27 January 2013

Power System Stability Interview Questions Answers

Define Infinite Bus in a Power System?
Answer: Infinite bus has constant voltage, constant electrical angle of the voltage, constant frequency, infinite fault level and therefore the quantities of the infinite bus do not get affected by connecting or disconnecting of individual generator or transmission line

Define Load angle of the generator?
Answer: Angle between rotor pole axis and stator rotating field axis (which is rotating at synchronous speed) is called load angle. It is expressed in electrical degrees or electrical radians

How steady state stability limit of a system can be improved?
Answer: Steady state stability of the system can be increased by either increasing the excitation of machine or group of machines, by reducing the transfer reactance

How transient stability limit can be increased?
Answer: Transient stability limit can be increased by:
  • Increasing the system voltage
  • By reduction in the transfer reactance
  • By using high speed circuit breakers
  • Automatic reclosing
  • Single pole switching
  • Turbine fast valving

Distinguish between steady state stability and transient stability?
Answer: Steady state stability refers to the conditions of the stability response to small and gradual changes of the load while transient stability corresponds to conditions of the stability in response to large sudden disturbances. A sudden large disturbances includes occurrence of faults in the system and clearing of faults, sudden load changes, in advent tripping of transmission lines or generators from the power system

On what basis can we conclude that synchronous generator goes out of stability?
Answer: If the power angle exceeds the critical angle of the load, synchronous machine goes out of stability

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