Electrical World

Why star delta starter is preferred with induction motor? Star delta starter is preferred with induction motor due to following reasons: • Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses. • Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused. • In addition, starting torque is increased and it prevents the damage of motor winding. State the difference between generator and alternator 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 ...

Q1: Where do we require single-phase induction motors? Ans: Single-phase induction motors are required where (i) 3 phase supply is not available  (ii) efficiency is of lesser importance (iii) Rating is less than one H.P.  (iv) Equipment is portable Q2: Why is the power factor of a single-phase induction motor low? Ans: It is due to the large magnetizing current which ranges from 60% to 70% of full-load current. As a result, even at no-load, these motors reach temperatures close to the full-load temperature. Q3: What is the function of centrifugal starting switch in a single-phase induction motor? Ans: The centrifugal switch is connected in series with the starting winding. The primary function of the centrifugal switch is to produce rotating flux in conjunction with main winding at the time of starting. When the motor has started and reaches nearly 75% of synchronous speed, it produces its own rotating field from the cross field effect. The starting ...

Electrical Engineering Interview Questions Part 1 Electrical Engineering Interview Questions Part 2 Electrical Engineering Interview Questions Part 3 Electrical Engineering Interview Questions Part 4 Electrical Engineering Interview Questions Part 5 Electrical Engineering Interview Questions Part 6 Electrical Engineering Interview Questions Part 7 Electrical Engineering Interview Questions Part 8 Electrical Engineering Interview Questions Part 9 Electrical Engineering Interview Questions Part 10 Electrical Engineering Interview Questions Part 11 Electrical Engineering Interview Questions Part 12 Electrical Engineering Interview Questions Part 13 Electrical Engineering Interview Questions Part 14 Electrical Engineering Interview Questions Part 16

Consider the rotating magnetic field as equivalent to physical rotation of two stator poles N 1 and S 1 .        Consider an instant when two poles are at such a position where stator magnetic axis is vertical, along A-B as shown in the Fig. 1(a).        At this instant, rotor poles are arbitrarily positioned as shown in the Fig. 1.        At this instant, rotor is stationary and unlike poles will try to attract each other. Due to this rotor will be subjected to an instantaneous torque in anticlockwise direction as shown in the Fig. 1(a).        Now stator poles are rotating very fast i.e. at a speed N s  r.p.m. Due to inertia, before rotor hardly rotates in the direction of  anticlockwise torque, to which it is subjected, the stator poles change their positions. Consider an instant half a period latter where stator poles are exactly rev...

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...

Electric Energy Generation Utilisation Interview Questions & Answers If you are preparing for a technical interview for a lighting systems related products(LED, Lamps etc) company, then you have landed in a correct page.  This post will serve to refresh the Lighting concepts, illuminations, related laws and important terms.  Here we had collected some of frequently asked questions related to illumination.  In addition to that we had added Anna university previous years questions on EEE 8th sem paper Electric Energy Generation Utilisation [Paper code EE1451].  [1] Define luminous flux It is defined as the total quantity of light energy emitted per second from a luminous body.  It is represented by symbol F and is measured in lumens.  The conception of luminous flux helps us to specify the output and efficiency of a given light source. [2] What is meant by luminance? It is defined as the luminous per unit ...

Special Machines (Permanent Magnet Synchronous Motor)  Interview Questions [1] What is the PMSM? In medium and small size synchronous motors, DC field can be produced by permanent magnets. Such kind of motors are called as PMSM [2] What are the advantages and disadvantages of PMSM Advantages Elimination of field copper loss Higher power density Lower rotor inertia Robust construction Disadvantages Power rating low Motor power factor can not be controlled because of field excitation cannot be controlled [3] What are the classification of PMSM Based on construction     Surface mounted PMSM     Interior mounted PMSM Based on the nature of voltage induced     Sinusoidally excited     Trapezoidally excited [4] Give some applications of PMSM Robots Machine tools [5] Define torque angle The angle between excitation emf and supply voltage. This angle is called torque angle or load or power angle . [6] What are the diffe...

Q1.What is the principle of the DC Motor ? A. If the current carrying conductor is placed in the maganetic field, mechanical forced is experienced on the conductor, and the direction of the force is given by the Fleming's left hand rule and hence conductor moves in the direction of force.     F  = B I L                   where   F = force                                                         B = magnetic field strength W/m2                           ...

Q1: Where do we require single-phase induction motors? Ans: Single-phase induction motors are required where (i) 3 phase supply is not available  (ii) efficiency is of lesser importance (iii) Rating is less than one H.P.  (iv) Equipment is portable Q2: Why is the power factor of a single-phase induction motor low? Ans: It is due to the large magnetizing current which ranges from 60% to 70% of full-load current. As a result, even at no-load, these motors reach temperatures close to the full-load temperature. Q3: What is the function of centrifugal starting switch in a single-phase induction motor? Ans: The centrifugal switch is connected in series with the starting winding. The primary function of the centrifugal switch is to produce rotating flux in conjunction with main winding at the time of starting. When the motor has started and reaches nearly 75% of synchronous speed, it produces its own rotating field from the cross field effect. The starting ...

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...