor of a motor disassembled for maintenance or overhaul, it should be ___________________. A. suspended by wire slings in one corner of the shop B. stowed upright on its shaft C. supported by two 'V' notched wood blocks D. returned to the frame as soon as the bearings are removed

Last Answer : Answer: C

The following air gap readings were obtained from a horizontally mounted, bilge pump, induction motor, equipped with sleeve bearings: FWD END-AFT END, Top .045 - .049, Right Side .045 - .047, Left Side .045 - .047, Bottom .045 - .041 Which of the f A. both the aft and foward bearings should be replaced. B. Shims should be removed from the aft bearing. C. The forward bearing should be lowered. D. The aft bearing should be lowered.

Description : The following air gap readings were obtained from a horizontally mounted, bilge pump, induction motor, equipped with sleeve bearings: FWD END-AFT END, Top .045 - .049, Right Side .045 - .047, Left ... the aft bearing. C. The forward bearing should be lowered. D. The aft bearing should be lowered.

Last Answer : Answer: A

To protect the rotor of a motor disassembled for maintenance or overhaul, it should be ___________________. A. suspended by wire slings in one corner of the shop B. wrapped in several layers of heavy paper or cardboard C. supported by flat wood blocks on the workbench D. returned to the frame as soon as the bearings are removed

Description : To protect the rotor of a motor disassembled for maintenance or overhaul, it should be ___________________. A. suspended by wire slings in one corner of the shop B. wrapped in several layers of heavy ... flat wood blocks on the workbench D. returned to the frame as soon as the bearings are removed

Last Answer : Answer: B

A split-phase induction squirrel-cage motor will not come up to speed, even though the rated voltage, rated frequency, and rated load are applied. The suspected trouble could be due to _____________. A. a faulty centrifugal switch B. broken rotor bars C. worn bearings D. all of the above

Description : A split-phase induction squirrel-cage motor will not come up to speed, even though the rated voltage, rated frequency, and rated load are applied. The suspected trouble could be due to _____________. A. a faulty centrifugal switch B. broken rotor bars C. worn bearings D. all of the above

Last Answer : Answer: D

One of the generator or motor bearings is generally insulated from the end housing in order to prevent ________. A. rapid brush wear B. current leakage from the shaft C. excessive field winding heat D. circulation of shaft currents induced in the machine's frame

Description : One of the generator or motor bearings is generally insulated from the end housing in order to prevent ________. A. rapid brush wear B. current leakage from the shaft C. excessive field winding heat D. circulation of shaft currents induced in the machine's frame

Last Answer : Answer: D

The following air gap readings were obtained from a horizontally mounted, bilge pump, induction motor, equipped with sleeve bearings: FWD END -AFT END, Top .045 - .049 , Right Side .045 - .047, Left Side .045 - .047 , Bottom .045 - .041 Which of the fo A. The aft bearing should be realigned or replaced. B. Shims should be removed from the aft bearing. C. The forward bearing should be lowered. D. The aft bearing should be lowered.

Description : The following air gap readings were obtained from a horizontally mounted, bilge pump, induction motor, equipped with sleeve bearings: FWD END -AFT END, Top .045 - .049 , Right Side .045 - .047, Left ... the aft bearing. C. The forward bearing should be lowered. D. The aft bearing should be lowered.

Last Answer : Answer: A

In the illustrated motor, roller bearings are used because __________. EL-0001 A. of their ability to absorb moderate thrust loads B. they electrically insulate the rotor from the frame reducing cross-currents C. the shafting and end bells do not require as close a tolerance to properly fit this type of bearing D. the clearance between the rotor and stator is generally as close as mechanical tolerance will permit

Description : In the illustrated motor, roller bearings are used because __________. EL-0001 A. of their ability to absorb moderate thrust loads B. they electrically insulate the rotor from the frame reducing ... clearance between the rotor and stator is generally as close as mechanical tolerance will permit

