Which of the listed faults cannot be eliminated, EXCEPT by turning or grinding a commutator with a rigidly supported tool?  A. Sparking brushes B. Eccentricity C. High mica D. Blackened commutator

1 Answer

Answer :

Answer: B

Related questions

Description : Which of the listed conditions might contribute to very rapid wearing of a DC machine's commutator bars? A. A grounded commutator bar B. Using improper carbon brushes C. Aligning the front and rear mica V-rings improperly D. An open circuit in the armature

Last Answer : Answer: B

Description : Sparking of D.C. motor brushes can be caused by __________. A. an open commutating winding B. many mechanical, electrical or operating faults C. an open interpole D. all of the above

Last Answer : Answer: B

Description : Brushes in a generator must be positioned in the neutral plane to avoid sparking between the brushes and the _____________. A. yoke B. armature windings C. field pole windings D. commutator

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Description : Sparking at the brushes of a running motor could be an indication of _____________. A. normal operation B. a dirty commutator C. increased brush capacity D. water vapor absorption

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Description : Temporary repairs to an open DC propulsion armature coil can be made by _____________. A. connecting the coil ends directly to a pair of negative brushes B. disconnecting coil ends, insulating ... C. grounding the coil ends and short circuiting the commutator bar D. removing the sparking brushes

Last Answer : Answer: B

Description : The function of the commutator in a DC motor is to ________. A. reverse the flow of current through the armature B. reverse the flow of current in the field poles C. reduce the reluctance of the magnetic path through the motor D. shift the neutral running plane of the brushes to prevent sparking

Last Answer : Answer: A

Description : The purpose of the commutator and brushes on a DC generator is to _____________. A. transfer generated direct current voltage from the armature to the line B. convert the alternating voltage ... contact method to excite the field D. reduce sparking between the armature and the carbon brushes

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Description : A shorted armature coil in a DC motor can be detected by _____________. A. sparking at the brushes B. shiny armature coil C. worn grooves in the armature D. undercut mica

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Description : Etched or burned bands on the contact faces of the brushes in a direct current generator can be caused by ____________. A. high mica segments B. copper drag on the commutator C. brushes improperly positioned D. copper embedded in the brushes

Last Answer : Answer: C

Description : Which of the listed conditions could cause a DC motor to have excessively hot windings and sparking at the brushes? A. Reversed interpole polarity B. High bar-to-bar voltage C. Loose brushes D. Excessive humidity

Last Answer : Answer: A

Description : Which of the conditions listed will indicate the need to clean the insulation on the windings of an electric motor? A. Higher than normal operating temperature. B. Excessive vibration at normal speed. C. Sparking at the brushes. D. High megger readings.

Last Answer : Answer: A

Description : Which of the damages listed can occur to the components of a winch master control switch, if the cover gasket becomes deteriorated? A. Overheating of the winch motor. B. Contamination of lube oil. C. Sparking at the winch motor brushes. D. Rapid corrosion of switch components.

Last Answer : Answer: D

Description : What causes sparking between the brushes and the commutator?

Last Answer : Improper commutation.

Description : The material for commutator brushes is generally (a) mica (b) copper (c) cast iron (d) carbon

Last Answer : Ans: d

Description : If only one brush on a commutator is sparking excessively, you should look for _____________. A. a high commutator bar B. copper imbedded in the brush C. a loose commutator bar D. flux in the commutating zone

Last Answer : Answer: B

Description : Due to which of the following factors the brush wear rate is altered ? (a) Speed of the machine (b) Contact pressure (c) Surface conditions of brush and commutator (d) Excessive sparking (e) All of the above

Last Answer : Ans: E

Description : In general, D.C. propulsion motor brush sparking can be caused by _______________. A. incorrect brush grade, pressure or position B. a concentric commutator C. a dark chocolate colored commutator D. all of the above

Last Answer : Answer: A

Description : Sparking at the brushes of a DC propulsion motor can be the result of ____________. A. improper brush pressure B. improper brush seating C. reversed interpole polarity D. all of the above

Last Answer : Answer: D

Description : An open armature connection in a DC propulsion motor could be caused by ____________. A. low-load operation B. clogged ventilation ducts C. sparking at the brushes D. a grounded shunt field coil

Last Answer : Answer: B

Description : Insufficient brush pressure on a DC motor may cause _______. A. generator overload B. excess residual magnetism C. water vapor absorption D. sparking of the brushes

Last Answer : Answer: D

Description : Modern DC generators are fitted with commutating poles to _____________. A. prevent motorizing B. reduce sparking C. reduce the load on the main poles D. reduce spring pressure on the brushes

Last Answer : Answer: B

Description : Which of the diagrams shown in the illustration depicts the proper method of aligning brushes on a commutator? EL-0057 A. A B. B C. C D. D

Last Answer : Answer: B

Description : Which of the following is a characteristic of fractional horsepower repulsion start motors? A. They start with a rotating stator field. B. The short circuiting ring is removed from the commutator while ... brushes are removed from the commutator while starting. D. They have a low starting torque.

