Electrical World

Ques.[1] For torque transmission over a long distance with the help of electrical wires only, which of the following two synchros are used ? (a)CX and CT (b)CX and CR (c)CX and CD (d)CT and CD Answer :B  Ques.[2] Squirrel-cage induction motor is finding increasing application in high-power servo systems because new methods have been found to (a) increase its rotor resistance (b) control its torque (c) decrease its intertia (d) decouple its torque and flux.   Answer:D   Ques.[3] The control ........................ synchro has three- phase winding both on its stator and rotor. (a) differential (b) transformer (c) receiver (d) transmitter Answer:A  Ques.[4] A dc servomotor is similar to a regular d.c. motor except that its design is modified to cope with (a) electronic switching (b) slow speeds (c) static conditions (d) both (b) and (c).   Answer:D  Ques.[4] The low-torque synchros cannot be used for (a) torque transmiss...

Q: Do you know the advantages of speed controlusing thyristor? A: Advantages: 1. Fast Switching Characterstics than Mosfet, BJT, IGBT 2. Low cost 3. Higher Accurate. Q: Name the different types of motors used in vacuum cleaners, phonographic appliances, vending machines, refrigerators, rolling mills, lathes, power factor improvement and cranes. A: Following motors are used: - • Vacuum cleaners- Universal motor. • Phonographic appliances – Hysteresis motor. • Vending machines – Shaded pole motor. • Refrigerators – Capacitor split phase motors. • Rolling mills – Cumulative motors. • Lathes – DC shunt motors. • Power factor improvement – Synchronous motors. Q: In the motors starting purpose why the armature rheostats at maximum position while the field rheostat is kept in minimum position? A: In the time of starting a motor the field rheostat is kept in minimum state for the high starting torque. In the time of starting a motor the armature rheostats is used to control or reduce the h...

Q :Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit? A :Link is provided at a Neutral common point in the circuit from which various connection are taken for the individual control circuit and so it is given in a link form to withstand high Amps. But in the case of Fuse in the Phase of AC circuit it is designed such that the fuse rating is calculated for the particular circuit (i.e load) only.So if any malfunction happen the fuse connected in the particular control circuit alone will blow off. Q :State the difference between generator and alternator A :Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction. Generator persists stationary magnetic field and rotating conductor which rolls on the armature with slip rings and brushes riding against each other, hence it converts the induced em...

Q : How can you start-up the 40w tube lite with 230v AC/DC without using any choke/Coil? A : It's possible with Electronic choke. otherwise it's not possible to ionize the particles in tube. light, with normal voltage. Q :What types domain of Laplace transforms? What behavior can Laplace transform predict how the system work? A :Types domain of Laplace transforms is s-domain, Laplace transforms provide a method to find position, acceleration or voltage the system will have. Q :In the magnetic fluxes, what is the role of armature reaction? A : The armature flux has an important role for the running condition. This armature flux can oppose the main flux or it may support the main flux for better running condition. This effect of supporting and opposing of main flux to armature flux is called armature reaction. Q :Explain thin film resistors and wire-wound resistors A :a:Thin film resistors- It is constructed as a thin film of resistive material is deposited on ...

Q uery : Difference between megger test equipment and contact resistance meter test instruments? Resolution : Megger test equipment used to measure cable electric resistance, conductor continuity, phase identification where as contact resistance meter test instruments used to measure low resistance like relays ,contactors. Q uery :When we connect the large capacitor bank in series ? Resolution :we connect large capacitor bank in series to improve the voltage power supply at the load end in balanced transmission line when there is considerable voltage drop along the balanced transmission line due to high impedance of the line.So in order to bring the voltage at the load terminals within its limits (i.e (+ or - %6 )of the rated high terminal voltage )the large capacitor bank is used in series. Q uery : What is electrical diversity factor in electrical installations? Resolution :Electrical diversity factor is the ratio of the sum of the individual maximum dem...