Last Answer : Answer: D

The air gap in an induction motor should be periodically checked with a feeler gage to prevent possible ___________. A. rotor contact with the stator B. axial misalignment of the rotor C. damage to the motor bearings D. electrical damage to the bearings

Description : The air gap in an induction motor should be periodically checked with a feeler gage to prevent possible ___________. A. rotor contact with the stator B. axial misalignment of the rotor C. damage to the motor bearings D. electrical damage to the bearings

Last Answer : Answer: A

When removing ball or roller bearings from the shaft of a motor, you should use a _____________. A. rawhide hammer B. brass mallet C. wheel puller D. soft iron pry bar

Description : When removing ball or roller bearings from the shaft of a motor, you should use a _____________. A. rawhide hammer B. brass mallet C. wheel puller D. soft iron pry bar

Last Answer : Answer: C

Rotor shaft of a large electric motor supported between short bearings at both ends shows a deflection of 1.8 mm in middle of motor. Assuming rotor to be perfectly balanced and supported at knife edges at both ends, likely critical speed (rpm) of shaft isA 350 B 4430 C 705 D 2810

Description : Rotor shaft of a large electric motor supported between short bearings at both ends shows a deflection of 1.8 mm in middle of motor. Assuming rotor to be perfectly balanced and supported at knife edges at both ends, likely critical speed (rpm) of shaft isA 350 B 4430 C 705 D 2810

Last Answer : C 705

On large generators, space heaters are used to ____________. A. keep the machine at ambient tmperature of the machinery space B. maintain rotor and stator winding temperatures above the dew point to prevent the formation of condensation C. prevent condensation in the lube oil D. prevent electrolysis due to condensation in the bearings

Description : On large generators, space heaters are used to ____________. A. keep the machine at ambient tmperature of the machinery space B. maintain rotor and stator winding temperatures above the dew point ... C. prevent condensation in the lube oil D. prevent electrolysis due to condensation in the bearings

Last Answer : Answer: B

What are the types of bearings are adopted for small motors and large motors?

Description : What are the types of bearings are adopted for small motors and large motors?

Last Answer : Small motors (LT motors) Horizontal mounted - deep groove ball bearing at both ends. Medium motors Roller bearing at DE and deep groove bearing at NDE. Large motors (HT motors above 750 kW) Horizontal ... mounted - face to face angular contact ball bearing at NDE and roller or ball bearing at DE.

For preparation of porous bearings by powder metallurgy, preferred particle shape is (A) Spherical (B) Nodular (C) Irregular (D) No preferred shape

Description : For preparation of porous bearings by powder metallurgy, preferred particle shape is (A) Spherical (B) Nodular (C) Irregular (D) No preferred shape

Last Answer : (A) Spherical

What types of slots are preferred for the induction motor?

Description : What types of slots are preferred for the induction motor?

Last Answer : Semi enclosed slots are preferred for induction motor. It results in less air gap contraction factor giving a small value of magnetizing currents, low tooth pulsation loss and much quieter operation(less noise)

Why star delta starter is preferred with induction motor?

Description : Why star delta starter is preferred with induction motor?

Last Answer : Star delta starter is preferred with induction motor due to following reasons: Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less ... caused. In addition, starting torque is increased and it prevents the damage of motor winding.

On electrical generators one of the bearings is isolated from the bedplate. This insulating block should not be painted and must be kept clean to ___________. A. protect operating personnel from shock B. create an isolated ground for the instrumentation C. allow for the expansion of the generator away from the prime mover as it warms up D. eliminate shaft currents to prevent damaging the bearings

Description : On electrical generators one of the bearings is isolated from the bedplate. This insulating block should not be painted and must be kept clean to ___________. A. protect operating personnel from shock ... the prime mover as it warms up D. eliminate shaft currents to prevent damaging the bearings

