:Electrical Interview:CAPACITOR CURRENT LEAD

                             Capacitor has the dielectric material in between the plates and the plates are separated by a distance"d".

                                                                        =>          

                                                            

                    When ever a potential difference is applied across the capacitor plates, the dielectric material of   the capacitor plates has the dielectric material ions. These ions  are firstly vibrating due to potential difference and then the positive ions of dielectric material are moves towards negative plate side and the negative ions of the dielectric material are moves towards the positive plate of the capacitor.Due to this movement of dielectric material ions, a small displacement current is produced in between the plates and then  some voltage is appears across the capacitor plates.

     Due to above operation, we said current is lead as compared to the voltage in the capacitor.

Electrical Interview:DIODE SWITCHING SPEED

  When the power diode is conducting in the forward direction, some excess charge carriers are stored in the device these charge carriers are mainly due to the minority carriers.

       When diode is switching from ON state to OFF state these carriers are still present in the device even after the anode current zero. In order to remove these excess charge carriers and to regain equilibrium state recombination takes place and hence reverse current flows in the device untill all the excess charge carriers are completely removed in the device.This process is known as reverse recovery process.If we reduce the reverse recovery time process, we can improve the switching(ON to OFF) process time.Practically for reducing  reverse recovery time by introducing GOLD, it increase the recombination rate in the diode.

                           
                  

Electrical Interview:WHAT IS CREEPING ON ENERGY METER

       Creeping is the considerable problem in the analog energy meter because the meter disk rotates even no electrical current flowing through current coil(on no load condition) and also slightly higher speed under lightly loaded condition.

         

                      

                                       

                                                                                                                                                                                 The main reason for creeping is over-compensation the aluminium disk to over come the static friction of disk and another reason is over voltage across the shunt magnet.Due to this creeping consumers suffers from high tariff. In order to prevent this creeping phenomenon two diametrically opposite holes are drilled on the aluminium disk,the disk will come to rest with one of the holes under the edge of a pole of the shunt magnet the rotation being thus limited to a maximum of  half a revolution.                                                                                                                             

Electrical Interview:THYRISTOR

                               Thyristor  is a semi controlled rectifier because when ever a positive voltage is applied at anode and negative voltage is applied at cathode,the thyristor goes in to forward blocking mode at this mode we can control the thyristor by using gate.                                                                                                   

                      

                            All power transistors and GTO are fully controlled rectifiers.                                                                                                                          but in the next case when ever a positive voltage is applied at cathode and negative voltage is applied at anode the thyristor goes in to reverse blocking mode,in this mode we can not apply the gate,otherwise the gate is applied the thyristor comes into thermal runaway,after some time the thyristor burned.Due to this thyristor is controlled only in one mode by using gate,according to this type of operation thyristor is called semi controlled rectifier.    

                                                                                                              

Electrical interview:ROTOR ROTATION

                        When the three phase stator windings, are fed by a three supply a magnetic flux of constant magnitude is producing and rotate at synchronous speed in the air gap, these flux sweeps past the rotor surface and so cuts the rotor conductors.Due to the relative speed between stator and rotor conductors, an e.m.f is induced in the rotor conductors, according to faraday's law.Due to induced e.m.f current is produce and force is induced, according to lenz's law for opposing the relative speed the rotor rotate in the stator field flux direction.                                                                                                                                                                                     

Electrical Interview:PMMC INSTRUMENT

      The equation for the developed torque of the PMMC can be obtained from basic law of electromagnetic torque. The deflecting torque is given by
                                 
                                                       Td = NBAI 
                                                       Td = KI
                                                                          Where G = NBA= constant.

    From the above conclusion the the developed torque(Td) is proportional to electrical current flowing in the coil(I).If this type of meter is connected in DC supply the produced torque is unidirectional and shows some  reading.Now PMMC connected in AC supply the PMMC for first positive half cycle produce positive torque for next negative half cycle produce negative torque,due to this problem the meter will show zero reading therefore the PMMC do not operate in AC supply practically. 

Electrical Interview: DAMAGED DAMPING SYSTEM

                                

Every analog meter has the three types of controlling torques.

    Deflecting torque:Which is required to move the pointer from initial position to final position.

    Controlling torque:Which is used to control the pointer.at the steady state deflecting torque equal to controlling torque and both are equal in magnitude and opposite to each other.

    Damping torque:Which is used to control the pointer oscillations in meter for getting faster readings.If the damper winding system is damaged,the meter will be working but it is a time consuming process in order to take readings. 

Electrical Interview: FINDING OF TRANSMISSION LINE RATING

          When ever we see the transmission lines on road side,we will find the rating of transmission line very  easy.First we calculate how many insulators are used for that transmission lines.

                Number of insulator disks = operating voltage per phase/maximum voltage of each disk(11KV )

                      Operating voltage of line = number of insulator disks x maximum voltage of each disk(11kv)
         By using this formula we can find any transmission line rating.for example
                                 
                                                  LINE                   NUMBER OF DISKS
                                                   33   kv                          3  disks
                                                   132 kv                          8  disks
                                                   220 kv                        13  disks

Electrical Interview:3-PHASE INDUCTION MOTOR ACTS AS 2-PHASE

              When a three phase supply is applied to the induction motor,the 3-phase winding (120 degrees) produce three phase magnetic flux. Let the maximum value of flux due to any one of the three phases be 

and the total resultant flux in air gap is 1.5 times of maximum flux  .If one of the phase in 3-phase  suddenly damaged the induction motor acts as 2-phase motor. Because the motor produce 2 phase flux in air gap,the total resultant flux in this 2-phase case is only .Due to that the speed in 2-phase motor  is reduced as compared to the 3-phase induction motor.

