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. What is Voltage sag or Voltage dip?

• Voltage sag is a decrease in rms voltage for a short duration due to short circuit, overload or starting of electric motor
• It usually happens when the voltage reduces between 10 to 90 % of nominal voltage for half cycle to one minute

6. What are the types of Faults?

• 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)

7. What is Load Flow Analysis?
Load flow Analysis is the study to determine whether the system voltages remain within specified limits under normal or emergency operating conditions, and whether equipment such as transformers and conductors are overloaded

8. What is Load bus?

• Load bus is defined as a Vδ bus, used to balance real and reactive power
• It is also called as slack bus or swing bus used to provide system losses by emitting or absorbing active or reactive power to and from the system

9. What are the methods of Load Flow Solutions?

• Gauss-seidal method using Y bus
• Newton-Raphson Method
• Power flow through line and slack bus power
• Decouple load flow method
• Fast Decouple load flow method

10. What is Gauss-Seidal method?
      It is also known as Liebmann method, a set of iterative method used to solve a linear system of equation

11. What is Newton Raphson Method?
      It is used to find better successive approximation to the roots or zeros of real valued function. It is used for complex systems

12. What is Electric Transient?
       Electric Transient is a sudden change of a system which leads to the energy burst for a short duration of time

13. What is Transient Voltage?
      Transient Voltage are the sudden burst of surges in the electrical system for a short duration of time due to sudden release of electrical energy  stored in inductive loads or lightening

14. What is Voltage Stability?
      Voltage stability is the ability of the system to maintain steady state voltage at all buses in the system after being subjected to disturbance from the initial operating point

15. What is stability of power system?
      Stability is the ability of the system to restore to its steady state condition after subjected to disturbances

16. What is stability limit?
      The maximum power that can flow through some particular point in a system maintaining entire stability of the system is called as stability limit

17. What is Transient stability?
       The ability of synchronous power system to return to its stable condition and maintain its synchronism after a large disturbance from faults, switch ON and OFF, circuit elements is called as transient stability

18. What is Load Angle?
      In synchronous generator the magnetic field rotates at synchronous speed and the the rotating magnetic field in stator are not fully aligned, they lags by the certain angle called load angle. It is also called as torque angle

19. What is Power angle?
       Power angle is the angle between a generator's internal voltage and its terminal voltage, or between the voltages at the source and load points of an electrical transmission

20. What is Alternator?
      Alternator is an electrical generator that converts electrical energy into mechanical energy in the form of alternating current

21. What is difference between Alternator and Generator?

• In generator poles are on stator and winding on rotor, A.C generates in winding,which converts to D.C through commutator segments , connected at the ends of each winding, is collected through brushes, mounted on neutral axis
• In alternator winding is on stator and poles are on rotor, hence simple in construction, absence of commutator makes it more simple in construction, hence all high rating machines used for generating electricity, are alternator, are having less maintenance and manufacturing cost than generator, and are more economical mainly used in power generation

    22. What happens when two alternator are connected in parallel with different frequency, terminal voltage and phase sequence?

•  Excess Voltage differences cause generators to create circulating currents when one generator tries to drive the other.
• Phase sequence will cause the big damage, the bigger the phase difference the more electro-mechanical force is between the two out of phase generators

23. What is the necessary condition for the two alternator to be connected in parallel?

• The rms line voltage of the running system and the new or incoming system must be equal
• The phase sequence of the two systems must match
• The phase angle be equal on both
• The frequencies of both systems must match