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Friday, June 18, 2010

Hydro Generator- Part 2

Generator components

Prime Mover
  • Source of mechanical power for relative motion
  • Two classes of Prime movers :
                            High Speed : Steam & Gas Turbines
                            Low Speed : IC engines, Water turbines and DC motors
  • Type of prime mover plays an important role in a generator installation. Many characteristics of alternator and its construction depend upon Speed at which the rotor is turned. 
 Rotors
  • Two types are used in rotating field alternators
            - Turbine driven rotor ( used where prime mover is a high speed turbine)

            - salient pole rotor( used with low speed prime movers)


Stator

Many types based on

                   - Power out put
                   - Voltage output
                  - Type of cooling
                  - Number of phases

Simplified schematic of 3 ph. Stator

  • Three single phase windings displaced by 120 degrees
  • Star or Delta connection
  • Neutral may or may not be brought out
  • No. of terminals can be 3,4, or 6








Out-puts from a Generator

  • Three phase ac power at :
                 -Rated Voltage
                 -Rated Frequency

Common Ratings
  • Small Generators : 25 kVA to 300 kVA
  • Medium Size Generators : 500 kVA to 1 MVA
  • Large size Generators : 1 MVA to 25 MVA
  • Power Plant Generators: 110 MW to 500 MW
Frequency
  • Frequency depends up on the Speed of Rotation ( direct proportion)
  • F = PN / 120 where F = frequency in Hz, P = No. of poles, N = speed of rotation in RPM, ( 120 is a constant to convert minutes to seconds and poles to pole pairs)
  • Nominal frequency = 50/60 Hz
  • Generator frequency can vary due to load fluctuations
  • Frequency Regulation is mainly by adjusting the speed
  • speed is controlled by varying the fuel input to the prime mover ( Governor control)
Read more in coming posts...

Monday, June 7, 2010

Hydro Generator- Part 1


GENERATOR BASICS

Generator Structure
  • Generator is a machine which converts Mechanical energy into Electrical energy
  • Magnetic Induction Principle
  • An emf is induced in a coil whenever
      • a coil cuts through a magnetic field
      • a magnetic field cuts through a coil
  • emf induction is due to relative motion between two parts ( coil & magnetic field)
  • Relative motion is by Rotation
  • Two mechanical parts :
      • Field - Part which produces magnetism (Rotor)
      • Armature – part where emf is induced (Stator)


Generator components
  • Prime Mover
  • Rotor (Exciter)
  • Stator

 
Read more in coming posts...