Description : What is the use of making rotor skewing?
Last Answer : 1. To run motor quickly by reducing magnetic hum. 2. It reduces locking tendency with the stator.
Description : Why is short pitch winding preferred over full-pitch winding ?
Last Answer : Advantages · Sinusoidal waveform: Waveform of the emf can be approximately made to a sine wave and distorting harmonics can be reduced or totally eliminated. · Economical :Conductor ... harmonics are eliminated, the eddy current and hysteresis losses are reduced which increases overall efficiency
Description : What is short pitch winding?
Last Answer : If coil pitch is equal to less than pole pitch it is called short pitch winding
Description : Skewing of rotor bars eliminate the: (1) Effect of space harmonics (2) Entire effect of crawling (3) Magnetic noise (4) Vibration due to unequal force developed on rotor
Last Answer : Skewing of rotor bars eliminate the: Effect of space harmonics
Last Answer : The purpose of skewing of rotor slots in induction motor is to reduce the locking tendency of rotor.
Description : How harmonics generated in electrical power distribution system?
Last Answer : Harmonic frequencies are integral multiples of the fundamental supply frequency, i.e. for a fundamental of 50 Hz, the third harmonic would be 150 Hz and the fifth harmonic would be 250 ... the corresponding application guides, since the electricity grid's protection system should cut off the fault.
Description : State advantages of short pitch winding over full pitch winding in alternators.
Last Answer : Advantages of Short Pitch Winding over Full Pitch Winding in Alternators: 1) Short pitching reduces the amount of copper needed for end connection when compared with full pitched coil. 2) They ... reduced, thereby increasing the efficiency. 4) The power quality of generated emf is improved.
Description : In an alternator if the winding is short pitched by 60 electrical degrees, its pitch factor will be: A) 1.0 B) 0.866 C) 0.75 D) 0.50
Last Answer : In an alternator if the winding is short pitched by 60 electrical degrees, its pitch factor will be: A) 1.0 B) 0.866 C) 0.75 D) 0.50
Description : A three phase slip ring induction motor is fed from the rotor side with stator winding short circuited stator is: (1) Slip frequency (2) Supply frequency (3) Frequency corresponding to rotor speed (4) Zero
Last Answer : A three phase slip ring induction motor is fed from the rotor side with stator winding short circuited stator is: Slip frequency
Description : Three factors responsible for the change in voltage as load is applied to an AC generator are: 1) the drop in resistance in the armature circuit, 2) the change in flux, and 3) the ____________. A. armature winding speed B. inductance load drop C. coil pitch factor D. armature reactance voltage drop
Last Answer : Answer: D
Description : What is full pitch winding?
Last Answer : If coil pitch is equal to pole pitch it is called full pitch winding
Description : If the residual flux is absent in the rotor iron of the isolated induction generator, a) it will not run. b) it will run as induction motor c) it will burn the winding d) it will not affect the characteristic of the generator
Last Answer : Ans: A
Description : 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 ... C. prevent condensation in the lube oil D. prevent electrolysis due to condensation in the bearings
Last Answer : Answer: B
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
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 : 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 : A characteristic of a wound-rotor induction motor, with a high resistance rotor winding, is _____________. A. low starting torque B. high starting torque C. high speed D. low starting voltage
Description : A characteristic of an induction motor with a low resistance rotor winding is _____________. A. high starting voltage B. high starting current C. high slippage D. low starting voltage
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 : The purpose of a cage rotor winding placed on the rotor of a synchronous motor is to _____________. A. provide excitation to the DC field B. start the machine as an induction motor C. contribute extra torque at synchronous speed D. prevent the machine from falling out of step
Description : Which of the following statements is true concerning a polyphase synchronous propulsion motor? A. The motor is started as an induction motor. B. Resistance is gradually added to the rotor circuit. C. ... is held below the rated current. D. The field winding is energized for starting purposes only.
Last Answer : Answer: A
Description : An operating characteristic appearing on the name plates of shipboard AC motors is _____________. A. the type of winding B. input kilowatts C. temperature rise D. locked rotor torque
Last Answer : Answer: C
Description : Will rotor earth fault relay operate for earth fault in main exciter winding or RCU Diode Bridge also?
Last Answer : Yes.
Description : A synchro has (A) a 3-phase winding on rotor and a single-phase winding on stator. (B) a 3-phase winding on stator and a commutator winding on rotor. (C) a 3-phase winding on stator and a single-phase winding on rotor. (D) a single-phase winding on stator and a commutator winding on rotor.
Last Answer : Ans: C Synchros : The basic synchro unit called a synchro transmitter. It’s construction similar to that of a Three phase alternator.
Description : Why skewing is done in squirrel cage Induction motor?