                                       
                                                   3-phase motor resultant flux is = 1.5 times maximum flux.

                                                   2-phase motor resultant flux is = maximum flux.

                                                       

Electrical Interview: INTERPOLES

         These are the small poles fixed to the yoke and spaced in between the main poles. They are wound with comparatively few heavy gauge copper wire turns and are connected in series with the armature so that they carry full armature current.Their polarity, in case of generator,is same that of main pole ahead in the direction of rotation.But in case of motor the pole polarity is opposite to direction. Inter poles reduce the commutation and also reduce the cross magnetization in their location due to that reason universally interpoles are used in dc machines.

Electrical Interview: SKEWED SLOTS

                  When a 3-phase supply is given to the squirrel cage induction motor and there is a automatic pole formation is occurred. The formation of poles both on  rotor and stator are same, the magnetic locking(cogging)  is take place between the rotor and stator.for eliminating the magnetic locking between these we are must able to skewed the rotor slots up to desired level by doing this process also increase the starting torque of squirrel cage induction motor. In slip-ring motor we can not use skewed slots because the poles on the rotor and stator are not equal and also high starting torque. 

Electrical Interview: RATING OF TRANSFORMER

 A typical name plate rating of a single phase electrical transformer is as follows: 20 KVA , 3300/220 V, 50 HZ. Here 20 KVA is the rated output at the secondary terminals. Note that the rated output is expressed in Kilo-volt-amperes (KVA) rather than in Kilowatts (KW). This is due to the fact that rated transformer output is limited by heating and hence by the losses in the transformer. 

                              

                                            

    

                                 The two types of losses in a transformer are core loss and ohmic losses. The core loss depends on  transformer voltage and ohmic loss on the transformer current. As these losses depend on transformer  voltage (V) and current (I) and are almost unaffected by the load power factor, the transformer rated output is expressed in VA or in KVA avd not in KW.                                                                                             

Electrical Interview: ESCALATOR MOTOR

The escalator is a moving belt in big shops and other places.Escalator consists of synchronous motor because synchronous motor does not depends on load up to certain limit,that is the load angle.if the load angle is reached above 90 degrees the motor comes out from synchronization due to the loss of sychronism motor stops. Because of synchronism every escalator has some people(load)  limit.

Electrical Interview:WHY SPARKS ARE APPEARS IN SKY

 The sky has so many clouds but these clods are having billion particles  are present and also the clouds have different shape.When the clouds are moving at that time some clouds are touch to each other,if the touched clouds have different shape and size at that time the large cloud charge is transfer to small size cloud and  remaining charge is transfer to earth that is the light hazards.                                                                      

Electrical Interview:THYRISTOR REVERSE OPERATION

                                   thyristor revere connection with gate

        When a positive voltage is applied at thyristor negative terminal and a negative voltage is applied at positive terminal of thyristor at that time the thyristor is in reverse baise.When a positive gate is applied at the thyristor reverse baise condition,at that time P and N+ are in forward baise and the N- and P+ are in reverse baise then the total reverse voltage is appears across the reverse baise layer at that time the juction temperature is very high and thermal run away appears and thyristor is damaged.

                 ANSWER: damaged

    

INDUCTION MOTOR POWERFACTOR

Slipring induction motor has the low power factor because the air gap between the stator and rotor is high.the slip ring motor draw large reactive power from mains due to large reactive power the power factor is reduced,but in squirrel cage motor has low air gap due to this reason the reactive power required is minimum the power factor is high as compared to slipring motor.

       ANSWER: slipring motor

Electrical Interview: ELECTRICAL CIRCUIT

It is one of the technical circuit when a dc supply is applied across this circuit the diode forward biased at that time diode acts as short circuit then the total circuit current flow through diode only that means the current through resistor is zero therefore voltage across resistor is zero.

                                             i.e V=IV=0
                       ANSWER: zero

TRANSFORMER WORK AT DC VOLTAGE

                     when dc voltage is applied to the transformer a constant flux is induced in the transformer winding.that instant the secondary winding do't cut the flux at that time no induced emf in the secondary winding after some tine the transformer heated very high the transformer is damaged.

                             ANSWER: damaged

Electrical Interview:D.C MOTOR

                         which motor has the high torqe
  1 series motor  2 shunt motor  3 induction motor  

answer is series motor because series motor torque is directly prportional to square of the electrical current flowing in the armature.practically series motors are used where highest starting torque required 

therefore series motors are used in hosting and cranes etc..

STARTER IN D.C MACHINES

         practically all d.c machines are started with the starter other wise d.c motor is burned because large current is flowing through armature. When ever a voltage is applied across the d.c motor with out a starter a large current is flowing through motor because at starting motor armature is standstill therefore back e.m.f is zero therefore it requires large current to start. For eliminate this situation we must insert a starter into the dc motor circuit then we control the starting current in the dc motor armature circuit.Starter is limit the starting current in the dc  motor armature circuit.