Description : Which of the following statements describes what will happen when both the polarity of the field poles, and the direction of current to the brushes of a DC motor are reversed? A. The motor will ... of rotation of the armature will remain the same. D. The field pole windings will become overheated.
Last Answer : Answer: C
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.
Description : A synchronous motor maintains synchronism with the rotating field because _____________. A. field strength varies directly with rotor slip B. DC current applied to the rotor coils causes the rotor ... the flux created by the excitation current D. the stator flux rotates in the opposite direction
Last Answer : Answer: B
Description : In an induction motor, rotor currents are circulated in the rotor by _____________. A. slip rings and brushes B. an armature and brushes C. inductive reaction of the rotating stator field D. external variable resistors
Description : If you reverse both the field and the armature connections to a DC propulsion motor, _____________. A. the direction of motor rotation will change B. the brushes will become overheated C. a magnetic lock will occur in the motor D. the direction of motor rotation will remain the same
Last Answer : Answer: D
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 direction of rotation of a DC propulsion motor can be changed by reversing the _____________. A. brush holder position B. polarity of the field poles C. brush staggered order D. motor interpole connections
Description : The synchronous speed of an induction motor is the ________. A. speed at which the rotor turns B. speed of the rotating field C. frequency of the rotor current D. slip in per cent of rotor RPM
Description : What is the need of staggering of brushes and helical grooves?
Last Answer : The need of staggering is for uniform wear of brush and slip rings. The helical grooved are provided to improve the brush performance by breaking air pockets. The forced ventilation fan removes carbon dust from the helical grooves.
Description : The speed of a squirrel-cage induction motor is determined by the ____________. A. diameter of the stator B. number of stator poles C. rotor winding resistance D. rotor conducting bars resistance
Description : The speed of a squirrel cage induction motor is determined by the _____________. A. diameter of the stator B. number of stator poles C. rotor winding resistance D. bar resistance of the conducting rotor
Description : The rotor of a synchronous motor operates in synchronism with the rotating field because ______________. A. of the amortisseur windings B. the rotor is magnetically locked into step with the ... field strength varies directly with rotor slip D. the stator flux rotates in the opposite direction
Description : What is the direction of rotation of rotor with respect to the rotating magnetic field?
Last Answer : Answer: Rotating Magnetic Field is set up when 3 phase ac supply is provided to the stator windings of the induction motor. Rotating Magnetic Field rotates at synchronous speed. Rotor rotates in the direction of the rotating magnetic field
Description : The most practical method of controlling the RPM of a step-speed AC motor is to _____________. A. change input voltage B. vary the number of poles C. vary power factor D. change the number of brushes
Description : Under normal conditions, the speed of a two-speed squirrel cage induction motor is changed by varying the ____________. A. frequency of the applied voltage B. resistance in the rotor circuit C. number of field poles D. amplitude of the applied voltage
Description : The speed of a wound-rotor induction motor _____________. A. will be fixed by the number of field poles B. can be varied by a rheostat-type control C. can only be synchronous speed at full load D. can only attain synchronous speed at no load
Description : In a single-phase induction motor, the operating direction is determined by the ________ A) Rotor B) Stator C) Starting circuit D) None of these
Last Answer : In a single-phase induction motor, the operating direction is determined by the Starting circuit
Description : In a three-phase, squirrel-cage type, induction motor the rotating magnetic field is established by the _____________. A. current induced in the rotor windings B. application of a three-phase voltage ... caused by the induced current in the squirrel-cage bars with the magnetic field of the stator
Description : Regarding an induction motor, the power developed by the rotor automatically adjusts itself to the _____________. A. power required to drive the load B. speed required to drive the load C. current flow in the motor stator D. torque developed by the rotating field
Description : If an AC generator experiences voltage failure, the cause may be _____________. A. an open in the field circuit B. the brushes shifting out of the neutral plane C. excessive locked-rotor current D. a rotating slip ring
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.
Description : In a d.c. machine, the armature mmf is (A) stationary w.r.t. armature. (B) rotating w.r.t. field. (C) stationary w.r.t. field. (D) rotating w.r.t. brushes.
Last Answer : (C) stationary w.r.t. field.
Description : You are reconnecting a three-phase induction motor to the supply line. To prevent possible damage to the load, due to the wrong direction of rotation, you should ____________. ... supply line phase sequence and motor rotation with appropriate indicators, then connect correspondingly marked leads
Description : Reversing any two of the three rotor leads on a wound-rotor induction motor will _____________. A. increase motor performance B. decrease motor performance C. reverse the motor rotation D. have no effect on the direction of rotation or motor performance
Description : What determines the number of field poles required to establish a rotating magnetic field in a multiphase motor stator?
Last Answer : The number of phases in the applied voltage.
Description : If the connections for the field and the armature on a DC motor are reversed, _____________. A. the motor will run as a generator B. the motor will not run C. the direction of rotation will be the same D. the direction of rotation will be reversed
Description : The rotation of a three-phase induction motor can be reversed by _____________. A. interchanging any two of the three line leads to the stator B. disconnecting one of the three line leads to the ... the shunt field coil leads D. permanently disconnecting any two of the three line leads to the stator
Description : Uneven wear of the commutator surface on a direct current propulsion motor can be caused by _____________. A. rapid change in load B. excessive operation at light load C. incorrect brush staggering D. unequal pole spacing
Description : The reversal of an AC, three-phase, induction motor is accomplished by ______________. A. changing all three motor leads B. reversing the position of the slip rings C. interchanging any two of the three motor leads D. interchanging any two brushes
Description : What are the materials used to manufacture the brushes for slip rings of an induction motor?