Last Answer : Answer: B

Description : In the illustrated test, if the lamp fails to light on any of the three windings then _________. EL-0027 A. all three windings are grounded and the motor should be sent out for repair B. ... the motor controller and the controller should be checked D. the test should be redone at a higher voltage

Last Answer : Answer: C

Description : A shunt-wound DC generator is one in which the shunt field windings are in parallel with the _____________. A. commutator B. brushes C. armature D. all of the above

Last Answer : Answer: D

Description : Which of the following components are used to convert alternating current produced in the generator windings to direct current? A. Armature and equalizer B. Commutator and brushes C. Rotor and interpoles D. Field and exciter

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Description : In an AC generator, direct current from a separate source is passed through the windings of the rotor _____________. A. by means of slip rings and brushes B. by means of a commutator C. by means of rotating bar magnet D. to minimize the danger of arc over

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Description : Voltage generated by most AC generators is fed from the machine to the bus by means of ____________. A. brushes on a commutator B. brushes on slip rings C. slip rings on a commutator D. direct connections from the stator

Last Answer : Answer: D

Description : The current from the stator of an alternator is taken out to the external load circuit through (A) slip rings. (B) commutator segments. (C) solid connections. (D) carbon brushes.

Last Answer : (C) solid connections.

Description : In addition to undercutting the mica, proper maintenance of a D.C. motor's commutator includes _______________. A. side-cutting the copper segments and insulating the slots B. coating the copper surface with light machine ... in an oven at a maximum of 95°C for not over 8 hours D. all of the above

Last Answer : Answer: A

Description : The most practical method used for resurfacing a ship's service motor commutator is to _____________. A. turn it down in the ship's lathe B. use a grinding rig C. use a hand stone D. burnish it with commutator stones

Last Answer : Answer: B

Last Answer : Sparking at the commutator of a D.C. motor may result in damage to commutator segments, damage to commutator insulation, increased power consumption.

Description : A hollow circular tube with a 2.3-cm I.D. and 2.5-cm O.D. is rigidly supported at its ends. A 2.5 kN-m torque is applied at the center of this tube. What is the maximum shear stress acting on this tube? (a) 2.87Mpa (b) 4.27 Mpa (c) 6.92 Mpa (d) 10.2 Mpa

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Description : The winch shown in the illustration operates in any of the positions with the master switch in the 'lower' direction, but will not 'hoist' in any of the master switch hoist positions. Which of the listed faults ... '2M' in the power circuit may be badly corroded. D. Series relay 'FR' may be open.

Last Answer : Answer: A

Description : Which of the listed colors properly describes a DC motor commutator when correct commutation is taking place? A. Shiny blue B. Burnished green C. Brick red D. Chocolate brown

Last Answer : Answer: D

Description : If a D.C. motor hums, but does not run when energized, which of the listed conditions could exist? A. Incorrect lead connections B. Incorrect brush setting C. A dirty commutator D. All of the above are correct.

Last Answer : Answer: D

Description : Which of the listed conditions will occur if dirt and grease are allowed to accumulate between the commutator segments of a motor? A. A partial short circuit. B. A dead short circuit. C. Misalignment of the motor shaft. D. Overspeeding of the motor.

Last Answer : Answer: A

Description : Which of the listed procedures should be carried out to prevent moisture damage to electrical apparatus during extended periods of idleness? A. Fill the motor housing with CO2 to inert the space. B. Strap ... C. Place heat lamps in the motor housings. D. Cover the equipment with a canvas tarpaulin.

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Description : Which of the listed conditions will occur if the polarity of the field poles and the direction of current to the brushes of a DC motor were both reversed? A. The motor would not start. ... direction of rotation of the armature would be unchanged. D. The field pole windings would become overheated.

Last Answer : Answer: C

Description : Which of the listed pairs of materials make the best insulators? A. copper and aluminum B. glass and mica C. dry air and a vacuum D. doped silicon and germanium

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Description : Which of the listed groups of electrical insulation materials is best suited for the highest operating temperatures? A. impregnated cotton and silk B. unimpregnated paper and cotton C. pure glass and quartz D. mica and porcelain with bonding agents

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Description : Which of the substances listed can be used to shield sensitive equipment from static magnetic fields? A. Glass B. Mica C. Bakelite D. Permeable iron

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

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Description : Which of the following are the parts of a DC generator that convert the AC in the armature to DC in the external circuit. Are these parts the: w) field poles x) slip rings and the brushes y) commutator and the brushes z) armature and the core

Last Answer : ANSWER: Y -- COMMUTATOR AND THE BRUSHES

Last Answer : The number of brushes in a commutator depends on amount of current to be collected.

Last Answer : In D.C. generators, the brushes on commutator remain in contact with conductors which lie under interpolar region.

Last Answer : The material for commutator brushes is generally carbon.

Last Answer : Commutator brushes are made up of carbon.