Last Answer : Answer: D

If the bearings of an electrical generator are failing more frequently than expected and the lubricating oil is sludging then you should ______________. A. check the connections to the output leads B. check the bearing insulating block on one end of the unit C. replace the bearing with a sealed roller type D. replace the thrust bearing of the prime mover

Description : If the bearings of an electrical generator are failing more frequently than expected and the lubricating oil is sludging then you should ______________. A. check the connections to the output leads B. ... replace the bearing with a sealed roller type D. replace the thrust bearing of the prime mover

Last Answer : Answer: B

Air gap readings should be taken on electrical generation machinery periodicly to _________. I. determine the need for cleaning II. check the condition of the bearings A. I only B. II only C. both I and II D. neither I or II

Description : Air gap readings should be taken on electrical generation machinery periodicly to _________. I. determine the need for cleaning II. check the condition of the bearings A. I only B. II only C. both I and II D. neither I or II

Last Answer : Answer: B

Air gap readings for electrical generating equipment should be taken periodicly. This is to _______. I. determine the condition of the bearings II. prevent damage to the rotor and stator A. I only B. II only C. both I and II D. neither I or II

Description : Air gap readings for electrical generating equipment should be taken periodicly. This is to _______. I. determine the condition of the bearings II. prevent damage to the rotor and stator A. I only B. II only C. both I and II D. neither I or II

Last Answer : Answer: C

If air gap readings for an electical generating machine have changed significantly from the last reading, you should check _________. A. the bearings B. insulation readings and machine cleanliness C. the prime mover thrust bearing D. the field coil bolts for the proper torque values

Description : If air gap readings for an electical generating machine have changed significantly from the last reading, you should check _________. A. the bearings B. insulation readings and machine cleanliness C. the prime mover thrust bearing D. the field coil bolts for the proper torque values

Last Answer : Answer: A

The failure of ball bearings used in electric motors can result from _____________. A. failure to clean the bearing before repacking B. failure to maintain proper alignment C. excess lubrication forcing the bearing full of grease and eliminating all areas of expansion D. all of the above

Description : The failure of ball bearings used in electric motors can result from _____________. A. failure to clean the bearing before repacking B. failure to maintain proper alignment C. excess lubrication forcing the bearing full of grease and eliminating all areas of expansion D. all of the above

Last Answer : Answer: D

Air gap readings should be taken periodicly on electrical generation equipment to __________. A. determine the amount of varnish that can be applied to correct insulation problems B. determine the condition of the bearings C. provide for the correct proper tightening of the field coil bolts and correct lateral adjustment of the field coils D. increase machine efficiency

Description : Air gap readings should be taken periodicly on electrical generation equipment to __________. A. determine the amount of varnish that can be applied to correct insulation problems B. determine the ... field coil bolts and correct lateral adjustment of the field coils D. increase machine efficiency

Last Answer : Answer: B

When disassembling electric motors for maintenance or overhaul, ________________. A. punch mark frame and end bells for proper assembly B. wrap bearings in lint free cloths if they are to be reused C. tag and store small parts in a box D. all of the above

Description : When disassembling electric motors for maintenance or overhaul, ________________. A. punch mark frame and end bells for proper assembly B. wrap bearings in lint free cloths if they are to be reused C. tag and store small parts in a box D. all of the above

Last Answer : Answer: D

The only point in the steering stand shown in the illustration which needs periodic lubrication is the ______________. EL-0098 A. repeater assembly ball bearings B. steering wheel bearing C. operation selector switch D. course selector pointer

Description : The only point in the steering stand shown in the illustration which needs periodic lubrication is the ______________. EL-0098 A. repeater assembly ball bearings B. steering wheel bearing C. operation selector switch D. course selector pointer

Last Answer : Answer: B

Before reassembling any machinery, you should _____________. A. replace all bearings regardless of length of service B. apply a heavy coat of oil to all mating surfaces C. clean any corroded surfaces and file all burrs smooth D. coat all parts with alemite grease

Description : Before reassembling any machinery, you should _____________. A. replace all bearings regardless of length of service B. apply a heavy coat of oil to all mating surfaces C. clean any corroded surfaces and file all burrs smooth D. coat all parts with alemite grease

Last Answer : Answer: C

What are the causes of failure of bearings?

