Skip to main content

EEE interview questions VI

1. What is Rectifier?
     It is an electrical device which converts Alternating current into Direct current which allows the current to flow in only one direction by using one or more PN junction diode.

2. What is Phase Controlled Rectifier?
     Phase Controlled Rectifier converts AC to DC by using thyristor instead of diode. As diode has no control over output, where as SCR can control it's output by adjusting firing angle

3. When Rectifier will acts as an inverter?
     When the phase angle alpha becomes greater than 90° rectifier will acts as an inverter

4. What is firing angle?
     SCR doesnot turn on until anode Voltage becomes greater than cathode Voltage. To make anode Voltage greater than cathode Voltage pulse Signal are applied to gate of SCR. The angle at which thyristor gate is fired with pulse Signal is called as firing angle

5. What is triggering in SCR?
   SCR has two stable states forward blocking state and forward conducting state. The process of bringing SCR from forward blocking to forward conducting state to turn ON SCR is called as triggering

6. What is the effect of reducing firing angle?
    SCR will remain in conducting state will it completes cycle. If firing angle is reduced SCR will turn on early in cycle which will result in increase of output power and Voltage

7. What are the variable required to turn ON SCR?
     To turn ON SCR it depends on

  • Supply Voltage 
  • Gate Current 
  • Temperature 
  • Triggering 
8. What are the turn ON methods of SCR?
  • Forward Voltage triggering 
  • Temperature triggering 
  • dv/dt triggering 
  • Light triggering 
  • Gate triggering 
9. What are the conditions for SCR to turn off?
  • Anode or forward Current of SCR must be equal to zero or less than the level of holding Current 
  • A sufficient reverse Voltage must be applied across SCR to regain its forward blocking state
10. What is latching current?
  •  It is defined as the minimum forward current flow in SCR to maintain it in its forward conducting mode at the time of triggering
  • It is in the order of 10 to 15 mA
  • If forward Current is less than latching current SCR song turn ON
11. What is holding current?
  • It is defined as the minimum forward current flow in SCR to keep it in forward conducting state
  • If forward Current is less than holding current SCR will turn off
  • It is the order of 8 to 10 mA
12. Which current is greater latching current or holding current?
        Latching current is always greater than holding current. If the latching current becomes less than holding current SCR will turn OFF

13. What is Cycloconverter?
       Cycloconverter is an electrical device which converts fixed Voltage and fixed frequency into variable Voltage and variable frequency without any intermediate DC link

14. What are the applicantion of Cycloconverter?

  • Very high. Power drive
  • HVDC transmission system
  • Static VAR generator
  • Aircraft 
  • Grinding mills
  • Mine wonders
  • Cement mills 
15. What are the advantages of Cycloconverter?
  • It directly converts AC into variable output where other system involves two power stages
  • It doesnot have any intermediate DC link
  • It uses Online commutation 
16. What are the disadvantages of Cycloconverter?
  • It produces distorted waveforms for higher frequency 
  • Its power factor gets affected while controlling the AC motor
  • It requires large number of SCR
  • It is costly 
17. What is Voltage controlled Current Source?
           In VCCS, the current changes depend upon the applied voltage

18. What is Current Controlled Voltage source?
         In CCVS, the current is directly proportional to the voltage independent of any other sources. It is similar to resistor, units are measured in ohms

19. What is UPS?
       Un interrupted power supply -UPS, it provides power back up when electrical power fails or drops to an unacceptable voltage level

20. How UPS works?
       UPS draws current from the AC supply converts and stores it in battery. Power cam be utilised from the battery in case of power failure

21. What are types of UPS?
       There are two types of UPS:

  • On line UPS
  • Offline UPS
22. What is offline UPS?
      In offline UPS, UPS is  directly connected to the battery by skipping the inverter. During the power failure the power line will be shifted to battery and power will be delivered through the inverter from battery

23. What is online UPS?
        In online UPS, Dual conversion process AC to DC, DC to Battery takes place. Such that Battery is connected to load directly through the inverter. It is costly 
       

Comments

Post a Comment

Popular posts from this blog

EEE Interview Questions IV

1. What is Power System? It is a branch of electrical engineering which deals with the study of generation, transmission, distribution and utilization of electrical energy 2. What is Power Factor? The cosine of angle between voltage and the current in an AC circuit is known as power factor 3. How should be power factor for the good working system? Power Factor should be less than 1 for the good working system 4. What is one line diagram? One line diagram is a single line representation of  three phase power system It consists of symbol representation of  bus bar, Generator, Alternator, e.t.c [caption id="attachment_91" align="alignnone" width="624"]                                                                one line diagram 5. W...
Post a Comment
Read more

EEE Interview Questions-1

Here are some of the basic questions asked in interviews for EEE students 1. what is the principle of motor?       The electric motor is based on the principle that whenever a current carrying conductor is placed in an magnetic field it experiences a mechanical force i.e turning or twisting movement is called as torque. 2. what is the principle of generator?   The electric generator is based on the principle of faraday's law of electromagnetic induction. Such that whenever a current carrying conductor is placed in an varying magnetic field it induces an emf in it. 3. what are the types of DC motor? Series motor Shunt motor Compound motor Permanent magnet DC motor 4. What are the types of AC motor? Synchronous motor Asynchronous motor 5. What is Synchronous motor?       Synchronous motor is a kind of AC motor where the rotation of the shaft is synchronized with the frequency of the supply current at steady ...
Post a Comment
Read more

Resistor - Basic Electrical Component I

Definition:  It is a two terminal passive electrical Component that resists the flow of current in circuit Resistor  How it Works: It converts electrical energy into heart which will dissipated into Air Uses of Resistor: Reduce Current Flow Adjust Signal levels Divide Voltage Bias Active Element Unit of Measurement:      Unit of Resistor is Ohm which is name after the scientist George Simon Ohm Types of Resistor: There are two main types of Resistor: Linear Resistor  Non-Linear Resistor  Linear Resistor: Linear Resistor is a resistor those Value changes with change in temperature and current  Types of Linear Resistor: Fixed Resistor  Variable Resistor  Fixed Resistor:  In this the Value of Resistor is fixed it doesnot change with changes with temperature and Current  Types of Fixed Resistor: Carbon Film Resistor  Wire wound Resistor  Thin Film Resist...
Post a Comment
Read more