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Electronics and Electrical Engineering interview Question and Answers for fresh engineers (Part 8)


Electronics and Electrical Engineering interview Question and Answers for fresh engineers (Part 8)

 In this topic we know about the substation and its some requirements for setup.


 Question: What do you mean by substation? Give some details.


Answer: The electric power is now generated in the form of alternating current. The electric power is produced in the power station, which is generally very far from the consumer premises. So, the generation, transmission and distribution are facing much difficulty. It is distributed to the consumer or user by the help of a very large interconnected network. In the network it is very important to change some characteristics for transmitting and distributing the electric power properly. Such as, ac to dc conversion (by using thyratron and mercury arc rectifier), voltage up or down (If the generating voltage is 11kv then transfer it to the high voltage range of 220kv), frequency change, power factor correction and improvement. This change needs a setup of some apparatus properly, in short this types of setup is called substation.

          The assembly of electrical apparatus whose purpose is changing the some major characteristics of the electric supply system is called substation.


            The substation is very important for achieving the continuity of supply to the consumers. In some cases the ac is need to convert in dc for running the dc motor, traction, electroplating processes this type of conversion is performed by the sub-station (ignitron).

electronics and electrical engineering interview question and answer: sub-station
SUB STATION


Question: What are the basic requirements for setup a substation? Or which conditions are considerable for setup a substation?


Answer: The continuity of electric energy supply system is solely depending on substation. So, enough care should be taken when designing and set upping a sub station in a suitable place.

Some points are as follows,

·        The substation must have the chance of easy operation and maintenance.
·        The place must be proper for setup a substation. It must be setup near the centre of the load.
·        The substation must have enough safety apparatus or safety setup. There must be enough chance for running the maintenance and clearing process. Also there should be setup for fire protection.
·        The system must be reliable. When designing protected gears and other instruments must be included. The construction process also maintained properly for reliable operation.
·        The capital cost must be as low as possible.

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Electronics and Electrical Engineering interview Question and Answers for fresh engineers (Part 9)

Electronics and Electrical Engineering interview Question and Answers for fresh engineers (Part 9)

In this topic we will know about motor protection

In the nameplate of the motor we see IP XY . i.e. IP 55
Example: With the IP rating IP 23, 

  • 2 describes the level of protection from solid objects and 
  • 3 describes the level of protection from liquids.

IP stands for 

Ingress Protection Ratings

 IP rating normally has two (or three) numbers:

  1. Protection from solid objects or materials
  2. Protection from liquids (water)
  3. Protection against mechanical impact 

specifying the environmental protection the enclosure provides.
Ingress Protection (IP) ratings are Introduced by the European Committee for Electro Technical Standardization .

 NEMA IEC 60529 Degrees of Protection Provided by Enclosures - IP Code,


IP First number - Indicates the Protection against solid objects. Which we indicates as X in the example

0 No special protection
1 Protected against solid objects over 50 mm, e.g. accidental touch by persons hands.
2 Protected against solid objects over 12 mm, e.g. persons fingers.
3 Protected against solid objects over 2.5 mm (tools and wires).
4 Protected against solid objects over 1 mm (tools, wires, and small wires).
5 Protected against dust limited ingress (no harmful deposit).
6 Totally protected against dust.

IP Second number -Indicates the Protection against liquids.Which we indicates as Y in the example 

0 No protection.
1 Protection against vertically falling drops of water e.g. condensation.
2 Protection against direct sprays of water up to 15o from the vertical.
3 Protected against direct sprays of water up to 60o from the vertical.
4 Protection against water sprayed from all directions - limited ingress permitted.
5 Protected against low pressure jets of water from all directions - limited ingress.
6 Protected against temporary flooding of water, e.g. for use on ship decks - limited ingress permitted.
7 Protected against the effect of immersion between 15 cm and 1 m.
8 Protects against long periods of immersion under pressure.



Example - IP 35

An electrical socket rated IP22 is protected against

  • Protected against solid objects over 2.5 mm (tools and wires).
  • Protected against low pressure jets of water from all directions - limited ingress.
IP stands for  Ingress Protection Ratings www.vivasolve.blogspot.com
IP stands for 
Ingress Protection Ratings

IP Third number - Indicates the Protection against mechanical impacts .

Its not used in normal cases. 

the third number is not available in IEC 60529

0 No protection.
1 Protects against impact of 0.225 joule
(e.g. 150 g weight falling from 15 cm height).
2 Protected against impact of 0.375 joule
(e.g. 250 g weight falling from 15 cm height).
3 Protected against impact of 0.5 joule
(e.g. 250 g weight falling from 20 cm height).
4 Protected against impact of 2.0 joule
(e.g. 500 g weight falling from 40 cm height).
5 Protected against impact of 6.0 joule
(e.g. 1.5 kg weight falling from 40 cm height).
6 Protected against impact of 20.0 joule
(e.g. 5 kg weight falling from 40 cm height).


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Electronics and Electrical Engineering interview Question and Answers for fresh engineers (Part 7)


Electronics and Electrical Engineering interview Question and Answers for fresh engineers (Part 7)

In this topic we know about the Power Factor, the leading and lagging condition for the power factor, the disadvantage of the low Power Factor and the main causes of the low power factor.

 Question: What is Power Factor?