Description : What are the causes of failure of bearings?

Last Answer : a) Faulty mounting b) Faulty lubrication c) Foreign matter in lubrication d) Water in the bearing arrangement e) Vibration f) Inoccurrences of form of shaft or housing seating. g) Passage of electric current. h) Metal fatigue

Why do we grease the bearings?

Description : Why do we grease the bearings?

Last Answer : a) Grease lubricant gives good protection against ingress of moisture and dirt into motor. b) Easy to seal against leakage of grease into motor compared to oil. c) Low friction torque at starting. 

Where preloaded ball bearings used?

Description : Where preloaded ball bearings used? 

Last Answer : If more vibration exists even when machine is not in running conditions.  

What is the operating life of bearings?

Description : What is the operating life of bearings? 

Last Answer : a) Continuous 24 hrs operation – 40000 to 50000 hrs. b) Affected by load axially or radial. c) Operating temperature. 

Tin based white metals are used, where bearings are subjected to (A) High pressure & load (B) Low pressure & load (C) High temperature (D) Large surface wear

Description : Tin based white metals are used, where bearings are subjected to (A) High pressure & load (B) Low pressure & load (C) High temperature (D) Large surface wear

Last Answer : (A) High pressure & load

Some large A.C. motors are equipped with with heaters. These could be ___________. I. resistance heaters bolted directly to the frame II. low voltage windings embedded in the motor windings A. I only B. II only C. either I or II D. neither I or II

Description : Some large A.C. motors are equipped with with heaters. These could be ___________. I. resistance heaters bolted directly to the frame II. low voltage windings embedded in the motor windings A. I only B. II only C. either I or II D. neither I or II

Last Answer : Answer: C

Which of the following procedures should be used to maintain a large electric motor during periods of inactivity? A. A thin layer of air-drying varnish should be applied on the windings. B. Compressed air should be blown over areas where dust is deposited. C. Spraying a solvent periodically to remove carbon dust. D. Space heaters should be used to prevent condensation of moisture.

Description : Which of the following procedures should be used to maintain a large electric motor during periods of inactivity? A. A thin layer of air-drying varnish should be applied on the windings. B. ... periodically to remove carbon dust. D. Space heaters should be used to prevent condensation of moisture.

Last Answer : Answer: D

When a megohmmeter is used to test the insulation of a large motor, the initial dip of the pointer toward 'zero' is caused by ____________. A. good insulation B. the capacitance of the windings C. the leakage of the current along the surface of dirty insulation D. the dielectric-absorption effect of the insulation

Description : When a megohmmeter is used to test the insulation of a large motor, the initial dip of the pointer toward 'zero' is caused by ____________. A. good insulation B. the capacitance of the ... of the current along the surface of dirty insulation D. the dielectric-absorption effect of the insulation

Last Answer : Answer: B

What are the advantages and disadvantages of large air gap length in induction motor?

Description : What are the advantages and disadvantages of large air gap length in induction motor?

Last Answer : Advantage: A large air gap length results in higher overload capacity, better cooling, reduction in noise and reduction in unbalanced magnetic pull. Disadvantages: The disadvantage of large air gap length is that it results in high value of magnetizing current.

Armature shunting method of speed control of dc shunt motor is preferred over annature resistance method...

Description : Armature shunting method of speed control of dc shunt motor is preferred over annature resistance method due to:  (1) Better speed regulation (2) Less loss in external resistance (3) Simplicity in control circuit (4) Reduced cost of controller

Last Answer : Armature shunting method of speed control of dc shunt motor is preferred over annature resistance method due to: Better speed regulation.

