electricalengineeringquestionanswer

Electrical Machines Viva Questions and Answers [1] How to reverse the direction of rotation of dc motor? To reverse direction of rotation of dc motor, either direction of main field produced by the field winding is reversed or direction of the current passing through the armature is reversed. By changing the direction of current passing through the field winding,the direction of the main field can be reversed. [2] What are the functions of yoke? what is the choice material for the yoke? It serves the purpose of outer most cover of the dc machine. so that the insulating material get protected from the harmful atmospheric environmental like noise, dust and various gases like SO2, acidic fumes etc. It provides mechanical support to the poles. It forms a part of the magnetic circuit. It provides a path of low reluctance for magnetic flux. It is prepared by using cast iron. For large machines, rolled steel, cast steel, silicon steel is used which provides high permeability. [3] Why generato...

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 different classifications of synchro...

Frequently Asked Interview Questions on Alternators In this post we had given few Alternators related Interview questions with solutions. We believe that it will be helpful for your interview preparation. Please leave your comments in comments section. [Q] What is meant by synchronising the alternators? The process of connecting two or more alternators in parallel for supplying a common load is called synchronising. [Q] What are the conditions to be satisfied for proper synchronising of alternators? (i) The terminal voltage of the incoming alternator must be the same as bus-bar voltage. (ii) The speed of the incoming alternator must be such that its frequency equals to the bus-bar frequency (iii) The phase sequence of the incoming alternator must be the same as that of the other alternators or busbars. [Q] What are the advantages of Parallel operation of alternators? (i) It ensures continuity of power supply to consumers in case of breakdown of an alternator in an generation station. (...

Basic Interview Questions on Induction Motors: [Q] How does the Induction motor work? (OR) Why does the Rotor rotate? When the 3 phase stator windings are fed by 3 phase supply, a magnetic flux of constant magnitude which is rotating at synchronous speed is set up.  The flux passes through the air-gap and sweeps past the rotor surface  thus it cuts the rotor conductors.  Due to the relative speed between the rotating flux and the stationary rotor conductors, an emf is induced in the stationary rotor conductors as per the Faraday's laws of electromagnetic induction. The frequency of the induced emf is the same as the supply frequency. Its magnitude is proportional to the relative velocity between the flux and the conductors. Its direction will be as per Fleming's right hand rule. Since the rotor conductors form a closed circuit the rotor current is produced. This current's direction will oppose the very cause producing it ( as per Len's law) Here the cause is the...