Description : The material for commutator brushes is generally (a) mica (b) copper (c) cast iron (d) carbon
Last Answer : Ans: d
Description : Brushes of D.C. machines are made of (a) carbon (b) soft copper (c) hard copper (d) all of above
Last Answer : Ans: a
Description : Copper brushes in D.C. machine are used (a) where low voltage and high currents are involved (b) where high voltage and small cur-rents are involved (c) in both of the above cases (d) in none of the above cases
Description : In a four-pole D.C. machine (a) all the four poles are north poles (b) alternate poles are north and south (c) all the four poles are south poles (d) two north poles follow two south poles
Last Answer : Ans: b
Last Answer : In lap winding, the number of brushes is always same as the number of poles.
Description : The insulating material used between the commutator segments is normally (a) graphite (b) paper (c) mica (d) insulating varnish
Last Answer : Ans: c
Description : In D.C. generators, current to the external circuit from armature is given through (a) commutator (b) solid connection (c) slip rings (d) none of above
Description : Iron losses in a D.C. machine are independent of variations in (a) speed (b) load (c) voltage (d) speed and voltage
Description : In case of D.C. machines, mechanical losses are primary function of (a) current (b) voltage (c) speed (d) none of above
Description : A separately excited generator as compared to a self-excited generator (a) is amenable to better voltage con-trol (b) is more stable (c) has exciting current independent of load current (d) has all above features
Description : In a commutator (a) copper is harder than mica (b) mica and copper are equally hard (c) mica is harder than copper (d) none of the above
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.
Last Answer : Answer: A
Description : The direction of rotation of an induction motor is ________. A. opposite the rotating field direction B. the same as the direction of the rotating field C. determined by the number of poles D. determined by the staggering of the brushes
Last Answer : Answer: B
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 : 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 : 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 : 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 : 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
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
Description : Number of commutator bars for a 4-pole, 2-layer, DC lap winding with 24 slots and one conductor per layer is (A) 48 (B) 24 (C) 192 (D) 96
Last Answer : Number of commutator bars for a 4-pole, 2-layer, DC lap winding with 24 slots and one conductor per layer is 24
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
Description : A 36 slot, 4 -pole, dc machine has a simplex lap winding with two conductors per slot. The back pitch and front pitch adopted could be respectively
Last Answer : A 36 slot, 4 -pole, dc machine has a simplex lap winding with two conductors per slot. The back pitch and front pitch adopted could be respectively 19,17
Last Answer : In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be 8.
Last Answer : Lap winding is composed of any even number of conductors.
Last Answer : In D.C. generators, lap winding is used for low voltage, high current.
Last Answer : In the case of lap winding resultant pitch is difference of front and back pitches.
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 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 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 : State the function of following parts of DC motor : i) Yoke ii) Poles iii) Field winding iv) Commutator.
Last Answer : Function : i) Yoke: The yoke serves the following two purposes. i) It supports the other components such as poles and provides mechanical protection for whole machine. ii) It forms a part of ... one pole to another and thus to help the motor to develop a continuous and unidirectional torque
Description : Electrical fault between two windings of same phase of a generator having double star winding can be detected by the following protection in a generator:
Last Answer : Electrical fault between two windings of same phase of a generator having double star winding can be detected by the following protection in a generator: inter turn fault protection
Description : When two plates butt together and are riveted with two cover plates with two rows of rivets, the joint is known as (A) Lap joint (B) Butt joint (C) Single riveted single cover butt joint (D) Double riveted double cover butt joint
Last Answer : (D) Double riveted double cover butt joint
Description : Which of the following statements is true concerning the operation of two alternators in parallel? A. The cycles per second of each alternator are the same. B. Both alternator governors must be set ... be the same on each alternator. D. The load must always be divided equally between alternators.
Description : A 4-pole, 3-phase, double-layer winding is housed in a 36-slot stator for an ac machine with 60o phase spread. Coil span is 7 short pitches. Number of slots in which top and bottom layers belong to different phases is (A) 24 (B) 18 (C) 12 (D) 0
Last Answer : A 4-pole, 3-phase, double-layer winding is housed in a 36-slot stator for an ac machine with 60o phase spread. Coil span is 7 short pitches. Number of slots in which top and bottom layers belong to different phases is 24
Description : 21.The ordinary two winding transformer's primary and secondary windings always have A. different no of turns B. same size of copper wire C. a common magnetic circuit D. separate magnetic circuits
Last Answer : C. A common magnetic circuit
Description : When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor?
Last Answer : When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor increases to two times the original value.
Description : A single-phase induction motor will only start if you spin the rotor rapidly with the line switch closed. After starting, its speed fluctuates between very slow and half-speed. The problem ... in the ________. A. starting winding B. centrifugal mechanism C. centrifugal switch D. running winding
Last Answer : Answer: D
Description : A single-phase induction motor fails to start. The rotor is spun rapidly with the line switch closed. Having started by this method it is noted that the motor fluctuates between a very slow ... lies in the ______ A. starting winding B. centrifugal mechanism C. centrifugal switch D. running winding
Description : Relative to the secondary winding of a step-up transformer, the primary winding will have _____________. A. more turns B. fewer turns C. half as many turns D. twice as many turns
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
Description : 28.In a two winding transformer, the emf /turn in secondary winding is always......the induced emf power turn in primary A. equal to k times B. equal to 1/k times C. equal D. greater than
Last Answer : C. equal
Description : 6 In a two winding transformer, the primary and secondary induced emf E1 & E2 are always A. equal in magnitude B. anti phase with each other C. in phase with each other D. determined by load on transformer secondary
Last Answer : C. In phase with each other
Description : When a bar magnet is cut into two equal halves, the pole strength of each piece (1) becomes double (2) becomes half (3) becomes zero (4) remains the same
Last Answer : (4) remains the same Explanation: The poles remains same whether the magnet is cut into two equal half or more and also pole strength remains same but magnetic moment reduces due to decrease in the length of ... is called north pole (N-poled of the magnet and the other end the south pole (S-pole).
Description : When a helical spring is cut into two halves, the stiffness of each half spring will be, (A) Same as original spring (B) Double of original spring (C) Half of original spring (D) One fourth of original spring
Last Answer : (B) Double of original spring
Description : When two Belleville springs are in parallel, half force is obtained for a given deflection. a) Half force b) Double force c) Same force d) Can’t be determined
Last Answer : b) Double force
Description : When two Belleville sprigs are arranged in series, half deflection is obtained for same force. a) One fourth deflection b) Double deflection c) Four time deflection d) None of the listed
Last Answer : b) Double deflection
Description : The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the (A) Solution has ... B) Evaporators operate under vacuum (C) Evaporators operate at atmospheric pressure (D) None of these
Last Answer : (A) Solution has an elevation of boiling point
Description : When two Belleville springs are in parallel, half force is obtained for a given deflection. (a) Half force (b) Double force (c) Same force (d) Can’t be determined
Last Answer : (b) Double force
Description : When two Belleville sprigs are arranged in series, half deflection is obtained for same force. (a) One fourth deflection (b) Double deflection (c) Four time deflection (d) None of the listed
Last Answer : (b) Double deflection
Description : A close –coiled helical spring is cut into two equal parts. The stiffness of the resulting springs will be (a) same (b) double (c) half (d) One-fourth
Last Answer : (b) double