Electrical and Electronics Engineering_Question&Answers:

 

Q1:- Is that true, that the use of dc motors are either essential or else is advantageous to a degree sufficient to make it preferable to alternating current?

Ans:- Few cases are listed below :

1: Because of their excellent starting and over load characteristic dc motors are most suitable for electric traction on tramways, sub urban and under ground railways.

2: DC is absolutely essential for electrolytic and electro-chemical processes such as electro platting, electro – refining , production of aluminium , Cu and other metals by electro-lysis and fertilizers

3: It is essential for battery charging work.

4: It is necessary for running arc lamps for cinema projectors and search lights and also for some types of arc- welding.

5 : The most important aspect of this is that, DC motors are more superior to a.c motors for duties where frequent starting against heavy torque ,close speed adjustment and frequent reversals are required for example elevators , printing process , large machine tools drivers and certain steel mill equipments

Q2 :- Inside a conducting sphere which thing is always remains constant ?

Ans:-  Potential should be remain constant inside a conducting sphere

Q3:- Like a resonant R – L – C circuits what should parallel resonant circuit also had ?

Ans:- Like a resonant RLC circuits parallel resonant circuit should also had a power factor of unity

Q4:- What are the advantages of P-N diode or PIN diode ?

Ans:-Decrease in capacitance because capcitance is inversely proportional to the separation of P and N regions, So it allows a diode a faster response time. Hence ,PIN or P-N diodes are used at higher frequencies Approximately 300 MHz or more then 300 MHz Another advantage is that, the possibility of greater electric field between P and N junctions. It enhances the electron-hole pair generation there by enabling PIN diode to process even for very weak input signals

 

Q5:- What is purpose of Transformer in Electrical engineering ?

Ans:- The job of transformer in electrical engineering is either step up or step down. Mostly step down transformers are used in electrical engineering. The job of transformer is to suit the requirment of the solid state electronic devices and circuits fed by the dc power supply. It also provide isolation from the supply line which is an important safety considration.

Q6:- Why we use underground cables ?

Ans:- underground cables are used where over-head lines are not possible as in large cities despite the fact that in their cost, cost per kW (kilo watt) per kilo meter is much more as compared to over head transmission lines. Another advantage of over-head system for distributors is that tapping can be made at any time with out having any disturbance which is very important for rapidly developing areas.

Q7:-How can you divide cables into group ?

Ans:- cables are divided in to three groups

1: Low tension cables — up to 1000 volts

2: High tension cables — up to 23000 volts

3: Super tension cables — from 66 kV to 132 kV

Q8:- What are the essential parts of the Generators ?

Ans:- The generator consist of the following essential parts: Magnetic Frame or Yoke, Pole shoes ,Pole coils or field coils , Armature core, Armature winding or conductors,

commutator and brushes and bearings

Q9:- What are the purpose of Yokes ?

Ans:- It provide mechanical support for the poles and acts as a protecting cover for the whole machine and it carries the magnetic flux produced by the poles.

Q10:- What is the purpose of armature core ?

Ans:- It houses the armature conductors or coils and causes them to rotate and hence cut the magnetic flux of the field magnets. In addition to this its the most important

function is to provide a path of very low reluctance to the flux through the armature from a N – Pole to a S – Pole.(It is cylindrical in shape and is built up of usually circular sheet steel discs or laminations approximately 0.55 mm thick)

Q11:- What is thyristor?

Ans:- The thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as a switch conducting when their gate receives a current pulse and continue to conduct for as long as they are forward biased.Thyristors are mainly used where high currents and voltages are involved and are often used to control alternating currents where the change of polarity of the current causes the device to automatically switch off; Thyristors can also be found in power supplies for digital circuits where they can be used as a sort of circuit breaker

Q12:- What is UPS ?

Ans:- UPS mean uninterruptible power supply. This system can be of two major types and work to ensure uninterruptible power within a specified period before backup comes in.

There is a static type and the mechanical type.

The static type is common and consists of the rectifier/battery/inverter making up the system where as the mechanical type consists of transfer switch backup generator and an electric motor directly coupled to motor-generator through a flywheel.

Static type has the advantage of less maintenance when compared with the mechanical type with rotating parts.

Q13:- What is the power ratio between power in Star and Delta circuit?

Ans:- power is same, its only the line currents and voltages which differ in star and delta circuits and you can say that it is 1:1

Q14:- What is a Transducer?

Ans:- Transducer is a device which converts physical quantity into electrical quantity. As-Thermocouple (convert temperature into electrical volt or current)