Query :What is the count of hvdc transmission lines in India? Resolution :At present there are three hvdc transmission lines in india 1)chandrapur to padghe(mumbai)--(1500 MW at ±500 kV DC) 2)rehand to delhi (1500 MW at ±500 kV DC) 3)talchal to kolar (2500 MW) Query :What is meant by regenerative braking? Resolution : When the supply is cutt off for a running motor, it still continue running due to inertia. In order to stop it quickly we place a load(resitor) across the armature winding and the motor should have maintained continuous field supply. so that back e.m.f voltage is made to apply across the resistor and due to load the motor stops quickly.This type of breaking is called as "Regenerative Breaking". Query :Why is the starting current high in a DC motor? Resolution : In DC motors, Voltage equation is V=Eb-IaRa (V = Terminal voltage,Eb = Back emf in Motor,Ia = Armature current,Ra = Aramture resistance).At starting, Eb is zero. Therefore, V=IaRa...

[1] For a pulse transformer, the material used for its core and the possible turn ratio from primay to secondary are respectively (a) ferrite; 20:1 (b) laminated iron; 1:1 (c) ferrite; 1:1 (d) powdered iron; 1:1 Ans: C [2] At the exact moment a 60Hz ac sine wave is at its positive peak voltage, the instantaneous rate of change in the voltage is a) Large and positive b) Small and negative c) Large and negative d) Small and negative e) Zero Ans: E [3] The peak voltage in an ac wave is always A. Greater than the average voltage B. Less than the average voltage C. Greater than or equal to average voltage D. Less than or equal to the average voltage Ans: C [4] If four resistors are connected in series, each with a value of 4Kohm, the total resistance is (a) 1kΩ (b) 4 kΩ (c) 8 kΩ (d) 16 kΩ Ans: D [5] Consider the following statements:  [IES2010] Piezoelectric materials serve as 1. A source of ultrasonic waves 2. When electric field is applied, the mechanical dimensions of the substances...

Q:Why we use ac system in India why not dc ? A:Firstly, the output of power stations comes from a rotary turbine, which by it's nature is AC and therefore requires no power electronics to convert to DC. Secondly it is much easier to change the voltage of AC electricity for transmission and distribution. thirdly the cost of plant associated with AC transmission (circuit breakers, transformers etc) is much lower than the equivilant of DC transmission AC transmission provides a number of technical advantages. When a fault on the network occurs, a large fault current  occurs. In an AC system this becomes much easier to interupt, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt. Q:Which type of motor is used in trains, what is the rating of supply used explain Working principal? A:Dc series is in the trains to get high starting torque while starting of the trains and operating voltage is 1500v dc. Q:Battery banks are in connected...

Q:What is inrush current? A:Inrush current is the current drawn by a piece of electrically operated equipment when power is first applied. It can occur with AC or DC powered equipment, and can happen even with low supply voltages. Q:In a Tap changing transformer where is the tap connected, is it connected in the primary side or secondary side? A:Tapings are connected to high voltage winding side, because of low current. If we connect tapings to low voltage side, sparks will produce while tap changing operation due to high current. Q:Why transformer ratings are in kva? A: Since the power factor of transformer is dependent on load we only define VA rating and does not include power factor .In case of motors, power factor depend on construction and hence rating of motors is in KWatts and include power factor. Q: What is difference between fuse and breaker? A: Fuses are burned at the time of over current flows in the circuit but breakers are just open(not burn) at the time of over current...

Q. What is meant by knee point voltage? A. Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated.(CT-current transformer). Query:What is reverse power relay? Resolution:Reverse Power flow relay are used in generating stations's protection. A generating stations is supposed to fed power to the grid and in case generating units are off,there is no generation in the plant then plant may take power from grid. To stop the flow of power from grid to generator we use reverse power relay. Q:What is the difference between Isolator and Circuit Breaker? A:Isolator is a off load device which is used for isolating the downstream circuits from upstream circuits for the reason of any maintenance on downstream circuits. it is manually operated and does not contain any solenoid unlike circuit breaker. it should not be operated while it is having load. first the load on it must be...