Last Answer : i) For more uniform torque ii) Reduction in noise iii) To decrease magnetic locking tendency
Description : What is skewing?
Last Answer : Skewing can be done by turning the rotor slots about 15° from the parallel position of slots with the shaft. That is rotor slots are not in parallel with the shaft but there is an angle of about 15° with the shaft.
Description : 7 The main advantage of auto transformer over a two winding transformer is A. Hysteresis losses are reduced B. Saving in winding material C. Copper losses are negligible D. Eddy losses are totally eliminated
Last Answer : A) hysteresis losses is reduced
Description : In testing a three-phase delta winding for an open circuit using a megohmmeter, you must ______________. A. test each phase with all connections intact B. measure the voltage across the open ... groups to avoid short circuiting D. open the delta-connections to avoid shunting the phase being tested
Description : Define distribution factor or winding factor or breadth factor or spread factor
Last Answer : The distribution factor is defined as the ratio of vector sum to arithmetic sum of emf induced in the conductor of one phase spread. OR It is ratio of resultant emf induced when coils are distributed to the resultant emf induced when coils are concentrated.
Description : Is winding up for the pitch kinetic or potential energy?
Last Answer : Potential
Description : The distance between the starts of two consecutive coils measured in terms of coil sides is called (a) front pitch (b) winding pitch (c) commutator pitch (d) back pitch
Last Answer : (b) winding pitch
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 the case of lap winding resultant pitch is difference of front and back pitches.
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 : In D.C. machines fractional pitch winding is used to reduce the sparking.
Description : When a CT is on electrical zero, what is the relationship between its rotor and the S2 winding?
Last Answer : They are perpendicular to each other.
Description : Direct water cooling of rotor winding presents (a) no mechanical difficulties (b) lesser mechanical difficulties (c) greater mechanical difficulties (d) none of the above
Last Answer : (c) greater mechanical difficulties
Description : For a DC motor, what major component in addition to the field winding and the armature winding is necessary? w) a commutator x) a stator y) a battery z) a rotor
Last Answer : ANSWER: W -- A COMMUTATOR
Description : What type of excitation is given to the rotor winding of a synchronous motor? (A) DC supply at 100 -250 V (B) AC supply at 400 V (C) Revolving field (D) Induction from stator currents
Last Answer : Dc supply of 100 to 250v is applied on the field circuit to make stable magnetic field which thens follow the rotating magnetic feild of stator or armature circuit.
Description : What do you mean by harmonics?
Last Answer : Definition for a harmonic is-a sinusoidal component of a periodic wave or quantity having a frequency that is an integral multiple of the fundamental frequency. The main sources of ... as they may cause overheating of capacitors and nearby generators and interfere with telecommunication systems.
Description : What are the disadvantages of the harmonics present in the inverter system?
Last Answer : a. Harmonic currents will lead to excessive heating in the induction motors. This will reduce the load carrying capacity of the motor. b. If the control and the regulating circuits are not ... affected. d. On critical loads, torque pulsation produced by the harmonic current can be useful.
Description : What are the reasons for harmonics in the motor?
Last Answer : Generally even harmonics are not expected to be present in three phase motors. Triple-n harmonics like 3rd, 9th, 15th etc. are also not expected. The dominant odd harmonics expected are 5th ... harmonic winding faults, short circuits. Hot spots in rotor or stator also may indicate higher harmonics.
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 : In order to reduce the harmful effects of harmonics on the A.C. side of a high voltage D.C. transmission system ______are provided. (A) synchronous condensers (B) shunt capacitors (C) shunt filters (D) static compensators
Last Answer : Ans: C Xc= 1/ ωc
Description : Which parameter indicates the rotor short-circuited turns (Not involving earthfault)?
Last Answer : Vibration increases.
Description : The problem of bus confect and sparse address distribution are eliminated by the use of ______ address technique: a. Fully decoding b. Half decoding c. Both a & b d. None of these
Last Answer : a. Fully decoding
Description : Select the TRUE statement. A)Wholesaling activities must be performed during distribution of all goods, whether or not a wholesaling institution is involved. B)Only wholesaling establishments ... )The biggest problem with the wholesaling process is that inefficient wholesalers are not eliminated.
Last Answer : A)Wholesaling activities must be performed during distribution of all goods, whether or not a wholesaling institution is involved.
Description : What Are The Advantages And Disadvantages Of Short-pitched Winding?
Last Answer : The advantages are: They save copper for end connections They improve the waveform of the generated EMF. The generated EMF can be made to approximate to a sine wave more easily and the distorting ... some what reduced. Because the voltage induced in the two coil sides are slightly out of phase.
Description : What Is Meant By Short Pitched Winding?
Last Answer : If the coil span is less than the pole pitch, the winding is called as shot-pitched winding. It is also known as short-chorded winding.