 Answer: In an a.c. circuit the cosine of angle between voltage and current is called as power factor.

power factor improvement vivasolve.blogspot.com
Fig: Power factor angles

 Question: What are the leading and lagging conditions in the power factor improvement?

 Answer: Normally there are two types of circuit, capacitive and inductive circuits.

·        In the capacitive circuits, current leads the voltage and power factor is called as leading.
·        In the inductive circuits, current lags behinds the voltage and power factor is called as lagging.

Question: What are the disadvantages of low power factor?

 Answer: The main disadvantages of low power factor are as follows,

1.     Large size of the Conductor.
2.     Large Kilo Volt Ampere rating of the electrical machinery or equipment.
3.     Poor or unaccepted voltage regulations.
4.     A big amount of Copper loss.
5.     The handling capacity of the system reduced.

Question: What are the main causes of the low power factor?

 Answer: In the supply system normally the power factor is lower then 0.8 for the overall load. Low Power factor is very undesirable, because it hampers the economic parameters for the power generation and distribution. Now, some short important causes are as follows,

·        In the low lagging factor some electrical equipment such as electric discharge lamps, Arc lamps and the industrial heating furnaces are running.
·        The power factor is also depending on the load conditions. The load is varying time to time.  The supply voltage is increasing in the low load period which increases the amount of the magnetization current. This magnetizing current is resulting in the decreased power factor.
·        The single phase and three phase ac motors have low lagging power factor and they are induction type also. The power factor is varying for these types of motor. It can run from 0.2 to 0.9 values depends on load. In the heavy load the power factor can be 0.8 or 0.9 and in the light load the power factor can be 0.2 to 0.3.


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Electronics and Electrical Engineering interview Question and Answers for fresh engineers (Part 6)


Electronics and Electrical Engineering interview Question and Answers for fresh engineers (Part 6)

 In this topic we know about different types of motors starting torque and current, rheostat position, role of armature reaction, stepper motor, KVAR.

 Question: In the synchronous motor, DC motor or Induction motor which types of the motor has the high starting torque and starting current? What are the load criteria for those motors on the starting condition?

Answer:  From these motors the starting torque is present at the DC motor.

The load criteria for the starting conditions are as follows,
·        The DC series motor can not start without the presence of the load.
·        The synchronous motor and Induction motor can not start at the presence of load.


Question:  In the motors starting purpose why the armature rheostats at maximum position while the field rheostat is kept in minimum position? 

Answer:  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 high starting current. This high starting current can damage the motors starting systems.

Question: What are the types of power in electrical power?

Answer:   There are normally three types of power are counted in electrical power. They are,

·        Apparent power
  • Active power
  • Reactive power

Question:  What does the KVAR means?

Answer: The KVAR indicates the electrical power. KVAR means

                   “Kilo Volt Amperes with Reactive components”

 Question: In the magnetic fluxes, what is the role of armature reaction?

Answer:  The armature flux plays an important role for the running condition. This armature flux can oppose the main flux or it may support the main flux for better running condition. This effect of supporting and opposing of main flux to armature flux is called armature reaction.

 Question: What do you understand by the two phase motor? Give us one example.

 Answer: The motor which have a phase split in the running and starting winding is called as a two phase motor.

Example: Servo motor is one types of two phase motor. In the servo motor there is phase difference of 90 degree between control winding and auxiliary winding.

 Question:  Define stepper motor. What is the use of stepper motor?


Answer: The motor which work or act on the applied input pulse in it, is called as stepper motor.
This stepper motor is under the category of synchronous motor, which does not fully depend of complete cycle. It likes to works in either direction related to steps. for this purpose it mainly used in automation parts.



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Job interview or viva Topics for Electrical Engineers (Part-6)

Electrical engineering interview question and answers:

Job interview or viva Topics for Electrical Engineers (Part-6)

21. Swing equation: 

During the transient state of the synchronous machine, the relation between the accelerating power and angular acceleration is called swing equation.
M (d²δ/dt²) = Ps – Pe

Here,
M = angular momentum of the rotor,
Ps = mechanical power input,
Pe = electrical power output,
δ= load angle,
t = time,

22. Swing Curve: 

The graph which shows the relation between δ versus t is called swing curve. These graphs provide the stability information. This swing curve information is useful for understanding the adequacy of relay protection in the power station. This information helps to solve the faults before one or more machines become unstable.

23. Unsymmetrical faults: 

The unbalanced conditions of the system are called unsymmetrical faults. If an unbalanced connection is attached at any point of the balanced system, then this point is called the fault point of the system. This unsymmetrical fault has normally two types:

1. Shunt fault. 
2. Series fault.

24. Shunt Fault:

An unbalanced shunt fault is an unbalanced condition between phases and ground or, an unbalance between phases.

25 Classification of shunt fault:

In a 3-phase system the shunt fault are as follows,

·        Single line to ground fault (LG).
·        Line to line fault (LL).
·        Double line to ground fault (LLG).
·        Three phase short Circuit fault (LLL).
·        Three phase to ground fault (LLLG).

Here,
·        LG, LL, LLG ---- unsymmetrical faults.
·        LLL, LLLG ---- symmetrical faults.

26. Series fault:

The unbalance in the line impedances is known as series fault.


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We will give more important questions and answers for electrical engineering interview very soon. Please subscribed to RSS feed or Email feed. We need your help for the betterment of the site. Please give comments and tell us what’s your opinions and needs from us. We will try to give your required things.