Description : Brush sparking during commutation may be caused by ________. A. eddy currents in the armature core B. laminations in the generator field pieces C. induced current opposite to coil inductance D. coil inductance discharge occurring at commutation
Last Answer : Answer: D
Description : Transformer cores are laminated to reduce _____________. A. eddy currents B. secondary flux C. leakage flux D. all of the above
Last Answer : Answer: A
Description : The armature cores of the D.C. motors are constructed with laminations to ___________. A. eliminate hysteresis B. minimize brush sparking C. reduce eddy current losses D. compensate for armature reaction
Last Answer : Answer: C
Description : If overloading a DC machine becomes necessary in an emergency, you should ____________. A. cool the machine with portable blowers and fans B. hold thermal overload relays open with blocks of ... the windings for cooling D. increase the residual magnetism value of windings to reduce eddy currents
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
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 : Eddy currents are induced in the pole shoes of a D.C. machine due to?
Last Answer : Eddy currents are induced in the pole shoes of a D.C. machine due to relative rotation between field and armature.
Description : An open shunt field in a direct current machine may be located by connecting the field circuit to an external power source, equal to the rated field voltage or less, and tested with a voltmeter from ... C. any suitable ground to any available line lead D. any field pole to each field coil lead
Description : Armature cores in a DC generator are made of laminated steel sheets to _____________. A. fit the curvature of the frame B. increase the hysteresis effect C. reduce eddy current losses D. allow for easy assembly
Description : The introduction of interpoles in between the main pole improves the performance of d.c. machines, because (A) The interpole produces additional flux to augment the developed torque. (B) The flux waveform is ... armature is removed. (D) A counter e.m.f. is induced in the coil undergoing commutation.
Last Answer : Ans: D Counter e.m.f is produced, it neutralizes the reactive emf.
Description : An electrical connection between the wiring of an electric motor and its metal frame is known as a/an _____________. A. eddy current B. ground C. impedance D. flux leakage
Last Answer : Answer: B
Description : The induced current in transformer which produced in the direction perpendicular to flux, is known as: a. Conventional current b. electronic current c. Perpendicular current d. Eddy current
Last Answer : c. Perpendicular current
Description : The device in figure 'B' shown in the illustration can be used to control an AC load yet maintain its high gain by ______________. EL-0091 A. connecting the load to the output side of the ... connecting the load to the input side of the bridge D. reversing the current flow through the bias winding
Description : The direction of rotation of the winch shown in the illustration is changed by reversing the _____________. EL-0102 A. direction of current through the shunt field B. polarity of voltage at 'S1' and 'S2' C. direction of current through the armature D. polarity of voltage at 'L1' and 'L2'
Description : In the illustration, if one of the devices labeled 'TURB' should fail the ___________. EL-0003 A. device labeled 'EXC' will drive the alternator B. device labeled 'BKR' for that ... -alternator D. emergency generator should automatically start and be placed on line to supply emergency load centers
Description : Which of the following precautions should be taken when troubleshooting various power circuits using a common solenoid-type mechanical voltage tester (wiggins)? A. Never use this tester on circuits greater ... voltage expected in the circuit in order to prevent damage from an off-scale reading.
Description : The purpose of amortisseur windings in a synchronous motor is to ______________. A. reduce eddy current losses B. produce a higher power factor C. provide a means for starting D. eliminate arcing between the stator and the rotor
Description : Amortisseur windings are installed in a synchronous motor to _____________. A. reduce eddy current losses B. produce a higher power factor C. provide a means for starting D. eliminate arcing between the stator and the rotor
Description : A loss of field excitation to an AC generator while operating in parallel will cause it to ____________. A. absorb more and more load due to decreased armature reaction B. lose its load due to ... polarity D. lose its load, begin to motorize, trip out on reverse power relay, and possibly overspeed
Description : A shading coil used in an AC magnetic controller, functions to _____________. A. reduce vibration and noise in the contactor B. prevent flux buildup in the operating coil C. eliminate arcing when the contacts close D. energize the operating coil and 'pull in' the contacts
Description : Eddy currents produced in the core of transformer are responsible for: a. heat loss b. Step up process c. Step down process d. induction phenomena
Last Answer : d. induction phenomena
Description : The direction of rotation of hysteresis motor is reversed by (A) Shift shaded pole with respect to main pole (B) Reversing supply lead (C) Either A or B (D) Neither A nor B
Last Answer : Ans: A This motor used single phase, 50Hz supply and stator has two windings. These are connected continuously from starting to running.
