Why rotor impedance testing done during static and running condition?

Why rotor impedance testing done during static and running condition? 
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1 Answer

Answer :

To detect rotor earth fault.  
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A four pole, 60 Hz, three-phase synchronous motor comes up to 1760 RPM when started as an induction motor. What is the percent slip after the rotor field is energized? A. 0 B. 1.1 C. 2.2 D. 3.3

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The torque and current curves for a three-phase induction motor with a cage rotor, are shown in the illustration. Which of the following statements is true concerning the depicted curves? EL-0056 A. As slip increases, rotor reactance decreases. B. The pullout point on the torque curve is about seven times the normal full load torque value. C. At stand still, stator current is 150% of normal. D. If the motor is loaded to the point where 40% slip has resulted, it will stall.

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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

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The speed of a squirrel-cage, multi-speed, induction motor, as used aboard ship, is varied by changing the __________. A. number of connected poles in the stator B. frequency to the motor C. excitation voltage D. resistance of the rotor circuit

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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

What is the rotor speed of a four pole, 60 cycle, induction motor operating at full load with 3% slip? A. 270 RPM B. 540 RPM C. 873 RPM D. 1746 RPM

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If the driving torque, such as that produced by a diesel engine, creates pulsations when coupled with a synchronous generator operating in parallel; the generator rotor may be periodically pulled ahead or behind its normal position as it rotates. This co A. hunting B. direct coupling C. peaking D. harmonic coupling

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Last Answer : Answer: A

The purpose of the item labeled 'Z' in assembly No. 2, shown in the illustration is to _____________. EL-0001 A. keep the rotor in balance B. align the rotor to the stator C. dynamically balance the rotor D. cool the motor

Description : The purpose of the item labeled 'Z' in assembly No. 2, shown in the illustration is to _____________. EL-0001 A. keep the rotor in balance B. align the rotor to the stator C. dynamically balance the rotor D. cool the motor

Last Answer : Answer: D

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

Discoloration of the rotor bars in a squirrel-cage motor is typical evidence of _____________. A. moisture B. overheating C. vibration D. all of the above

Description : Discoloration of the rotor bars in a squirrel-cage motor is typical evidence of _____________. A. moisture B. overheating C. vibration D. all of the above

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

A DC generator is used to supply direct current in order to maintain an AC generator field and is known as a/an _____________. A. rotor B. stator C. exciter D. armature

Description : A DC generator is used to supply direct current in order to maintain an AC generator field and is known as a/an _____________. A. rotor B. stator C. exciter D. armature

Last Answer : Answer: C

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

In the illustrated device, the part labeled '1A' _________. EL-0001 A. are start and run windings for a single phase shaded pole induction motor B. is the stator for a polyphase induction motor C. is the armature for a squirrel cage rotor motor D. are direct current shunt field windings for a universal motor

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Last Answer : Answer: B

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

In the illustration, the assembly labeled 2 is a ________. EL-0001 A. wound rotor and shaft for a single phase induction motor B. conduction rotor and shaft for a polyphase induction motor C. squirrel cage rotor and shaft for a polyphase motor D. squirrel cage rotor for a single phase induction motor

Description : In the illustration, the assembly labeled 2 is a ________. EL-0001 A. wound rotor and shaft for a single phase induction motor B. conduction rotor and shaft for a polyphase induction motor C. ... cage rotor and shaft for a polyphase motor D. squirrel cage rotor for a single phase induction motor

Last Answer : Answer: C

The air gap in an induction motor should be checked periodically with a feeler gage to detect ____________. A. rotor contact with the laminations B. changes in armature magnetic strength C. excessive bearing wear D. electrical damage to the rotor

Description : The air gap in an induction motor should be checked periodically with a feeler gage to detect ____________. A. rotor contact with the laminations B. changes in armature magnetic strength C. excessive bearing wear D. electrical damage to the rotor

Last Answer : Answer: C

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

If the driving torque, such as that produced by a diesel engine, creates pulsations when coupled with a synchronous generator operating in parallel; the generator rotor may be periodically pulled ahead or behind its normal position as it rotates. This hu A. amortisseur windings B. direct coupling C. increase governor speed droop D. decreasing governor speed droop

Description : If the driving torque, such as that produced by a diesel engine, creates pulsations when coupled with a synchronous generator operating in parallel; the generator rotor may be periodically pulled ... windings B. direct coupling C. increase governor speed droop D. decreasing governor speed droop

Last Answer : Answer: A

Routine A.C. motor maintenance should include periodic ______________. A. thermometer readings at normal loads to detect abnormal temperature rises B. inspection of the motor's internals for loose rotor bars or field poles C. bearing replacement each year using sealed units if available D. all of the above

Description : Routine A.C. motor maintenance should include periodic ______________. A. thermometer readings at normal loads to detect abnormal temperature rises B. inspection of the motor's internals for loose rotor bars ... C. bearing replacement each year using sealed units if available D. all of the above

Last Answer : Answer: A

In D.C. motor construction, commutating windings are wound on _________________. A. opposite main poles B. interpoles C. adjacent main poles D. the rotor core

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