Q.1 What does 10V AC mean? Is it the RMS voltage or Peak voltage or Average voltage? Answer. In general,  AC voltages and currents are mentioned in RMS values only. It is sensible to compare with steady DC voltages and currents. For example 230V AC supply means, 230Vrms AC Supply. Q.2  What does the Voltmeter in AC mode show? Is it RMS value or peak value? Answer. Multimeter in AC mode shows RMS value of the voltage or current. Also when it is DC mode it will show the RMS value only. Q.3 Can fuses with an AC voltage rating be used in a DC applications? Answer: Fuses must be rated for the voltage AC or DC in which they will be used. Generally, fuses have a DC voltage rating that is half of the maximum AC voltage rating. Q.4 Why in a three pin plug the earth pin is thicker and longer than the other pins? Answer: It depends upon R=ρL/A where area (A) is inversely proportional to resistance (R), so if  area (A) increases, R decreases & if R is less the l...

Q. What is an Electric circuit? A. An electric circuit is an inter connection of electrical elements. Q. What do you mean by independent and dependent sources? A. An ideal independent source is an active element that provides a specified voltage or current that is completely independent of other circuit variables where as an ideal dependent source is an active element in which the source quantity is controlled by another voltage or current. Q. What are the types of dependent sources? A.1.Voltage controlled voltage source 2. Current controlled voltage source 3. Voltage controlled current source 4. Current controlled current source Q. Explain ohm’s law? A. At constant temperature, current flowing through an element is directly proportional to the potential difference across it. Q. What is open circuit and short circuit? A. An open circuit is a circuit element approaching infinite resistance and short circuit is a circuit element with resista...

Ques.[1] For torque transmission over a long distance with the help of electrical wires only, which of the following two synchros are used ? (a)CX and CT (b)CX and CR (c)CX and CD (d)CT and CD Answer :B  Ques.[2] Squirrel-cage induction motor is finding increasing application in high-power servo systems because new methods have been found to (a) increase its rotor resistance (b) control its torque (c) decrease its intertia (d) decouple its torque and flux.   Answer:D   Ques.[3] The control ........................ synchro has three- phase winding both on its stator and rotor. (a) differential (b) transformer (c) receiver (d) transmitter Answer:A  Ques.[4] A dc servomotor is similar to a regular d.c. motor except that its design is modified to cope with (a) electronic switching (b) slow speeds (c) static conditions (d) both (b) and (c).   Answer:D  Ques.[4] The low-torque synchros cannot be used for (a) torque transmiss...

Ques.[1] A variable reluctance stepper motor is constructed of .................. material with salient poles. (a) paramagnetic (b) ferromagnetic (c) diamagnetic (d) non-magnetic Answer: B Ques.[2] In a three-stack 12/8-pole VR motor, the rotor pole pitch is (a) 15º (b) 30º (c) 45º (d) 60º Answer: C Ques.[3] A stepper motor having a resolution of 300 steps/rev and running at 2400 rpm has a pulse rate of— pps. (a) 4000 (b) 8000 (c) 6000 (d) 10,000   Answer: C Ques.[4] If a hybrid stepper motor has a rotor pitch of 36º and a step angle of 9º, the number of its phases must be (a)4 (b)2 (c)3 (d)6 Answer: A Ques.[5] The rotor of a stepper motor has no (a) windings (b) commutator (c) brushes (d) all of the above. Answer: D Ques.[6] A stepping motor is a .................. device. (a) mechanical (b) electrical (c) analogue (d) incremental Answer: D Ques.[7] The rotational speed of a given stepper motor is determined solely by t...

 Hello Engineers. Welcome to Electrical Engineering Interview Questions Blog. Today i am going to share mcq based on single phase motor. Lets start... Ques: 1 A repulsion motor is equipped with   (a) a commutator   (b) slip-rings (c) a repeller   (d) neither (a) nor (b).   Answer : A  Must Read: Single Phase Induction MCQ Part 2 Interview Questions On Transformer Ques:2 If starting winding of a single-phase induction motor is left in the circuit, it will (a) draw excessive current and overheat (b) run slower (c) run faster (d) spark at light loads. Answer : A   Ques:3 Each of the following statements regarding a shaded-pole motor is true except (a) its direction of rotation is from un- shaded to shaded portion of the poles (b) it has very poor efficiency (c) it has very poor p.f. (d) it has high starting torque. Answer : D Ques:4 The direction of rotation of a single-phase motor can be reversed by (a) reversing con...