Last Answer : A:The slip rings are made of brass and phosphor bronze. The brushes are made of metal graphite which is an alloy of copper and carbon.
Description : If the synchronous speed of a 12 pole, polyphase, induction motor operating at 60 Hz were 600 RPM, how many poles will be required in a similar motor operating at the same frequency but having a synchronous speed of 900 RPM? A. 4 B. 6 C. 8 D. 18
Description : The speed of a multi-speed, squirrel-cage, induction motor operating in a fixed frequency system can be changed by _____________. A. reconnecting stator windings for different numbers of poles B. ... sequence of the applied voltage D. reconnecting the stator so that no poles have the same polarity
Description : The direction of rotation of a DC propulsion motor can be reversed by __________. A. reversing the field connections B. reversing the field and the armature connections C. wiring the field and armature in parallel D. wiring the field and armature in series
Description : As shown in the illustration, the D.C. motor's direction of rotation in changed by changing the _________________. EL-0101 A. polarity of the generator field B. direction of three-phase motor rotation C. direction of generator rotation D. polarity of the motor field
Description : 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
Description : If a three-phase induction motor is operated under a light load and it develops an open in one of its supply lines, the motor will _____________. A. continue to run, but will vibrate and have reduced ... speed up due to the reduced number of poles C. run cooler due to reduced current flow D. stop
Description : The speed of a three-phase squirrel-cage induction-type motor operating in a fixed frequency system is varied by changing the _____________. A. number of phases to the motor B. number of stator poles C. locked rotor current D. resistance of the rotor winding
Description : The synchronous speed for a 3 phase 6-pole induction motor is 1200 rpm. If the number of poles is now reduced to 4 with the frequency remaining constant, the rotor speed with a slip of 5% will be _________. (A) 1690 rpm (B) 1750 rpm (C) 1500 rpm (D) 1710 rpm
Last Answer : (D) 1710 rpm
Description : The division of kilowatt load between two paralleled alternators is determined by the _____________. A. amount of field excitation to the leading machine B. load-speed characteristics of the governors C. amount of field excitation to the lagging machine D. number of field poles per alternator
Description : Which of the methods listed is used to start a AC generator turning? A. Residual magnetism remaining in the field poles. B. Residual magnetism remaining in the field coils. C. Residual magnetism remaining in the armature. D. Rotation by a mechanical prime mover.
Description : Why Induction motor is called rotating transformer?
Last Answer : Transformer has two sides: primary & secondary. Transformer transforms energy from primary to secondary by induction. Similarly, Induction motor has primary (stator) & secondary (rotor). Voltage is ... magnitude i.e. the process of induction Thus induction motor treated as a rotating transformer.
Description : A 3 phase 50 Hz induction motor has full load speed of 970 rpm. Calculate no of poles and slip frequency.
Last Answer : The number of poles in an induction motor can be calculated using the following formula: No. of poles = (120 * frequency) / speed In this case, the number of poles would be calculated as follows: No. of poles = ( ... ) - 50 Hz = 8.08 Hz So the motor has 6 poles and a slip frequency of 8.08 Hz.
Description : A three-phase, squirrel cage, induction motor will run hot due to _____________. A. open stator coils B. high power factor C. dirty or corroded slip rings D. reversed commutating poles
Description : A 400kW, 3-phase, 440V, 50Hz induction motor has a speed of 950 r.p.m. on fullload. The machine has 6 poles. The slip of the machine will be _______________. (A) 0.06 (B) 0.10 (C) 0.04 (D) 0.05
Last Answer : Ans: D N = Ns (1-S) 950 = 120 x 50 (1-S)/6 S = 0.05
Description : Which of the following statements is true concerning all three-phase alternators? A. Each has three separate but identical armature windings acted on by one system of rotating magnets. B. Each has one ... The three phases always provide power to the load through three sets of slip rings and brushes.
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
Last Answer : The direction of rotation of an hysteresis motor is determined by position of shaded pole with respect to main pole.
Description : Explain how in a 3 phase induction motor to a rotating magnetic field is developed.
Last Answer : Production of Rotating Magnetic Field in Three-phase Induction Motor: In three-phase induction motor, the three-phase stator windings are displaced in space by 120° and their three-phase currents are displaced ... time by 120°. Such fluxes give rise to the resultant rotating magnetic field.
Description : Define rotating magnetic field of an induction motor.
Last Answer : Rotating magnetic field of an induction motor: A rotating magnetic field is a magnetic field that has moving polarities in which its opposite poles rotate about a central point or axis.
Description : A 3-phase, 4-pole, 50Hz induction motor runs at a speed of 1440 rpm. The rotating field produced by the rotor rotates at a speed of ________ rpm with respect to stator field. (A) 1500 (B) 0 (C) 1440 (D) 60
Last Answer : 0