In case of travelling cranes, the motor preferred for boom hoist is _________.

Last Answer : In case of travelling cranes, the motor preferred for boom hoist is slip ring induction motor.

Which D.C. motor is generally preferred for cranes and hoists ?

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

Which D.C. motor is preferred for elevators ?

Last Answer : Cumulative compound D.C. motor is preferred for elevators.

If a D.C. motor is to be selected for conveyors, which motor would be preferred ?

Last Answer : If a D.C. motor is to be selected for conveyors, Series motor would be preferred.

An auto transformer is preferred over an ordinary two winding transformer due to: a) Safety of operation b) Availability of taps on secondary c) Copper savings d) All the above

Description : An auto transformer is preferred over an ordinary two winding transformer due to: a) Safety of operation b) Availability of taps on secondary c) Copper savings d) All the above

Last Answer : Ans: C

Locations where Gas Insulated Substation is preferred

Description : Locations where Gas Insulated Substation is preferred

Last Answer : Gas Insulated Substations are preferred in the places where land requirement for the substation is difficult such as in populated areas and highly polluted areas where outdoor switchyard is not ... pollution and saline environment. Under such case indoor GIS substation is very much helpful.

Why Negative Feedback is preferred in the Control System?

Description : Why Negative Feedback is preferred in the Control System?

Last Answer : The role of Feedback in control system is to take the sampled output back to the input and compare output signal with input signal for error ( deviation from the desired result). ... and is less sensitive to the parameter variations. Hence in control systems negative feedback is considered.

Why thyristors are not preferred for inverters?

Description : Why thyristors are not preferred for inverters?

Last Answer : Thyristors require extra commutation circuits for turn off which resulting Increased complexity of the circuit. For these reasons thyristors are not preferred for inverters.

Which type of winding is preferred for armature windings of alternator? Why?

Description : Which type of winding is preferred for armature windings of alternator? Why?

Last Answer : Double layer, short pitched and distributed type of armature winding. It eliminates high frequency harmonics hence it makes induced emf more sinusoidal.

Why is short pitch winding preferred over full-pitch winding ?

Description : Why is short pitch winding preferred over full-pitch winding ?

Last Answer : Advantages · Sinusoidal waveform: Waveform of the emf can be approximately made to a sine wave and distorting harmonics can be reduced or totally eliminated. · Economical :Conductor ... harmonics are eliminated, the eddy current and hysteresis losses are reduced which increases overall efficiency

Where oil lubrication is preferred over grease lubrication?

Description : Where oil lubrication is preferred over grease lubrication?

Last Answer : a) Determined by speed and operating temperature. b) Oil lubrication recommended. c) When speed and temperature is high. d) When heat to be conducted away from bearing. e) When adjacent machine ... High viscous oil for low speed machine, low viscous oil for high speed machine. g) At temp

Why resistance grounding preferred for less than 33 kV and more than 415 V?

Description : Why resistance grounding preferred for less than 33 kV and more than 415 V?

Last Answer : a) To limit the earth fault current for equipment safety else, high short ckt forces dislocate in windings/bus bars etc, b) Over voltage due to arcing ground reduced c) Permits earth fault protection (not possible in ungrounded system)

Why core balance CT is preferred over residual connected CT’s to sense earth fault in 6.6 kV feeders?

Description : Why core balance CT is preferred over residual connected CT’s to sense earth fault in 6.6 kV feeders?

Last Answer : a) To avoid relay mal-operation due to CT saturation b) Better sensitivity is got. c) High pickup and TMS avoided in IDMT earth fault relay. 

Why copper is only preferred as material for grounding?

Description : Why copper is only preferred as material for grounding?

Last Answer : An advantage of use of copper is in addition to their high conductivity, has the advantage of being resistant to underground corrosion. Copper is cathodic with respect to other metals that are ... and zinc reduces by about 50% and practically eliminates this potential with respect to lead.