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IRCON Technical Interview Questions
1:- What are the various kind of cables used for transmission?
Cables, which are used for transmitting power, can be categorized in three forms:
Low-tension cables, which can transmit voltage upto 1000 volts.
High-tension cables can transmit voltage upto 23000 volts.
Super tension cables can transmit voltage 66 kV to 132 kV.
2:- Why back emf used for a dc motor? highlight its significance.
The induced emf developed when the rotating conductors of the armature between the poles of magnet, in a DC motor, cut the magnetic flux, opposes the current flowing through the conductor, when the armature rotates, is called back emf. Its value depends upon the speed of rotation of the armature conductors. In starting, the value of back emf is zero.
3:- What is slip in an induction motor?
Slip can be defined as the difference between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol S.
Explain the application of storage batteries.
Storage batteries are used for various purposes, some of the applications are mentioned below:
For the operation of protective devices and for emergency lighting at generating stations and substations.
For starting, ignition and lighting of automobiles, aircrafts etc.
For lighting on steam and diesel railways trains.
As a supply power source in telephone exchange, laboratories and broad casting stations.
For emergency lighting at hospitals, banks, rural areas where electricity supplies are not possible.
4:- What are the advantages of P-N diode or PIN diode ?
Ans:-Decrease in capacitance because capacitance 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
5:- How can you convert AC input signal into DC output signal using power supply and which components are used in this procedure ?
Ans:- AC input signal can be converted in to DC output signal by using REGULATED power supply and the components used for the procedure are transformer,rectifier,filter,Voltage regulator and voltage dividor
6:- 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 requirement 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 consideration.
7:- 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.
8:-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
9:- 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
10:- 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 cylinderical in shape and is built up of usually circular sheet steel discs or laminations approximately 0.55 mm thick)
11:- 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.
12:- 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 angainst heavy torque ,close speed adjustment and frequent reversals are required for example elevators , printing process , large machine tools drivers and certain steel mill equipments
13 :- Inside a conducting sphere which thing is always remains constant ?
Ans:- Potential should be remain constant inside a conducting sphere
14:- 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
15:- 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
16:- 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
17:- 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)
18:- 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.
19:- For an 100kw generator, only 50kw of load is connected. will the generator generate only 50kw or 100kw?
Ans :- If we have 100KW generator and load is 50Kw generator generate only 50kw.but If we have 100KW generator and connected more then 100KW the generator tripped at overload (if there is circuit breaker).
20:- 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 which rolls on the armature with slip rings and brushes riding against each other, hence it converts the induced emf into dc current for external load whereas an alternator has a stationary armature and rotating magnetic field for high voltages but for low voltage output rotating armature and stationary magnetic field is used.
21:-Why AC systems are preferred over DC systems?
Due to following reasons, AC systems are preferred over DC systems:
a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution.
b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission
c. From power stations, AC is produced so it is better to use AC then DC instead of converting it.
d. When a large fault occurs in a network, it is easier to interrupt in an AC system, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt.
22:- How can you relate power engineering with electrical engineering?
Power engineering is a sub division of electrical engineering. It deals with generation, transmission and distribution of energy in electrical form. Design of all power equipments also comes under power engineering. Power engineers may work on the design and maintenance of the power grid i.e. called on grid systems and they might work on off grid systems that are not connected to the system.
What are the uses of PLL circuits?
What is voltage build up of a generator?
Differentiate between MC and MI instruments?
Are Single induction motor self starting?
How is the alternator synchronized to the main busstar?
what is arc formation?
What is the basic circuitry for voltage stabilizer?
what do the three pin of a socket represents?
what is regenerative breaking?
Give an example where a transformer is used in a DC application?