Description : On tank vessels with an electrically-driven capstan, the motor should be meggered periodically to test _____________. A. insulation resistance B. eddy currents C. capacitance D. armature reactance
Description : In the illustration shown, coil 'MR' is a ____________. EL-0012 A. running contactor coil B. rupture (blowout) coil C. resistance coil D. reversing coil
Description : Currents that flow in circles inside a disc are known as A. eddy currents B. circular currents C. air currents D. alternating curent
Last Answer : eddy currents
Description : Diamagnetic materials are magnetised (A) Strongly (B) Only slightly (C) With eddy currents only (D) In a direction opposite to that of the applied field
Last Answer : (D) In a direction opposite to that of the applied field
Description : Diamagnetic materials (A) Are magnetised by eddy currents only (B) Are non-magnetic and cannot be magnetised (C) Are magnetised in direction opposite to the magnetic field (D) Can be magnetised in one direction only
Last Answer : (C) Are magnetised in direction opposite to the magnetic field
Description : A current of 2 A is made to flow through a coil which has only one turn. The magnetic field produced at the centre is`4pi xx 10^(-6) "Wb"//m^(2).` the
Last Answer : A current of 2 A is made to flow through a coil which has only one turn. The magnetic field produced at the centre is` ... m` C. `0.1 m` D. `0.001 m`
Description : As an armature revolves within a magnetic field, friction is developed between the rotated magnetized particles as they pass through each magnetization cycle. This results in ____________. A. copper loss B. eddy-current loss C. hysteresis loss D. armature reaction
Description : The rotor slots of a repulsion-type motor are generally skewed (placed nonparallel to the rotor axis) to _________. A. produce a constant starting torque B. permit a greater air gap with the starter C. permit a smaller air gap with the starter D. reduce eddy current losses
Description : The armature of a dc machine is laminated to reduce: (A) Eddy current loss (B) Hysteresis loss (C) copper losses (D) friction and windage losses
Last Answer : Ans: A Thinner the laminations, greater is the resistance offered to the induced e.m.f., smaller the current and hence lesser the I2R loss in the core.
Description : The amount of mechanical force or torque produced by an electric motor depends on the ________________. A. strength of its magnetic field B. amount of armature current flow C. length of conductor in the field D. all of the above
Description : A series wound DC motor has its armature and field connected in series with a resistor. When the motor is disconnected from its power supply, this motor will exemplify __________. A. the ... the proper connections for an automatic strip heater C. a reversing controller circuit D. dynamic braking
Description : If a DC motor runs faster than designed, with all other conditions being normal, the possible cause could be a/an ______________. A. shorted shunt field coil B. open armature coil C. reversed commutating pole D. overload
Description : A megohmmeter can be used to test for _____________. A. an open field coil B. a shorted field pole C. undercut mica D. reversed polarity
Description : In DC generators, armature reaction is produced actually by (A) Its field current. (B) Armature conductors. (C) Field pole winding. (D) Load current in armature.
Last Answer : Ans: D Because load current in armature gives rise to armature mmf which react with main field mmf.
Description : When charging a 100 amp-hour lead-acid battery, ___________. A. the temperature of the electrolyte should not be allowed to exceed 90°F B. the charging rate should be no greater than 125% of the ... nearing full charge and it will be necessary to reduce the charging current to a low finishing rate
Description : The true power indicated by a wattmeter depends on the current flow through the load, the magnitude of the potential across the load, and the _____________. A. power factor of the load B. angle of coil displacement C. inertia of the movable coil D. high resistance from the load
Description : The true power indicated by the pointer movement of a wattmeter depends on the current flow through the load, the magnitude of the potential across the load, and the ____________. A. power factor of the ... B. angle of coil displacement C. inertia of the movable coil D. high resistance from the load
Description : In a dc generator why does total flux per pole decrase if the load on the machine increases even thought the field current is constsn?
Last Answer : Due to armature reaction
Description : Fleming's left hand rule is used to find (a) direction of magnetic field due to current carrying conductor (b) direction of flux in a solenoid (c) direction of force on a current carrying conductor in a magnetic field (d) polarity of a magnetic pole
Last Answer : (c) direction of force on a current carrying conductor in a magnetic field
Description : The eddy current loss in a dc generator is 400 W at 40 Hz frequency of reversal and constant flux density. When frequency is increased to 50 Hz., eddy current loss is : (A) 256 W (B) 320 W (C) 500 W (D) 625 W
Last Answer : The eddy current loss in a dc generator is 400 W at 40 Hz frequency of reversal and constant flux density. When frequency is increased to 50 Hz., eddy current loss is : 625 W
Last Answer : The direction of rotation of universal motor can be reversed the by reversing the flow of current through either armature winding or field winding.
Description : iv) A rectangular coil free to rotate is placed in uniform magnetic field with its plane parallel to the magnetic lines of force. Then the coil willa) rotate to maximize the magnetic flux through ... since the magnetic flux through its plane is zero.d) experience the constant torque equal to NBIA
Last Answer : iv) A rectangular coil free to rotate is placed in uniform magnetic field with its plane parallel ... d) experience the constant torque equal to NBIA
Description : Why not reduce the noise in the core by reducing the amount of flux?
Last Answer : Transformer voltages are fixed by system requirements. The ratio of these voltages to the number of turns in the winding determines the amount of magnetization. This ratio of voltage to turns is determined ... flux at the normal voltage is fixed. This also fixes the level of noise and vibration.
Description : Federal Regulations (46 CFR) require the circuit in the illustration to _________. EL-0009 A. be at the vessel's ship's service generator distribution switchboard for normal power, normal lighting ... ground will interfere with the operation of electronic equipment D. All the above are correct
Description : ___________ is not affected by a magnetic field a) Change in magnetic flux b) a moving electron c) a stationary proton d) current flowing in a conductor
Last Answer : c) a stationary proton
Description : A four-pole induction motor, operating on three-phase 60 cycle current will operate at approximately ___________. A. 850 RPM B. 1,150 RPM C. 1,750 RPM D. 3,550 RPM
Description : When field is parallel to plane of area, magnetic flux through coil isA. zero B. infinite C. 2 D. 5
Last Answer : zero